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"New Brunswick ran arguably one of the largest aerial spray programs of DDT ever undertaken on planet Earth," said Kurek, lead author of a study published in the journal PLOS One this week

The insecticide was used to control spruce budworm, which mainly feeds on balsam fir and white spruce, and is a natural pest found in the province's forests.

For the study, researchers analyzed fish, invertebrates and sediment in seven lakes alongside publicly available data on how much DDT had been sprayed.

"What our study showed is there's incredibly high amounts of DDT in the sediments of our lakes, but also in brook trout," Kurek said. "These are brook trout that are just a few years old, and they're exposed to this legacy DDT mostly through their diet."

Brook trout mainly feed on small aquatic insects although their diet consists of a variety of prey, he said. The insects live in the mud at the bottom of lakes, rivers and wetlands, which have large amounts of DDT in the sand, he said. 

"We showed that brook trout in five study lakes in this part of the world are about 10 times above levels that the ºÃÉ«tv Council of Ministers of the Environment considers as sort of safe levels for DDT for wildlife," he said.

"There's a saying, 'You are what you eat.' If there's huge amounts of DDT in the mud at the bottom of New Brunswick lakes, any organism that is feeding on invertebrates or small fish or frogs that are living in these lakes is probably exposed to extremely high amounts, arguably some of the highest amounts in North America."

A 2010 document from the department that was then known as Indian and Northern Affairs Canada said DDT acts as a nerve poison to kill insects, but its exact effect on the nervous system is poorly understood.

"New DDT contamination is the result of long-range atmospheric transport and the accumulation of the chemical in soil, water and snow," the document said. "DDT has been detected in air, rain, snow, surface water and soil, as well as in the tissues of plants and animals."

The insecticide, it said, degrades much more slowly in cold climates than warmer ones. The document said DDT, which stands for dichlorodiphenyltrichloroethane, is toxic to fish and "moderately toxic" to humans, mainly affecting the nervous system and liver.

Kurek said brook trout are a prized fish by New Brunswick anglers, making them one of the sources of DDT for humans. He undertook the study because he is interested in the impact of so-called legacy pollution on biodiversity and aquatic life today, he added. 

DDT is considered a persistent organic pollutant, meaning it lasts a "very, very long time" in the environment, Kurek said. Studies show that it takes up to 150 years for DDT to break down, he noted.

"And really, that's what our research shows, (that) decisions that were made over half a century ago still have impacts on today's ecosystems."

 This report by ºÃÉ«tvwas first published April 23, 2025.