Neonicotinoid pesticides in drinking water in agricultural regions of southern Ontario, Canada.

Because of the persistence and solubility of neonicotinoid insecticides (NNIs), there is concern that these compounds may contaminate sources of drinking water. The objective of this project was to evaluate the distribution of NNIs in raw and treated drinking water from selected municipalities that draw their water from the lower Great Lakes in areas of southern Ontario, Canada where there is high intensity agriculture. Sites were monitored using Polar Organic Chemical Integrative Samplers (POCIS) and by collecting grab samples at six drinking water treatment plants. Thiamethoxam, clothianidin and imidacloprid were detected in both POCIS and grab samples of raw water. The frequency of detection of NNIs was much lower in treated drinking water, but some compounds were still detected at estimated concentrations in the low ng L range. Thiamethoxam was detected in one grab sample of raw drinking water at a mean concentration of 0.28 μg L, which is above the guidelines for drinking water recommended in some jurisdictions, including the European Union directive on pesticide levels <0.1 μg L in water intended for human consumption. Further work is required to determine whether contamination of sources of drinking water with this class of insecticides is a global problem in agricultural regions.