Tracking Recent DDT Contamination in a Northern New England Watershed

Abstract

Ecological research since 2005 into potential causes of declines in loon population at Squam Lake, New Hampshire, U.S.A., revealed multiple potential causes, but no particular source of contaminants. In 2017, tributary sediment analyses revealed specific sub-watersheds transporting contaminants to the lake (Vogel, 2019). For this study, from 2018 to 2020, we used an approach to this problem that allowed for rapid source area determination of DDT using soil and sediment analyses. We find modern presence of p,p’ isomers of DDT and DDE within the Bennett Brook sub-watershed, arising from 60-year-old orchard applications and a former barn. Highest concentrations, 723 μg/kg p,p’ DDT and 721 μg/kg p,p’ DDE, occur near the barn’s foundation rubble. DDT exceeds that of the daughter product, DDE, in some of the sub-watershed’s soils, including but not limited to the barn site. In the soils where DDT>DDE, we infer delayed breakdown of DDT. DDT<DDE occurs in the streambed and lake deposits, as well as some soils. A Pb-210 dated sediment core, collected near the outlet of Bennet Brook, shows continuous accumulation of the daughter products, DDE and DDD, from 1951 to the present. Residuals are derived from multiple sources within the sub-watershed, including orchard soils, the barn site, and sediment accumulations in the stream. These DDT residues fall below mandatory soil remediation levels for the State of New Hampshire, but exceed some sediment quality guidelines for protection of aquatic life. Bioaccumulation of p,p’ DDE is evident in crayfish that reside in Bennett Brook.