A team of biologists has found that DDT levels in fish are ten times higher than what ecological guidelines recommend, decades after it was last used.

Researchers detected high concentrations of the pesticide in brook trout throughout New Brunswick, raising concerns about the impacts on fish-eating wildlife.

The study, published this week in the journal PLOS One, highlights the pollution legacy of one of North America’s largest aerial spray programs of insecticides.

Between the 1950s and 1960s, prior being banned, dichlorodiphenyltrichloroethane (DDT) was used to control insect populations in forests, farmlands and urban areas. Commonly sprayed over forests by airplane, DDT has lingered in the environment for decades, gradually washing into lakes from surrounding land. Fish absorb DDT through the food they eat.

“We have learned many tough lessons from the heavy use of DDT in agriculture and forestry in North America,” says McMaster University professor and study co-author Karen Kidd, the Stephen A. Jarislowsky Chair in Environment and Health.

“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.”

“Pesticides like DDT are boomerangs, they keep cycling and posing risks in our environment long after we originally threw them there.”

The researchers examined 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, as well as publicly available data on where, when, and how much DDT was applied, provides a very powerful approach to studying pollution from decades ago.

“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 Josh Kurek, associate professor of Environmental Science 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.”

Researchers say the findings confirm legacy DDTs are 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 anglers in the province.

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