Aquatic risk assessment of a novel strobilurin fungicide: A microcosm study compared with the species sensitivity distribution approach

• The recommended Regulatory Acceptable Concentration based on the ecological recovery option (ERO-RAC) of pyraoxystrobin was 0.33 µg/L based on the aquatic microcosm study.
• The median HC5s of pyraoxystrobin were 0.80/1.1 µg/L, and the LL-HC5s were 0.34/0.26 µg/L by different SSD models, respectively.
• Both in the microcosm and the SSD test, Sinodiaptomus sarsi (Copepoda) was the most sensitive to pyraoxystrobin exposure.
• The acute L(E)C50-based LL-HC5s can be adequately used for deriving protective concentrations of pyraoxystrobin and also strobilurin fungicides.

The ecotoxicological effects of pyraoxystrobin, a novel strobilurin fungicide, were studied using outdoor freshwater microcosms and the species sensitivity distribution approach. The microcosms were treated with pyraoxystrobin at concentrations of 0, 1.0, 3.0, 10, 30 and 100 µg/L. Species sensitivity distribution (SSD) curves were constructed by means of acute toxicity data using the BurrliOZ model for fourteen representatives of sensitive invertebrates, algae and fish and eleven taxa of invertebrates and algae, respectively.The responses of zooplankton, phytoplankton and physical and chemical endpoints in microcosms were studied. Zooplankton, especially Sinodiaptomus sarsi was the most sensitive to pyraoxystrobin exposure in the microcosms. Short-term toxic effects (<8 weeks) on zooplankton occurred in 1 µg/L treatment group. The duration of toxic effects on S. sarsi could not be evaluated within the initial 56 days. Significant long-term toxic effects were observed at 10, 30 and 100 µg/L (>281 days) for S. sarsi and the zooplankton community. Based on the results obtained from the organisms in the microcosm system, 1 µg/L was recommended as the NOEAEC (no observed ecologically adverse effect concentration). Also, 0.33 µg/L was derived as the Regulatory Acceptable Concentration based on the ecological recovery option (ERO-RAC) of pyraoxystrobin. For all fourteen tested species, the median HC5 (hazardous concentration affecting 5% of species) was 0.86 µg/L, and the lower limit HC5 (LL-HC5) was 0.39 µg/L. For the eleven taxa of invertebrates and algae tested, the median HC5 was 1.1 µg/L, and the LL-HC5 was 0.26 µg/L. The present study positively contributes to the suggestion of adequately using acute L(E)C50-based HC5/ LL-HC5 for deriving protective concentrations for strobilurin fungicides, and it should be valuable for full comprehension of the potential toxicity of pyraoxystrobin in aquatic ecosystems.