Distribution and persistence of DDT in soil at a sand dune-marsh environment: Point Pelee, Ontario, Canada

Abstract

DDT was applied at Point Pelee, Ontario, Canada, between 1948 and 1970 for mosquito control in recreational areas and pest control in former agricultural areas. Recent soil sampling programs produced 275 analyses enabling a statistical comparison of DDT concentrations with land use areas, soil conditions, and hydrologic characte ristics. Concentrations of ΣDDT ranged over several orders of magnitude, with the highest concentrations (maximum 316 000 ng g-1) in former agricultural areas and the lowest concentrations in the natural sand dunes (maximum of 116 ng g-1). DDT is undergoing degradation at Point Pelee along two pathways. DDT is transformed aerobically to DDE within the sandy soils exhibiting average %DDT, %DDE and %DDD of 40%, 55%, and 5% of ΣDDT, respectively. DDT is transformed anaerobically to DDD and DDE within the marsh and flooded soils averaging 14% DDT, 44% DDE, and 42% DDD, respectively. The half-lives for the transformation of DDT to DDE within the well-drained and aerobic sandy soils at Point Pelee are highly variable and were estimated to range from 20 to 50 yr. Given the high concentrations of ΣDDT at Point Pelee and the long half-life, it is expected that DDT will remain at concentrations of concern for many decades. Key words: DDT, persistence, degradation rates, concentrations, sandy soil, marshy soil