Some 50 years after the ban on DDT, it is still found in some Canadian lakes



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A beaver lodge stands in the middle of a small lake in the New Brunswick forest.

(Thierry Falise / LightRocket via Getty Images)

  • DDT pesticides were originally used in the 1940s to control mosquitoes.
  • The United States and Canada banned their use in 1972.
  • A recent study found "levels of concern" of DDT in some Canadian lakes.

Nearly fifty years after the ban on its use, the pesticide DDT is still present at "levels of concern" in some isolated Canadian lakes, according to a new study.

"The use of DDT has forever changed the ecology of our study lakes, and probably hundreds or even thousands of others, given its widespread use in the 1950s and 1960s," Joshua Kurek, professor Assistant Professor of Geography and Environment at Mount Allison University and lead author of the study, told weather.com in an email.

DDT, abbreviated to dichlorodiphenyltrichloroethane, was an ingredient in pesticides originally used in the 1940s to kill mosquitoes and other disease-carrying insects, according to the US Environmental Protection Agency. In the 1950s and 1960s, DDT-based pesticides were used in agriculture and vegetable gardens. They have also been widely applied in the forests of eastern North America, often by plane, to combat insect infestations such as spruce budworm. .

The pesticide eventually seeps into lakes and other water bodies.

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"In similar regions in eastern Canada, DDT levels still persist at levels that may pose a threat to aquatic biota," Kurek said.

Kurek and his team studied sediment samples from five lake lakes in New Brunswick. They found that the oldest layers of sediment contained higher concentrations of DDT, but that the more modern layers also showed levels higher than those considered harmful. to the environment, according to a press release from the university.

The researchers also studied zooplankton, a tiny aquatic organism that feeds on algae and is an important food source for fish.

"The use of DDT has had an impact on zooplankton populations, resulting in an almost complete loss or reduction of large zooplankton," Kurek said. "This has implications for the algae and fish of these lakes."

Rachel Carson's 1962 Silent Spring book sparked public outrage at the dangers of DDT and other pesticides. The United States and Canada banned DDT in 1972. Today, the EPA considers it a "probable carcinogen to humans".

He noted that the presence of DDT in the lakes studied posed no risk to human health, but Mr. Kurek expressed his dismay that the banned pesticide continues to threaten the environment.

"We stopped using DDT more than 50 years ago!" he wrote in the e-mail. "Yet he is still present in these lakes at levels that, as we know, are dangerous to aquatic life."

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