SACKVILLE, NB and HAMILTON, ON — New findings published by PLOS One reveal that DDT, a pesticide last used 60 years ago, continues to impact freshwater lakes in New Brunswick. The study, led by researchers from Mount Allison University and McMaster University, shows that DDT levels remain up to 10 times above ecological guidelines in Brook Trout, a key species in aquatic food webs. 

“Despite the last use of DDT in 1968, past problems caused by reliance on pesticides remain an issue today,” says lead author Dr. Josh Kurek, associate professor at Mount Allison University. “Rachel Carson warned us in 1962 in her seminal book Silent Spring. We now know a nasty legacy of pollution likely exists across half of New Brunswick.” 

The research team analyzed fish, lake sediments, and aquatic invertebrates from lakes within forests treated with DDT, often applied by airplanes in the 1950s and 1960s. Results were compared to lakes without a known history of DDT use. 

The findings confirm that DDT persists in the environment for decades after its application, washing into lakes from the surrounding landscape. Fish accumulate DDT through their diet.  By combining data from fish, sediments, and invertebrates, plus publicly available data on where, when, and how much DDT was applied, the study presents a powerful approach to studying how pollution has lasted for decades.  

“We have learned a lot of tough lessons from the heavy use of DDT in agriculture and forestry. The biggest one is that this pesticide was concentrated through food webs to levels that caused widespread raptor declines in North America,” notes McMaster University professor and study co-author Dr. Karen Kidd, Jarislowsky Chair in Environment and Health. “The lesson from our study is that pesticide use can result in persistent and permanent changes in aquatic ecosystems.” 

The findings highlight the pollution legacy — the long-term environmental impact left behind by past pollution — from one of the largest aerial spray programs of insecticides ever coordinated by forest industry stakeholders in North America.

We can now confirm that legacy DDTs are also very high in Brook Trout — levels above the threshold where harmful effects tend to occur. Brook Trout are the most common fish targeted and consumed by more than 50,000 recreational anglers in New Brunswick. 

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

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