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Decades later, DDT still poisoning Canadian lakes

Friday, June 14th 2019, 3:05 pm - The harmful chemicals are still having an effect long after being banned.

High levels of a once-common insecticide still linger in lakes almost half a century after it was banned, according to a new study.

Scientists at New Brunswick's Mount Allison University tested sediment from five lakes in different watersheds in the province for the chemical dichlorodiphenyltrichloroethane, popularly known as DDT.

They found that not only was DDT still present, the levels were high enough to still cause biological damage to the lakes' organisms.

"What was considered yesterday’s environmental crisis in the 1950s through 1970s remains today’s problem,” lead author Dr. Josh Kurek, Assistant Professor in Geography and Environment at Mount Allison University, said in a release.

DDT was widely used from the 1950s up to the 1970s, often being sprayed aerially onto forests to manage naturally-occurring insect outbreaks. The Canadian Press reports New Brunswick was heavily dependent on the chemical due to its extensive forest industry before it was banned in North America in 1972. Though the lakes weren't the target, rainfall would have washed the DDT residue into lakes and rivers, where it has apparently endured. The authors also point to a particular kind of water flea, Daphnia sp., whose decline they say coincides with high DDT levels, with knock-on effects up the food chain.

"We have learned a lot of tough lessons from the heavy use of DDT in agriculture and forestry. The biggest one is that this pesticide was concentrated through food webs to levels that caused widespread raptor declines in North America," McMaster University professor and study co-author Dr. Karen Kidd, says.

The study, "Ecological Legacy of DDT Archived in Lake Sediments from Eastern Canada," was published this month in the journal *Environmental Science and Technology*.

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