Evaluation of suitable endpoints for assessing the impacts of toxicants at the community level

Abstract

Assessment of ecological impacts of toxicants relies currently on extrapolation of effects observed at organismal or population levels. The uncertainty inherent to such extrapolations, together with the impossibility of predicting ecological effects of chemical mixtures, can only be resolved by adopting approaches that consider toxicological endpoints at a community or ecological level. Experimental data from micro- and mesocosms provide estimates of community effect levels, which can then be used to confirm or correct the extrapolations from theoretical methods such as species sensitivity distributions (SSDs) or others. When assessing impacts, the choice of sensitive community endpoints is important. Four community endpoints (species richness, abundance, diversity and similarity indices) were evaluated in their ability to assess impacts of two insecticides, imidacloprid and etofenprox, and their mixture on aquatic and benthic communities from artificial rice paddies. Proportional changes of each community endpoint were expressed by ratios between their values in the treatment and control paddies. Regression lines fitted to the endpoint ratios against the time series of chemical concentrations were used to predict percentile impacts in the communities. The abundance endpoint appears to be the most sensitive indicator of the communities' response, but the Czekanowski similarity index described best the structural changes that occur in all communities. Aquatic arthropods were more sensitive to the mixture of both insecticides than zooplankton and benthic communities. Estimated protective levels for 95% of aquatic species exposed to imidacloprid (<0.01-1.0 μg l(-1)) were slightly lower than predicted by SSD, whereas for etofenprox the protective concentrations in water (<0.01-0.58 μg l(-1)) were an order of magnitude lower than SSD's predictions.

Environmental Risk Assessment of Agrochemicals — A Critical Appraisal of Current Approaches

“…Following this procedure, the laboratory toxicity data can then be compared to the field or mesocosms toxicity data to either prove or correct the findings [136]. Effects of chemicals on communities can be measured in a similar way as in typical toxicity tests, and dose-response relationships can be obtained for some endpoints, typically the abundance or species richness [137]. The communities' data can also be subjected to multivariate statistical analysis such as principal component analysis (PCA) or, even better, principal response curves (PRCs) [138].…”

“…This can be demonstrated by using similarity indices, a tool commonly used in ecological studies that can also be applied to assess the changes occurring in a community of arthropods during and after the exposure to insecticides [142]. Biodiversity indices, on the other hand, are poor indicators of ecosystem changes [137,143]. Similarity indices have also been used to estimate chemical thresholds that protect ecological communities from contaminants in freshwater systems [144].…”

Using species sensitivity distribution approach to assess the risks of commonly detected agricultural pesticides to Australia's tropical freshwater ecosystems

“…Imidacloprid trigger values for either freshwater or tropical marine waters are currently not available in Australia. Our MRETVs, however, are lower than those predicted by SSDs (1.04-2.54 mg/L) for 95% protection level of aquatic species, in a freshwater mesocosm study based on 4 community endpoints [39]. To generate tropical freshwater trigger values for imidacloprid with higher reliability, chronic toxicity data must be generated using invertebrates considering the toxic mechanism of this pesticide.…”

Comparison of acute toxicity of two neonicotinoid insecticides, imidacloprid and clothianidin, to five cladoceran species

“…Most pesticides exert negative impacts on non-target organisms in natural ecosystems. [2][3][4] Thus, the development and use of pesticides with low ecological impact on non-target organisms is imperative for the protection of biodiversity and the ecosystem. Pesticide risk assessment at the community level based on longterm monitoring is essential to accomplish those purposes.…”