Pesticide freshwater species sensitivity

Toxicity data for saltwater organisms are often insufficient to assess risks. Freshwater toxicity data are usually more plentiful, and their use may provide a suitable surrogate for saltwater data. Wheeler et al. (2002b) used species sensitivity distributions to determine if freshwater data sets are adequately protective of saltwater species assemblages for 21 chemical substances. For ammonia and metal compounds, freshwater organisms tended to be more sensitive than saltwater species, whereas the opposite was true for pesticides and narcotic compounds (Wheeler et al. 2002b). De Zwart (2002), who compared 160 compounds, including 92 pesticides, concluded... 

Wheeler et al. (2002) established acute freshwater and saltwater SSDs for 21 substances, including ammonia, metals, several pesticides, and narcotic substances. Using HC5 calculations and curve slope, they found freshwater species were either more sensitive (ammonia, copper, nickel, or zinc) or less sensitive (chlordane, endosulfan, pentachlorophenol) than saltwater species. In some cases, the distributions were very similar however, the taxonomic compositions of the freshwater and saltwater data sets were not always comparable. Maltby et al. (2005) analyzed SSDs for 16 insecticides and inter alia compared SSDs based on saltwater and freshwater species. They concluded (page 379) that the taxonomic composition of the species assemblage used to construct the SSD does have a significant influence on the assessment of hazard, but the habitat and geographical distribution of the species do not. Differences in freshwater and saltwater SSDs were primarily driven by taxonomy (e.g., both crustaceans and insects are present in freshwater, but only crustaceans are found in seawater). Correcting for the disparity in taxonomy removed habitat differences. 

Studies investigating the effects of pesticides on crustaceans should be of high priority. Crustaceans are very important consumers and prey in various aquatic systems and there are delicate relationships between crustacean plankton prey and fish predators in the pelagic zone that can and have been shown to be disturbed. It is known that pesticides are present in surface waters and it is especially urgent to study the effects of insecticides on freshwater species and species that are present in estuaries and coastal waters with high risks of contamination due to vicinity to the sources. In acute toxicity tests crustaceans were much more (often 10-times more) sensitive to insecticides than fish (Maltby et al. 2005), and some of the chemicals probably affect behaviors at very low concentrations. As there are very few studies done on pesticide effects on crustacean chemoreception it is not possible to compare their sensitivity with fish, but it is likely that there are differences. The few crustaceans studied concerning effects of copper indicate that they are less sensitive to the metal compared with fish. 

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