Acute and Chronic Effects of Clothianidin, Thiamethoxam and Methomyl on Chironomus dilutus

Organism tolerance thresholds for emerging contaminants are vital to the development of water quality criteria. Acute (96-h) and chronic (10-day) effects thresholds for neonicotinoid pesticides clothianidin and thiamethoxam, and the carbamate pesticide methomyl were developed for the midge Chironomus dilutus to support criteria development using the UC Davis Method. Median lethal concentrations (LC50s) were calculated for acute and chronic exposures, and the 25% inhibition concentrations (IC25) were calculated for the chronic exposures based on confirmed chemical concentrations. Clothianidin effect concentrations were 4.89 mu g/L, 2.11 mu g/L and 1.15 mu g/L for 96-h LC50, 10-day LC50 and 10-day IC25, respectively. Similarly, thiamethoxam concentrations were 56.4 mu g/L, 32.3 mu g/L and 19.6 mu g/L, and methomyl concentrations were 244 mu g/L, 266 mu g/L and 92.1 mu g/L. Neonicotinoid effect concentrations compared favorably to previously published 96-h and 14-day LC50 concentrations, and methomyl effect concentrations were within the acute survival range reported for Chironomus species and other organisms.

Automated summary

This study provides important data on the tolerance thresholds of Chironomus dilutus to neonicotinoid and carbamate pesticides, supporting the development of water quality criteria. The results show that the effect concentrations of neonicotinoids compared favorably to previously published LC50 concentrations, while carbamate pesticide concentrations were within the acute survival range for Chironomus species.