Ecological Legacy of DDT Archived in Lake Sediments from Eastern Canada

Historic forest management practices led to widespread aerial application of insecticides, such as dichlorodiphenyltrichloroethane (DDT), to North American conifer forests during ∼1950-1970. Lake basins thus may provide an important archive of inputs and aquatic responses to these organochlorines. We use dated sediment cores from five study lakes in multiple watersheds in New Brunswick (NB), Canada, to provide a regional paleo-ecotoxicological perspective on this potential legacy stressor in remote lake ecosystems. Peak sedimentary levels of p, p'- and o, p'-DDT (ΣDDT) and breakdown products ΣDDE (dichlorodiphenyldichloroethylene) and ΣDDD (dichlorodiphenyldichloroethane) generally occurred during the 1970s to 1980s. Sediments exceeded probable effect levels (PELs) by ∼450 times at the most impacted lake. Modern sediments in all study lakes still contained levels of DDT-related compounds that exceed PELs. For the first time, we show that aerial applications of DDT to eastern Canadian forests likely resulted in large shifts to primary consumers within several lake food webs, principally through lake-specific impacts on zooplankton community composition. Modern pelagic zooplankton communities are now much different compared to communities present before DDT use, suggesting that a regional organochlorine legacy may exist in the modern food webs of many remote NB lakes.