Nematode Community of a Natural Grassland Responds Sensitively to the Broad-Spectrum Fungicide Mancozeb in Soil Microcosms.

Fungicides make up the largest part of total pesticide use, with the dithiocarbamate mancozeb being widely applied as a nonsystemic contact pesticide to protect a wide range of field crops against fungal diseases. Although nematodes are key drivers of soil functioning, data on effects of fungicides, and especially mancozeb, on these nontarget organisms are scarce. Therefore, the effects of mancozeb on a soil nematode community from a natural grassland were assessed in small-scale soil microcosms. Nematodes were exposed to mancozeb-spiked soil in six nominal concentrations (7-133 mg/kg dry soil) and analyzed after 14, 56, and 84 days in terms of densities, genus composition, and functional traits. Because this fungicide is known to quickly degrade in soils (50% degradation time <1 day), mancozeb concentrations were analyzed for all sampling occasions. Chemical analysis revealed considerably lower measured concentrations compared with the aimed nominal soil concentrations at the beginning of the exposure (1-18 mg/kg dry soil), suggesting fast degradation during the spiking process. Nevertheless, the native nematode community responded sensitively to the fungicide mancozeb, revealing lower no-observed-effect concentration and 10% effect concentration (EC10) values than reported for other soil invertebrates such as springtails and earthworms. Using the EC10 for the most sensitive nematode community endpoint (percentage of predators and omnivores: 1.2 mg/kg dry soil), the risk assessment exhibited a toxicity exposure ratio of 0.66 and, thus, a high risk of mancozeb for soil nematodes. Keeping in mind their abundance and their central roles in soil food-web functioning, the demonstrated sensitivity to a widely applied fungicide underscores the relevance of the inclusion of nematodes into routine risk-assessment programs for pesticides. Environ Toxicol Chem 2022;41:2420-2430. © 2022 SETAC.