'Cautionary tale:' High DDT levels in New Brunswick lakes decades after ban

Several remote New Brunswick lakes still have high levels of a pesticide banned 46 years ago — findings with significant implications for today, says the scientist behind a study on DDT published Wednesday.

"This is definitely a cautionary tale," said Joshua Kurek of Mount Allison University in Sackville, N.B.

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"At the time, we applied these synthetic chemicals thinking they'd have tremendous benefits. And look, 50 years later we're still dealing with the fallout."

New Brunswick, heavily dependent on the forest industry, was one of the heaviest users of DDT in North America. Between 1952 and 1968, at least 5.7 million kilograms of DDT were applied to the province's forests to control spruce budworm.

Canada banned DDT in 1972. Kurek wondered what happened to all that poison.

He and his colleagues looked at sediments in five northern lakes far from communities or any other source of contamination. He found, as expected, large concentrations of DDT in sediment that dated from the spraying era. He did not expect the other results.

"The surprise is that there is no recovery."

On average, sediments exposed to water and organisms on the lake bottom still had DDT levels 16 times higher than those at which the chemical would start to affect aquatic life. Kurek suspects DDT continues to be washed into the water from the forest floor.

As well, the sediments also revealed something odd about the tiny animals that form the basis of the lake's food web.

One species of zooplankton fell off drastically as DDT levels increased. Another species increased markedly — a species shown in previous research to be a good index of how much stress an ecosystem is suffering.

"When conditions in a lake become more stressful, they're often able to withstand those conditions longer," Kurek said.

The findings aren't limited to the five New Brunswick lakes, as the province wasn't the only place enthusiastic about DDT.

"There are hundreds and hundreds of other lakes probably in eastern North America where we could potentially have very high concentrations of DDT still present in the water column, still present in the organisms," Kurek said.

One of Canada's top water ecologists, John Smol of Queen's University in Kingston, Ont., said Kurek's work should be studied closely.

"There's this legacy effect 50 years later in the aquatic ecosystem that has important implications for lake ecology. Nature is slow to pardon our mistakes and we're overly optimistic."

DDT levels are generally falling. But Smol said the chemical compound pops up over the long term in unexpected places and creates unexpected effects.

It gets transported by birds to nesting colonies, where it concentrates in soil from bird droppings. It may be behind the increase in toxic algae blooms, as it kills off tiny algae-grazers.

"Governments think four years," Smol said. "CEOs, at best, seem to think in 90-day cycles.

"Ecosystems don't keep a political or industrial timetable. Things happen on much longer time cycles."

The study didn't look for impacts on fish or birds. Kurek said that's next.

Kurek said pesticides applied almost five decades ago still being active in the environment are reason to think hard about current practices.

"You could substitute DDTs with plastic pollution, with greenhouse gases, with salting on our roads — any contaminant that you put in our environment over a massive region is going to have tremendous effects and sometimes surprise effects."

— Follow Bob Weber on Twitter at @row1960

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