Organochlorine pesticides and polychlorinated biphenyls along an east-to-west gradient in subtropical North Atlantic surface water

Despite the fact that most persistent toxic substances have hardly been primarily emitted for several decades, their concentrations are only slowly decreasing in the global oceans. Surface seawater samples were collected along a 38°-24° N/28°-67° W transect in the subtropical North Atlantic Ocean. While the concentration levels of hexachlorobenzene (2.1-6.1 pg L-1), dichlorodiphenyltrichloroethane (DDT, up to 2.1 pg L-1) and polychlorinated biphenyls (PCB, 10.8-24.9 pg L-1) were in the same range as observed earlier in the North Atlantic, hexachlorocyclohexane (HCH, 90-627 pg L-1) was found elevated, partly also relative to previous measurements in the same sea region. Hereby, the ratio α-HCH/γ-HCH was very low, 0.09-0.13. Chlordane and endosulfan were found in the range <3.0-11.1 and <5.8-8.8 pg L-1 respectively. DDT metabolites, endrin and related pesticides were found below quantification limits. Spatial pollution patterns in surface seawaters seem to be determined by atmospheric and oceanic transport patterns, rather than by mixing and air-sea equilibrium. The comparison with global multicompartment chemistry-transport model predictions of surface seawater levels indicate underestimated degradation of PCBs and overestimated emissions of endosulfan.