Urban Atmospheric Deposition of Selected Pesticides In Winnipeg, Canada.

Bulk atmospheric deposition, consisting of both rainfall and particulate matter, is an example of a non-point source by which pesticides can enter surface waters in rural regions of Manitoba. However, pesticides are also applied in urban environments such as the City of Winnipeg for which the occasional use of malathion to control adult mosquito populations is most often debated by its citizens. The objective of this study was to monitor deposition levels of seventy-two pesticides at two locations in southern Winnipeg. Bulk deposition samples were collected weekly during the period of May to September 2010 and rainfall volume and intensity were also recorded. 2,4-D had the highest rate of detection with 94% of samples having detectable levels followed by glyphosate (66%). Malathion was detected in 42% of the samples and only occurred from late June to August, the majority of which followed application of malathion by the City of Winnipeg. Atrazine, a chemical with generally very low usage in Manitoba, was detected in 39% of the samples with the majority of detections occurring from May to July, possibly reflecting spring applications of the herbicide in the United States. No legacy pesticides (α-benzene hexachloride (α-BHC), γ-BHC) were detected in any of the samples. In addition to being detected in weeks with rainfall, glyphosate, 2,4-D, atrazine, dicamba, bromoxynil, MCPA, MCPP and malathion were all detected during a week where rainfall was not recorded, therefore demonstrating that deposition of particulate matter is a contributor to overall atmospheric deposition of those pesticides.