Temporal Trends in Gas-Phase Concentrations of Chlorinated Pesticides Measured at the Shores of the Great Lakes

Abstract

Multiple regression was used to examine the temperature dependence and to elucidate temporal trends of atmospheric gas-phase partial pressures of 10 organochlorine pesticides at five sites near the Great Lakes. The relation ship of temperature to gas-phase partial pressures was examined using the Clausius−Clapeyron equation, and environmental phase-transition energies were calculated for each of the pesticides. A first-order rate constant for the decline in gas-phase partial pressures was estimated from the regression, and corresponding regional atmospheric half-lives were determined. The atmospheric half-lives of the hexachlorocyclohexanes ranged from 2.2 yr for γ-HCH at Lake Michigan to 7.3 yr for γ-HCH at Lake Ontario. The half-life for hexachlorobenzene ranged from 3.3 yr at Lake Michigan to 12 yr at Lake Superior. The half-life for p,p‘-DDT was less than 3 yr at Lakes Superior, Michigan, and Erie. A decreasing trend for chlordanes could only be discerned at Lakes Michigan, Erie, and Ontario, where half-lives ranged from 3.2 yr for γ-chlordane at Lake Michigan and Lake Erie to 9.2 yr for trans-nonachlor at Lake Ontario. Using these half-lives and atmospheric concentra tions, virtual elimination dates were estimated for the pesticides in the atmosphere. These virtual elimination dates ranged from about 2010 for p,p‘-DDT to about 2060 for hexachlorobenzene. This study provides evidence that regulatory controls on pesticides have been effective in reducing the concentration of organochlorine pesticides in the environment.