Atmospheric concentrations of current-use pesticides across south-central Ontario using monthly-resolved passive air samplers

In this study passive air samplers (PAS) were deployed on a monthly basis at a number of sites along a south-north transect, extending 700 km north from Toronto, Ontario, characterizing an urban-agricultural-forested gradient, to investigate the spatial and temporal trends of current-use pesticides (CUPs), between spring 2003 and spring 2004. The most frequently detected CUPs were chlorpyrifos, dacthal, trifluralin, and α-endosulfan. Highest air concentrations of chlorpyrifos were observed in May, whereas α-endosulfan and dacthal peaked in July and August, reflecting differences in usage patterns. At the agricultural site, representing the source region of CUPs, chlorpyrifos air concentrations (pg m−3) varied from 2700 to 3.2 and α-endulsulfan from 1600 to 19. The most frequently detected legacy pesticides were the hexachlorocylcohexanes (α-HCH and γ-HCH). For the forested sites, located on the Precambrian Shield, a region with limited agricultural activity, seasonal differences were less pronounced and air concentrations were observed to be much lower. For instance, air concentrations (pg m−3) of chlorpyrifos and α-endosulfan ranged from 7.6 to 0.3 and 50 to 2.0, respectively. By combining PAS data with trajectory air shed maps it is demonstrated that potential source–receptor relationships can be assessed. Air shed maps produced in this study indicate a potential of increased deposition of CUPs to Lake Erie and Lake Ontario.