A novel method to infer historical DDT use on Cape Cod, Massachusetts (USA), based on ΣDDT degradation and 210Pb dating in lake sediment cores

dichlorodiphenyltrichloroethane was used on cape cod, massachusetts (usa), for mosquito and gypsy moth mitigation, from 1948 until the insecticide was banned in the 1970s. there are historical accounts of major spray events, and ddt was expected to have remained immobile in the organic-rich sediments of local ponds. we investigated the potential for sediment cores from lakes on cape cod to reveal the depositional history of ddt. this compound and its metabolites dichlorodiphenyldichloroethane and dichlorodiphenyldichloroethylene (σddt) were examined in sediment cores from four kettle lakes on cape cod that lie between the towns of brewster and harwich, where there is a detailed history of aerial spraying. sediment cores were dated via 210pb and analyzed for water content, total carbon, total organic carbon, and organochlorine pesticide concentrations. use of fallout 137cs to confirm 210pb dates was unsuccessful, probably because of post-depositional migration of 137cs. σddt inventories in each lake were determined to be ~ 10 ng cm−2, which represents about 0.1% on an aerial basis of the quantity known to have been sprayed. compared to the recorded spraying history, the concentration-depth maxima appear decades later than expected. the overall low quantity and unexpected temporal distribution of pesticide residues are probably explained by natural degradation of ddt in the sediment. a novel mathematical correction to ddt concentrations was applied and yielded adjusted inventories close to expected values, and moved the pesticide concentration maxima to the 1950s and 1960s, when they were expected to have occurred.