Environmental factors affecting the levels of legacy pesticides in the airshed of Delaware and Chesapeake Bays, USA.

Organochlorine insecticides and their degradation products contribute to toxicity in Chesapeake Bay, USA, sediments and affect the reproductive health of avian species in the region; however, little is known of atmospheric sources or temporal trends in concentrations of these chemicals. Weekly air (n = 265) and daily rain samples (n = 494) were collected over 2000 to 2003 from three locations in the Delmarva Peninsula, USA. Pesticides were consistently present in the gas phase with infrequent detection in the particle phase. Hexachlorocyclohexanes (HCHs) and cis- and trans-chlordane were detected most frequently (95-100%), and cis- and trans-nonachlor, oxychlordane, heptachlor, heptachlor epoxide, dieldrin, and 1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene (4,4'-DDE) were also detected frequently. The highest mean air concentrations were for dieldrin (60-84 pg/m(3)), gamma-HCH (37-83 pg/m(3)), and 4,4'-DDE (16-80 pg/m(3)). Multiple regression analyses of air concentrations with temperature and wind conditions using modified Clausius-Clapeyron equations explained only 30 to 60% of the variability in concentration for most chemicals. Comparison of the air concentrations and enthalpy of air-surface exchange values at the three sites indicate sources of chlordanes and alpha-HCH sources are primarily from long-range transport. However, examination of chlordane isomer ratios indicates some local and regional contributions, and gamma-HCH, 4,4'-DDE, dieldrin, heptachlor, heptachlor epoxide, and oxychlordane also have local or regional sources, possibly from contaminated soils. Median rain sample volumes of 1 to 3 L led to infrequent detections in rain; however, average measured concentrations were 2 to 10 times higher than in the Great Lakes. Dissipation half-lives in air were well below 10 years for all chemicals and below published values for the Great Lakes except dieldrin, which did not decline during the sample period.