From 1852 to 1968, about 6,280 tons of dichlorodiphenyltrichloroethane (DDT) were sprayed over forests in New Brunswick, Canada, to prevent severe outbreaks of the spruce budworm.
Now, over 50 years later, researchers have detected that sediments of DDT remain in New Brunswick lakes, even long after these insecticides were deemed harmful to wildlife and the spraying stopped.
Able to enter bodies of water through atmospheric deposition and land runoff, DDT may have also reached surface water through direct application, which could have occurred during the period of spraying.
Image: Western spruce budworm control project in Oregon. Photo: USDA Forest Service, Pacific Northwest Region, State and Private Forestry, Forest Health Protection. Collection: Portland Station Collection; La Grande, Oregon.
During the 50 year period where these pesticides were sprayed annually over the forests, between 0.2 and 5.2 million acres were sprayed with phosphamidon and phosphamidon.
Overall, 5.7 million kg of DDT were applied to the New Brunswick forests, making them one of the most heavily sprayed forests in the North America region, according to the study in the American Chemical Society’s Environmental Science & Technology.
The researchers collected sediment core samples from five lakes with a 7.6 diameter gravity core, and dates of the sediment were determined with an Ortec High Purity Germanium Gamma Spectrometer.
After dating results were determined, the researchers then selected 12 to 15 sediment intervals from each core and assessed the legacy DDT congeners from aerial spraying, the study states.
The DDT concentrations were analyzed, including the toxic breakdown in sections of the sediments.
According to the analysis, peak DDT use did occur from the 1970s to the 1980s, and sediments analyzed recently still exceeded levels deemed unsafe for aquatic wildlife.
Sediment records revealed the widespread use of DDT reflected in the five lakes during the mid-20th century when the DDT spraying occurred—and the researchers hypothesize that heavy DDT use altered the assemblage structure of pelagic cladocerans, or water fleas.
“Our study provides an additional ecological context to DDT as a legacy stressor by examining responses of key invertebrates within aquatic food webs,” the ACS paper states.
The team also examined subfossil remains of crustacean zooplankton from sediments during this peak exposure to DDT, after the spraying stopped and before the spraying began, and revealed the lakes shifted from large-bodied zooplankton to small-bodied zooplankton. (Small-bodied zooplankton are more tolerant to contaminants.)
“Chronic stress from DDT inputs of lake ecosystems may also contribute to the long-term trajectory of zooplankton within the pelagic zone that, over recent decades, have likely experienced longer growing seasons, warmer surface water temperatures and more stable thermal stratification due to climate change,” the authors conclude.
For about 2,500 lakes in New Brunswick, the aerial spraying programs may have created long-term consequences to these lake environments.
According to a study in 2018, researchers observed meltwater releasing DDT into the aquatic ecosystem in Alaska—where residents may have been consuming it from fish, potentially exposing them to increased cancer risks.