Fungicide risk assessment for aquatic ecosystems: importance of interspecific variation, toxic mode of action, and exposure regime.

The risk assessment of fungicides in Europe uses information from ecotoxicity studies performed on vertebrates, invertebrates, and primary producers, but not nontarget fungi. But which toxicity data should be used to assess risk and how important are modes of action and exposure regimes? A data set was compiled comprising acute single-species toxicity data for 42 fungicides, semifield data for 12 fungicides, and covering seven toxic modes of action and different exposure regimes. Most fungicides were general biocides and data from all taxonomic groups were used to construct species sensitivity distributions (SSDs) and assess risk. The derived lower-limit HC5 values and HCl values were always protective of adverse ecological effects in semifield studies and HC5 values were protective for at least 3 of the fungicides. Expanding the analysis to include insecticides and herbicides, the following threshold values, derived from SSDs based on the most sensitive taxonomic group, are proposed to protect against adverse ecological effects from pesticide exposure: (i) the HC5 can be used for short-term exposures; (ii) the HC5 divided by 1.5 can be used for medium-term exposures; (iii) either the HCl or the HC5 divided by 3 can be used for long-term exposures.