50 years later, DDT still pollutes lakes

A new study reveals that DDT, banned decades ago, continues to impact New Brunswick’s lakes. Brook trout in lakes once sprayed with DDT carry alarmingly high concentrations of the pesticide’s breakdown products, highlighting the long-term persistence of legacy chemicals in the environment and emphasizing the importance of careful chemical regulation.

Read the full article at https://www.paperleap.com/blog/articles/50-years-later-ddt-still-contaminates-new-brunswick-lakes-0cccy1

Episode Transcript

Speaker 1 (00:00):
Welcome to the paper Leap podcast, where a science takes
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(00:21):
Don't forget to subscribe so you never miss an insight.
All the content is also available on paper leap dot com. Okay, ready,
let's start. You would never imagine what you would find
if you went lake fishing in northern New Brunswick. The
water is cold, clear and seemingly untouched as you would expect,

(00:44):
but lurking beneath the surface, inside the very fish people
prize for dinner, lies a chemical ghost from the nineteen
fifties VDT. A study published in Plows one shows that
this once celebrated insecticide banned decades ago, continues to shape
the ecology of Canadian lakes. Researchers Joshua Curic, Megan Fraser,

(01:09):
Bobby Nakamoto, Karen Kidd, and Christopher Edge conducted a study
that revealed that brook trout in Lakes, once sprayed with DDT,
carry concentrations of the breakdown products of the pesticide at
levels ten times higher than what's considered safe for wildlife consumers. DDT,

(01:30):
short for dichloral diphenal trichloroethane, was hailed as a miracle
chemical when it emerged in the nineteen forties. It killed mosquitoes, ticks, lice,
and crop pests with stunning efficiency. During World War II,
it was sprayed over soldiers to prevent malaria and typhus.

(01:50):
After the war, DDT became a household name, used widely
in agriculture, forestry, and even sprayed on suburban lawns. But
the wonder chemical had a dark side. By the nineteen sixties,
scientists were uncovering alarming patterns birds of prey like eagles
and falcons, or vanishing their eggshells thinned by DDT exposure.

(02:16):
Rachel Carson's landmark book nineteen sixty two Silent Spring galvanized
public concern, eventually leading to bands in North America and
Europe by the nineteen seventies. Yet, unlike pests, DDT doesn't
die easily. It lingers in soils and sediments, breaking down

(02:38):
only slowly into metabolites called dd and DDD, which are
themselves toxic. These compounds, cling to organic matter, settle into
lake bottoms and creep up the food chain. Between nineteen
fifty two and nineteen sixty eight, New Brunswick started one
of the largest aerial pesticide spray programs in the world.

(03:01):
The goal was to stop outbreaks of the spruce budworm,
a moth caterpillar that devours conifer needles and can devastate forests.
Planes rumbled over the province's vast spruce and fir forests,
releasing five point seven million kilograms of DDT over eleven
point eight million hectors. By nineteen ninety three, nearly every

(03:25):
corner of New Brunswick six point two million hectors of
forest had been sprayed with some kind of insecticide. The
ecological bill for that campaign is still coming due To
understand the legacy of DDT products, the research team studied
seven lakes in New Brunswick, five impact lakes where DDT

(03:45):
had been sprayed, and two reference lakes outside the spray zone.
They collected sediment cores from the lake bottoms, which act
like time capsules, preserving layers of pollution. They also caught
brook trout the iconic beckled fish beloved by anglers, and
analyzed their muscle tissue for traces of DDT and its metabolites.

(04:07):
Stable isotope tests were also run to confirm that the
fish were feeding at similar positions in the food web,
ruling out diet as the main driver of contamination differences. Unfortunately,
the results show that lake sediments still contain high levels
of DDT's breakdown products even fifty years later. In some lakes,

(04:28):
concentrations exceed Canadian safety thresholds many times over. Also, Brook
trout and spray lakes had DDT levels ten times higher
than the Canadian guideline for protecting wildlife. At California Lake,
for example, trout carried an average of one hundred and
seventy nine nanograms per gram wetweight equivalent, compared with the

(04:51):
safe guideline of just fourteen. In contrast, trout from the
two reference lakes had negligible levels, often below detection limit.
Most of the contamination came from dd and DDD, the
weathered remnants of the original DDT. This shows the problem
isn't new spraying, but the slow leaking of legacy chemicals

(05:13):
from sediments into the food chain. As you might know.
Brook trout Salvenus fontanalis are a cultural icon in Atlantic Canada,
a top predator in lake ecosystems, and a crucial link
in the food web. When brook trout are contaminated, it
signals that everything below them zoplankton, insects, smaller fish, is

(05:35):
touched by the same legacy. The researchers also point out
that what affects brook trout ripples outward birds, mammals, and
even people who consume these fish could be exposed. DDT
and its metabolites are known to disrupt hormones, damage nervous systems,
and transfer from motherfish to eggs, threatening future generations. The

(05:59):
five lakes in this study are just a sample. The
authors estimate that of New Brunswick's roughly twenty five hundred lakes,
about five hundred lie within watersheds that were sprayed with DDT.
That means nearly a quarter of the province's lakes could
host fish carrying unsafe levels of contamination, even though Canada
banned DDT in the early nineteen seventies. The study highlights

(06:22):
in unsettling reality, chemicals don't obey political calendars. What was
sprayed from crop dusters half a century ago is still
shaping ecosystems today. This story isn't unique to Canada. Around
the world, lakes and rivers bear the chemical fingerprints of
the mid twentieth century. In Michigan, fish still show traces

(06:44):
of DDT. In northern Italy, alpine glaciers released DDT into
downstream lakes as they melt. In parts of Africa and Asia,
DDT is still used in malaria control programs, raising concerns
about its persistence in soils and waterways. The Canadian findings
join a global chorus of warnings. Once unleashed, persistent pollutants

(07:08):
like DDT remain part of the ecological fabric for generations.
Careful testing, regulation and monitoring aren't bureaucratic red tape their
safeguards against repeating mistakes of the past. In their paper,
the authors note that local residents still share memories of
the era when the forests were sprayed. For many, it

(07:31):
was an accepted part of life. Planes flying overhead misting
forests and lakes, few could have guessed that the mist
would linger invisibly for half a century. Now we know
that what seemed like progress in the nineteen fifties is
a persistent problem in twenty twenty five, but perhaps we

(07:51):
can learn the lesson and start avoiding casting such long
toxic shadows in the future. That's it for this episode
of the paper Leaf podcast. If you found it thought provoking, fascinating,
or just informative, share it with the fellow science nerd.
For more research highlights and full articles, visit paperleaf dot com.

(08:15):
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