Effects of cadmium and resource quality on freshwater detritus processing chains: a microcosm approach with two insect species

Toxicokinetics of silver and silver sulfide nanoparticles in Chironomus riparius under different exposure routes

Engineered nanoparticles released into surface water may accumulate in sediments, potentially threatening benthic organisms. This study determined the toxicokinetics in Chironomus riparius of Ag from pristine silver nanoparticles (Ag NPs), a simulating aged Ag NP form (Ag₂S NPs), and AgNO₃ as an ionic control. Chironomid larvae were exposed to these Ag forms through water, sediment, or food. The potential transfer of Ag from larvae to adult midges was also evaluated. Results revealed higher Ag uptake by C. riparius upon exposure to Ag₂S NPs, while larvae exposed to pristine Ag NPs and AgNO₃ generally presented similar uptake kinetics. Uptake patterns of the different Ag forms were generally similar in the tests with water or sediment exposures, suggesting that uptake from water was the most important route of Ag uptake in both experiments. For the sediment bioaccumulation test, uptake was likely a combination of water uptake and sediment particles ingestion. Ag uptake via food exposure was only significant for Ag₂S NPs. Ag transfer to the terrestrial compartment was low. In our environmentally relevant exposure scenario, chironomid larvae accumulated relatively high Ag concentrations and elimination was extremely low in some cases. These results suggest that bioaccumulation of Ag in its nanoparticulate and/or ionic form may occur in the environment, raising concerns regarding chronic exposure and trophic transfer. This is the first study determining the toxicokinetics of NPs in Chironomus, providing important information for understanding chironomid exposure to NPs and their potential interactions in the environment.

Responses of benthic macroinvertebrate communities to a Bti-based insecticide in artificial microcosm streams

Bioinsecticides based on the bacterium Bacillus thuringiensis subsp. israelensis (Bti) are increasingly being applied directly into aquatic compartments to control nuisance mosquitoes and blackflies and are generally considered environmentally friendly alternatives to synthetic insecticides. Bti-based insecticides are considered highly selective, being Diptera-specific, and supposedly decompose rapidly in the environment. Nevertheless, their safety to non-target species and freshwater ecosystems has been questioned by recent studies, which in fact document possible indirect effects in aquatic food webs such as the decrease of prey availability to predators. This work aimed to evaluate the potential effects of a Bti-based insecticide (VectoBac® 12AS) on a freshwater macroinvertebrate community and on stream ecological functions by using artificial microcosm streams. Artificial microcosm streams were colonized with a macroinvertebrate community plus periphyton collected in a stream together with Alnus glutinosa leaf packs. They were exposed for 7 days to different Bti treatments (0, 12, 120, 1200 μg/L), which are within the recommended concentrations of application in aquatic compartments for blackfly and mosquito control. Besides invertebrate community structure and abundance, effects were evaluated regarding leaf decomposition and primary production as measures of ecosystem functioning. Community structure was significantly altered in all Bti treatments after 7 days of exposure, mostly due to a decline in chironomids, followed by oligochaetes, which both belong to the deposit-feeders' functional group. Direct effects on oligochaetes are surprising and require further research. Also, reductions of leaf decomposition due to Bti-induced sublethal effects on shredders (reduced feeding) or mortality of chironomids (that can also feed on coarse organic matter) observed in our study, represent potential indirect effects of Bti in aquatic ecosystems. Our short-exposure experiment evidenced some negative effects on stream benthic invertebrate communities and on ecosystem functioning that must be considered whenever Bti is used in water bodies for blackfly or mosquito control programs.

Effect of cadmium contamination on the eutrophic secondary pollution of aquatic macrophytes by litter decomposition

The objective of this study was to identify the effect of cadmium (Cd) contamination on the decomposition of aquatic macrophyte litter and its eutrophic secondary pollution. A laboratory experiment was conducted with three treatments: water Cd contamination (Cd-w), litter Cd contamination (Cd-l) and control (CK). The results showed that CK and Cd-w exhibited the typical decomposition dynamics of litter, i.e., early rapid decomposition followed by slow decomposition, while the litter biomass loss (BL) in Cd-l exhibited an approximately linear relationship with time over the 64-day experimental period. The BL in Cd-l was only 10.8% in the initial 4 days, while that in CK and Cd-w was 59.0% and 54.8%, respectively. Cd inhibited the fluctuation of the water chemical oxygen demand (COD) by reducing both the early increase and the subsequent decrease. The increases in water total nitrogen (TN) and total phosphorus (TP) were inhibited by Cd contamination throughout most of the decomposition period. The alterations of litter quality during the plant growth period and of the bacterial community during the litter decomposition period by Cd contamination could explain the variations in litter decomposition rate and its eutrophic secondary pollution during the early and late decomposition stages, respectively. The Cd inhibition of the eutrophic secondary pollution of aquatic macrophytes has great significance for the improved evaluation of Cd contamination.

Combined effects of insecticide exposure and predation risk on freshwater detritivores

Insecticides usually present in low concentrations in streams are known to impair behaviour and development of non-target freshwater invertebrates. Moreover, there is growing awareness that the presence of natural stressors, such as predation risk may magnify the negative effects of pesticides. This is because perception of predation risk can by itself lead to changes on behaviour and physiology of prey species. To evaluate the potential combined effects of both stressors on freshwater detritivores we studied the behavioural and developmental responses of Chironomus riparius to chlorantraniliprole (CAP) exposure under predation risk. Also, we tested whether the presence of a shredder species would alter collector responses under stress. Trials were conducted using a simplified trophic chain: Alnus glutinosa leaves as food resource, the shredder Sericostoma vittatum and the collector C. riparius. CAP toxicity was thus tested under two conditions, presence/absence of the dragonfly predator Cordulegaster boltonii. CAP exposure decreased leaf decomposition. Despite the lack of significance for interactive effects, predation risk marginally modified shredder effect on leaf decomposition, decreasing this ecosystem process. Shredders presence increased leaf decomposition, but impaired chironomids performance, suggesting interspecific competition rather than facilitation. C. riparius growth rate was decreased independently by CAP exposure, presence of predator and shredder species. A marginal interaction between CAP and predation risk was observed regarding chironomids development. To better understand the effects of chemical pollution to natural freshwater populations, natural stressors and species interactions must be taken into consideration, since both vertical and horizontal species interactions play their role on response to stress.

A standardized tritrophic small-scale system (TriCosm) for the assessment of stressor-induced effects on aquatic community dynamics

Chemical impacts on the environment are routinely assessed in single-species tests. They are employed to measure direct effects on nontarget organisms, but indirect effects on ecological interactions can only be detected in multispecies tests. Micro- and mesocosms are more complex and environmentally realistic, yet they are less frequently used for environmental risk assessment because resource demand is high, whereas repeatability and statistical power are often low. Test systems fulfilling regulatory needs (i.e., standardization, repeatability, and replication) and the assessment of impacts on species interactions and indirect effects are lacking. In the present study we describe the development of the TriCosm, a repeatable aquatic multispecies test with 3 trophic levels and increased statistical power. High repeatability of community dynamics of 3 interacting aquatic populations (algae, Ceriodaphnia, and Hydra) was found with an average coefficient of variation of 19.5% and the ability to determine small effect sizes. The TriCosm combines benefits of both single-species tests (fulfillment of regulatory requirements) and complex multispecies tests (ecological relevance) and can be used, for instance, at an intermediate tier in environmental risk assessment. Furthermore, comparatively quickly generated population and community toxicity data can be useful for the development and testing of mechanistic effect models. Environ Toxicol Chem 2018;37:1051-1060. © 2017 SETAC.

Energetic costs and biochemical biomarkers associated with esfenvalerate exposure in Sericostoma vittatum

Pyrethroid insecticides have been used for decades and their worldwide market continues to increase, despite their high toxicity to non-target insects. Recent studies reveal that it is essential to investigate the secondary mechanisms of action of type II pyrethroids to understand their cellular effects on invertebrates. The aim of this study was to evaluate the lethality, behaviour and physiological alterations and energetic costs in caddisfly larvae exposed to environmentally relevant concentrations of esfenvalerate (ESF). ESF caused both mortality and feeding inhibition of exposed caddisfly larvae: nominal ESF 96 h LC₅₀ was 2.29 μg/L; feeding activity was impaired at concentrations equal or above 0.25 μg/L. At the cellular level, glutathione-S-transferase (GST) activity was increased on caddisfly larvae exposed to 0.25 and 0.5 μg/L ESF, which might contribute to prevent oxidative damage since levels of lipid peroxidation (LPO) were not altered. The energy budget of exposed caddisfly larvae was impaired by exposure to 0.25 μg/L ESF since sugar and protein contents decreased, while a decline of energy consumption was observed. The analysis of feeding, energy reserves and consumption data through structural equation modelling (SEM) allowed to quantify the direct and indirect effects of ESF exposure on bioenergetics of caddisfly larvae. SEM analysis showed a strong negative direct influence of ESF onto feeding activity, sugars content and energy consumption, highlighting a significant positive relationship between sugars and protein contents. These results show that energy expenditure is related to oxidative defense mechanisms induced by ESF stress that may lead to deleterious effects on growth and development.

Ecotoxicity of two organic UV-filters to the freshwater caddisfly Sericostoma vittatum

Organic ultraviolet filters (UV-filters) used for protection against radiation in personal care products and other materials (e.g. textiles, plastic products) are considered emerging contaminants of aquatic ecosystem. Benzophenone-3 (BP3) and 3-(4-methylbenzylidene)camphor (4-MBC) are the most commonly used organic UV-filters and have been reported in freshwater environments due to contamination through discharges from wastewater treatment plants and swimming pools or by direct contamination from recreational activities. Our aim was to evaluate the ecotoxicological effects of these UV-filters using the freshwater caddisfly Sericostoma vittatum' biochemical biomarkers and energy processing related endpoints (feeding behaviour, energy reserves and cellular metabolism). In laboratory trials, both compounds induced feeding inhibition of S. vittatum at 3.55 mg/kg of BP3 and at concentrations ≥2.57 mg/kg of 4-MBC, decreased carbohydrates content at 3.55 and 6.95 mg/kg of BP3 and 4-MBC respectively, and increased total glutathione levels at concentrations ≥1.45 and 1.35 mg/kg of BP3 and 4-MBC respectively. No significant effects were observed on endpoints associated with oxidative stress, antioxidant defences, phase II biotransformation or neurotoxicity after exposure to the two UV-filters. Our results show that environmental relevant concentrations of BP3 and 4-MBC, can negatively impact freshwater insects and demonstrate the importance of monitoring the ecological effects of organic UV-filters using non-model invertebrate species.

Population genetic structure and hybridization patterns in the cryptic sister species Chironomus riparius and Chironomus piger across differentially polluted freshwater systems

Chironomids are an integral and functionally important part of many freshwater ecosystems. Yet, to date, there is limited understanding of their microevolutionary processes under chemically polluted natural environments. In this study, we investigated the genetic variation within populations of the ecotoxicological model species Chironomus riparius and its cryptic sister species Chironomus piger at 18 metal-contaminated and reference sites in northwestern Portugal. Microsatellite analysis was conducted on 909 samples to answer if metal contamination affects genetic variation in natural chironomid populations as previously suggested from controlled laboratory experiments. Similarly high levels of genetic diversity and significant but weak genetic substructuring were found across all sites and temporal replicates, with no effects of metal contamination on the genetic variation or species' abundance, although C. piger tended to be less frequent at highly contaminated sites. Our results indicate that high levels of gene flow and population dynamic processes may overlay potential pollutant effects. At least for our study species, we conclude that the "genetic erosion hypothesis", which suggests that chemical pollution will reduce genome-wide genetic variability in affected populations, does not hold under natural conditions. Interestingly, our study provides evidence of successful hybridization between the two sister species under natural conditions.

Exposure to chlorantraniliprole affects the energy metabolism of the caddisfly Sericostoma vittatum

Caddisflies have been included in ecotoxicological studies because of their sensitivity and ecological relevance. The present study aimed to assess the sublethal effects of an anthranilic diamide insecticide, chlorantraniliprole (CAP), to Sericostoma vittatum. Used worldwide, CAP is a persistent compound that has been found in surface waters at concentrations from 0.1 μg/L to 9.7 μg/L. It targets the ryanodine receptors, and the present ecotoxicological assessment focused on biomarkers related to neurotransmission, biotransformation, oxidative stress damage, and endpoints related to energy processing (feeding, energy reserves, and cellular metabolism). Six days of exposure trials revealed that feeding activity was significantly decreased in S. vittatum larvae exposed to 0.9 μg/L CAP. Concomitantly, a reduction in cellular metabolism and a significant decrease in protein content were also observed in caddisfly larvae exposed to CAP, suggesting metabolic depression. The results show that sublethal concentrations of CAP can cause detrimental sublethal effects on S. vittatum total glutathione content at concentrations as low as 0.2 μg/L. Bioenergetics can be used to assess physiological effects of contaminants, and the present results show that exposure to low, environmentally relevant, concentrations of CAP alter energy acquisition and metabolism in nontarget aquatic insects with potential population level effects. Environ Toxicol Chem 2017;36:1584-1591. © 2016 SETAC.

The role of genetic diversity and past-history selection pressures in the susceptibility of Chironomus riparius populations to environmental stress

Natural populations experiencing intense selection and genetic drift may exhibit limited potential to adapt to environmental change. The present study addresses the following aspects of the "genetic erosion" hypothesis in the midge Chironomus riparius: does long-term mercury (Hg) contamination affect the Hg tolerance of midge populations inhabiting such impacted areas? If so, is there any fitness cost under changing environmental conditions? And does genetic impoverishment influence the susceptibility of C. riparius to cope with environmental stressful conditions? For this end, we tested the acute and chronic tolerance to Hg and salinity in four C. riparius populations differing in their levels of genetic diversity (assessed through microsatellite markers) and past-histories of Hg exposure. Results showed that the midge population collected from a heavily Hg-contaminated site had higher Hg tolerance compared to the population collected from a closely-located reference site suggesting directional selection for Hg-tolerant traits in its native environment despite no genetic erosion in the field. No increased susceptibility under changing environmental conditions of salinity stress was observed. Moreover, results also showed that populations with higher genetic diversity performed better in the partial life-cycle assays providing evidence on the key role that genetic diversity plays as mediator of populations' susceptibility to environmental stress. Our findings are discussed in terms of the suitability of C. riparius as a model organism in evolutionary toxicology studies as well as the validity of ecotoxicological assessments using genetically eroded laboratory populations.

An evaluation of EDTA additions for improving the phytoremediation efficiency of different plants under various cultivation systems

Previous studies have shown that phytoremediation usually requires soil amendments, such as chelates, to mobilize low bioavailability heavy metals for better plant absorption and, consequently, for remediation efficiency. A total dry biomass of 3.39 and 0.0138 kg per plant was produced by a phytoremediator, Eucalyptus globulus, and a nitrogen fixing crop, Cicer arietinum (chickpea), respectively. The accumulation of Pb in E. globulus and chickpea reached 1170.61 and 1.33 mg per plant (700 and 324 mg kg(-1)), respectively, under an ethylene diamine tetraacetic acid (EDTA) treatment, which was a five and sixfold increase over the value in untreated experiments, respectively. EDTA enhanced the phytoremediation efficiency and increased the heavy metal concentration in the soil solution. In pot experiments, approximately 27 % of the initial Pb leached from the spiked soil after EDTA and 25 mm artificial precipitation additions into soil without plants, which was considerably larger than the value under the same conditions without EDTA application (7 %). E. globulus planted in a mixed culture had higher water use efficiency than monocultures of either species in field experiments, and E. globulus intercepted almost all of the artificial precipitation in the pot experiments. This study demonstrates that E. globulus can maximize the potential of EDTA for improving the phytoremediation efficiency and minimizing its negative effects to the environment simultaneously by absorbing the metal-rich leachate, especially in a mixed culture of E. globulus and chickpeas.

Are insect repellents toxic to freshwater insects? A case study using caddisflies exposed to DEET

Stream ecosystems face ever-increasing pressures by the presence of emergent contaminants, such as, personal care products. N, N-diethyl-3-methylbenzamide (DEET) is a synthetic insect repellent that is being found in surface waters environments in concentrations up to 33.4 μg/L. Information concerning DEET's toxicity in the aquatic environment is still limited and focused only on its acute effects on model species. Our main objective was to assess the effects of DEET exposure to a caddisfly non-target species using sub-lethal endpoints. For that, we chose Sericostoma vittatum, an important shredder in Portuguese freshwaters that has been already used in different ecotoxicological assays. Besides acute tests, S. vittatum were exposed during 6 days to a gradient of DEET concentrations (8, 18 and 40.5 mg/L) to assess effects on feeding behaviour and biochemical responses, such as, lipid peroxidation levels (LPO), catalase and acetylcholinesterase (AChE) activities, and also assess effects on energy reserves and consumption. Acute tests revealed a 48 h-LC50 of 80.12 mg/L and DEET exposure caused feeding inhibition with a LOEC of 36.80 mg/L. Concerning the biochemical responses, DEET caused no effects in LPO nor on catalase activity. A non-significant decrease in AChE activity was observed. Regarding energetic reserves, exposure to DEET caused a significant reduction in S. vittatum carbohydrates levels. These results add important information for the risk assessment of insect repellents in the aquatic environment and suggest that reported environmental concentrations of DEET are not toxic to non-target freshwater insects.

Responses of the aquatic midge Chironomus riparius to DEET exposure

N,N-diethyl-3-methylbenzamide (DEET) is the active ingredient of many commercial insect repellents. Despite being detected worldwide in effluents, surface water and groundwater, there is still limited information on DEET's toxicity toward non-target aquatic invertebrates. Thus, our main objective was to assess the effects of DEET in the life cycle of Chironomus riparius and assess its biochemical effects. Laboratory assays showed that DEET reduced developmental rates (reduced larval growth, delayed emergence) of C. riparius larvae and also caused a decrease in the size of adult midges. Concerning the biochemical responses, a short exposure to DEET caused no effects in lipid peroxidation, despite the significant inhibition of catalase and glutathione-S-transferase activities and of total glutathione contents. Moreover, inhibition of acetylcholinesterase activity was also observed showing neurotoxic effects. Environmental risk assessment of insect repellents is needed. Our results showed moderate toxicity of DEET toward C. riparius, however, due to their mode of action, indirect ecological effects of DEET and of other insect repellents cannot be excluded and should be evaluated.

Effects of anthropogenic heavy metal contamination on litter decomposition in streams - A meta-analysis

Many streams worldwide are affected by heavy metal contamination, mostly due to past and present mining activities. Here we present a meta-analysis of 38 studies (reporting 133 cases) published between 1978 and 2014 that reported the effects of heavy metal contamination on the decomposition of terrestrial litter in running waters. Overall, heavy metal contamination significantly inhibited litter decomposition. The effect was stronger for laboratory than for field studies, likely due to better control of confounding variables in the former, antagonistic interactions between metals and other environmental variables in the latter or differences in metal identity and concentration between studies. For laboratory studies, only copper + zinc mixtures significantly inhibited litter decomposition, while no significant effects were found for silver, aluminum, cadmium or zinc considered individually. For field studies, coal and metal mine drainage strongly inhibited litter decomposition, while drainage from motorways had no significant effects. The effect of coal mine drainage did not depend on drainage pH. Coal mine drainage negatively affected leaf litter decomposition independently of leaf litter identity; no significant effect was found for wood decomposition, but sample size was low. Considering metal mine drainage, arsenic mines had a stronger negative effect on leaf litter decomposition than gold or pyrite mines. Metal mine drainage significantly inhibited leaf litter decomposition driven by both microbes and invertebrates, independently of leaf litter identity; no significant effect was found for microbially driven decomposition, but sample size was low. Overall, mine drainage negatively affects leaf litter decomposition, likely through negative effects on invertebrates.