Spatial and temporal trends in the concentrations of selected organochlorine pesticides (OCs) and polynuclear aromatic hydrocarbons (PAHs) in Great Lakes basin precipitation, 1986 to 1999

Environment Canada has operated a network of atmospheric precipitation stations located along the Canadian shoreline of the Great Lakes basin since the mid-1980s. The number of stations has increased from four at the program's inception in 1986 to nine. Precipitation samples have been analyzed for organochlorine pesticides (OCs) and polynuclear aromatic hydrocarbons (PAHs). The variation in organic pollutant volume weighted mean (VWM) concentrations at the nine stations over the period 1995-1999 ranged between 9 and 90%. Non-parametric analysis of the data showed both north/south latitudinal Great Lake basin differences and within-lake basin differences in their spatial concentration distributions. On a temporal scale, the hexachlorocyclohexanes (HCHs) exhibited significant declines over the past decade, and several of the in-use OCs showed seasonal patterns, which coincided with their tin e of application.