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

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 sprayed 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. 

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.