Tracking Recent DDT Contamination in a Northern New England Watershed: A Geosciences Approach

Abstract

The p,p’ isomers of DDT, DDE, and DDD were analyzed in soils, sediments, and crayfish in the Squam Lake watershed in central New Hampshire (NH), U.S.A. Bennett Brook sources elevated levels of DDT residues to Squam Lake through sediment transport, likely due to legacy contamination from applications to an apple orchard surrounding the stream in the mid 1900s. Results reveal a point source located at a barn used during the orchard operation, which was burned down around 1967, with up to 723 µg/kg p,p’ DDT and 721 µg/kg p,p’ DDE in the soils. Higher DDT than DDE in soil samples, but not in sediment samples, suggests persistence of the contaminant in watershed soils, and faster degradation once mobilized into Bennett Brook and Squam Lake. DDT residues in the lake sediments from 1951 to the present, reveal DDT has consistently been entering Squam Lake since usage began in the U.S. There are likely multiple sources that have contributed to the constant supply, including the orchard soils treated with DDT serving as a nonpoint source, the barn site, and DDT-laden soils vulnerable to erosion, including stream banks and logged or steeply sloped land. Detections of residues in the stream and lake sediments exceed certain sediment quality guidelines for the protection of aquatic life. Higher p,p’ DDE levels in crayfish collected in the mouth of Bennett Brook versus crayfish collected in Squam Lake, distant from Bennett Brook, suggests that residues sourcing from this sub-watershed are entering the aquatic food chain at levels higher than other parts of the lake.