DDT’S lasting legacy
How the plan for pumping the powerful pesticide over Canadian forests is impacting ecosystems to this day
SSOME EVIL SPELL had settled on the community: mysterious maladies swept the flocks of chickens; the cattle and sheep sickened and died. Everywhere was a shadow of death. The farmers spoke of much illness among their families. In the town the doctors had become more and more puzzled by new kinds of sickness appearing among their patients. There had been several sudden and unexplained deaths, not only among adults but even among children, who would be stricken suddenly while at play and die within a few hours.
This fable sets the stage for Rachel Carson’s 1962 Silent Spring, her gamechanging environmental exposé on the effects of indiscriminate pesticide use. The book sparked an international dialogue on pesticide policies and eventually led the United States, Canada and Europe to ban DDT (dichloro-diphenyltrichloroethane), one of the most egregiously toxic human-made pesticides, in the 1970s. While Carson’s community was fictional, her descriptions were drawn from real accounts of DDT poisoning — the damage had already been done.
Sixteen years before the book was released, Natural Resources Canada produced this 1946 map (above, left) of DDT spray patterns to control spruce budworm at Eaglehead Lake in Ontario’s Thunder Bay region. From 1909 to 1946, infestations of the little moth larva, one of the most devastating insects to North American conifer forests, had destroyed an estimated 250 million cords of cut spruce and balsam in Eastern Canada alone, a great loss to the postwar forest industry. So the federal government turned to largescale aerial-spraying operations, coating forests with more than 200,000 litres of DDT, the latest and most effective insecticide.
DDT reached peak popularity during the Second World War, when troops and civilians abroad were sprayed with the stuff to control insect-borne disease, such as typhus and malaria (DDT is still used in parts of Africa to control malaria). Back home, trucks and planes spewed the colourless, odourless liquid over
In 1945, Canso aircraft (above) were leased from the Royal Canadian Air Force by the Ontario Department of Lands and Forests and fitted with DDT spraying attachments to control spruce budworm.
crops, forests and even suburban neighbourhoods to combat insects, while children played in the fog.
But what scientists at Natural Resources Canada and elsewhere did not know then was that although DDT is not acutely toxic, meaning adverse effects don’t show up from just one exposure or a few in a short period of time, the chemical persists and builds up in the environment, infiltrating food webs and damaging the nervous systems of humans and wildlife — particularly raptors — for generations to come.
DDT’S dangerous persistence was exposed yet again in a recent study published in the journal Environmental Science
& Technology in summer 2019, nearly 50 years after the pesticide was banned. It found that remote lakes in New Brunswick
still have toxic levels of DDT (in one lake, more than 450 times the safe level), the result of spruce budworm spraying.