New study shows risk of pesticide DDT in likely hundreds of lakes 50-70 years after its use

New findings of a university-government research team show the toxic pesticide DDT in fish at 10 times above guidelines more than half a century after it was last used, concentrating to high levels in Brook Trout and likely affecting fish-eating wildlife.

“Despite half a century after DDT was last used, environmental problems caused by DDT remain today’s problems, as Rachel Carson warned long ago in Silent Spring”, says lead author Dr. Josh Kurek, Associate Professor at Mount Allison University. “New Brunswick is known as The Picture Province in Canada, but what we discovered in fish and lake mud is not a pretty picture.”

Between the 1950s and 1960s prior to its ban, dichlorodiphenyltrichloroethane (DDT) was used to control insect populations in forests, farmlands, and urban areas. Often applied by airplane to forests, DDT persists in the environment for decades and washes into lakes from the landscape. Fish accumulate DDTs through their diet. This study looked at Brook Trout from New Brunswick lakes where DDT was heavily used and compared results to lakes where DDT was never used. Combining evidence from fish, sediments, and invertebrates, plus publicly available data on where, when, and how much DDT was applied, provides a very powerful approach to studying pollution from decades ago.  

The study was recently published as open access in the journal PLOS One. Findings highlight the pollution legacy of among North America’s largest aerial spray programs of insecticides.

We can now confirm that legacy DDTs are also very high in Brook Trout—above levels where harmful effects may occur for fish-eating wildlife. Brook Trout are the most common fish targeted and consumed by New Brunswick’s 50,000+ licensed anglers.

**NB DDT Study Lakes.** Map of study lakes and total amount of DDT applied between 1952 and 1968 in New Brunswick, Canada. Airplanes were used to apply insecticides to conifer forests resulting in one of the largest aerial insecticide spray programs ever undertaken in North America. Credit: J Kurek

“We have learned many tough lessons from the heavy use of DDT in agriculture and forestry in North America. The biggest one is that this pesticide was concentrated through food webs to levels that caused widespread raptor declines for decades, starting in the 1960s,” notes McMaster University professor and study co-author Dr. Karen Kidd, Jarislowsky Chair in Environment and Health. “Pesticides like DDT are boomerangs, they keep cycling and posing risks in our environment long after we originally threw them there.”

Funding was provided by Natural Sciences and Engineering Research Council of Canada (NSERC) and New Brunswick Wildlife Trust Fund.

NOTE: This study can be obtained FREE from PLOS One https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0320665, or by contacting jkurek@mta.ca