Laboratory and In situ Selenium Bioaccumulation Assessment in the Benthic Macroinvertebrates Hyalella azteca and Chironomus dilutus

Selenium (Se) bioaccumulation and toxicity in aquatic vertebrates have been thoroughly investigated. Limited information is available on Se bioaccumulation at the base of aquatic food webs. In this study, we evaluated Se bioaccumulation in two benthic macroinvertebrates (BMI), Hyalella azteca and Chironomus dilutus raised in the laboratory and caged in-situ to a Canadian boreal lake e (i.e., McClean Lake) that receives continuous low-level inputs of Se (< 1 μg/L) from a uranium mill. Additional Se bioaccumulation assays were conducted in the laboratory with these BMI to (i) confirm field results, (ii) compare Se bioaccumulation in lab-read and native H. azteca populations and (iii) identify the major Se exposure pathway (surface water, top 1 cm and top 2-3 cm sediment layers) leading to Se bioaccumulation in H. azteca. Field and laboratory studies indicated overall comparable Se bioaccumulation and trophic transfer factors (TTFs) in co-exposed H. azteca (whole-body Se 0.9-3.1 µg/g d.w; TTFs 0.6-6.3) and C. dilutus (whole-body Se at 0.7-3.2 µg Se/g d.w.; TTFs 0.7-3.4). Native and lab-reared H. azteca populations exposed to sediment and periphyton from McClean Lake exhibited similar Se uptake and bioaccumulation (NLR, p = 0.003; 4.1 ± 0.8 µg Se/g d.w), demonstrating that lab-reared organisms are good surrogates to assess on-site Se bioaccumulation potential. The greater Se concentrations in H. azteca exposed to the top 1-3 cm sediment layer relative to waterborne exposure, corroborates the importance of the sediment-detrital pathway leading to greater Se bioaccumulation potential to higher trophic levels via BMI.

Effects of diluted effluent on aquatic macroinvertebrate communities at the McClean Lake uranium operation in northern Saskatchewan

Diluted treated effluent from the McClean Lake uranium mill in northern Saskatchewan is released into Vulture Lake, which flows into the east basin of McClean Lake; this input could potentially cause a variety of disturbances to the aquatic systems. This study aimed to determine the potential effects of diluted effluent exposure (metals and major ions) on benthic macroinvertebrates in Vulture Lake and McClean Lake. Two monitoring locations located in Vulture Lake and eight in McClean Lake were used for collection water, sediment, and benthic macroinvertebrates. Complementary surface water bioassays were performed with larvae of the midge Chironomus dilutus using lake water from selected sites. Results indicated that total macroinvertebrate abundance and Margalef index (MI) did not follow the diluted effluent pattern. In addition, while the MI from artificial substrate samplers showed higher values in Vulture Lake and lower values at McClean Lake sites 4 and 5 (closer to effluent diffuser), the values recorded for sediment grab samples registered lower indices in Vulture Lake and higher values for sites 4 and 5. The final model from a Generalized Additive Modelling (GAM) approach suggested that electrical conductivity (EC), selenium (Se), and chloride (Cl) in water, and total organic carbon (TOC) and cadmium (Cd) in sediment are key variables that collectively may have influenced macroinvertebrate community composition at the study sites. Finally, across all test endpoints in the bioassays, exposure to lake water from Vulture Lake and McClean Lake had no statistically significant effects on C. dilutus.

Cross-species apical microinjected selenomethionine toxicity in embryo-larval fishes

Selenium (Se) is an essential micronutrient that becomes toxic when exposures minimally exceed those that are physiologically required. Studies on Se contaminated aquatic environments have identified that embryo-larval fishes are at particular risk of Se toxicity, primarily due to maternal Se transfer to developing eggs during oogenesis. This study emulated these exposures in embryo-larval fathead minnow (FHM), rainbow trout (RBT), white sucker (WSu), and white sturgeon (WSt) using embryonic selenomethionine (SeMet) microinjections. Adverse Se-outcomes observed across these species included spinal and edematous deformities, total individuals deformed, and reduced survival. Spinal deformity was the most sensitive sublethal endpoint and developed at the lowest concentrations in WSt (10 % effects concentration (EC10) = 12.42 μg (total) Se/g dry weight (d.w.)) followed by WSu (EC10 = 14.49 μg Se/g d.w.) and FHM (EC10 = 18.10 μg Se/g d.w.). High mortality was observed in RBT, but SeMet influences were confounded by the species' innate sensitivity to the microinjections themselves. 5 % hazardous concentrations derived across exposure type data subsets were ∼49 % higher when derived from within-species maternal transfer exclusive data as opposed to all, or within-species microinjection exclusive, data. These results support the current exclusion of SeMet microinjections during regulatory guideline derivation and their inclusion when studying mechanistic Se toxicity across phylogenetically distant fishes.

The influence of sampling method and season on modeling of selenium into coldwater fish and implications on tissue-based water quality benchmarks

Selenium (Se) contamination of aquatic ecosystems has led to the local extirpation of some Se-sensitive fish species. Although Se exposure occurs primarily via diet, considerable uncertainty lies in modeling Se transfer and bioaccumulation from sediment, detritus, and/or periphyton through benthic macroinvertebrates (BMI) to fish. Here we estimated Se concentrations in four coldwater fish species (northern pike, white sucker, lake whitefish, and ninespine stickleback) inhabiting boreal lakes downstream from a uranium mill in northern Canada. In addition, we evaluated the potential effects of BMI and periphyton sampling methods (artificial substrates vs. grab samples), seasons (summer vs. winter), and models (USEPA vs. Assessment of the Dispersion and Effects of Parameter Transport) on the estimated Se concentrations in fish tissue. Results were compared with site-specific benchmarks and observed Se concentrations in resident fish. In summer 2019, periphyton and BMI were sampled at 10 sampling stations (two in Vulture Lake and eight in McClean Lake) using artificial substrates (n = 4) and sediment grab samples (n = 3). In winter 2021, samples were collected in McClean Lake (n = 3) through ice holes using a sediment grab sampler. Estimated Se concentrations in fish tissue depended on the surface sediment or periphyton Se concentrations used in the models. At Vulture Lake, Se concentrations in northern pike muscle estimated using the grab sample data (17.3 ± 11.5 µg/g DW), but not the artificial substrates (34.5 ± 1.2 µg/g DW), were comparable with the observed mean concentration (19.0 ± 1.4 µg/g DW) in this species. At McClean Lake, Se body burdens in forage fish estimated using data from both sampling methods were comparable with measured data. Significantly lower mean whole-body Se concentrations were estimated for all fish species in winter (1.0 ± 0.3 µg/g DW) relative to summer (4.8 ± 1.6 µg/g DW). Further investigation is necessary to understand how potential seasonal shifts in dietary Se exposure relate to fish reproduction and early life stages. Integr Environ Assess Manag 2023;00:1-15. © 2023 SETAC.

Sampling method and season influence selenium dynamics at the base of a boreal lake food chain

Few studies have investigated the potential influence of sampling method and season on Se bioaccumulation at the base of the aquatic food chain. In particular, the effects of low water temperature associated with prolonged ice-cover periods on Se uptake by periphyton and further transfer to benthic macroinvertebrates (BMI) have been overlooked. Such information is crucial to help improve Se modelling and risk assessment at sites receiving continuous Se inputs. To date, this seems to be the first study to address these research questions. Here, we examined potential differences related to sampling methods (artificial substrates vs. grab samples) and seasons (summer vs. winter) on Se dynamics in the benthic food chain of a boreal lake (McClean Lake) receiving continuous low-level Se input from a Saskatchewan uranium milling operation. During summer 2019, water, sediment grab samples and artificial substrates were sampled from 8 sites with varying mill-treated effluent exposure. In winter 2021, water and sediment grab samples were sampled at 4 locations in McClean Lake. Water, sediment, and biological samples were subsequently analyzed for total Se concentrations. Enrichment functions (EF) in periphyton and trophic transfer factors (TTF) in BMI were calculated for both sampling methods and seasons. Periphyton collected with artificial substrates (Hester-Dendy samplers and glass plates) exhibited significantly higher mean Se concentrations (2.4 ± 1.5 μg/g d.w) than periphyton collected from the surface of sediment grab samples (1.1 ± 1.3 μg/g d.w). Selenium concentrations in periphyton sampled in winter (3.5 ± 1.0 μg/g d.w) were significantly greater than summer (1.1 ± 1.3 μg/g d.w). Nevertheless, Se bioaccumulation in BMI was similar between seasons, possibly suggesting that invertebrates are not actively feeding in winter. Further investigations are necessary to verify if peak Se bioaccumulation in BMI takes place in spring, coinciding with the reproductive and developmental windows of some fish species.

Application of autonomous sensor technology to estimate selenium exposure and a site-specific selenium threshold in a Canadian boreal lake

There is an increasing trend in the use of real-time sensor technology to remotely monitor aquatic ecosystems. Commercially available probes, however, are currently not able to measure aqueous selenium (Se) concentrations. Because of the well-described bioaccumulation potential and associated toxicity of Se in oviparous vertebrates, it is crucial to monitor Se concentrations at sites receiving continuous effluent Se input. This study aimed to estimate Se concentrations in a boreal lake (McClean Lake) downstream from a Saskatchewan uranium mill using real-time electrical conductivity (EC) data measured by autonomous sensors. Additionally, this study aimed to derive a site-specific total aqueous Se (TSe) threshold based on Se concentrations in periphyton and benthic macroinvertebrates sampled from the same lake. To characterize effluent distribution within the lake, eight Smart Water (Libelium) sensor units were programmed to report EC and temperature for five and seven consecutive weeks in 2018 and 2019, respectively. In parallel, periphyton and benthic macroinvertebrates were sampled with Hester-Dendy's artificial substrate samplers (n = 4) at the same sites and subsequently analyzed for Se concentrations. Electrical conductivity was measured with a handheld field meter for sensor data validation and adjusted to the median lake water temperature (13 °C) registered for the deployment periods. Results demonstrated good accuracy of sensor readings relative to handheld field meter readings and the successful use of real-time EC in estimating TSe exposure (r = 0.87; r²  = 0.84). Linear regression equations derived for Se in detritivores versus Se in periphyton and Se in periphyton versus sensor-estimated TSe were used to estimate a site-specific TSe threshold of 0.7 µg/L (±0.2). Moreover, mean Se concentrations in periphyton (16.7 ± 4.4 µg/g dry weight [d.w.]) and benthic detritivores (6.0 ± 0.4 µg/g d.w.) from one of the exposure sites helped identify an area with potential for high Se bioaccumulation and toxicity in aquatic organisms in McClean Lake. Integr Environ Assess Manag 2023;19:395-411. © 2022 SETAC.

Selenium Distribution and Trophic Transfer in the Periphyton-Benthic Macroinvertebrate Food Chain in Boreal Lakes Downstream from a Milling Operation

Selenium (Se) is an essential micronutrient with a narrow essentiality-toxicity range known to bioaccumulate in aquatic food webs. Selenium uptake and trophic transfer at the base of aquatic food chains represent a great source of uncertainty for Se risk assessment. The goal of the present study was to investigate Se distribution in water and sediment and its subsequent transfer into the periphyton-benthic macroinvertebrate (BMI) food chain in boreal lakes downstream from a Saskatchewan uranium mill. In particular, the present study aimed to assess potential differences in Se bioaccumulation patterns by BMI taxa to contribute to the current knowledge gap. During summer 2018 and 2019, water, sediment, periphyton, and BMI were sampled at two sites in Vulture Lake, seven sites in McClean Lake east basin, and one reference site in McClean Lake west basin. Periphyton and BMI taxa were sampled with artificial substrates (Hester-Dendy) deployed for 5 weeks in 2018 and 7 weeks in 2019; BMI were sorted into the lowest practical achievable taxonomic level and analyzed for total Se concentrations. At the diluted effluent exposure sites, Se concentrations in BMI ranged from 1.3 to 18.0 µg/g dry weight and from 0.3 to 49.3 µg/g dry weight in 2018 and 2019, respectively, whereas concentrations ranged from 0.01 to 3.5 µg/g dry weight at the reference site. Selenium concentrations in periphyton and some BMI taxa sampled near the effluent diffuser (Se < 1 µg/L) reached levels comparable to higher effluent exposure sites (Se > 2 µg/L). Despite differences in Se bioaccumulation among BMI taxa, an approximately one-to-one trophic transfer ratio was observed for benthic primary consumers and benthic predatory taxa. Environ Toxicol Chem 2022;41:2181-2192. © 2022 SETAC.

Effects of in situ experimental selenium exposure on finescale dace (Phoxinus neogaeus) gut microbiome

Selenium (Se) is an environmental contaminant of global concern that can cause adverse effects in fish at elevated levels. Fish gut microbiome play essential roles in gastrointestinal function and host health and can be perturbed by environmental contaminants, including metals and metalloids. Here, an in-situ Se exposure of female finescale dace (Phoxinus neogaeus) using mesocosms was conducted to determine the impacts of Se accumulation on the gut microbiome and morphometric endpoints. Prior to this study, the gut microbiome of finescale dace, a widespread Cyprinid throughout North America, had not been characterized. Exposure to Se caused a hormetic response of alpha diversity of the gut microbiome, with greater diversity at the lesser concentration of 1.6 μg Se/L, relative to that of fish exposed to the greater concentration of 5.6 μg Se/L. Select gut microbiome taxa of fish were differentially abundant between aqueous exposure concentrations and significantly correlated with liver-somatic index (LSI). The potential effects of gut microbiome dysbiosis on condition of wild fish might be a consideration when assessing adverse effects of Se in aquatic environments. More research regarding effects of Se on field-collected fish gut microbiome and the potential adverse effects or benefits on the host is warranted.

Delineating Effluent Exposure and Cumulative Ecotoxicological Risk of Metals Downstream of a Saskatchewan Uranium Mill Using Autonomous Sensors

There is increasing interest in using autonomous sensor technology to monitor aquatic ecosystems in real time and in employing such monitoring data to perform better ecological risk assessments. At seven locations in McClean Lake in northern Saskatchewan (Canada) that received diluted uranium milling effluent, we deployed sensor units to track effluent distribution and help predict potential biological effects on aquatic invertebrates. Water was also collected from each location on multiple occasions to measure major ions, dissolved metals, and routine water quality, and sediment was sampled to analyze total metals. The ecotoxicological risk to aquatic invertebrates was estimated using hazard quotients (HQs). The cumulative risk was estimated by summing the individual HQs, and the major ions risk was based on total osmolarity. The results indicated temporal and spatial variations in effluent exposure based on sensor electrical conductivity (EC) measurements in the McClean Lake East Basin. Individual HQs for water ranged from "moderate" (0.40-0.69) to "very high" (greater than 1) for silver, cadmium, arsenic, selenium, mercury, iron, and thallium. At all sites, major ions risk was less than 1. Individual HQs for sediment were "moderate" (0.40-0.69), "high" (0.7-0.99), and "very high" (greater than 1) for vanadium and cadmium. The cumulative risk in water and sediment for all metals combined was greater than 1 at some sites in Vulture Lake (which discharged into McClean Lake) and in McClean Lake itself. A more detailed estimation of the risks for aqueous selenium and arsenic (the only two metals that had good correlation with sensor EC data) indicated that their 90th percentile HQ values were less than 1 in McClean Lake, suggesting that these contaminants of concern do not represent a significant direct risk to aquatic invertebrate communities. Environ Toxicol Chem 2022;41:1765-1777. © 2022 SETAC.

Response of Crustacean Zooplankton and Benthic Macroinvertebrate Communities to Selenium Additions in a Boreal Lake

Selenium (Se) is a contaminant of concern in Canada mainly due to its teratogenic effects on fish and birds. However, few studies have assessed the effects of Se on invertebrates in a field setting. The objective of this experiment was to assess potential community-level impacts of Se additions on zooplankton and benthic macroinvertebrates in a boreal lake ecosystem. From June to August 2018, Se (as selenite) was added to six limnocorrals in Lake 239 at the International Institute for Sustainable Development-Experimental Lakes Area, Northwestern Ontario, Canada, to achieve mean measured aqueous concentrations of 0.4, 0.8, 1.6, 3.4, 5.6 and 7.9 µg Se/L, with three untreated limnocorrals serving as controls (background Se = 0.08-0.09 µg/L). Periphyton, phytoplankton, and invertebrates (zooplankton and benthos) were monitored for 63 days. Zooplankton community composition shifted as a function of Se exposure, with Cladocera biomass and density decreasing with increasing Se concentrations. Similarly, cumulative abundance and biomass of Heptageniidae decreased with increasing Se treatment throughout the experimental period. The present study demonstrated that Se can have impacts on aquatic invertebrates at environmentally relevant exposure levels, and that future ecological risk assessments should consider the impacts of Se on both vertebrates and invertebrates. Environ Toxicol Chem 2022;41:95-107. © 2021 SETAC.

Cadmium bioaccumulation and distribution in the freshwater bivalve Anodonta woodiana exposed to environmentally relevant Cd levels

Anodonta woodiana is a globally distributed freshwater bivalve, which is a unique bioindicator in the "Freshwater Mussel Watch" project. Numerous countries have used A. woodiana for biomonitoring the aqueous cadmium (Cd) contamination. However, the bioaccumulation and distribution characteristics of environmentally relevant Cd concentrations in the bivalve were unknown. In this study, A. woodiana was exposed to aqueous Cd concentrations (1.1, 2.6, and 5.5 μg/L) for 30 days. The concentrations of Cd in the whole soft tissues were linearly and positively correlated with the aqueous Cd concentrations and exposure time (P < 0.05). Analysis of the organic bioaccumulation and distribution showed that Cd concentrations and proportions in the gills and mantle were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). Analyses of the subcellular fractions showed that Cd concentrations and proportions in the metal-rich granule (MRG) were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). This suggests that the gills and mantle could be the main target organs for Cd bioaccumulation, and that the MRG could be the major site for Cd bioaccumulation and distribution. These results improve our understanding of the bioaccumulation and distribution mechanisms of Cd in bivalves.

Trophic dynamics of selenium in a boreal lake food web

Selenium (Se) is both an essential micronutrient and a contaminant of concern that is of particular interest in mining-influenced waterbodies in Canada. The objective of this research was to characterize the trophic dynamics of selenium along a gradient of exposure concentrations in a Canadian boreal lake ecosystem. From June 20 to August 22, 2018, six limnocorrals (littoral, ∼3000 L enclosures) were spiked with mean measured concentrations of 0.4, 0.8, 1.6, 3.4, 5.6 and 7.9 μg Se/L as selenite, and three limnocorrals served as untreated controls (background aqueous Se = 0.08-0.09 μg/L). Total Se (TSe) concentrations in water, periphyton, phytoplankton, sediment, benthic macroinvertebrates, zooplankton and female finescale dace (Phoxinus neogaeus; added on day 21 of the experiment) were measured throughout and at the end of the experiment. Total Se bioaccumulation by organisms was generally non-linear. Greater uptake by phytoplankton than periphyton was observed. Taxonomic differences in accumulation of TSe by invertebrates (Heptageniidae = Chironomidae > zooplankton) were observed as well. Fish muscle and ovary tissue TSe bioaccumulation was more variable than that at lower trophic levels and uptake patterns indicated that fish did not reach steady state concentrations. This research provides field-derived models for the uptake of Se by algae and invertebrates, and contributes to a better understanding of the dynamics of TSe bioaccumulation over a gradient of exposure concentrations in cold-water lentic systems.

Binding properties to nicotinic acetylcholine receptors can explain differential toxicity of neonicotinoid insecticides in Chironomidae

Neonicotinoids are neuroactive insecticides commonly detected in freshwater ecosystems. Recent studies have indicated that these compounds are markedly toxic to Chironomidae, a widespread family of ecologically important aquatic insects. However, despite their sensitivity, the pharmacological mechanisms driving neonicotinoid toxicity have yet to be characterized in these insect species. Here, we used a combination of saturation and competition binding studies to characterize neonicotinoid binding properties to nicotinic acetylcholine receptors (nAChR) in two different Chironomidae (Chironomus riparius and Chironomus dilutus) at two different life stages (larval and adult). Using radiolabeled imidacloprid ([³H]-IMI), we characterized and compared receptor density (B_max), imidacloprid binding affinity (K_D), and receptor binding affinity (K_i) to three different neonicotinoid competitors (imidacloprid, clothianidin, and thiamethoxam). We then compared receptor density and binding affinity parameters derived for Chironomidae to data previously generated for other dipterans and agricultural pests. We found that there were limited differences in neonicotinoid binding between C. riparius and C. dilutus, with both organisms demonstrating high affinities for imidacloprid (K_D = 0.22-0.87 nM) and high receptor densities (B_max = 0.92-6.53 pmol/mg). However, there were significant differences between life-stages, with larvae expressing higher densities of nicotinic acetylcholine receptors and higher imidacloprid affinities than adults. Moreover, there were compound-specific differences in receptor affinity, with larval stages displaying relative affinities (K_i) that generally correlated with acute neonicotinoid toxicity (e.g. clothianidin ≥ imidacloprid >>> thiamethoxam). Finally, compared to other dipterans and agricultural pests, Chironomidae display very high densities of high affinity nicotinic acetylcholine receptors, which likely contribute to their sensitivity. Results indicated that receptor-level differences in neonicotinoid binding may be responsible for ecotoxicological differences amongst distinct insect species, and they likely play a role in life stage-, and compound-level toxicity differences previously observed for Chironomidae. Overall, this study highlights the value of understanding the toxicological mechanisms of action of neonicotinoids in sensitive, non-target aquatic insects, to better predict adverse effects associated with unintentional neonicotinoid exposure.

Investigating the mechanism of vanadium toxicity in freshwater organisms

Vanadium (V) could present a risk for aquatic organisms from the Alberta oil sands region, if present in high concentrations. An industry pilot project has used petroleum coke (PC) as a sorbent to remove organic toxicants from oil sands process-affected water (OSPW), but it also caused V to leach from PC into the OSPW, reaching concentrations of up to 7 mg V/L (a level known to be toxic to aquatic organisms). Vanadium is a transition metal with several oxidation states, which could potentially elicit its toxicity through either ion imbalance or oxidative stress. This study investigated the effect of V on Daphnia magna and Oncorhynchus mykiss. Daphinds and O. mykiss were exposed to concentrations of V up to their respective calculated median lethal concentration (LC₅₀): 3 mg V/L for D. magna and 7 mg V/L for O. mykiss. For both organisms, the influence of V on sodium flux and whole body sodium was evaluated. Its effect on whole body calcium and the oxidative stress responses in O. mykiss at the gill and liver levels was also studied. Results suggested that 3.1 mg V/L for D. magna and 6.8 mg V/L for O. mykiss caused an overall increase in sodium influx in both the daphnids and rainbow trout. However, concentrations of V ranging between 0.2 and 4 mg V/L for D. magna and 1.8 and 6 mg V/L for O. mykiss reduced whole body sodium in both organisms and whole body calcium in O. mykiss. Concentrations above 3.6 mg V/L caused significant lipid peroxidation in the gills and liver of rainbow trout, while 1.9 mg V/L produced a substantial decrease in the fish gill GSH:GSSG ratio, but no change in the ratio between these thiols in the liver. Concentrations of 6.62 mg V/L sharply increased catalase activity in the liver but not in the gills. Neither liver nor gill superoxide dismutase was altered by V. Overall, results suggest that both ion imbalance and oxidative stress are part of the mechanism of toxicity of V in D. magna and O. mykiss and that further research is warranted to fully elucidate the mechanism(s) of V toxicity in aquatic organisms.

Comparative analysis of cadmium uptake and distribution in contrasting canadian flax cultivars

Objective

Humans consume low quantities of cadmium (Cd), a non-nutritive and potentially toxic heavy metal, primarily via the dietary intake of grains. A trial experiment was conducted to investigate physiological and developmental differences in Cd content in four flax cultivars (‘AC Emerson’, ‘Flanders’, ‘CDC Bethune’, and ‘AC McDuff’) as part of a study to provide information that will assist in the breeding of low Cd-accumulating flax cultivars. Our objective was to identify varietal differences in the uptake and distribution of Cd in various tissues among flax cultivars grown in naturally Cd-containing soil in a controlled environment.

Results

Cadmium concentration was dependent on genotype, developmental stage, and tissue type, as well as their interaction. Cadmium concentration was higher in roots and leaves, relative to all other tissues, with a general trend of decreasing Cd content over time within leaves and stems. Notably, the concentration of Cd was higher in ‘AC Emerson’ relative to ‘AC McDuff’ across tissues and ages, including the seeds, while the concentration of ‘Flanders’ was higher than in ‘AC McDuff’ in seeds and other reproductive organs but similar in roots and leaves. The results suggest varietal differences in the mechanisms that determine Cd content in seeds.

Multiple Linear Regression Modeling Predicts the Effects of Surface Water Chemistry on Acute Vanadium Toxicity to Model Freshwater Organisms

Multiple linear regression (MLR) modeling has been successfully used to predict how water chemistry variables influence the toxicity of cationic metals to aquatic organisms, but no MLR model exists for vanadium (V). Recent research has indicated that an increase in pH (from 6 to 9), or high concentrations of sodium (473 mg Na⁺ /L), increase V toxicity to Daphnia pulex. In contrast, increases in alkalinity (>100 mg as CaCO₃ ) and sulfate (>100 mg SO₄^2- /L) reduce V toxicity. How these variables influence V toxicity to Oncorhynchus mykiss (rainbow trout) was still unknown. Our results show that increasing pH from 6.2 to 8.9 tended to decrease the 96-h median lethal concentration (LC50) for V toxicity to O. mykiss by 9.6 mg V/L. An alkalinity increase from 71 to 330 mg/L as CaCO₃ tended to increase the 96-h LC50 by 3.3 mg V/L, whereas when SO₄^2- rose from 150 to 250 mg/L, the LC50 significantly increased by 0.3 mg V/L followed by a significant decrease of 1 mg V/L when SO₄^2- was >250 mg/L. Sodium (between 100 and 336 mg/L) showed no effect on V toxicity to O. mykiss. The toxicity patterns for O. mykiss were similar to those observed for D. pulex, except for that of SO₄^2- , potentially indicating different mechanisms of V uptake or regulation in the 2 species. The LC50s and associated water chemistry were combined to develop an MLR model for O. mykiss and D. pulex. Alkalinity and pH modified V toxicity to both species, whereas SO₄^2- influenced V toxicity to D. pulex. Overall, MLR models should be considered for creating new local benchmarks or water quality guidelines for V. Environ Toxicol Chem 2020;39:1737-1745. © 2020 SETAC.

Spatial distribution of agricultural pesticide use and predicted wetland exposure in the Canadian Prairie Pothole Region

Agricultural pest control products are a major cause of degradation of water quality and biodiversity loss worldwide. In the Canadian Prairie Pothole Region, the landscape is characterized by millions of ecologically important wetlands, but also large farm sizes and high agrochemical use. Despite the region's agricultural intensity, the spatial extent of pesticide use and likelihood of pesticides contaminating surface water has been poorly studied. Here, we estimated the pesticide use patterns for three main groups (herbicides, fungicides and insecticides) using the most recent (2015) pesticide use survey data and digital crop maps. Furthermore, we developed a Wetland Pesticide Occurrence Index (WPOI; 1 km² resolution), to robustly estimate potential wetland exposure using spatially explicit data on pesticide use density, wetland density, precipitation and pesticide-specific physicochemical properties. In total, 39,236 metric tonnes of pesticides consisting of 94 active ingredients were applied to the Prairies in 2015. Herbicides had the highest density of use (24-183 kg/km²), followed by fungicides (0.4-23.8 kg/km²) and insecticides (0.4-3.6 kg/km²). Pesticide use differed by province; however, the major pesticides applied (e.g., glyphosate, prothioconazole, and thiamethoxam) were consistent across the region and were largely associated with wheat and canola crops. Although insecticides and fungicides had lower mass applied than herbicides, they had slightly higher overall WPOI scores. The predicted pesticide occurrence for insecticides and fungicides in wetlands was higher in the wetter central and eastern part of the Prairie region (WPOI = 0.6-1) compared to the drier western and southwestern part (WPOI = 0.1-0.6), suggesting that wetlands in much of Saskatchewan and southern Manitoba may be more vulnerable to higher and frequent contamination. Identifying crops, chemicals and landscapes with the greatest likelihood of pesticide contamination to wetlands will help prioritize future environmental monitoring programs and aid in assessing the ecological risk of specific pest control products in Canada's most agriculturally intensive region.

Chronic Toxicity of Surface Water from a Canadian Oil Sands End Pit Lake to the Freshwater Invertebrates Chironomus dilutus and Ceriodaphnia dubia

Permanent reclamation of tailings generated by surface mining in the Canadian oil sands may be achieved through the creation of end pit lakes (EPLs) in which tailings are stored in mined-out pits and capped with water. However, these tailings contain high concentrations of dissolved organics, metals, and salts, and thus surface water quality of EPLs is a significant concern. This is the first study to investigate the chronic toxicity of surface water from Base Mine Lake (BML), the Canadian oil sands first large-scale EPL, to aquatic invertebrates that play a vital role in the early development of aquatic ecosystems (Chironomus dilutus and Ceriodaphnia dubia). After exposure of C. dilutus larvae for 23 days and C. dubia neonates for 8 days, no mortality was observed in any treatment with whole BML surface water. However, the emergence of C. dilutus adults was delayed by nearly 1 week, and their survival was significantly reduced (36%) compared with the controls. Reproduction (fecundity) of C. dubia was reduced by 20% after exposure to 2014 BML surface water; however, the effect was not observed after exposure to BML surface water collected a year later in 2015. Despite some adverse effects, the results of this study indicate that BML surface water quality is improving over time and is able to support certain salt-tolerant aquatic organisms. Because salinity within BML will persist for decades without manual intervention, the ecological development of the lake will likely resemble that of a brackish or estuarine ecosystem with reduced diversity.

Comparing the Acute Toxicity of Imidacloprid with Alternative Systemic Insecticides in the Aquatic Insect Chironomus dilutus

Acute (96-h) toxicities of 5 systemic insecticides (chlorantraniliprole, cyantraniliprole, flupyradifurone, flubendiamide, and sulfoxaflor) were tested on larval Chironomus dilutus and compared with the neonicotinoid imidacloprid. Three insecticides were less acutely toxic than imidacloprid (2.5-25 times lower). However, chlorantraniliprole and cyantraniliprole were 1.5 to 1.8 times more toxic to C. dilutus. Thus, these ryanodine receptor agonists could pose a higher risk to aquatic insects than their neonicotinoid predecessors, warranting further studies. Environ Toxicol Chem 2020;39:587-594. © 2019 SETAC.

In ovo exposure of fathead minnow (Pimephales promelas) to selenomethionine via maternal transfer and embryo microinjection: A comparative study

Selenium (Se) is an essential trace element of concern that is known to contaminate aquatic ecosystems as a consequence of releases from anthropogenic activities. Selenium is of particular toxicological concern for egg-laying vertebrates as they bioaccumulate Se through the diet and deposit excess Se to embryo-offspring via maternal transfer, a process which has been shown to result in significant teratogenic effects. The purpose of the present study was to determine and compare the in ovo effects of Se exposure on early development of a laboratory model fish species native to North American freshwater systems, the fathead minnow (Pimephales promelas), through two different exposure routes, maternal transfer and microinjection. For maternal transfer studies, fathead minnow breeding groups (3 females: 2 males) were exposed to diets containing Se-background levels (1.21 μg Se/g food, dry mass [dm]) or environmentally relevant concentrations of selenomethionine (SeMet; 3.88, 8.75 and 26.5 μg Se/g food dm) and bred for 28 days. Embryos were collected at different time points throughout the study to measure Se concentrations and to assess teratogenicity in embryos. While exposure to dietary Se did not negatively affect fecundity among treatment groups, the lowest treatment group (3.88 μg Se/g food dm) produced on average the most embryos per day, per female. The maternal transfer of excess Se occurred rapidly upon onset of exposure, reaching steady-state after approximately 14 days, and embryo Se concentrations increased in a dose-dependent manner. The greatest concentrations of maternally transferred Se significantly increased the total proportion of deformed embryo-larval fathead minnows but did not impact hatchability or survival. In a second study, fathead minnow embryos were injected with SeMet at concentrations of 0.00 (vehicle control), 9.73, 13.5 and 18.9 μg Se/g embryo dm. Microinjection of SeMet did not affect hatchability but significantly increased the proportion of deformed embryo-larval fish in a dose-dependent manner. There was a greater proportion of deformed fathead minnows at embryo Se concentrations of 18.9 μg Se/g embryo dm when exposed via microinjection versus maternal transfer at concentrations of 28.4 μg Se/g embryo dm. However, the findings suggest that both exposure routes induced analogous developmental toxicities in early life stage fish at Se concentrations between 9.73 and 13.5 μg Se/g embryo dm. Overall, this study demonstrated that microinjection has utility for studying the effects of Se in embryo-larval fish and is a promising method for the study of early life stage Se exposure in egg-laying vertebrates.

Evaluation of Lethal Fish Sampling and the Nonlethal Alternative Under the Canadian Metal and Diamond Mining Environmental Effects Monitoring Program

The Environmental Effects Monitoring (EEM) program, federally mandated to metal and diamond mines and mills in Canada, aims to ensure that fish, fish use, and their environment are sufficiently protected by the Metal and Diamond Mining Effluent Regulations (MDMER). Concerns have been raised regarding lethal fish sampling conducted for the program and the potential risk to fish populations. This study endeavored to calculate the extent of fish sacrificed during lethal EEM fish surveys to provide a more informed characterization for stakeholders. By extrapolating data from 28 studies conducted at 8 metal mines in Saskatchewan between 2004 and 2017, it was conservatively estimated that 60 060 ± 19 978 fish have been sacrificed for the program nationwide since its promulgation in 2002. This is almost 2 times greater than guidance recommendations due to numerous factors. Challenges faced when implementing the nonlethal fish population survey alternative were also evaluated, and some of these included data interpretation inconsistencies due to the lack of critical effect sizes (CES) included in the regulations for nonlethal effect endpoints, and reliance on capturing young of the year fish to assess the prescribed effect endpoints. Finally, a case study conducted to evaluate the congruity of lethal and nonlethal fish population survey results identified that the effect endpoints often produced conflicting conclusions for the same response variable. Ultimately, this study highlights that in order to strengthen and promote the use of nonlethal fish sampling as an alternate to the current standard of conducting lethal fish population surveys under the EEM program, the effect endpoints, study designs, and adoption of CES need to be thoroughly evaluated and included in the MDMER. If nonlethal sampling designs adequately provide the required data and meet program objectives, then there would be no need to continue sacrificing fish for the Canadian metal and diamond mining EEM program. Integr Environ Assess Manag 2019;00:1-10. © 2019 SETAC.

Effects of selenium on benthic macroinvertebrates and fathead minnow (Pimephales promelas) in a boreal lake ecosystem

Selenium (Se) is a contaminant of concern in many aquatic ecosystems due to its narrow range between essentiality and toxicity in oviparous (yolk-bearing) vertebrates. The objective of the present study was to determine the effects of Se, experimentally added to in situ limnocorrals as selenite, on invertebrate communities and fathead minnow (Pimephales promelas) at environmentally realistic Se concentrations. Nine limnocorrals were deployed in a mesotrophic lake at the International Institute for Sustainable Development - Experimental Lakes Area in Ontario, Canada in May 2017. From June 1 to August 17, 2017, selenite was added to six enclosures to attain mean measured aqueous Se concentrations of 1.0 ± 0.10 or 8.9 ± 2.7 μg/L Se (in triplicate) and three limnocorrals were untreated controls (background mean aqueous Se = 0.12 ± 0.03 μg/L). Benthic macroinvertebrates were collected throughout and at the end of the exposure period using artificial substrates to determine density, dry biomass, diversity, and taxa richness at the family level. Reproductively mature female fathead minnows (added on d 33 of the study) were collected throughout and at the end of the exposure period. After 77 d, Chironomidae and Gammaridae densities and biomass were significantly lower in the 8.9 μg/L Se treatment relative to the 1.0 μg/L Se treatment and the control. Invertebrate diversity (measured as Shannon's and Simpson's indices) significantly declined in the 1.0 μg/L and 8.9 μg/L Se treatments relative to the control (0.12 μg/L Se group). Fulton's condition factor for fathead minnow was significantly less in the 8.9 μg/L treatment compared to 0.12 and 1.0 μg/L Se experimental groups. The results of this study indicated that exposure to relatively low aqueous selenite concentrations can negatively affect invertebrate density and biomass, as well as fish condition. More research is necessary to characterize the risk of selenite exposure to aquatic invertebrates under realistic field conditions, and future risk assessments may need to consider reduced food availability as a factor that may impair the health of higher trophic level organisms in areas with elevated selenite.

Selenium oxyanion bioconcentration in natural freshwater periphyton

Selenium (Se) enrichment has been demonstrated to vary by several orders of magnitude among species of planktonic algae. This is a substantial source of uncertainty when modelling Se biodynamics in aquatic systems. In addition, Se bioconcentration data are largely lacking for periphytic species of algae, and for multi-species periphyton biofilms, adding to the challenge of modelling Se transfer in periphyton-based food webs. To better predict Se dynamics in periphyton dominated, freshwater ecosystems, the goal of this study was to assess the relative influence of periphyton community composition on the uptake of waterborne Se oxyanions. Naturally grown freshwater periphyton communities, sampled from five different water bodies, were exposed to environmentally relevant concentrations of selenite [Se(IV)] or selenate [Se(VI)] (nominal concentrations of 5 and 25 μg Se L^-1) under similar, controlled laboratory conditions for a period of 8 days. Unique periphyton assemblages were derived from the five different field sites, as confirmed by light microscopy and targeted DNA sequencing of the plastid 23S rRNA gene in algae. Selenium accumulation demonstrated a maximum of 23.6-fold difference for Se(IV) enrichment and 2.1-fold difference for Se(VI) enrichment across the periphyton/biofilm assemblages tested. The assemblage from one field site demonstrated both high accumulation of Se(IV) and iron, and was subjected to additional experimentation to elucidate the mechanism(s) of Se accumulation. Selenite accumulation (at nominal concentrations of 5 and 25 μg Se L^-1 and mean pH of 7.5 across all treatment replicates) was assessed in both unaltered and heat-killed periphyton, and in periphyton from the same site grown without light to exclude phototrophic organisms. Following an exposure length of 8 days, all periphyton treatments showed similar levels of Se accumulation, indicating that much of the apparent uptake of Se(IV) was due to non-biological processes (i.e., surface adsorption). The results of this study will help reduce uncertainty in the prediction of Se dynamics and food-chain transfer in freshwater environments. Further exploration of the ecological consequences of extracellular adsorption of Se(IV) to periphyton, rather than intracellular absorption, is recommended to further refine predictions related to Se biodynamics in freshwater food webs.

Models for the acute and chronic aqueous toxicity of vanadium to Daphnia pulex under a range of surface water chemistry conditions

Alberta's oil sands petroleum coke (PC) generation has in recent years surpassed 10 million tonnes. Petroleum coke has been proposed as an industrial-scale sorbent to reduce concentrations of organic chemicals in oil sands process-affected water (OSPW). However, PC contains up to 1000 mg of vanadium (V) per kg of PC, and during the treatment it leaches from coke reaching levels of up to 7 mg/L in "treated" OSPW. Little information is available on how common water quality variables affect the toxicity of V to aquatic organisms. Here descriptive relationships are presented to describe how site-specific surface water characteristics representative of the Alberta oil sands region influence the toxicity of V to Daphnia pulex. Results revealed that when D. pulex was exposed to an increase in pH, a threshold relationship was found where acute V toxicity increased from a lethal median concentration (LC₅₀) of 1.7 to 1.2 mg V/L between pH 6 and 7 and then levelled off at around 1 mg V/L. When alkalinity (from 75 to 541 mg/L as CaCO₃) and sulphate (from 54 to 394 mg/L) increased, the acute toxicity of V decreased slightly with LC₅₀s changing from 0.6 to 1.6, and from 0.9 to 1.4, respectively. When the length of V exposure was extended (from 2 to 21 d), only an increase of sulphate from 135 to 480 mg/L caused a slight increase in V toxicity from a LC₅₀ of 0.6 to 0.4 mg V/L, the opposite trend seen in the acute exposures. In addition, the influence of two OSPW representative mixtures of increasing sodium and sulphate, and increasing alkalinity and sulphate on V acute toxicity to D. pulex were evaluated; only the mixture of increasing sodium (from 18 to 536 mg/L) and sulphate (from 55 to 242 mg/L) caused a slight decrease in V acute toxicity (LC₅₀ 1.0-2.1 mg V/L). Evidence is presented that variations in surface water chemistry can affect V toxicity to daphnids, although only to a small degree (i.e. within a maximum factor of 2 in all cases evaluated here). These relationships should be considered when creating new water quality guidelines or local benchmarks for V.

Distribution of Experimentally Added Selenium in a Boreal Lake Ecosystem

Human activities have increased the release of selenium (Se) to aquatic environments, but information about the trophic transfer dynamics of Se in Canadian boreal lake systems is limited. In the present study, Se was added as selenite to limnocorrals (2-m-diameter, 3000-L in situ enclosures) in a boreal lake in northwestern Ontario to reach nominal concentrations of 1 and 10 µg Se/L in triplicate each for 77 d, and 3 additional limnocorrals were controls with no Se added. Total Se concentrations were determined in water, sediment, periphyton, benthic macroinvertebrates, zooplankton, and reproductively mature female fathead minnows (Pimephales promelas; added on day 33) collected throughout (and at the end of) the exposure period. Mean measured water Se concentrations in the control, 1-, and 10-µg/L treatments were 0.12, 1.0, and 8.9 µg/L. At the end of exposure (day 77), enrichment functions ranged from 7772 L/kg dry mass in the 8.9-µg/L treatment to 23 495 L/kg dry mass in the 0.12-µg/L treatment, and trophic transfer factors for benthic macroinvertebrates ranged from 0.49 for Gammaridae to 2.3 for Chironomidae. Selenium accumulated in fathead minnow ovaries to concentrations near or above the current US Environmental Protection Agency criterion (15.1 µg/g dry mass for fish ovary/egg) in the 1.0- and 8.9-µg/L treatments, suggesting that, depending on aqueous Se speciation, such exposures have the potential to cause Se accumulation in fish to levels of concern in cold-water, boreal lake systems. Environ Toxicol Chem 2019;38:1954-1966. © 2019 SETAC.

Neonicotinoids and other agricultural stressors collectively modify aquatic insect communities

Threats to wetland water quality and aquatic insect secondary production in agricultural landscapes are multifaceted and are known to vary spatially and temporally. We designed this study with the aim to disentangle the effects of multiple stressors on emerging aquatic insects from wetlands impacted by intensive agricultural practices and receiving runoff from neonicotinoid-treated canola. A total of 22 semi-permanent wetlands were monitored over two growing seasons (11 different wetlands per year) in central Saskatchewan, Canada. Over the two sampling years, dipterans from the families Chironomidae (60-67%), Muscidae (13-15%) and Ceratopogonidae (7-13%) made up the majority of emergent taxa, representing 80-95% of the total emergence. Multivariate ordination analyses of eight water quality and nine wetland habitat variables revealed that neonicotinoid concentration, turbidity, vegetation disturbance, and continuity of a vegetative grass buffer zone were significant factors influencing the aquatic insect taxa composition. Generalized linear mixed effects models indicated that total insect emergence over time was significantly predicted by neonicotinoid concentrations (imidacloprid toxic equivalency, TEQ) and vegetation disturbance. Higher neonicotinoid concentrations negatively affected insect emergence over time, whereas vegetation disturbance increased total emergence, likely due to the abundance of disturbance-tolerant taxa. Overall, we observed community-level responses driven by multiple indicators of wetland degradation (insecticides, turbidity, and vegetation disturbance). Collectively, these multivariate field data provide an in-depth understanding of how agricultural management practices, including neonicotinoid use, interact to shape wetland aquatic insect communities.

Neonicotinoid insecticide mixtures: Evaluation of laboratory-based toxicity predictions under semi-controlled field conditions

Neonicotinoid insecticide mixtures are frequently detected in aquatic environments in agricultural regions. Recent laboratory studies have indicated that neonicotinoid mixtures can elicit greater-than-additive toxicity in sensitive aquatic insects (e.g. Chironomus dilutus). However, this has yet to be validated under field conditions. In this study, we compared the chronic (28- and 56-day) toxicity of three neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) and their mixtures to natural aquatic insect communities. Using experimental in-situ enclosures (limnocorrals), we exposed wetland insects to single-compounds and binary mixtures at equitoxic concentrations (1 toxic unit under the principle of Concentration Addition). We assessed the composition of all emerged insect taxa and the cumulative Chironomidae emergence and biomass over time. In treated limnocorrals, there were subtle shifts in community composition, with greater mean proportions of emergent Trichoptera and Odonata. Cumulative emergence and biomass increased over time and there was a significant interaction between time and treatment. At 28 days, cumulative Chironomidae emergence and biomass were not significantly different between neonicotinoid treatments and controls. However, cumulative emergence in the imidacloprid, clothianidin, and clothianidin-thiamethoxam treatments were 42%, 20%, and 44% lower than predicted from applied doses. At 56 days, effects on cumulative emergence and biomass were significant for imidacloprid, clothianidin, and the clothianidin-thiamethoxam mixture. Contrary to laboratory predictions, mixtures were not more toxic than single compounds under semi-controlled field settings. Furthermore, only clothianidin significantly shifted sex-ratios towards female-dominated populations. Results showed that the responses of natural Chironomidae populations to neonicotinoids and their mixtures cannot be adequately predicted from laboratory-derived single-species models, and although occasional overdosing may have influenced the magnitude of effects, reductions in Chironomidae emergence and biomass can occur at average neonicotinoid concentrations below some current water quality guidelines. Therefore, neonicotinoid guidelines should be revised to ensure that Chironomidae and other sensitive aquatic insects inhabiting agricultural wetlands are adequately protected.

Early chemical and toxicological risk characterization of inorganic constituents in surface water from the Canadian oil sands first large-scale end pit lake

End pit lakes (EPLs) have been proposed as a method for the long-term reclamation of process water and fluid fine tailings (FFT) produced from surface mining within the Canadian oil sands. These waste products contain elevated concentrations of dissolved organics, metals, and salts which reduce surface water quality and are toxic to aquatic organisms. This study measured the concentrations of inorganic constituents in surface water from the industry's first large-scale EPL over the course of a three-year period (2014-2016). The toxicological risk was subsequently assessed to identify constituents of concern that may impair surface water quality necessary for the development of a functional aquatic ecosystem or for release to the surrounding environment. Changes in surface water concentrations over the three-year period were strongly correlated with hydrological processes occurring within the lake: advective-diffusive chemical influx from FFT pore water to the overlying surface water was offset by efflux via continuous manual pumping (freshwater in, process water out). These processes resulted in a net dilution effect of approximately 5-10% per year, however, a significant chemical mass is expected to persist within the underlying FFT. Elevated salinity (as Na⁺, Cl^-, HCO₃^-) and concentrations of boron and nickel were predicted to pose very high toxicological risk to aquatic organisms. Despite these risks, the discovery of wild Daphnia pulex in the August 2016 sample suggested that surface water quality was sufficient to support populations of certain salt-tolerant zooplankton and primary producers. However, the time required for development into a robust aquatic ecosystem remains unknown.

Trapped river otters (Lontra canadensis) from central Saskatchewan differ in total and organic mercury concentrations by sex and geographic location

Mercury (Hg) in wildlife remains of great concern, especially for apex piscivores. Despite this, exposure information from many species in many areas is lacking, so that management decisions are hampered. Here we examine Hg concentrations in fur, liver, and kidney tissues from river otters ( Lontra canadensis (Schreber, 1777)) ( n = 203) to quantify existing Hg concentrations over a broad geographic area in Saskatchewan. Mean fur total Hg (THg) (9.68 ± 7.52 mg/kg fresh weight (f.w.)) was significantly correlated with THg and organic Hg (OHg) in liver and kidney tissue, showcasing the potential for using fur as a noninvasive method of monitoring Hg in top-level mammals. Livers of males had higher mean OHg concentrations than livers of females (males: 2.71 mg/kg d.w., females: 1.87 mg/kg d.w.), but not significantly so. No sex-related differences were observed in kidney OHg concentrations. THg concentrations in otter fur collected in the Boreal Shield ecozone (Churchill River Upland) were significantly higher (mean = 16.1 mg/kg f.w.) than in otter fur collected from the Boreal Plain ecozone (mean = 8.59 mg/kg f.w.). Fur from otters ( n = 20; trapping block N66) trapped near a decommissioned smelter contained the highest concentrations of THg in the study (mean = 18.4 mg/kg f.w.).

Community-level and phenological responses of emerging aquatic insects exposed to 3 neonicotinoid insecticides: An in situ wetland limnocorral approach

Seasonal aquatic insect emergence represents a critical subsidy link between aquatic and terrestrial ecosystems. Early and late instar larvae developing in wetlands near neonicotinoid-treated cropland can be at risk of chronic insecticide exposure. In the present study, an in situ wetland limnocorral experiment compared emergent insect community responses to imidacloprid, clothianidin, and thiamethoxam. Twenty-one limnocorrals were dosed weekly for 9 wk to target peak nominal doses of 0.0, 0.05, or 0.5 μg/L, followed by a 6-wk recovery period. Thirty-nine aquatic insect taxa were recorded but 11 taxa groups made up 97% of the community composition. Principal response curves (PRCs) indicated that during the dosing period, community composition among the treatments resembled the controls. During the 6-wk recovery period, significant deviance was observed in the high imidacloprid treatment with similar trends in the clothianidin treatment, suggesting that community effects from neonicotinoid exposure can be delayed. Non-biting midges (Diptera: Chironomidae) and damselflies (Odonata: Zygoptera) emerged 18 to 25 d earlier than controls in the imidacloprid and clothianidin neonicotinoid treatments, with no effects from thiamethoxam treatments. These data suggest that phenology and subtle community effects can occur at measured neonicotinoid concentrations of 0.045 (imidacloprid) and 0.038 μg/L (clothianidin) under chronic repeated exposure conditions. Synchronization and community dynamics are critical to aquatic insects and consumers; thus, neonicotinoids may have broad implications for wetland ecosystem function. Environ Toxicol Chem 2018;37:2401-2412. © 2018 SETAC.

Can chronic exposure to imidacloprid, clothianidin, and thiamethoxam mixtures exert greater than additive toxicity in Chironomus dilutus?

Widespread agricultural use of neonicotinoid insecticides has resulted in frequent detection of mixtures of these compounds in global surface waters. Recent evidence suggests that neonicotinoid mixtures can elicit synergistic toxicity in aquatic insects under acute exposure conditions, however this has not been validated for longer exposures more commonly encountered in the environment. Therefore, we aimed to characterize the chronic (28-day) toxicity of imidacloprid, clothianidin, and thiamethoxam mixtures under different doses and mixture ratios to determine if the assumption of synergistic toxicity would hold under more environmentally realistic exposure settings. The sensitive aquatic insect Chironomus dilutus was used as a representative test species, and successful emergence was used as a chronic endpoint. Applying the MIXTOX modeling approach, predictive parametric models were fitted using single-compound toxicity data and statistically compared to observed toxicity in subsequent mixture tests. Imidacloprid-clothianidin, clothianidin-thiamethoxam and imidacloprid-clothianidin-thiamethoxam mixtures did not significantly deviate from concentration-additive toxicity. However, the cumulative toxicity of the imidacloprid-thiamethoxam mixture deviated from the concentration-additive reference model, displaying dose-ratio dependent synergism and resulting in up to a 10% greater reduction in emergence from that predicted by concentration addition. Furthermore, exposure to select neonicotinoid mixtures above 1.0 toxic unit tended to shift sex-ratios toward more male-dominated populations. Results indicate that, similar to acute exposures, the general assumption of joint additivity cannot adequately describe chronic cumulative toxicity of all neonicotinoid mixtures. Indeed, our observations of weak synergism and sex-ratio shifts elicited by some mixture combinations should be considered in water quality guideline development and environmental risk assessment practices for neonicotinoid insecticides, and explored in further investigations of the effects of neonicotinoid mixtures on aquatic communities.

Predicting the bioavailability of sediment-bound uranium to the freshwater midge (Chironomus dilutus) using physicochemical properties

Assessment of uranium (U)-contaminated sediment is often hindered by the inability to accurately account for the physicochemical properties of sediment that modify U bioavailability. The present goal was to determine whether sediment-associated U bioavailability could be predicted over a wide range of conditions and sediment properties using simple regressions and a geochemical speciation model, the Windermere Humic Aqueous Model (WHAM7). Data from a U-contaminated field sediment bioaccumulation test, along with previously published bioaccumulation studies with U-spiked field and formulated sediments, were used to examine the models. Observed U concentrations in Chironomus dilutus larvae exposed to U-spiked and U-contaminated sediments correlated well (r²  > 0.74, p < 0.001) with the WHAM-calculated concentration of U bound to humic acid, indicating that humic acid may be a suitable surrogate for U binding sites (biotic ligands) in C. dilutus larvae. Subsequently, the concentration of U in C. dilutus was predicted with WHAM7 by numerically optimizing the equivalent mass of humic acid per gram of organism. The predicted concentrations of U in C. dilutus larvae exposed to U-spiked and U-contaminated field sediment compared well with the observed values, where one of the regression models provided a slightly better fit (mean absolute error = 18.1 mg U/kg dry wt) than WHAM7 (mean absolute error = 34.2 mg U/kg dry wt). The regression model provides a predictive capacity with a minimal number of variables, whereas WHAM7 provides additional complementary insight into the chemical variables influencing the speciation, sorption, and bioavailability of U in sediment. The present results indicate that physicochemical properties of sediment can be used to account for variability in U bioavailability as measured through bioaccumulation in chironomids exposed to U-contaminated sediments. Environ Toxicol Chem 2018;37:1146-1157. © 2017 SETAC.

Influence of different revegetation choices on plant community and soil development nine years after initial planting on a reclaimed coal gob pile in the Shanxi mining area, China

In order to identify suitable pioneer plant species for future revegetation of coal gob piles, a field survey was conducted to assess the success of different revegetation species and their influence on soil development nine years after initial planting on a reclaimed coal gob pile in the Yangquan mining area of Shanxi province, China. Data were analyzed using a quantitative classification method (TWINSPAN), ordination techniques (DCA and DCCA), Principal Component Analysis (PCA) and a geo-accumulation index (Igeo). The results revealed that the low levels of soil moisture and available N were the major limiting factors affecting plant community development on the coal gob pile, not metal toxicity. The plant communities that developed had significantly improved the topsoil (0-10cm) quality on the reclaimed coal gob pile nine years after initial planting (p<0.05), but the degree of improvement varied greatly with different planted species. Revegetation types comprised of the planted leguminous species, Medicago sativa and Amorpha fruticosa, and the non-leguminous species, Populus tomentosa and Salix babylonica had the best ecological restoration effects on the reclaimed coal gob pile. Revegetation using these species is therefore recommended for future reclamation of abandoned coal gob piles in this region.

Cumulative toxicity of neonicotinoid insecticide mixtures to Chironomus dilutus under acute exposure scenarios

Extensive agricultural use of neonicotinoid insecticide products has resulted in the presence of neonicotinoid mixtures in surface waters worldwide. Although many aquatic insect species are known to be sensitive to neonicotinoids, the impact of neonicotinoid mixtures is poorly understood. In the present study, the cumulative toxicities of binary and ternary mixtures of select neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) were characterized under acute (96-h) exposure scenarios using the larval midge Chironomus dilutus as a representative aquatic insect species. Using the MIXTOX approach, predictive parametric models were fitted and statistically compared with observed toxicity in subsequent mixture tests. Single-compound toxicity tests yielded median lethal concentration (LC50) values of 4.63, 5.93, and 55.34 μg/L for imidacloprid, clothianidin, and thiamethoxam, respectively. Because of the similar modes of action of neonicotinoids, concentration-additive cumulative mixture toxicity was the predicted model. However, we found that imidacloprid-clothianidin mixtures demonstrated response-additive dose-level-dependent synergism, clothianidin-thiamethoxam mixtures demonstrated concentration-additive synergism, and imidacloprid-thiamethoxam mixtures demonstrated response-additive dose-ratio-dependent synergism, with toxicity shifting from antagonism to synergism as the relative concentration of thiamethoxam increased. Imidacloprid-clothianidin-thiamethoxam ternary mixtures demonstrated response-additive synergism. These results indicate that, under acute exposure scenarios, the toxicity of neonicotinoid mixtures to C. dilutus cannot be predicted using the common assumption of additive joint activity. Indeed, the overarching trend of synergistic deviation emphasizes the need for further research into the ecotoxicological effects of neonicotinoid insecticide mixtures in field settings, the development of better toxicity models for neonicotinoid mixture exposures, and the consideration of mixture effects when setting water quality guidelines for this class of pesticides. Environ Toxicol Chem 2017;36:3091-3101. © 2017 SETAC.

Genetic Characterization of Periphyton Communities Associated with Selenium Bioconcentration and Trophic Transfer in a Simple Food Chain

A major source of uncertainty in predicting selenium (Se) distribution in aquatic food webs lies in the enrichment factor (EF), the ratio of Se bioconcentration in primary producers and microorganisms relative to the concentration of Se in the surrounding water. It has been well demonstrated that EFs can vary dramatically among individual algal taxa, but data are lacking regarding the influence of periphyton community composition on EFs for a given geochemical form of Se. Therefore, the goals of this study were first to assess whether different periphyton communities could be established in aquaria with the same starting inoculum using different light and nutrient regimes, and second, to determine if the periphyton assemblage composition influences the uptake of waterborne Se (as selenite) and subsequent Se transfer to a model macroinvertebrate primary consumer. Periphyton biofilms were grown in aquaria containing filtered pond water (from Saskatoon, SK) spiked with approximately 20 μg Se/L (mean measured concentration 21.0 ± 1.2 μg Se/L), added as selenite. Five different light and nutrient regimes were applied to the aquaria (three replicates per treatment) to influence biofilm community development. After 6 weeks of biofilm maturation, 40 to 80 immature cultured snails (Stagnicola elodes) were added to each aquarium. The bacterial and algal members of the periphyton community were characterized by targeted metagenomic analyses before and after addition of snails to ensure the snails themselves did not significantly alter the biofilm community. Samples were collected for Se analysis of water, periphyton, and whole-body snail. The nutrient and light treatments resulted in substantially different compositions of the periphytic biofilms, with each being relatively consistent across replicates and throughout the study. Although the aqueous concentration of dissolved Se administered to treatments was constant, uptake by the different periphytic biofilms differed significantly. Both the low-light (61.8 ± 12.1 μg Se/g d.w.) and high-light (30.5 ± 4.7 μg Se/g d.w.) biofilms, which were found to have high proportions of cyanobacteria, contained statistically higher concentrations of Se relative to the other treatments. Furthermore, the concentration of Se in bulk periphyton was predictive of Se bioaccumulation in grazing snails but as an inverse relationship, opposite to expectations. The trophic transfer factor was inversely correlated with periphyton enrichment factor (r = -0.841). A number of different bacterial and algal taxa were correlated (either positively or negatively) with Se accumulation in periphyton biofilm and snails. Recent advancements in genetic methods make it possible to conduct detailed characterization of periphyton assemblages and begin to understand the influence that periphyton composition has on Se biodynamics in aquatic systems.

Toxicity of aqueous vanadium to zooplankton and phytoplankton species of relevance to the athabasca oil sands region

Vanadium (V) is an abundant trace metal present in bitumen from the Athabasca Oil Sands (AOS) region in Alberta, Canada. The upgrading of bitumen can result in the production of large volumes of a carbonaceous material referred to as petroleum coke that contains V at elevated levels compared to the native bitumen. Previous studies have shown that coke has the capacity to leach ecotoxicologically relevant levels of V into water it contacts, yet limited data are available on the toxicity of aqueous V to planktonic organisms. Therefore, this study set out to evaluate the acute and chronic toxicity of V (as vanadate oxyanions) to freshwater zooplankton and phytoplankton species that are either commonly-used laboratory species, or species more regionally-representative of northern Alberta. Four cladoceran (2-d and 21-d tests) and two algal (3-d tests) species were exposed to V to obtain both acute and chronic toxicity estimates. Acute V toxicity (LC50s) ranged from 0.60mgV/L for Ceriodaphnia quadrangula to 2.17mgV/L for Daphnia pulex. Chronic toxicity estimates (EC50s) for cladoceran survival and reproduction were nearly identical within species and ranged from a low of 0.13 to a high of 0.46mgV/L for Daphnia dentifera and D. pulex, respectively. The lack of sublethal V toxicity in daphnia suggests a direct mechanism of toxicity through ion imbalance. Growth inhibition (EC50) of green algae occurred at concentrations of 3.24 and 4.12mgV/L for Pseudokirchneriella subcapitata and Scenedesmus quadricauda, respectively. Overall, cladocerans were more sensitive to V than green algae, with survival of the field-collected D. dentifera being approximately 2.5 to 3.5 times more sensitive to acute and chronic V exposure than the standard test species D. pulex. However, there were no significant differences in V toxicity between the field-collected cladocerans Simocephalus serrulatus and C. quadrangula, compared to the respective standard species D. pulex and Ceriodaphnia dubia. Similarly, there were no significant differences in sensitivity to V in the two algal species evaluated. Based on V concentrations reported in laboratory-generated coke leachates, zooplankton survival could be adversely impacted under conditions of chronic leachate exposure if V concentrations in the environment exceed 0.1mg/L. Furthermore, toxicity thresholds from commonly-used planktonic test species would likely have sufficed for derivation of a V water quality guideline (WQG) for protection of local aquatic communities near oil sands operations, but the new data presented here on V toxicity to more regionally-representative species will strengthen the database for WQG derivation.

Reduction of neonicotinoid insecticide residues in Prairie wetlands by common wetland plants

Neonicotinoid insecticides are frequently detected in wetlands during the early to mid-growing period of the Canadian Prairie cropping season. These detections also overlap with the growth of macrophytes that commonly surround agricultural wetlands which we hypothesized may reduce neonicotinoid transport and retention in wetlands. We sampled 20 agricultural wetlands and 11 macrophyte species in central Saskatchewan, Canada, over eight weeks to investigate whether macrophytes were capable of reducing movement of neonicotinoids from cultivated fields and/or reducing concentrations in surface water by accumulating insecticide residues into their tissues. Study wetlands were surrounded by clothianidin-treated canola and selected based on the presence (n=10) or absence (n=10) of a zonal plant community. Neonicotinoids were positively detected in 43% of wetland plants, and quantified in 8% of all plant tissues sampled. Three plant species showed high rates of detection: 78% Equisetum arvense (clothianidin, range: <LOQ-2.01μg/kg), 65% Alisma triviale (imidacloprid, range: <LOQ-2.51μg/kg), and 45% Typha latifolia (imidacloprid, range: <LOQ-2.61μg/kg, thiamethoxam, range: <LOQ-8.44μg/kg). Overall, unvegetated wetlands had higher detection frequency and water concentrations of clothianidin (β±S.E.: -0.77±0.26, P=0.003) and thiamethoxam (β±S.E.: -0.69±0.35, P=0.049) than vegetated wetlands. We assessed the importance of wetland characteristics (e.g. vegetative zone width, emergent plant height, water depth) on neonicotinoid concentrations in Prairie wetlands over time using linear mixed-effects models. Clothianidin concentrations were significantly lower in wetlands surrounded by taller plants (β±S.E.: -0.57±0.12, P≤0.001). The results of this study suggest that macrophytes can play an important role in mitigating water contamination by accumulating neonicotinoids and possibly slowing transport to wetlands during the growing season.

Comparative chronic toxicity of imidacloprid, clothianidin, and thiamethoxam to Chironomus dilutus and estimation of toxic equivalency factors

Nontarget aquatic insects are susceptible to chronic neonicotinoid insecticide exposure during the early stages of development from repeated runoff events and prolonged persistence of these chemicals. Investigations on the chronic toxicity of neonicotinoids to aquatic invertebrates have been limited to a few species and under different laboratory conditions that often preclude direct comparisons of the relative toxicity of different compounds. In the present study, full life-cycle toxicity tests using Chironomus dilutus were performed to compare the toxicity of 3 commonly used neonicotinoids: imidacloprid, clothianidin, and thiamethoxam. Test conditions followed a static-renewal exposure protocol in which lethal and sublethal endpoints were assessed on days 14 and 40. Reduced emergence success, advanced emergence timing, and male-biased sex ratios were sensitive responses to low-level neonicotinoid exposure. The 14-d median lethal concentrations for imidacloprid, clothianidin, and thiamethoxam were 1.52 μg/L, 2.41 μg/L, and 23.60 μg/L, respectively. The 40-d median effect concentrations (emergence) for imidacloprid, clothianidin, and thiamethoxam were 0.39 μg/L, 0.28 μg/L, and 4.13 μg/L, respectively. Toxic equivalence relative to imidacloprid was estimated through a 3-point response average of equivalencies calculated at 20%, 50%, and 90% lethal and effect concentrations. Relative to imidacloprid (toxic equivalency factor [TEF] = 1.0), chronic (lethality) 14-d TEFs for clothianidin and thiamethoxam were 1.05 and 0.14, respectively, and chronic (emergence inhibition) 40-d TEFs were 1.62 and 0.11, respectively. These population-relevant endpoints and TEFs suggest that imidacloprid and clothianidin exert comparable chronic toxicity to C. dilutus, whereas thiamethoxam induced comparable effects only at concentrations an order of magnitude higher. However, the authors caution that under field conditions, thiamethoxam readily degrades to clothianidin, thereby likely enhancing toxicity. Environ Toxicol Chem 2017;36:372-382. © 2016 SETAC.

The role of sediment properties and solution pH in the adsorption of uranium(VI) to freshwater sediments

Uranium (U) can enter aquatic environments from natural and anthropogenic processes, accumulating in sediments to concentrations that could, if bioavailable, adversely affect benthic organisms. To better predict the sorption and mobility of U in aquatic ecosystems, we investigated the sediment-solution partition coefficients (K_d) of U for nine uncontaminated freshwater sediments with a wide range of physicochemical characteristics over an environmentally relevant pH range. Test solutions were reconstituted to mimic water quality conditions and U(VI) concentrations (0.023-2.3 mg U/L) found downstream of Canadian U mines. Adsorption of U(VI) to each sediment was greatest at pH 6 and 7, and significantly reduced at pH 8. There were significant differences in pH-dependent sorption among sediments with different physicochemical properties, with sorption increasing up until thresholds of 12% total organic carbon, 37% fine fraction (≤50 μm), and 29 g/kg of iron content. The K_d values for U(VI) were predicted using the Windermere Humic Aqueous Model (WHAM) using total U(VI) concentrations, and water and sediment physicochemical parameters. Predicted K_d-U values were generally within a factor of three of the observed values. These results improve the understanding and assessment of U sorption to field sediment, and quantify the relationship with sediment properties that may influence the bioavailability and ecological risk of U-contaminated sediments.

Associations between omega-3 fatty acids, selenium content, and mercury levels in wild-harvested fish from the Dehcho Region, Northwest Territories, Canada

To better understand the risks and benefits of eating wild-harvested fish from the Northwest Territories, Canada, levels of total mercury (HgT) and selenium (Se) and composition of omega-3 fatty acid (n-3 FA) were measured in muscle tissue of fish harvested from lakes in the Dehcho Region, Northwest Territories, Canada. Average HgT levels ranged from 0.057 mg/kg (cisco) to 0.551 mg/kg (northern pike), while average n-3 FA concentrations ranged from 101 mg/100 g (burbot) to 1,689 mg/100 g (lake trout). In contrast to HgT and n-3 FA, mean Se concentrations were relatively similar among species. Consequently, species such as lake whitefish, cisco, and longnose sucker displayed the highest nutrient levels relative to HgT content. Levels of HgT tended to increase with fish size, while Se and n-3 FA levels were typically not associated with fork length or fish weight. Interestingly, HgT concentration was occasionally inversely related to tissue nutrient content. Significant negative correlations were observed between Hg and n-3 FA for lake trout, northern pike, and walleye. There were also significant negative correlations between Hg and Se noted for lake whitefish, cisco, and northern pike. Samples with the highest nutritional content displayed, on occasion, lower levels of HgT. This study provides valuable information for the design of probabilistic models capable of refining public health messaging related to minimizing Hg risks and maximizing nutrient levels in wild-harvested fish in the Canadian subarctic.

Sediment properties influencing the bioavailability of uranium to Chironomus dilutus larvae in spiked field sediments

The partitioning of metals between dissolved and solid phases directly affects metal bioavailability to benthic invertebrates and is influenced by metal-binding properties of sediment phases. Little research has been done examining the effects of sediment properties on the bioavailability of uranium (U) to freshwater benthic invertebrates. In the present study, 18 field sediments with a wide range of properties (total organic carbon, fine fraction, cation exchange capacity, and iron content) were amended with the same concentrations of U to characterize the effects of these sediment properties on U bioavailability to freshwater midge, Chironomus dilutus. Bioaccumulation of U by C. dilutus larvae varied by over an order of magnitude when exposed to sediments spiked with 50 mg U kg(-1) d.w. (5-69 mg U kg(-1) d.w.) and 500 mg U kg(-1) d.w. (20-452 mg U kg(-1) d.w.), depending on the type of sediment. Variance in U bioaccumulation was best explained by differences in the cation exchange capacity, fine fraction (≤50 μm particle size), and Fe content of U-spiked sediment, with generated regression equations predicting observed bioaccumulation within a factor of two. The presented regression equations offer an easy-to-apply method for accounting for the influence of sediment properties on U bioavailability in freshwater sediment, with fine fraction being the single most practical variable. This research strongly supports that risk assessments and guidelines for U-contaminated sediments should not ignore the influence of sediment properties that can result in substantial differences in the bioaccumulation of U in benthic invertebrates.

Reconstructing the ecological impacts of eight decades of mining, metallurgical, and municipal activities on a small boreal lake in northern Canada

As a result of long-term metal mining and metallurgical activities, the sediment of Ross Lake (Flin Flon, MB, Canada) is highly contaminated with metals and other elements. Although the effluents likely were discharged into Ross Lake as early as the late 1920s, lake biophysical data were not collected until 1973, more than 4 decades after the onset of mining and municipal activities. The early influence of these activities on the ecology of Ross Lake is unknown, as are the effects of improvements to metallurgical effluent quality and discontinuation of municipal wastewater discharge into the lake's north basin. To address this knowledge gap, analyses typical of paleolimnological investigations were applied to cores of sediment collected in 2009 from the south basin of Ross Lake. Stratigraphic analyses of physicochemical sediment characteristics (e.g., the concentrations of metals and other elements, organic C, total N, and δ(13)C and δ(15)N values) and subfossil remains (diatoms, Chironomidae, Chaoborus, and Cladocera) were used to infer historical biological and chemical changes in Ross Lake. With the onset of mining activities, concentrations of various elements (e.g., As, Cr, Cu, Zn, and Se) increased dramatically in the sediment profile, eventually declining with improved tailings management. Nevertheless, concentrations of metals in recent sediments remain elevated compared with pre-industrial sediments. Constrained cluster analyses demonstrated distinct pre-industrial and postindustrial communities for both the diatoms and chironomids. The biodiversity of the postindustrial diatom assemblages were much reduced compared with the pre-industrial assemblages. The postindustrial chironomid assemblage was dominated by Chironomus and to a lesser extent by Procladius, suggesting that Ross Lake became a degraded environment. Abundances of Cladocera and Chaoborus were severely reduced in the postindustrial era, likely because of metals toxicity. Overall, improvements to the management of both metallurgical and municipal effluent are reflected in the physicochemical sediment record; nevertheless, the ecology of Ross Lake remains impaired and shows minimal signs of returning to a pre-industrial state. Recommendations are made regarding possible future investigations at this site and the need for a framework to help assess causation using paleolimnological and other site data.

Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: a review

Neonicotinoids, broad-spectrum systemic insecticides, are the fastest growing class of insecticides worldwide and are now registered for use on hundreds of field crops in over 120 different countries. The environmental profile of this class of pesticides indicate that they are persistent, have high leaching and runoff potential, and are highly toxic to a wide range of invertebrates. Therefore, neonicotinoids represent a significant risk to surface waters and the diverse aquatic and terrestrial fauna that these ecosystems support. This review synthesizes the current state of knowledge on the reported concentrations of neonicotinoids in surface waters from 29 studies in 9 countries world-wide in tandem with published data on their acute and chronic toxicity to 49 species of aquatic insects and crustaceans spanning 12 invertebrate orders. Strong evidence exists that water-borne neonicotinoid exposures are frequent, long-term and at levels (geometric means=0.13μg/L (averages) and 0.63μg/L (maxima)) which commonly exceed several existing water quality guidelines. Imidacloprid is by far the most widely studied neonicotinoid (66% of the 214 toxicity tests reviewed) with differences in sensitivity among aquatic invertebrate species ranging several orders of magnitude; other neonicotinoids display analogous modes of action and similar toxicities, although comparative data are limited. Of the species evaluated, insects belonging to the orders Ephemeroptera, Trichoptera and Diptera appear to be the most sensitive, while those of Crustacea (although not universally so) are less sensitive. In particular, the standard test species Daphnia magna appears to be very tolerant, with 24-96hour LC50 values exceeding 100,000μg/L (geometric mean>44,000μg/L), which is at least 2-3 orders of magnitude higher than the geometric mean of all other invertebrate species tested. Overall, neonicotinoids can exert adverse effects on survival, growth, emergence, mobility, and behavior of many sensitive aquatic invertebrate taxa at concentrations at or below 1μg/L under acute exposure and 0.1μg/L for chronic exposure. Using probabilistic approaches (species sensitivity distributions), we recommend here that ecological thresholds for neonicotinoid water concentrations need to be below 0.2μg/L (short-term acute) or 0.035μg/L (long-term chronic) to avoid lasting effects on aquatic invertebrate communities. The application of safety factors may still be warranted considering potential issues of slow recovery, additive or synergistic effects and multiple stressors that can occur in the field. Our analysis revealed that 81% (22/27) and 74% (14/19) of global surface water studies reporting maximum and average individual neonicotinoid concentrations respectively, exceeded these thresholds of 0.2 and 0.035μg/L. Therefore, it appears that environmentally relevant concentrations of neonicotinoids in surface waters worldwide are well within the range where both short- and long-term impacts on aquatic invertebrate species are possible over broad spatial scales.

Direct and indirect responses of a freshwater food web to a potent synthetic oestrogen

Endocrine-disrupting chemicals (EDCs) in municipal effluents directly affect the sexual development and reproductive success of fishes, but indirect effects on invertebrate prey or fish predators through reduced predation or prey availability, respectively, are unknown. At the Experimental Lakes Area in northwestern Ontario, Canada, a long-term, whole-lake experiment was conducted using a before-after-control-impact design to determine both direct and indirect effects of the synthetic oestrogen used in the birth control pill, 17α-ethynyloestradiol (EE2). Algal, microbial, zooplankton and benthic invertebrate communities showed no declines in abundance during three summers of EE2 additions (5-6 ng l(-1)), indicating no direct toxic effects. Recruitment of fathead minnow (Pimephales promelas) failed, leading to a near-extirpation of this species both 2 years during (young-of-year, YOY) and 2 years following (adults and YOY) EE2 additions. Body condition of male lake trout (Salvelinus namaycush) and male and female white sucker (Catostomus commersonii) declined before changes in prey abundance, suggesting direct effects of EE2 on this endpoint. Evidence of indirect effects of EE2 was also observed. Increases in zooplankton, Chaoborus, and emerging insects were observed after 2 or 3 years of EE2 additions, strongly suggesting indirect effects mediated through the reduced abundance of several small-bodied fishes. Biomass of top predator lake trout declined by 23-42% during and after EE2 additions, most probably an indirect effect from the loss of its prey species, the fathead minnow and slimy sculpin (Cottus cognatus). Our results demonstrate that small-scale studies focusing solely on direct effects are likely to underestimate the true environmental impacts of oestrogens in municipal wastewaters and provide further evidence of the value of whole-ecosystem experiments for understanding indirect effects of EDCs and other aquatic stressors.

Integrative assessment of selenium speciation, biogeochemistry, and distribution in a northern coldwater ecosystem

For the past decade, considerable research has been conducted at a series of small lakes receiving treated liquid effluent containing elevated selenium (Se) from the Key Lake uranium (U) milling operation in northern Saskatchewan, Canada. Several studies related to this site, including field collections of water, sediment, and biota (biofilm and/or periphyton, invertebrates, fish, and birds), semicontrolled mesocosm and in situ caging studies, and controlled laboratory experiments have recently been published. The aim of the present investigation was to compile the site-specific information obtained from this multidisciplinary research into an integrative perspective regarding the influence of Se speciation on biogeochemical cycling and food web transfer of Se in coldwater ecosystems. Within lakes, approximately 50% of sediment Se was in the form of elemental Se, although this ranged from 0% to 81% among samples. This spatial variation in elemental Se was positively correlated with finer particles (less sand) and percent total organic C content in sediments. Other Se species detected in sediments included selenosulfides, selenite, and inorganic metal selenides. In contrast, the major Se form in sediment-associated biofilm and/or periphyton was an organoselenium species modeled as selenomethionine (SeMet), illustrating the critical importance of this matrix in biotransformation of inorganic Se to organoselenium compounds and subsequent trophic transfer to benthic invertebrates at the base of the food web. Detritus displayed a Se speciation profile intermediate between sediment and biofilm, with both elemental Se and SeMet present. In benthic detritivore (chironomid) larvae and emergent adults, and in foraging and predatory fishes, SeMet was the dominant Se species. The proportion of total Se present as a SeMet-like species displayed a direct nonlinear relationship with increasing whole-body Se in invertebrates and fishes, plateauing at approximately 70% to 80% of total Se as a SeMet-like species. In fish collected from reference lakes, a selenocystine-like species was the major Se species detected. Similar Se speciation profiles were observed using 21-day mesocosm and in situ caging studies with native small-bodied fishes, illustrating the efficient bioaccumulation of Se and use of these semicontrolled approaches for future research. A simplified conceptual model illustrating changes in Se speciation through abiotic and biotic components of lakes was developed, which is likely applicable to a wide range of northern industrial sites receiving elevated Se loading into aquatic ecosystems.

Reconstructing long-term trends in municipal sewage discharge into a small lake in northern Manitoba, Canada

Ross Lake lies within the City of Flin Flon (Manitoba, Canada), a mining community originally formed by the Hudson Bay Mining and Smelting Company (now Hudbay Minerals Inc.) in 1927. At the time of this investigation, a continuous effluent stream from Hudbay Minerals (approximately 80 years) and a discontinuous and unknown amount of raw and minimally treated municipal sewage (>20 years, likely ending in 1951) was discharged into the north basin of the lake. Maximum concentrations of fecal sterols, such as coprostanol and terrestrial phytosterols, such as: β-sitosterol, campesterol, stigmastanol were measured in vertical sections of sediment cores, collected from Ross Lake, in the 15-16-cm section, which likely corresponds to the 1930s. Concentrations of coprostanol increased from <1 μg g(-1) in older sediments, to 252.3 μg g(-1) organic carbon at the peak. Observed changes in concentrations of sterols, in combination with radiometric dating and changes to sediment physicochemical characteristics, support the conclusion that sediments of a depth of less than 17.5-cm depth were deposited during the post-industrial era from approximately 1930 onwards. Ratios of coprostanol to cholesterol>1, peaking at 3.6 are consistent with anecdotal information that municipal sewage was discharged into Ross Lake during the early years of urbanization, prior to changes in treatment of sewage and discharge practices that began in 1951. Finally, historical concentrations of terrestrial phytosterols followed trends similar to those of coprostanol and cholesterol and may possibly be the result of an increase in the flux of terrestrial organic matter into Ross Lake as the result of regional deforestation due to logging and fire.

Effects of Columbia River water on early life-stages of white sturgeon (Acipenser transmontanus)

The white sturgeon (Acipenser transmontanus) population that resides in the Columbia River in British Columbia (BC), Canada, has suffered recruitment failures for more than three decades. During the summers of 2008 and 2009, studies were performed to determine whether exposure to water downstream of a metal smelter in Trail, BC affected survival or growth of early life-stages of white sturgeon through 60+ days post-fertilization (dpf). In both years, there were no significant differences in survival of fish that were exposed to water from downstream compared to water from upstream of the smelter. At 20-21dpf, average mortality was 2.4 percent and 12 percent in upstream water for 2008 and 2009, respectively, which was similar to the average mortality of 3.8 percent and 7.2 percent in downstream water for 2008 and 2009, respectively. Relatively great mortality after 20-21dpf complicated analysis of the subchronic exposure, but use of a survival analysis indicated that the average fish died at 25-29dpf, regardless of whether the water to which they were exposed came from upstream or downstream of the smelter. In addition, measured concentrations of metals in river water were less than the threshold for adverse effects on early life stages of white sturgeon. Based upon these analyses, it is not likely that current concentrations of metals in the Columbia River in southern BC are adversely affecting survival of early life stages of white sturgeon larvae.

An in situ assessment of selenium bioaccumulation from water-, sediment-, and dietary-exposure pathways using caged Chironomus dilutus larvae

An in situ caging study was conducted downstream of a metal mine in northern Canada to determine the significance of surface water versus sediment exposure on selenium (Se) bioaccumulation in the benthic invertebrate Chironomus dilutus. Laboratory-reared C. dilutus larvae were exposed to either site-specific whole-sediment and surface water or surface water only for 10 d at sites with differing sediment and Se characteristics. Results showed elevated whole-body Se concentrations in C. dilutus larvae when exposed to sediment and water, compared with larvae exposed to Se in the surface water only at concentrations ranging from <1 µg Se/L to 12 µg Se/L. In response to these findings, a second in situ experiment was conducted to investigate the importance of dietary Se (biofilm and detritus) versus whole-sediment-exposure pathways. Larvae exposed to sediment detritus had the highest Se concentrations after 10 d of exposure (15.6 ± 1.9 µg/g dry wt) compared with larvae exposed to whole-sediment (12.9 ± 1.7 µg/g dry wt) or biofilm (9.9 ± 1.6 µg/g dry wt). Detritus and biofilm appear to be enriched sources of organic Se, which are more bioaccumulative than inorganic Se. Midge larvae from the reference treatment contained elevated concentrations of diselenides (i.e., selenocystine), while larvae from the biofilm treatment had the highest concentrations of selenomethionine-like compounds, which may be a biomarker of elevated Se exposures derived from anthropogenic sources. Whenever possible, Se concentrations in the organic fraction of sediment should be measured separately from whole-sediment Se and used for more accurate ecological risk assessments of potential Se impacts on aquatic ecosystems.

Derivation of no-effect and reference-level sediment quality values for application at Saskatchewan uranium operations

To date, the majority of empirical approaches used to derive sediment quality values (SQVs) have focused on metal concentrations in sediment associated with adverse effects on benthic invertebrate communities. Here, we propose the no-effect (NE) approach. This SQV derivation methodology uses metal concentrations in sediment associated with unaffected benthic communities (i.e., from reference sites and lightly contaminated no-effect sites) and accounts for local benthic invertebrate tolerance and potential chemical interactions at no-effect exposure sites. This NE approach was used to propose alternative regional SQVs for uranium operations in northern Saskatchewan. Three different sets of NE values were derived using different combinations of benthic invertebrate community effects criteria (abundance, richness, evenness, Bray-Curtis index). Additionally, reference values were derived based solely on sediment metal concentrations from reference sites. In general, NE values derived using abundance, richness, and evenness (NE1 and NE2 values) were found to be higher than the NE values derived using all four metrics (NE3 values). Derived NE values for Cr, Cu, Pb, and V did not change with the incorporation of additional effects criteria due to a lack of influence from the uranium operations on the concentrations of these metals in sediment. However, a gradient of exposure concentrations was apparent for As, Mo, Ni, Se, and U in sediment which allowed for tolerable exposure levels of these metals in sediment to be defined. The findings from this assessment have suggested a range of new, alternate metal SQVs for use at uranium operations in northern Saskatchewan.