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By Peter Rejcek
More than three decades after much of the world banned
or restricted its use, the pesticide known as DDT is still
showing up at consistent levels in the tissue of Adélie
penguins in Antarctica.
That’s the finding recently published online in
the journal Environmental Science & Technology by
scientists studying ecosystem processes and climate change
in the Antarctic Peninsula. They concluded that because
most countries have banned or severely restricted DDT
use since the 1970s, the source of the insecticide is
most likely glacial meltwater.
The idea is that the chemical has been stored in the
ice, but glaciers have transported it to the coast. The
scientists estimate that glaciers are releasing 1 to 4
kilograms of DDT per year into coastal waters along the
West Antarctic ice sheet.
The paper’s lead author, Heidi Geisz, a PhD student
at Virginia Institute of Marine Science (VIMS), said the
birds are probably not suffering any ill effects from
the powerful insecticide based on levels the researchers
found.
“We know that DDT can affect [seabird] reproductive
systems and their endocrine systems … but these studies
have not been done on Antarctic penguins,” she said.
“The levels that we’re seeing in these penguins
wouldn’t even be approaching levels where we’ve
seen effects in other birds.”
However, Geisz said that DDT tends to occur with other
persistent organic pollutants (POPs), such as polychlorinated
biphenyls, better known as PCBs. These industrial chemicals
were used in a number of products, from coolants to sealants,
before being banned in the 1970s.
“We would like to do a long-term study on some of
those other chemicals, such as PCBs, but the methods for
investigating those chemicals have changed so much over
the years it wouldn’t be reliable to compare current
data to historical data, but DDT we were able to do that,”
Geisz explained. “That’s why we chose DDT, not
for any political reasons, it just happened to be the
chemical for which we have reliable long-term data, but
we know those other chemicals have been there and are
still there.”
First synthesized in 1874, DDT wasn’t used as an
insecticide until around World War II, when it was employed
to control mosquitoes spreading malaria and other diseases.
Certain characteristics of DDT that contributed to its
popularity, particularly its persistence, later caused
public concern, according to a history of the chemical
published by the U.S. Environmental Protection Agency.
Although scientists warned against its hazards as early
as the mid-1940s, it was the publication of Rachel Carson’s
book “Silent Spring” in 1962 that stimulated
widespread concern over use of the chemical. DDT was blamed
for thinning the eggshells of bald eagles and other birds,
nearly leading to the extinction of the American icon.
Ten years later, the EPA banned its use domestically.
On a side note: A 20-year study by NOAA scientists released
in May showed that environmental laws enacted in the 1970s
are having a positive effect on reducing overall contaminant
levels in coastal waters of the United States. However,
the report said elevated levels of metals and organic
contaminants persist near urban and industrial areas of
the coasts.
“It’s interesting to note that pesticides,
such as DDT, and industrial chemicals, such as PCBs, show
significant decreasing trends around the nation, but similar
trends were not found for trace metals,” said Gunnar
Lauenstein, manager of the NOAA Mussel Watch program.
“What is of concern is that there are contaminants
that continue to be problematic, including oil-related
compounds from motor vehicles and shipping activities.”
NOAA’s Mussel Watch Program, founded in 1986, is
the nation’s longest continuous national contaminant-monitoring
program in U.S. coastal waters. The program keeps collected
tissue samples frozen so that scientists can retroactively
analyze overlooked or newly emerging contaminants.
The United States is one thing, but how did a contaminant
used to kill mosquitoes end up on a continent virtually
without any insects in the first place? Atmospheric circulation,
Geisz said. The bottom of the food chain, phytoplankton,
ingest the chemical as it enters the ecosystem. Krill
eat the phytoplankton, and then larger predators gobble
up the contaminated krill.
“It’s incorporated into the fat and lipid tissues
of these animals, and it persists up the food chain,”
Geisz explained. “You get a magnification effect
in the higher predators like penguins.”
That magnification effect, called biomagnification, means
chemicals like DDT do more damage the higher up the food
chain they move. The chemicals are slow to break down,
though DDT will eventually become a metabolite called
DDE, which persists for even longer.
“We are talking about thousands of years for the
ultimate breakdown,” Geisz said. “We have other
professors [at VIMS] who have found this stuff in the
deep sea. It’s everywhere.”
Geisz has helped with research in the Antarctic Peninsula
area for eight seasons, focusing on the effects of climate
change on seabirds with scientist and co-author Bill Fraser
of the Polar Oceans Research Group. During that time she
learned about a study Hugh Ducklow, now with the Marine
Biological Laboratory in Woods Hole, Mass., and Rebecca
Dickhut, chair of the Physical Sciences Department at
VIMS, were doing on contaminants in phytoplankton and
krill.
“I thought that was really interesting,” she
said of the work by Ducklow and Dickhut, also co-authors
on the journal paper. “We talked about looking at
birds and starting a graduate program, and it sort of
developed from there.”
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