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Freshwater ecosystems are essential for humans; however, input of several types of contamination has led to the degradation of these ecosystems. Thus, it is urgent to assess their health to allow actions for prevention and remediation. The level of trace metals can be enhanced by natural or anthropogenic sources. Essential metals, such as copper and zinc, become toxic when present in the environment above threshold concentrations. To evaluate the physiological effects of these 2 essential metals for 2 freshwater detritivores, the shrimp Atyaephyra desmarestii and the amphipod Echinogammarus meridionalis, acute tests were performed. Forty-eight hour median lethal concentration (LC50) values were estimated for these species using static bioassays with copper and zinc. Sublethal assays for both metals with several phases were also done to evaluate the effects on feeding behavior. The LC50 values of copper for the shrimp A. desmarestii and amphipod E. meridionalis were 0.128 mg/L and 0.050 mg/L and those of zinc were 7.951 mg/L and 11.860 mg/L, respectively. The results indicated that copper is more toxic to both species. Only E. meridionalis showed deleterious effects of copper on feeding rate. Zinc showed some tendency for feeding inhibition in both species. Environ Toxicol Chem 2016;35:1442-1448. © 2015 SETAC., (© 2015 SETAC.)

Studies investigating the use of biomarkers in pesticide risk assessment have greatly increased in recent years; however, issues concerning the ecological meaning of enzymatic responses have proved controversial. Ideally a good biomarker response should be modulated by the environmental contaminants alone and demonstrate a predictable behavior towards certain types of toxins. As these premises are rarely observed, the present study aims to outline research that has contributed to an understanding of the behavior of two widely used biomarkers, cholinesterase and glutathione-S-transferase, describing environmental and biotic factors that affect their response in freshwater invertebrates. Studies were performed in the main classes of aquatic invertebrates with these biomarkers and conclusions were reached concerning their behavior towards the main classes of pesticides. Links between biomarker responses and conventional endpoints were evaluated so that ecological relevance could be attributed to enzymatic responses. Toxicity of mixtures was investigated, and cases of synergism and antagonism were pointed out as factors changing the expected toxicity of aquatic systems and leading to misinterpretations of biomarker responses. Finally, the use of biomarkers as a tool for biomonitoring and in situ assays was investigated, with discussion of advantages and disadvantages of their use.

The fate and effects of the insecticide chlorpyrifos were studied in plankton-dominated, freshwater microcosms in Thailand. Disappearance rates of chlorpyrifos from the water column in the present study were similar to those in temperate regions. Insecticide accumulation in the sediment was relatively small, with the major part in the top layer (depth, 1.5 cm). Application of chlorpyrifos led to significant changes in freshwater biological communities. Clam shrimps (Conchostraca) and the cladoceran Moina micrura were the most susceptible species (no-observed-effect concentration [NOEC], 0.1 microg/L) and macroinvertebrates the most sensitive community (NOEC, 0.1 microg/L). These results are in agreement with those from semifield experiments with chlorpyrifos in temperate regions. The results of an in situ bioassay were used to calculate a NOEC of 0.1 microg/L and a 48-h median lethal concentration of 0.6 microg/L for M. micrura, which are similar to toxicity values reported for Daphnia magna in studies in temperate regions. Overall, these findings support the use of toxicity data from temperate regions for the risk assessment of low-persistent insecticides like chlorpyrifos for aquatic communities in tropical regions.

We used bioassays employing head capsule width and body length increase of Chironomus riparius larvae as end points to evaluate metal contamination in streams. Bioassays were performed in situ near an abandoned Portuguese goldmine in the spring of 2003 and 2004. Bioassays also were performed under laboratory conditions with water and sediment collected from each stream to verify if laboratory bioassays could detect in situ toxicity and to evaluate the relative contribution of sediment and water to overall toxicity. We used field sediments with control water and control sediments with field water to discriminate between metal contamination in water and sediment. Field water with dry and sieved, organic matter-free, and nontreated sediments was used to determine the toxicity of heavy metals that enter the organism through ingested material. In both in situ and laboratory bioassays, body length increase was significantly inhibited by metal contamination, whereas head capsule width was not affected. Body length increase was more affected by contaminated sediment compared to contaminated water. The lowest-effect level of heavy metals was observed in the dry and sieved sediment that prevented ingestion of sediment particles by larvae. These results suggest that body length increase of C. riparius larvae can be used to indicate the impact of metal contamination in rivers. Chironomus riparius larvae are more affected by heavy metals that enter the organism through ingested sediment than by heavy metals dissolved in the water column. Nevertheless, several factors, such as the particle size and organic matter of sediment, must be taken into account.