Temporal trends and spatial distribution of DDT in bivalves from the coastal marine environments of the continental United States, 1986–2009

•DDT and breakdown products continue to be available to bivalves in continental U.S. coastal areas.•Concentrations in the coastal areas are decreasing with half-lives of about 10–14years.•Average concentrations will decrease below 10% of today’s concentrations by approximately 2050.•Highest concentrations are correlated to areas where DDT was produced or heavily used.•In some areas, agricultural soils, watersheds and marine sediments may continue to be sources of DDTs. Analysis of DDT isomers and breakdown products, DDD and DDE, in over 3500 bivalve samples collected from more than 300 locations along the continental United States indicates that concentrations are decreasing. Overall average concentrations for the East (45.8±24.6ng/gdw), Gulf (42.4±21.1ng/gdw), and West (90.9±43.3ng/gdw) coasts are declining with an environmental half-life between 10 and 14years and are predicted to decrease below 10% of today’s concentrations by 2050. Geographically, areas with high and low levels are well identified. Bivalves yielding the highest concentrations were collected in areas linked to areas of DDT production or heavy usage. These areas are clustered in the southern California and San Francisco area, on the West coast; Delaware and Hudson/Raritan Estuary, on the East coast; and in Alabama and northwestern Florida, on the Gulf of Mexico. Statistically significant decreasing trends in ΣDDT concentrations are apparent at most of these locations.