USE OF GEOLOGICAL APPROACHES IN DETERMINING THE SOURCE, TRANSPORTATION PATHWAYS AND FOOD CHAIN IMPACTS OF RECENT DDT CONTAMINATION IN SQUAM LAKE, NH

High levels of DDT (exceeding levels of its degradation products) were detected in surface sediments for two inlets into Squam Lake, NH in 2017. One of these inlets, Bennett Brook, has DDT concentrations 48,000 times background levels (pers. comm., Loon Preservation Committee). It drains a watershed dominated by apple orchards from the 1920’s to 1950’s that used DDT. Today, erosion associated with flooding, mass wasting of river banks or beaver pond scouring may be mobilizing sediments and soils that had stored and preserved remnants of the DDT applications. To determine contamination source areas, I use Gas Chromatography to analyze DDT in strategically selected soil and sediment samples. Freeze coring methodology, applied to lake, stream and soil sites, helps determine the extent of DDT through discrete subsampling of cored material. The timing of recent inputs of DDT to the lake is determined by freeze coring near the mouth of Bennett Brook, and is established by dating and high-frequency analysis of the sediments for DDT. The dates of first re-occurrence of DDT are compared to meteorological records of extreme precipitation and watershed erosion events, and to historical records of land use to establish the probable trigger for this contamination issue. To determine if new DDT has entered the food chain, I test benthic macroinvertebrates in the inlet streams for DDT. Macroinvertebrates are in the bottom levels of the aquatic food chain, where sediments and biological systems most strongly interact, and so should be sensitive indicators of even low concentrations of DDT. Results (so far) indicate that while the highest concentration of DDT occurs directly downslope of an abandoned farm dump, there are also elevated DDT concentrations near two culverts upstream of the dump site. Thus, the contaminant likely comes from more than one source area. This study calls attention to possible ongoing threats of persistent chemicals like DDT, despite bans in use decades ago.