It's no secret that the now-infamous bug-killer, DDT,
persists stubbornly in the environment. Still, what scientists
found in lake sediments they recently analyzed in the Atlantic province, 50 years after it was last used there, shocked them. The
sediment in all five lakes they tested (representing numerous watersheds), were
laced with DDT at levels up to 450 times beyond what would be considered safe
for key aquatic species and even entire food webs.
by Larry Powell
In some ways, it was like a real war.
A plane sprays DDT on bud worms in Oregon, 1955.
Photo by Forest Health Protection.
In the early fifties, governments and the
forest industry teamed up in New Brunswick to launch a massive aerial assault
against spruce bud worms.
The pests had probably been eating their way through
conifer stands in eastern Canada and the U.S. for thousands of
years. But now, they were causing hundreds of millions of dollars of damage yearly
to forests of mostly spruce and fir, highly valued by a growing human population.
By 1968, almost six million kilograms of DDT had
been unleashed on the worms. The area treated, varied widely from year to
year - from about 80 thousand hectares to two million. Some years, the same
area was treated once - others, twice.
“Budworm City,” established in the early 1950s and used
as a base for DDT spray operations in northern
New Brunswick. Photo credit: D.C. Anderson.
Then, some two years later, as awareness of the harm the product was doing to fish and wildlife grew,
authorities stopped using it altogether.
But not before copious amounts had washed off the land and settled into the water directly from the air.
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But this latest research builds even further on what was known back then.
In the words of the researchers, "Surprisingly, DDT and its toxic
breakdown products are still very high in modern sediments - above levels where
harmful biological effects tend to occur."
Populations of a small water flea, Daphnia sp. (below) were found to have gone down
significantly in the lakes tested. While such a creature may not sound impressive, it's considered an important invertebrate in the food webs of lakes.
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An image of the aquatic organism Daphnia, commonly known as a water flea. They are often numerous in lakes and important grazers of algae, and are eaten by small fish, waterfowl, and large invertebrates. Daphnia are sensitive to their aquatic environment, including DDT levels and other contaminants. Daphniids are used worldwide in toxicology and ecology studies, and are often considered a keystone aquatic species. The postabdominal claw (indicated by the arrow) of Daphnia are preserved in lake sediments and useful to their identification. Photo credit: Kim Lemmen (Queen's University).
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L. to r. Environmental Scientist and lead author Dr Josh Kurek,
study co-author Sarah Veinot, field assistant Marley Caddell, and study
co-author Paul MacKeigan at a remote New Brunswick lake.
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The study's lead author, Dr. Joshua Kurek, tells PinP, "Just to be clear, the loss/reduction of Daphnia is
a concern, as Daphnia eat algae and are also food for fish. Fewer Daphnia mean
less food for fish (and other organisms). It also means less grazing pressure
on algae. It's very difficult to quantify. But other studies do show more algae
(and blooms of algae), when Daphnia are fewer in lakes."
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Excessive growth of sometimes toxic algae can clog lakes, robbing them of their oxygen
and killing fish. It has become a huge problem in waterways, worldwide.
Because New Brunswick had likely become the most heavily-sprayed
forested region on the continent, DDT's harmful legacy could well be playing
out well beyond the five lakes that were studied. (There are about 2,500
in the province, in all.)
Another co-author, Dr. Karen Kidd of McMaster University, adds a
cautionary note of her own. "The lesson from our study is that pesticide
use can result in persistent and permanent changes in aquatic environments."
DDT's "rap sheet" is a long one.
Rachel Carson's famous book, "Silent Spring," published in the early 60s, dedicates almost an entire chapter (l.) to the New Brunswick experience. Called "Rivers of Death," it documents the loss of countless fish, insects and birds along the Mirimachi River, one of North America's best salmon-fishing spots, in the wake of the spraying. She noted the pilots made no effort to avoid spraying directly over waterways. She also observed that the spraying was having questionable results, in any event, since the amounts applied kept having to be increased, just to keep ahead of the hungry worms.
Also, years ago, DDT was found to cause a thinning of the eggshells of dozens of bird species, leading to reproductive failure. While their numbers have since recovered, raptors, notably the bald eagle, were especially hard hit.
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A swift, as depicted in
Bird Craft - 1897. |
And, by killing the bugs they eat, DDT has, for some time, been recognized as instrumental in widespread declines in insectivorous birds such as the swift (r), as well.
