A new study reveals that DDT, a pesticide banned in Canada nearly 60 years ago, persists in New Brunswick lakes at levels up to 10 times higher than ecological guidelines.
The research, a collaboration between Mount Allison University and McMaster University, highlights the long-term environmental impact of past pesticide use.
“In the 1950s to 1990s, New Brunswick ran arguably the world’s largest spray program of pesticides,” explains Josh Kurek, an environmental science program advisor at Mount Allison.
“It’s also a probable carcinogen to humans; we studied that in fish in New Brunswick lakes.”
He adds that DDT’s persistence is a major concern.
“We know DDT is a persistent pollutant, meaning it sticks around the environment for a long time. We don’t want high concentrations of DDT in our ecosystems. If organisms are exposed to that pollution, they tend to have poor reproductive fitness, and some cancers can be caused by the DDTs in their systems,” he says.
“Insects at the bottom of the lakes that are exposed to DDT in the mud will transfer that DDT to organisms that eat them in the lake and also outside of the lake… so at the bottom of lakes and wetlands and ponds, it’s the perfect environment to preserve DDT."
Kurek notes DDT can remain in the environment for up to 150 years.
Mike Rushton of the Greater Kouchibouguac Watershed Association expressed surprise and concern at the findings.
“It’s kind of disheartening to learn that it’s still an issue after all these decades of it being banned,” he says.
“Our big focus is fish and fish habitat restoration, so we deal with Atlantic salmon and brook trout. Many other fish species are struggling due to many other issues and threats, but this is just another one to add on the pile.”
Rushton says DDT has been shown to cause harm to fish, reducing their overall survival and impacting various functions.
“We take this issue very seriously… fish accumulate this most likely by eating aquatic insects, which shows just how interconnected everything is in nature, and then that poses a risk to humans who might be consuming anything that’s been contaminated, whether it’s plants or animals."
Rushton points to the historical impact on bald eagles as a stark example.
“One of the more obvious examples of that, some people might remember, is the severe impacts that DDT had on bald eagle populations; it was causing the thinning of their eggshells, so it caused a major decline in population. Once it was finally banned in the ’80s and it wasn’t being sprayed anymore, we all witnessed the population really rebound, which is great, but those chemicals ran off into the soils and the sediments, and they’re very persistent; they’re still here to this day.”
He also emphasizes the need for caution when using chemicals.
“Humans love to try and control nature, and it’s very hard to control without it biting back at you. So if we’re going to use chemicals to try and regulate many things… we really have to consider the potential side effects.”
The study also revealed the scale of DDT application.
Kurek states, “Stakeholders applied DDT by airplane to about half the province, so when you look at the maps that are produced from government collaborators, basically north of Fredericton… DDTs were applied decades ago and they still exist in today’s environment at very, very high levels, some of the highest recorded in North America.”
Looking ahead, Kurek plans further research into environmental toxins.
“I think we have to think very carefully about our long-term decisions and using synthetic pesticides. There are many surprises that we uncovered; we’ve got to do things differently… there are modern comparisons that can be made,” he says.
“We apply a lot of glyphosate, which is herbicide, and we use a lot of road salt in this part of the world. Those are contaminants toxic to organisms, and we’re applying them broadly, so they will have environmental effects down the road. We’re expanding our research; we’re looking at dozens and dozens of lakes. We’ve worked with our university and government collaborators to really refine where we choose our study sites, so we’ll be able to capture ecological responses to DDT pollution gradient in this province.”
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