Occurrence and Distribution of Carbamate Pesticides and Metalaxyl in Southern Ontario Surface Waters 2007-2010.

Surface water sampling in 2007-2010 measured the occurrence of carbamates and metalaxyl during base flow conditions and wet weather events in southern Ontario surface waters. Carbaryl, metalaxyl and pirimicarb were the most frequently detected compounds. In 2008 these three compounds were detected in over 50 % of the samples. Overall mean concentrations of carbaryl and metalaxyl over the course of the study (2007-2010) were 15 and 18 ng/L, respectively. Elevated concentrations of carbaryl (~100 to ~950 ng/L) appeared associated with wet weather (high flow) events, while highest concentrations of metalaxyl (~20-1330 ng/L) were correlated with base flow conditions. We attributed these observations as the result of runoff of carbaryl from the watershed during rain events, while metalaxyl contamination may have resulted primarily from spray drift.

Examining impacts of current-use pesticides in Southern Ontario using in situ exposures of the amphipod Hyalella azteca.

In situ exposures with Hyalella azteca were used to assess impacts of current-use pesticides in Southern Ontario, Canada. Exposures were conducted over 2 growing seasons within areas of high pesticide use: 1 site on Prudhomme Creek and 3 sites on Twenty Mile Creek. Three sites on Spencer Creek, an area of low pesticide use, were added in the second season. Surface water samples were collected every 2 wk to 3 wk and analyzed for a suite of pesticides. Hyalella were exposed in situ for 1 wk every 4 wk to 6 wk, and survival and acetylcholinesterase (AChE) activity were measured. Pesticides in surface waters reflected seasonal use patterns: lower concentrations in spring and fall and higher concentrations during summer months. Organophosphate insecticides (chlorpyrifos, azinphos methyl, diazinon) and acid herbicides (2,4-dichlorophenoxyacetic acid [2,4-D], mecoprop) were routinely detected in Prudhomme Creek, whereas neutral herbicides (atrazine, metolachlor) dominated the pesticide signature of Twenty Mile Creek. Spencer Creek contained fewer pesticides, which were measured at lower concentrations. In situ effects also followed seasonal patterns: higher survival and AChE activity in spring and fall, and lower survival and AChE activity during summer months. The highest toxicity was observed at Prudhomme Creek and was primarily associated with organophosphates. The present study demonstrated that current-use pesticides in Southern Ontario were linked to in situ effects and identified sites of concern requiring further investigation.