A province-wide survey of neonicotinoids, chlorantraniliprole, atrazine, metolachlor, and other pesticides in drinking water of Québec, Canada

A reconnaissance survey was conducted at a province-wide scale to document the occurrence of pesticides in drinking water from Québec, Canada. Twenty-four target pesticides were investigated in tap water from 340 municipalities across 17 administrative regions. Of 425 samples, 398 (94%) had detectable levels of at least one target pesticide (maximum: 16 pesticides). The most frequently detected compounds were atrazine (detection rate = 72%; min-max ≤0.01-51 ng/L; 95th percentile = 33 ng/L) and its degradation products desethylatrazine (52%; <0.20-59 ng/L; 95th percentile = 31 ng/L) and hydroxyatrazine (78%; <0.01-28 ng/L; 95th percentile = 13 ng/L). Neonicotinoids were rarely detected in finished tap water (e.g., detection rates of imidacloprid and thiamethoxam: 9-11%). Most tap water samples had low pesticide levels, with profiles typically dominated by triazines. However, a multivariate analysis revealed watershed-specific trends that correlated with the water source and known regional uses. For instance, tap water samples produced from the St. Lawrence River (Great Lakes watershed) had greater levels and prevalence of triazines. Hexazinone was more frequently detected in tap water from the Saguenay-Lac-Saint-Jean, likely related to its use in blueberry fields. Hot spots with relatively high levels of insecticide residues included 3 sites from Portneuf's Regional County Municipality (ΣNeonicotinoids up to 250 ng/L) and 2 sites from Montérégie (chlorantraniliprole up to 66 ng/L), all sourced from groundwater. Tap water samples were all compliant with Québec and Canadian drinking water guidelines and almost all compliant (99% of samples) with the European Union guideline of 100 ng/L for individual pesticides, indicating the good quality of drinking water with respect to pesticide exposure.