TEMPORAL TRENDS IN GAS-PHASE CONCENTRATIONS OF CHLORINATED PESTICIDESMEASURED AT THE SHORES OF THE GREAT-LAKES

Multiple regression was used to examine the temperature dependence and to elucidate temporal trends of atmospheric gas-phase partial pressur es of 10 organochlorine pesticides at five sites near the Great Lakes. The relationship of temperature to gas-phase partial pressures was ex amined using the Clausius-Clapeyron equation, and environmental phase- transition energies were calculated for each of the pesticides. A firs t-order rate constant for the decline in gas-phase partial pressures w as estimated from the regression, and corresponding regional atmospher ic half-lives were determined. The atmospheric half-lives of the hexac hlorocyclohexanes ranged from 2.2 yr for gamma-HCH at Lake Michigan to 7.3 yr for gamma-HCH at Lake Ontario. The half-life for hexachloroben zene ranged from 3.3 yr at Lake Michigan to 12 yr at Lake Superior. Th e half-life for p,p'-DDT was less than 3 yr at Lakes Superior, Michiga n, 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 gamma-chlordane at lake Michigan and Lake Erie to 9.2 yr for trans-nonachlor at Lake Ontario. Using these half-lives and atmospheri c concentrations, virtual elimination dates were estimated for the pes ticides in the atmosphere. These virtual elimination dates ranged from about 2010 for p,p'-DDT to about 2060 for hexachlorobenzene. This stu dy provides evidence that regulatory controls on pesticides have been effective in reducing the concentration of organochlorine pesticides i n the environment.