Wet deposition loadings of organic contaminants to Lake Ontario: Assessing the influence of precipitation from urban and rural sites

Wet deposition to Lake Ontario has been examined through a comparison of concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and brominated flame retardants (BFRs) in precipitation at three sites on the north shore of Lake Ontario: one rural, one suburban, and one urban site. Concentrations of ΣPAHs, BFRs, ΣPCBs, Σchlordanes and γ-HCH in precipitation are highest at the urban site, while concentrations of other OCPs were similar across all three sites. Loadings via wet deposition range from 0.42 kg year−1 for Σchlordanes to 1900 kg year−1 for ΣPAHs. The distribution of concentrations reflects the use/emission pattern of the persistent organic pollutants (POPs), and indicates that concentrations in precipitation are predominantly the result of local sources rather than long-range transport from other regions. While elevated urban concentrations increase wet deposition in the urban region itself, this influence decreases rapidly downwind of the urban area. Chemical loads in precipitation from the highly urbanized regions bordering the Great Lakes are estimated to increase wet deposition loadings to lake areas adjacent to the urban areas. Estimates of annual wet deposition loadings of POPs to Lake Ontario indicate that when considering the influence of elevated loadings from Toronto, loadings via precipitation are 2.5%–42% higher depending on the compound, with the greatest relative increase in loadings resulting from PCBs and Σchlordanes.