Temporal trends of persistent organic pollutant concentrations in precipitation around the Great Lakes

The concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and several chlorinated insecticides in precipitation have been measured in samples collected every month since 1997 at six sites on the shores of the North American Great Lakes. We report here the geometric mean concentrations for each of these compounds for each year and at each site. Assuming a first-order rate decline for these data, we have calculated the time it takes for these concentrations to decrease by half. The halving times are not statistically distinguishable among the sites. Overall, the observed halving times are 11 ± 2 years for the PCBs, 14 ± 3 years for the PAHs, 4.0 ± 0.2 for the hexachlorocyclohexanes, 8.0 ± 0.9 for the DDTs, 5.1 ± 0.8 for the chlordanes, and 8.4 ± 0.6 for the endosulfans. In general, the halving times calculated from precipitation concentrations agree with those calculated from atmospheric vapor and particle phase concentrations. - Highlights: • Concentrations of most POPs are decreasing in precipitation collected near the Great Lakes. • POP concentrations in precipitation are decreasing following a first-order rate of decline. • Rates of POPs decrease are similar in precipitation and in the atmospheric gas-phase. - The levels of PCBs, PAHs, HCHs, DDTs, chlordanes, and endosulfans in precipitation from the shores of the Great Lakes are decreasing by a factor of 2 every 4–14 years.