Suitability of five cladoceran species from Mexico for in situ experimentation

Sensitivity of tropical cladocerans to chlorpyrifos and other insecticides as compared to their temperate counterparts

The use of temperate toxicity data in tropical risk assessments has often been disputed. Previous sensitivity comparisons between temperate and tropical species, however, have not shown a consistent sensitivity difference between climatically-distinct species. Such comparisons were often limited by a small tropical toxicity dataset. In addition, differences in the taxonomic compositions of the temperate and tropical species assemblages used to construct species sensitivity distributions curves also hampered direct comparisons (e.g. type and ration of crustaceans and insects). The aim of the present study was to compare the sensitivity of temperate and tropical cladocerans to insecticides. Acute laboratory toxicity tests were conducted with five Neotropical cladocerans exposed to a concentration series of the insecticide chlorpyrifos. Subsequently, their EC₅₀ values were compared with those reported in the literature for non-tropical cladocerans. An additional literature toxicity data search for insecticides other than chlorpyrifos was also conducted for both temperate and tropical cladocerans to enable a comparison for a wider range of insecticides and taxa. The order of sensitivity of the native cladocerans to chlorpyrifos was Ceriodaphnia silvestrii (0.039 μg L^-1) > Diaphanosoma birgei (0.211 μg L^-1) = Daphnia laevis (0.216 μg L^-1) > Moina micrura (0.463 μg L^-1) = Macrothrix flabelligera (0.619 μg L^-1). A regulatory acceptable concentration based on temperate cladoceran toxicity data of both chlorpyrifos and other insecticides also appeared to be sufficiently protective for tropical cladoceran species. Implications for the use of temperate toxicity data in tropical risk assessments and indications for tropical cladoceran test species selection are discussed.

An estuarine mudsnail in situ toxicity assay based on postexposure feeding

In situ assays provide more realistic exposure scenarios than laboratory assays, which is particularly pertinent for estuaries because exposure conditions are difficult to simulate. Traditionally, sublethal toxicity testing endpoints, such as growth, emergence, and reproduction, imply time-delayed extrapolations from individuals to populations, communities, and ecosystems. Sublethal responses mechanistically linked to ecosystem functions have been largely neglected. Feeding is an unequivocal ecologically meaningful response because its impairment has direct and immediate effects on ecosystems, by hampering key functions such as organic matter decomposition, long before its effects at the individual level have consequences at successively higher levels of biological organization. The ultimate goal of the present study was to widen the range of ecosystem functions for estuarine quality assessments. Specifically, a short-term in situ assay based on the postexposure feeding of the mudsnail Hydrobia ulvae is presented. Methodologies to quantify precisely postexposure egestion as a surrogate of feeding were achieved. A multiple regression model from laboratory experiments was successfully applied to an in situ assay at reference (Mira River) and contaminated Portuguese estuaries (Sado River) for predicting reference results and allowing unraveling confounding factors during exposure (temperature, salinity, sediment grain size). Sensitivity comparisons of postexposure feeding with survival and growth, after Cu exposure, were carried out and used for a first preliminary appraisal of the relative consequences of ecosystem-level immediate effects.