Selenium toxicity to invertebrates: will proposed thresholds for toxicity to fish and birds also protect their prey?

Guidance on assessing the potential impacts of selenium in freshwater ecosystems

Despite decades of fate and effects studies, environmental selenium (Se) contamination and management remain an issue for many freshwater systems in North America. Several regulatory bodies have promulgated updated targets or management levels for Se; however, additional guidance on best practices for monitoring Se to protect freshwater aquatic life is warranted. In this article, we describe current approaches to assessing the ecological risks of Se in impaired freshwater systems and outline recommended methods for collecting and analyzing biological and abiotic samples and interpreting data. Because reproductive impairment of fish populations is most commonly used to determine the potential impacts of Se, several biological factors that could affect Se toxicity are explored, including diet, trophic positions, reproductive biology, body size and maturity, migratory movements, and use of seasonal habitats. Measuring Se concentrations in mature eggs is the most reliable metric for estimating potential reproductive impairment in fish populations because the range of toxicity thresholds is relatively narrow for all but a few tolerant fish species. In situations where collecting mature eggs is not feasible, we review the use of alternative fish tissue for estimating potential effects. Factors affecting Se uptake from freshwater are also considered with guidance on collecting abiotic (e.g., water and sediment) and biotic components of aquatic food webs (e.g., macroinvertebrates, biofilm). Integr Environ Assess Manag 2024;00:1-16. © 2024 SETAC.

Mechanistic characterization of waterborne selenite uptake in the water flea, Daphnia magna, indicates water chemistry affects toxicity in coal mine-impacted waters

Concentrations of selenium that exceed regulatory guidelines have been associated with coal mining activities and have been linked to detrimental effects on aquatic ecosystems and the organisms therein. Although the major route of selenium uptake in macroinvertebrates is via the diet, the uptake of waterborne selenite (HSeO3-), the prominent form at circumneutral pH, can be an important contributor to selenium body burden and thus selenium toxicity. In the current study, radiolabelled selenite (Se75) was used to characterize the mechanism of selenite uptake in the water flea, Daphnia magna. The concentration dependence (1-32 μM) of selenite uptake was determined in 1-hour uptake assays in artificial waters that independently varied in bicarbonate, chloride, sulphate, phosphate and selenate concentrations. At concentrations representative of those found in highly contaminated waters, selenite uptake was phosphate-dependent and inhibited by foscarnet, a phosphate transport inhibitor. At higher concentrations, selenite uptake was dependent on waterborne bicarbonate concentration and inhibited by the bicarbonate transporter inhibitor DIDS (4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid). These findings suggest that concentrations of phosphate in coal mining-affected waters could alter selenite uptake in aquatic organisms and could ultimately affect the toxic impacts of selenium in such waters.

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.

The impact of selenium on insects

Selenium, a naturally occurring metalloid, is an essential trace element for many higher organisms, including humans. Humans primarily become exposed to selenium by ingesting food products containing trace amounts of selenium compounds. Although essential in these small amounts, selenium exhibits toxic effects at higher doses. Previous studies investigating the effects on insects of order Blattodea, Coleoptera, Diptera, Ephemeroptera, Hemiptera, Hymenoptera, Lepidoptera, Odonata, and Orthoptera revealed impacts on mortality, growth, development, and behavior. Nearly every study examining selenium toxicity has shown that insects are negatively affected by exposure to selenium in their food. However, there were no clear patterns of toxicity between insect orders or similarities between insect species within families. At this time, the potential for control will need to be determined on a species-by-species basis. We suspect that the multiple modes of action, including mutation-inducing modification of important amino acids as well as impacts on microbiome composition, influence this variability. There are relatively few studies that have examined the potential effects of selenium on beneficial insects, and the results have ranged from increased predation (a strong positive effect) to toxicity resulting in reduced population growth or even the effective elimination of the natural enemies (more common negative effects). As a result, in those pest systems where selenium use is contemplated, additional research may be necessary to ascertain if selenium use is compatible with key biological control agents. This review explores selenium as a potential insecticide and possible future directions for research.

Laboratory study of Se speciation in the sediment and oligochaete Lumbriculus variegatus from an aquatic environment

Sediments are the major sink for selenium (Se) in aquatic environments. Se speciation in sediments is crucial for its bioavailability and toxicity in benthos, but this is relatively understudied. In this study, the background levels of Se in the river sediments, fish flakes, and Lumbriculus variegatus were also detected. Then, the dynamic changes of selenium speciation and concentrations in sediments were investigated after adding selenite (Se(IV)) and seleno-L-methionine (Se-Met) in the sediments for 90 and 7 days, and the accumulation and depuration of Se(IV) and Se-Met for 7 days in the oligochaete L. variegatus were also explored. Without the presence of worms, the levels of Se(IV) in the sediments were relatively stable within 7 days but showed a decreasing trend during the 90 days of aging. In contrast, Se-Met in the sediments showed a sharp decrease within 3 days of aging. The LC₅₀-96 h values of Se(IV) and Se-Met in L. variegatus were 372.6 and 9.4 μg/g, respectively. Interestingly, the dominant Se species in Se(IV)- or Se-Met-treated L. variegatus was Se-Met, whose level was increased with time in 7 days of exposure. Se was barely depurated from L. variegatus during the 8 days of the depuration period. This study has provided indispensable data on the levels of total Se in the abiotic and biotic matrices and the biodynamics of Se in a representative benthos, which could better understand the ecological risk of Se to the freshwater benthic communities.

Probiotics as a promising prophylactic tool to reduce levels of toxic or potentially toxic elements in bees

Bees are precious living beings for our planet. Thanks to their essential service of pollination, these insects allow the maintenance of biodiversity and the variety and amount of food available. Unfortunately, we are observing an increasingly devastating reduction of bee families and other pollinating insects for factors related to human activities, environmental pollution, diseases and parasites, compromise of natural habitats, and climate change. We show that probiotics can protect bees from element pollution. We collected bees, beeswax, honey, pollen, and propolis directly from hives in a rural area of central Italy to investigate the content of 41 elements in control (not supplemented with probiotics) and experimental (supplemented with probiotics) groups. Our data show a significantly lower concentration of some elements (Ba, Be, Cd, Ce, Co, Cu, Pb, Sn, Tl, and U) in experimental bees than in control groups, indicating a possible beneficial effect of probiotics in reducing the absorption of chemicals. This study presents the first data on element levels after probiotics have been fed to bees and provides the basis for future research in several activities relating to the environment, agriculture, economy, territory, and medicine.

Longer-Term Adverse Effects of Selenate Exposures on Hematological and Serum Biochemical Variables in Air-Breathing Fish Channa punctata (Bloch, 1973) and Non-air Breathing Fish Ctenopharyngodon Idella (Cuvier, 1844): an Integrated Biomarker Response Approach

To examine the spectrum of selenium toxicity between hardy and less hardy species of the same life stages, short-term and longer-term exposures in juvenile air-breathing fish Channa punctata (Bloch, 1973) and non-air-breathing fish Ctenopharyngodon idella (Cuvier, 1844) were assessed. Acute exposures revealed a greater 96-h median lethal concentration (LC₅₀) for C. punctata (14.67 mg/l) compared to C. idella (7.98 mg/l). During their chronic exposure, both fishes' hemoglobin content (Hb), red blood cells (RBC), and hematocrit (HCT) markedly decreased (p < 0.05), although their clotting time (CT) significantly increased. At 96 h, immune-modulation was observed where total protein and serum globulin levels in both fishes considerably decreased (p < 0.05) compared to the first exposure at 0 days, although total glucose, triglyceride, cholesterol, and albumin levels in both fishes significantly increased (p < 0.05) at 30 days. The lower cholesterol levels in C. punctata compared to C. idella are suggestive of a disrupted cholesterol transformation pathway. The greater total protein, triglyceride, albumin, and globulin levels in C. punctata compared to C. idella are suggestive of a comparatively robust immune capacity. In essence, selenium toxicity in the wild could manifest as disrupted metabolic pathways and downregulated immune capacity for less hardy species. In general, both fish species displayed significant alterations in their hematological and biochemical responses with increased exposure duration and elevated toxicant concentrations. This comparative investigation could improve the knowledge-spectrum of selenium toxicity in the wild as well as an understanding of secondary stress responses critically evident in hematological and biochemical parameters.

Relative importance of two correlated variables on aquatic macroinvertebrate communities in a Colorado Front Range river: selenium and urbanization

Urbanization and elevated selenium can negatively affect aquatic macroinvertebrate communities. These factors are often highly correlated in streams along the Front Range of the Rocky Mountains, USA. Understanding which factor is the primary driver of macroinvertebrate community health would aid in the development of appropriate management actions to mitigate their influence. Data collected from three sites in the Big Thompson River, Colorado, in seven different years from 2006 to 2016 were used to develop a random forest model to determine the relative importance of an index of urbanization and dissolved selenium levels in predicting the relative status of macroinvertebrate communities as measured by Colorado multi-metric index (MMI) scores. Based on the percent increase in mean square error (%incMSE) variable importance measure, dissolved selenium has a greater influence on MMI scores than a development index (19.5% vs 15.2%). There is a significantly negative relationship between MMI scores and dissolved selenium levels. This relationship predicts a MMI score of 29.2 under the current dissolved selenium standard of 4.6 µg/L and 38.6 under the suggested lower standard of 3.1 µg/L. Although improvements in MMI score may result with any reduction in dissolved selenium, other factors may limit the maximum expected MMI scores in the absence of selenium as the intercept of the relationship is 57.9 on a scale of 0-100.

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.

Developing As and Cu Tissue Residue Thresholds to Attain the Good Ecological Status of Rivers in Mining Areas

The study was performed on residue-effects datasets from polluted and unpolluted sites in the Nalón River basin (northern Spain). The effects were measured in terms of alteration of field macroinvertebrate communities, and measured as ecological status scores, and number of families and abundance of Ephemeroptera, Plecoptera and Trichoptera (EPT). Non-linear regression models of the field-measured tissue residues in 10 taxa related to the ecological status of the macroinvertebrate communities were used to derive effective tissue residues (ERs). These were estimated for the good/moderate boundary defined by the ecological quality ratio (EQRs) score and for the 50% reduction of EQR and EPT metrics. As, Cu, Hg and Se ERs were calculated for several macroinvertebrate taxa with different feeding styles. The ER dataset allowed us to estimate As and Cu hazardous concentrations (HC), using species sensitivity distribution models, and were interpreted as community thresholds. Further studies for Hg and Se are needed to complete the database required for HC estimation. The reliability and differences of the several thresholds were tested in a risk assessment using a tissue-residue approach (TRA) conducted with field organisms from Cauxa Creek, a tributary from the same basin exposed to high levels of metals in the sediments due to gold mining activities. This risk assessment identified that As and Cu tissue residues satisfactorily explained the reduction in the ecological status of the macroinvertebrate assemblages. Our results indicate that TRA can help in setting future environmental quality standards for the protection of aquatic biota.

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.

Lethal impacts of selenium counterbalance the potential reduction in mercury bioaccumulation for freshwater organisms

Mercury (Hg), a potent neurotoxic element, can biomagnify through food webs once converted into methylmercury (MeHg). Some studies have found that selenium (Se) exposure may reduce MeHg bioaccumulation and toxicity, though this pattern is not universal. Se itself can also be toxic at elevated levels. We experimentally manipulated the relative concentrations of dietary MeHg and Se (as selenomethionine [SeMet]) for an aquatic grazer (the mayfly, Neocloeon triangulifer) and its food source (diatoms). Under low MeHg treatment (0.2 ng/L), diatoms exhibited a quadratic pattern, with decreasing diatom MeHg concentration up to 2.0 μg Se/L and increasing MeHg accumulation at higher SeMet concentrations. Under high MeHg treatment (2 ng/L), SeMet concentrations had no effect on diatom MeHg concentrations. Mayfly MeHg concentrations and biomagnification factors (concentration of MeHg in mayflies: concentration of MeHg in diatoms) declined with SeMet addition only in the high MeHg treatment. Mayfly MeHg biomagnification factors decreased from 5.3 to 3.3 in the high MeHg treatment, while the biomagnification factor was constant with an average of 4.9 in the low MeHg treatment. The benefit of reduced MeHg biomagnification was offset by non-lethal effects and high mortality associated with 'protective' levels of SeMet exposure. Mayfly larvae escape behavior (i.e., startle response) was greatly reduced at early exposure days. Larvae took nearly twice as long to metamorphose to adults at high Se concentrations. The minimum number of days to mayfly emergence did not differ by SeMet exposure, with an average of 13 days. We measured an LC50_SeMet for mayflies of 3.9 μg Se/L, with complete mortality at concentrations ≥6.0 μg Se/L. High reproductive mortality occurred at elevated SeMet exposures, with only 0-18% emergence at ≥4.12 μg Se/L. Collectively, our results suggest that while there is some evidence that Se can reduce MeHg accumulation at the base of the food web at specific exposure levels of SeMet and MeHg, Se is also toxic to mayflies and could lead to negative effects that extend across ecosystem boundaries.

Current permissible levels of metal pollutants harm terrestrial invertebrates

The current decline of invertebrates worldwide is alarming. Several potential causes have been proposed but metal pollutants, while being widespread in the air, soils and water, have so far been largely overlooked. Here, we reviewed the results of 527 observations of the effects of arsenic, cadmium, lead and mercury on terrestrial invertebrates. These four well-studied metals are considered as priorities for public health and for which international regulatory guidelines exist. We found that they all significantly impact the physiology and behavior of invertebrates, even at levels below those recommended as 'safe' for humans. Our results call for a revision of the regulatory thresholds to better protect terrestrial invertebrates, which appear to be more sensitive to metal pollution than vertebrates. More fundamental research on a broader range of compounds and species is needed to improve international guidelines for metal pollutants, and to develop conservation plans to protect invertebrates and ecosystem services.

Impacts to water quality and biota persist in mining-influenced Appalachian streams

Elevated dissolved major ions (salinization) from surface coal mining are a common impact to central Appalachian headwater streams. Salinization is associated with alterations of benthic macroinvertebrate communities, as many organisms are adapted to the naturally dilute streams of the region. These geochemical and biological alterations have been observed in streams decades after mining, but it remains unclear whether and at what rate water quality and aquatic biota recover after mining. To address this issue, we analyzed temporal trends in specific conductance (SC), ion matrix ratios, and benthic macroinvertebrate communities over an eight-year period in 23 headwater streams, including 18 salinized by surface coal mining. We found strong, negative correlations between SC and diversity of benthic macroinvertebrate communities. Temporal trend analysis demonstrated limited recovery of water chemistry to natural background conditions. Five of the 18 mining-influenced streams exhibited declining SC; however, annual rates of decline in these streams ranged from 1.9% to 3.7% of mean annual SC, suggesting long time periods will be required to reach established benchmark values (ca. 25 years) or values observed in our five reference study streams (ca. 40 years). Similarly, there was limited evidence for recovery of macroinvertebrate community metrics, even in the few mining-influenced streams with decreasing SC. These findings indicate that salinization and its biological effects persist, likely for decades, in central Appalachian headwater streams. Our work also highlights the value of long-term monitoring data for assessing recovery potential of salinized freshwaters, as well as the need for improved understanding of water quality and biological recovery processes and time frames.

Selenium Bioaccumulation Across Trophic Levels and Along a Longitudinal Gradient in Headwater Streams

Toxic effects of selenium (Se) contamination in freshwaters have been well documented. However, study of Se contamination has focused on lentic and larger order lotic systems, whereas headwater streams have received little scrutiny. In central Appalachia, surface coal mining is a common Se source to headwater streams, thus providing a useful system to investigate Se bioaccumulation in headwater food chains and possible longitudinal patterns in Se concentrations. Toward that end, we assessed Se bioaccumulation in 2 reference and 4 mining-influenced headwater streams. At each stream, we sampled ecosystem media, including streamwater, particulate matter (sediment, biofilm, leaf detritus), benthic macroinvertebrates, salamanders, and fish, every 400 m along 1.2- and 1.6-km reaches. We compared media Se concentrations within and among streams and evaluated longitudinal trends in media Se concentrations. Selenium concentrations in sampled media were higher in mining-influenced streams compared with reference streams. We found the highest Se concentrations in benthic macroinvertebrates; however, salamanders and fish bioaccumulated Se to potentially harmful levels in mining-influenced streams. Only one stream demonstrated dilution of streamwater Se with distance downstream, and few longitudinal patterns in Se bioaccumulation occurred along our study reaches. Collectively, our results provide a field-based assessment of Se bioaccumulation in headwater food chains, from streamwater to fish, and highlight the need for future assessments of Se effects in headwater streams and receiving downstream waters. Environ Toxicol Chem 2020;39:692-704. © 2020 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.

Mortality, growth and metabolic responses by 1H-NMR-based metabolomics of earthworms to sodium selenite exposure in soils

The rapid development of selenium-enriched agriculture leads to the accumulation of selenium in the soil, which has an adverse impact on terrestrial ecosystems. In the present study, the mortality, growth inhibition rate and metabolism of earthworms were examined to investigate the toxicological effects of sodium selenite (Na₂SeO₃) on earthworms (Eisenia fetida) after exposuring for 14 days (d). We used ¹H-NMR-based metabolomics to identify sensitive biomarkers and explored the metabolic responses of earthworms exposed to Na₂SeO₃. The mortality and growth inhibition rate of earthworms exposed to 70 and 90 mg/kg Na₂SeO₃ were significantly higher than the rate of control group. The LC₅₀ (the median lethal concentration) of Na₂SeO₃ was 57.4 mg/kg in this artificial soil test of E. fetida exposed to Na₂SeO₃ for 14 d. However, there was no significant differences when earthworms were exposed to different concentrations of Na₂SeO₃. The selected metabolic markers were ATP, lactic acid, leucine, alanine, valine, glycine, glutamic acid, lysine, α-glucose and betaine. Na₂SeO₃ affected the metabolic level of earthworms, as the percentage of metabolic markers in the earthworm changes when exposed to different concentrations of Na₂SeO₃. The metabolic disturbances were greater with increasing concentrations of Na₂SeO₃. The differential metabolic markers were significantly changed when exposed to Na₂SeO₃ comparing to those in the control group, affecting the tricarboxylic acid cycle process and breaking the metabolic balance. This study showed that Na₂SeO₃ had toxic effect on the growth and development of earthworms. In addition, this study provided a biochemical insights for the development of selenium-enriched agriculture.

Effect of sub-chronic dietary L-selenomethionine exposure on reproductive performance of Red Swamp Crayfish, (Procambarus clarkii)

The effect of selenium (Se) on the reproductive system has been investigated in both humans and vertebrates, but few studies of female fertility and reproduction in invertebrate have been reported. This study is aimed to investigate the effect of SeMet on growth performance and reproductive system after crayfish were fed with graded levels of dietary SeMet (0, 1.49, 3.29, 10.02, 30.27 or 59.8 μg Se/g dry weight) for 60 days. Crayfish treated with the high levels of SeMet (10.02, 30.27 and 59.76 μg Se/g) exhibited decreasing FW and CL in both male and female. Interestingly, Se accumulation was higher in ovary than in other tissues, suggesting that ovary may serve as a target organ for Se accumulation. We found that dietary Se concentration of 10.02 μg Se/g significantly improved the spawning rate, promoted the synchronized spawning, and up-regulated the expressions of mRNA of cdc2 and vitellogenin, with significantly increased E2 and VTG concentrations in hemolymph of female crayfish. However, a marked decrease of the E2 contents and spawning rate was observed in the groups treated with 30.27 and 59.76 μg Se/g diets. In conclusion, the results of this study indicated that the Se had maximum accumulation in ovary, affecting the reproductive capacity by intervening the expression of cdc2 and vitellogenin in the reproductive system. The LOAEL to induce FW was observed in crayfish fed with 10.02 μg Se/g diet, and its value can cause toxicity within the range of natural concentration, so the addition of Se in the feed should be within 10.02 μg Se/g.

Evidence for exposure to selenium by breeding interior snowy plovers (Charadrius nivosus) in saline systems of the Southern Great Plains

Interior snowy plover (Charadrius nivosus) population declines and deteriorating conditions throughout the Southern Great Plains (SGP) of Texas, New Mexico, and Oklahoma may be linked to environmental contaminants. Concentrations of V, As, Cd, Pb, and Se were quantified in breeding snowy plover blood, feathers (5th primary; P5), and potential prey (tiger beetles [Cicindela circumpicta and C. togata]). Se was (a) most commonly detected relative to other quantified elements and (b) frequently quantified at levels exceeding background or toxicity thresholds. Of samples greater than instrumentation detection limits, 98% of snowy plover blood and 22% of feather samples were greater than Se toxicity thresholds of 1 ppm ww for blood and 5 ppm dw for feathers (blood quantifiable range: 0.83-15.12 ppm; feathers quantifiable range: 1.90-27.47 ppm). Almost all tiger beetle Se concentrations were below reported invertebrate thresholds of 30 ppm dw (quantifiable range: 0.54-45.84 ppm). Snowy plover blood Se concentrations were related to sex, individual body condition, and local tiger beetle Se concentrations, while plover P5 Se concentrations were related to state, sex, and presence of body molt. Tiger beetle Se concentrations were related to individual study sites in Texas. These results provide some of the first evidence of Se exposure risk for interior snowy plovers nesting in saline lake and alkali flat environments of the SGP. Future efforts should focus upon specific Se uptake pathways during breeding and nonbreeding seasons, as snowy plovers breeding in the SGP appear to be exposed to Se throughout their annual cycle.

Chemical, Physical, and Biological Factors Shape Littoral Invertebrate Community Structure in Coal-Mining End-Pit Lakes

Aquatic invertebrates form the base of the consumer food web in lakes. In coal-mining end-pit lakes, invertebrates are exposed to an environment with potentially challenging physical and chemical features. We hypothesized that the physical and chemical features of end-pit lakes reduce critical littoral habitat and thus reduce invertebrate diversity, thereby limiting the potential for these lakes to be naturalized. We used a multivariate approach using principle component analysis and redundancy analysis to study relationships between invertebrate community structure, habitat features, and water quality in five end-pit lakes and five natural lakes in the Rocky Mountain foothills of west-central Alberta, Canada. Results show a significantly different invertebrate community structure was present in end-pit lakes as compared with reference lakes in the same region, which could be accounted for by water hardness, conductivity, slope of the littoral zone, and phosphorus concentrations. Habitat diversity in end-pit lakes was also limited, cover provided by macrophytes was scarce, and basin slopes were significantly steeper in pit lakes. Although water chemistry is currently the strongest influencing factor on the invertebrate community, physical challenges of habitat homogeneity and steep slopes in the littoral zones were identified as major drivers of invertebrate community structure. The addition of floating wetlands to the littoral zone of existing pit lakes can add habitat complexity without the need for large-scale alterations to basing morphology, while impermeable capping of waste-rock and the inclusion of littoral habitat in the planning process of new pit lakes can improve the success of integrating new pit lakes into the landscape.

Surface coal mining influences on macroinvertebrate assemblages in streams of the Canadian Rocky Mountains

To determine the region-specific impacts of surface coal mines on macroinvertebrate community health, chemical and physical stream characteristics and macroinvertebrate family and community metrics were measured in surface coal mine-affected and reference streams in the Canadian Rocky Mountains. Water chemistry was significantly altered in mine-affected streams, which had elevated conductivity, alkalinity, and selenium and ion concentrations compared with reference conditions. Multivariate redundancy analysis (RDA) indicated alterations in macroinvertebrate communities downstream of mine sites. In RDA ordination, Ephemeroptera family densities, family richness, Ephemeroptera, Plecoptera, Trichoptera (EPT) richness, and % Ephemeroptera declined, whereas densities of Capniidae stoneflies increased along environmental gradients defined by variables associated with mine influence including waterborne Se concentration, alkalinity, substrate embeddedness, and interstitial material size. Shifts in macroinvertebrate assemblages may have been the result of multiple region-specific stressors related to mining influences including selenium toxicity, ionic toxicity, or stream substrate modifications.

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.

Assessing different mechanisms of toxicity in mountaintop removal/valley fill coal mining-affected watershed samples using Caenorhabditis elegans

Mountaintop removal-valley fill coal mining has been associated with a variety of impacts on ecosystem and human health, in particular reductions in the biodiversity of receiving streams. However, effluents emerging from valley fills contain a complex mixture of chemicals including metals, metalloids, and salts, and it is not clear which of these are the most important drivers of toxicity. We found that streamwater and sediment samples collected from mine-impacted streams of the Upper Mud River in West Virginia inhibited the growth of the nematode Caenorhabditis elegans. Next, we took advantage of genetic and transgenic tools available in this model organism to test the hypotheses that the toxicity could be attributed to metals, selenium, oxidative stress, or osmotic stress. Our results indicate that in general, the toxicity of streamwater to C. elegans was attributable to osmotic stress, while the toxicity of sediments resulted mostly from metals or metalloids.

Effects of selenium supplemented diets on growth and condition indexes in juvenile red swamp crayfish, Procambarus clarkii

Effects of selenium diets (Se, 0.3 and 1.2mgkg(-1)) on juvenile red swamp crayfish Procambarus clarkii were observed for eight weeks. Growth, condition factors and Se levels in exoskeleton and hepatopancreas for both sexes and diets were evaluated at three endpoints. The specific growth rate (SGR) showed a faster, but not statistically significant growth in Se exposed specimens. Se levels were higher in exoskeleton and hepatopancreas of both Se exposed males and females, when compared to controls. The abdomen-total weight relationship (Tw/B) showed no significant differences between Se exposed and control groups. A constant decline of HI values was recorded in both Se exposed sexes and the same trend was observed in control males. Se exposed females evidenced lower HI after 4 and 8 weeks when compared to controls. Therefore, evident reductions of the health indicator values HI suggested that selenium can deplete the hepatopancreas energy reserves, mainly in juvenile male crayfish.

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/NO2

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.

Bioconcentration and biotransformation of selenite versus selenate exposed periphyton and subsequent toxicity to the Mayfly Centroptilum triangulifer

Little is known about the bioaccumulation dynamics, biotransformation processes, or subsequent toxicity to consumers of dissolved selenite (SeO3) versus selenate (SeO4) uptake into aquatic primary producer communities. To address these data gaps, we examined SeO3 and SeO4 bioconcentration into complex freshwater periphyton communities under static and static-renewal conditions. Further, we explored periphyton biotransformation of Se species using X-ray absorption near edge structure (XANES) spectroscopy analysis and changes in the periphyton associated microbial consortium using denaturing gradient gel electrophoresis (DGGE). Last, we fed differentially treated periphyton to the mayfly Centroptilum triangulifer in full life cycle exposures to assess toxicity. Selenite exposed periphyton readily bioconcentrated Se while, in contrast, initial periphyton uptake of SeO4 was negligible, but over time periphyton [Se] increased steadily in conjunction with the formation of dissolved SeO3. XANES analyses revealed that both SeO3 and SeO4 treated periphyton biotransformed Se similarly with speciation dominated by organo-selenide (∼61%). Mayfly survival, secondary production, and time to emergence were similar in both SeO3 and SeO4 treated periphyton exposures with significant adverse effects at 12.8 μg g(-1) ((d.w.) secondary production) and 36 μg g(-1) ((d.w.) survival and development time). Overall, dissolved selenium speciation, residence time, and organisms at the base of aquatic food webs appear to be the principal determinants of Se bioaccumulation and toxicity.

Selenium bioaccumulation in stocked fish as an indicator of fishery potential in pit lakes on reclaimed coal mines in Alberta, Canada

Pit lakes are a common reclamation strategy for open pit mines; however, there is a concern about their water quality and suitability as fish habitat because they are often contaminated by metals or metalloids. This study assessed the exposure of fish and invertebrates to selenium (Se) and other metals and metalloids in pit lakes formed by open pit coal mining in Tertiary (thermal coal) and in Cretaceous (metallurgical coal) bedrock. Juvenile hatchery rainbow trout, Oncorhynchus mykiss, and brook trout, Salvelinus fontinalis, were stocked into two thermal coal pit lakes (water Se < 2 μg/L, low water Se) and two metallurgical coal pit lakes (water Se > 15 μg/L, high water Se). Se accumulation in stocked fish and concentrations in invertebrates were characterized over a period of 2 years. In the metallurgical pits, invertebrates had higher Se concentrations and fish accumulated Se to higher levels (exceeding USEPA tissue Se guidelines) than biota in the thermal pits. Rainbow and brook trout accumulated similar concentrations of Se in their muscle and exhibited a similar relationship between whole-body and muscle Se concentrations. These results may be used by resource managers to assess compliance with whole-body tissue Se guidelines and to determine if pit lakes in coal mining areas pose a significant Se risk to wildlife or human health. The high Se exposure in metallurgical coal pits indicates that under the current mining and reclamation strategy, these lakes are not suitable for management as recreational "put and take" fisheries.

Selenium biotransformations in an engineered aquatic ecosystem for bioremediation of agricultural wastewater via brine shrimp production

An engineered aquatic ecosystem was specifically designed to bioremediate selenium (Se), occurring as oxidized inorganic selenate from hypersalinized agricultural drainage water while producing brine shrimp enriched in organic Se and omega-3 and omega-6 fatty acids for use in value added nutraceutical food supplements. Selenate was successfully bioremediated by microalgal metabolism into organic Se (seleno-amino acids) and partially removed via gaseous volatile Se formation. Furthermore, filter-feeding brine shrimp that accumulated this organic Se were removed by net harvest. Thriving in this engineered pond system, brine shrimp ( Artemia franciscana Kellogg) and brine fly (Ephydridae sp.) have major ecological relevance as important food sources for large populations of waterfowl, breeding, and migratory shore birds. This aquatic ecosystem was an ideal model for study because it mimics trophic interactions in a Se polluted wetland. Inorganic selenate in drainage water was metabolized differently in microalgae, bacteria, and diatoms where it was accumulated and reduced into various inorganic forms (selenite, selenide, or elemental Se) or partially incorporated into organic Se mainly as selenomethionine. Brine shrimp and brine fly larva then bioaccumulated Se from ingesting aquatic microorganisms and further metabolized Se predominately into organic Se forms. Importantly, adult brine flies, which hatched from aquatic larva, bioaccumulated the highest Se concentrations of all organisms tested.

A method for assessing the potential for confounding applied to ionic strength in central Appalachian streams

Causal relationships derived from field data are potentially confounded by variables that are correlated with both the cause and its effect. The present study presents a method for assessing the potential for confounding and applies it to the relationship between ionic strength and impairment of benthic invertebrate assemblages in central Appalachian streams. The method weighs all available evidence for and against confounding by each potential confounder. It identifies 10 types of evidence for confounding, presents a qualitative scoring system, and provides rules for applying the scores. Twelve potential confounders were evaluated: habitat, organic enrichment, nutrients, deposited sediments, pH, selenium, temperature, lack of headwaters, catchment area, settling ponds, dissolved oxygen, and metals. One potential confounder, low pH, was found to be biologically significant and eliminated by removing sites with pH < 6. Other potential confounders were eliminated based on the weight of evidence. This method was found to be useful and defensible. It could be applied to other environmental assessments that use field data to develop causal relationships, including contaminated site remediation or management of natural resources.

Bioavailability, toxicity and biotransformation of selenium in midge (Chironomus dilutus) larvae exposed via water or diet to elemental selenium particles, selenite, or selenized algae

Elemental selenium (Se) is generally considered to be biologically inert due to its insolubility in water. It is a common form of Se in sediment near uranium mining and milling operations in northern Saskatchewan, Canada. Nanosized particles of many materials exhibit different properties compared with their bulk phases, in some cases posing health and ecological risks. Here we investigated the bioavailability and toxicity of Se nanoparticles (SeNPs) using 10-day waterborne and dietary exposures to larvae of Chironomus dilutus, a common benthic invertebrate. For comparison, larvae were also exposed to waterborne dissolved selenite and to dietary selenomethionine as selenized algae. Larval Se accumulation was evaluated using graphite furnace atomic absorption spectroscopy or inductively coupled plasma mass spectroscopy for total Se and X-ray absorption spectroscopy for Se chemical speciation. Exposure to nanoparticulate Se resulted in Se bioaccumulation, at high concentrations, inhibiting larval growth in both waterborne and dietary exposures; larvae predominantly accumulated selenomethionine-like species regardless of uptake route or form of Se tested. Despite the observed Se accumulation, our findings suggest there is little risk of direct SeNP toxicity to benthic invertebrates in Se-contaminated sediments in northern Saskatchewan. Nevertheless, elemental Se in sediments may be biologically available and may contribute directly or indirectly to the risk of Se toxicity to egg-laying vertebrates (fish and piscivorous birds) in Se-contaminated aquatic systems. It thus may be necessary to include elemental Se as a source of potential Se exposure in ecological risk assessments.

Food rationing affects dietary selenium bioaccumulation and life cycle performance in the mayfly Centroptilum triangulifer

Selenium effects in nature are mediated by the relatively large bioconcentration of aqueous Se by primary producers and smaller, yet critical, dietary transfers to primary consumers. These basal processes are then propagated through food webs to higher trophic levels. Here we quantified the movement of dissolved Se (as selenite) to periphyton, and used the resultant periphyton as a food source for conducting full life-cycle dietary Se exposures to the mayfly Centroptilum triangulifer. Periphyton bioconcentrated Se ~2,200-fold from solution in a log-linear fashion over dissolved Se concentrations ranging from 1.1 to 23.1 μg L(-1). We examined the influence of two feeding ration levels (1x and 2x) on trophic transfer, tissue Se concentrations, maternal transfer, and functional endpoints of mayfly performance. Mayflies fed a lesser ration (1x) displayed greater trophic transfer factors (mean TTF, 2.8 ± 0.4) than mayflies fed 2x rations (mean TTF, 1.1 ± 0.3). In 1x exposures, mayflies exhibited significant (p < 0.05) reductions in survivorship and total body mass at dietary [Se] ≥ 11.9 μg g(-1), reduced total fecundity at ≥ 4.2 μg g(-1), and delayed development at ≥ 27.2 μg g(-1). Mayflies fed a greater ration (2x) displayed reduced tissue Se concentrations (apparently via growth dilution) relative to 1x mayflies, with no significant effects on performance. These results suggest that the influence of Se on mayfly performance in nature may be tied to food resource availability and quality. Furthermore, nutritional status is an important consideration when applying laboratory derived estimates of toxicity to risk assessments for wild populations.

Selenium bioaccumulation and speciation in Chironomus dilutus exposed to water-borne selenate, selenite, or seleno-DL-methionine

The objective of the present study was to describe the uptake and elimination kinetics of selenium (Se) administered in the forms of selenate, selenite, and selenomethionine (seleno-DL-methionine) in different life stages of the midge Chironomus dilutus, and to determine the relationship between Se bioavailability and Se speciation using X-ray absorption spectroscopy (XAS). Midge larvae exposed to 4.3 µg/L as dissolved selenate for 10 d of had negligible accumulation of Se (indistinguishable from control organisms). However, larvae rapidly accumulated Se over 10 d of exposure to 3.8 and 1.8 µg/L selenite and seleno-DL-methionine (Se-met), respectively. Most Se accumulated by larvae exposed to selenite or Se-met was retained after 10 d of elimination in clean water. When additional midge larvae were exposed to Se until emergence, Se accumulated during the larval stage was largely retained in the adults. Although a strong correlation was found between the adult whole-body Se concentration and the Se concentration in the exuvia after emergence, only a minor loss of Se occurred in the shed exuvia compared with larvae and adult whole-body concentrations. X-ray absorption spectroscopy analysis showed that organic selenides and diselenides, modeled as Se-met and selenocystine, respectively, were the dominant forms of Se in both the larval and adult insect stages. The proportion and concentration of organic selenides (selenomethionine) increased in larvae and adults exposed to Se-met and selenite compared with larvae exposed to selenate, whereas the concentration of diselenides (selenocystine) remained relatively constant for all treatments.

Conducting site-specific assessments of selenium bioaccumulation in aquatic systems

Selenium (Se) is a chemical of concern at many locations across North America and elsewhere, and site-specific conditions are important when evaluating its bioaccumulation and effects in aquatic ecosystems. Most regulatory criteria and guidelines are based on waterborne Se concentrations. In contrast, the draft water quality chronic criterion of the US Environmental Protection Agency (USEPA) is based on Se concentrations in whole-body fish, and current information suggests the agency will issue a new draft criterion based in part on fish egg and/or ovary Se concentrations. However, implementation guidance is not available from the agency for either of these tissue-based criteria. Therefore, we describe a phased approach for field and laboratory assessments of Se bioaccumulation in fish and aquatic-dependent birds that can be applied in different environmental settings with the goal of developing and interpreting a tissue-based Se value. We recommend here the use of decision trees, conceptual models, and data quality objectives toward defining what should be done during the assessment, plus sampling and monitoring procedures for the assessment. First, available tissue or waterborne Se concentrations should be compared to tissue residue guidelines or adopted water quality criteria and guidelines. When needed, reproductive toxicity testing and assessment of fish populations should also be conducted in the area of interest. In addition, extensive data on the effects of Se on fish and bird species have been developed, and describing the associations between fish or bird egg tissue, aqueous Se, and potential effects is important for sites where Se may be a concern. Selenium bioaccumulation and toxicity also are of concern for amphibians and oviparous reptiles, but interpretive information is very limited for those species. Recent science indicates that effects are more strongly related to tissue concentrations of Se (especially in the eggs or ovaries of oviparous vertebrates) than to waterborne concentrations. Overall, we conclude that the approach for site-specific assessment must be flexible enough to allow what is appropriate for the situation. Furthermore, risk management and remediation decisions should be based on combined biology and chemistry data, using multiple lines of evidence in the assessment.

Effects of selenium diets on growth, accumulation and antioxidant response in juvenile carp

An 8-week feeding trial was undertaken with Cyprinus carpio to determine the effects of two commercial Se diets (HSe 1.0 mg kg⁻¹ and LSe 0.25 mg kg⁻¹) on growth, accumulation and antioxidant response in juveniles at time 0, 30 and 60 days. HSe carp had higher mean weight (W) values than LSe group at 60 days and the Fulton condition factor (K) indicated good fish health for both diet groups. Among the investigated HSe tissues, kidney and liver were mainly involved in Se accumulation, whereas the Se level in muscle indicated a very low Se contamination risk for human health. Selenium accumulation levels in HSe tissues followed this order: kidney>liver>muscle. Although growth was not impaired, biochemical antioxidant indicators in liver and kidney evidenced an oxidative stress condition in HSe juveniles. Furthermore, selenium supplementation levels, higher than the one employed in this study, might worsen the antioxidant status of carp.

Biodynamics, subcellular partitioning, and ultrastructural effects of organic selenium in a freshwater bivalve

Selenium is a trace element characterized by concentrations that narrowly range between being essential and being toxic. Even though inorganic selenite and selenate are the predominantchemicalforms ofSe in surfacewaters, the toxicity of Se to aquatic organisms is mostly governed by the bioavailability of organic selenium within food webs. The present study was designed to evaluate organic selenium bioaccumulation and toxicity patterns in the freshwater sentinel species Corbicula fluminea. Waterborne selenomethionine (SeMet) exposure was used to mimic dietary organo-Se uptake. Our results demonstrate that SeMet is accumulated to a relatively high extentwith a concentration factor of 770 (wet weight basis). Higher uptake than depuration rates suggest that bivalves deal with high Se amounts using a strategy of detoxification based on Se sequestration that could involve granules, as shown by a strong increase of Se in the particulate subcellular fraction. Selenium is persistent in the cytosol of bivalves exposed to SeMet where it is found in proteins of a wide range of molecular mass, indicating a possible replacement of methionine by selenomethionine. A subsequent alteration of protein function might be one of the mechanisms of Se toxicity that could explain the histopathological effects we observed in gills by using transmission electronic microscopy. Those analyses showed changes in gill filament ultrastructure and suggested mitochondria asthefirsttargetfor SeMet cytotoxicity, with alterations of the outer membrane and of cristae morphology. Organo-Se would thus not only be toxic via indirect mechanisms of maternal transfer as it was suggested for fish but also directly. Our results on Se distribution agree with studies that used dietary Se transfer, and highlight the relevance (and less expensive way) of using SeMet water-only exposure protocols to mimic the real environment.

Accumulation of selenium in aquatic systems downstream of a uranium mining operation in northern Saskatchewan, Canada

The objective of this study was to investigate the accumulation of selenium in lakes downstream of a uranium mine operation in northern Saskatchewan, Canada. Selenium concentrations in sediment and biota were elevated in exposure areas even though water concentrations were low (<5 microg/L). The pattern (from smallest to largest) of selenium accumulation was: periphyton<plankton and filterer invertebrates<detritivore and predator invertebrates<small bodied (forage) fish and predatory fish. Biomagnification of selenium resulted in an approximately 1.5-6 fold increase in the selenium content between plankton, invertebrates and forage fish. However, no biomagnification was observed between forage fish and predatory fish. Selenium content in organisms from exposure areas exceeded the proposed 3-11 microg/g (dry weight) dietary toxicity threshold for fish, suggesting that the selenium released into these aquatic systems has the potential to bioaccumulate and reach levels that could impair fish reproduction.