DDT in lake sediments

where it all started…

Outbreaks of eastern spruce budworm (Choristoneura fumiferana) across the province of New Brunswick led to an aerial pesticide spray program that applied ~5.7 million kg of DDT, between 1952 and 1968. About 97% of New Brunswick’s forests have been treated with at least one insecticide, making the Canadian maritime province of New Brunswick one of the most heavily sprayed forest regions in North America. While outbreaks of eastern spruce budworm caused millions of dollars in damage to the forest industry, the adverse effects of DDT on freshwater ecosystems and wildlife were largely unknown until the 1960s. Rachel Carson was among the first to link DDT exposure to ecological effects in her seminal book “Silent Spring”. We now know that this persistent organic pollutant is very harmful to wildlife and humans. DDT and its toxic breakdown products, DDD and DDE, are persistent in the environment for decades to centuries owing to their low water solubility, high partitioning to organic matter and lipids, and resistance to biodegradation. Conditions at the bottom of lakes are ideal for the preservation of DDT, DDD, and DDE. In the profundal zone, DDT and its breakdown products come into contact with benthic invertebrates and the resting stages of zooplankton, potentially altering species abundance, community composition, and organism health. DDT, DDD, and DDE can accumulate in the tissues of organisms, and eventually enter higher trophic levels of the food web. If DDT bioaccumulates then it can reach harmful levels in consumers. Despite being banned in Canada for over five decades, humans today are exposed to DDT and its breakdown products when we consume wild fish and other organisms.

The application of DDT across New Brunswick could be a legacy stressor to lake ecosystems.

We plan to use dated sediment cores from headwater lakes to examine the spatial and temporal differences in DDT concentrations and metrics of key aquatic organisms across lakes in the province. Using dated sediment cores from 30 strategically-selected lakes across New Brunswick, our goal is to assess the long-term consequences of DDT and its breakdown products on the community composition of invertebrates. Within lake sediments lie the fossil remains of chironomids (midge fly larva) and zooplankton. These bioindicators can be identified to genus or species level and provide ecological information about aquatic conditions. The presence or absence of specific taxa can be linked to environmental changes within or surrounding the lake. Many groups of invertebrates are sensitive to pesticides and can be used as indicators of sediment toxicity. The chronic stress from past DDT inputs and its breakdown products, as well as environmental changes in the aquatic environment, such as longer growing seasons, warmer surface water temperatures, and stronger thermal stratification due to climate changes post-1970, could have negative long-term impacts on contemporary aquatic ecosystems, as well as the wildlife that rely on aquatic resources. Our research goal is to understand impacts from legacy stressors and how they interact with recent environmental changes to drive ecosystem trajectories.