High levels of DDT found in N.B. brook trout decades after spraying

CBC

28-04-2025

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A pesticide sprayed on New Brunswick forests more than 55 years ago can still be found in some brook trout in the province, according to a new study.
DDT was s prayed from planes across northern and central New Brunswick — more than half the province — between 1952 and 1968 to control the spruce budworm feeding on coniferous trees.
And the synthetic insecticide left a residue that hasn't disappeared.
"I think it's important that people are aware of the fact that this legacy pollutant exists in today's environment at very high concentrations," said Joshua Kurek, an associate professor of environmental science at Mount Allison University and the principal investigator on the study.
Kurek said his research team sampled and studied trout, which he described as one of the most harvested fish in New Brunswick, from seven lakes across the province.
The harmful environmental effects of DDT became widely known to the public after Rachel Carson's influential book about pesticides, Silent Spring, came out in the early 1960s.
New Brunswick stopped spraying DDT in the late 1960s, instead going with other pesticides, including fenitrothion, which was also controversial but was found to break down quickly and not persist in nature. The province now takes a more targeted approach to controlling the budworm.
But DDT, though it was not the most commonly used pesticide in the spray program, has persisted in soil and in New Brunswick's aquatic environment.
WATCH | 'That is how DDT is transferred through the food web':
New research finds high concentrations of DDT in some New Brunswick brook trout
2 hours ago
Duration 2:51
When Kurek looked at its presence in some brook trout populations, he discovered DDT in concentrations 10 times greater on average than the levels identified in Canadian ecological guidelines as being healthy for wildlife.
The guidelines say up to 14 nanograms of DDT per gram of trout, for example, would not be expected to cause adverse effects in wildlife that eat the fish.
Five of the seven lakes Kurek studied were in areas where DDT was sprayed: Upsalquitch, Goodwin, California, Sinclair and the Middle Peaked Mountain.
The remaining two — Anthony and Bennett — were outside the spray zones and were chosen for DDT comparisons across the province, Kurek said.
He said the dark and cool environment at the bottom of these lakes is favourable for preserving DDT.
"Typically, organisms acquire DDT through their diet, what they are eating," Kurek said.
Insects that live in the lake mud will eat sediment with DDT content. These insects are food to the brook trout, then further consumed by loons, minks, otters and humans, said Kurek.
"So if it's in the trout, it's in these other organisms as well, because they form part of the the broader food web."
Kurek described DDT as a "probable" carcinogen.
The World Health Organization's International Agency for Research on Cancer and the U.S. Environmental Protection Agency have recognized DDT as a probable human carcinogen.
Low levels of DDT were detected in trout from the two lakes outside the spray zones, which shows the insecticide travels in the environment, Kurek said.
He said it can travel atmospherically, and it can be carried from land to nearby water bodies by heavy rain or surface water.
DDT present in the food web associated with these lakes bio-accumulates, or keeps building up in the tissues of organisms such as trout, Kurek said.
"And then as you move up the food chain, its abundance in organisms also is magnified, and so organisms at higher levels in the food chain tend to have higher concentrations of pollutants like DDT in their tissues," he said.
Kurek said his next research requires sampling more lakes to further understand how the pollutant enters the lakes from forest soil.
"We want fish populations that are doing well," he said. "When they have high amounts of contaminants like DDT in their tissue, they're not going to do very well."
A spokesperson for New Brunswick's Department of Health said in an email that the DDT levels found in the brook trout research exceed guideline levels for wildlife that consume trout, but not those for humans.
"The guidelines developed to protect human health have levels that are many hundred times higher because wildlife consumers, like birds of prey, have very different diet patterns than human," spokesperson Tara Chislett said.
Chislett advised New Brunswickers to follow the provincial fish consumption limits, for various species, including trout.
According to New Brunswick's fish consumption guidelines, people 12 or older can have eight monthly servings of brook trout that are shorter than 25 centimetres. Pregnant or breastfeeding women, infants and children up to the age of 11 should have only one monthly serving.
With fish that are more than 25 centimetres long, the guidelines recommend people 12 or older have no more than four monthly servings, while pregnant or breastfeeding women, infants, and children up to the age of 11 should not eat any.
The serving sizes mentioned in the provincial guidelines are 75 grams, 125 millilitres or "a portion of cooked fish that fits in the palm of the consumer's hand."
The reason for the vast gap between human and wildlife consumption guidelines is that humans only eat fillets, while the wildlife would consume the entire fish, hence consuming more DDT, said Kurek.