DDT Still Turning
Up In Songbirds
April 14, 2005
This story was
written by Mark Clayton.
When R. Given Harper set out to understand why North America's
migratory birds were declining, he set a unique course. While
other researchers zeroed in on habitat loss as a key problem, he
decided, on a hunch, to look at an old culprit - the pesticide DDT
- and its specific effects on songbirds.
The results were intriguing. Traces of DDT and other related
chemicals were showing up in the birds. But the real shock came
when Dr. Harper, a biology professor at Illinois Wesleyan
University in Bloomington, compared his results with DDT levels in
nonmigrating songbirds. These year-round residents of North
America - including a who's who of birds like the northern
cardinal, black-capped chickadee, and dark-eyed junco - had more
kinds of chemicals and dramatically higher levels of them than the
Those are surprising results. Heavily restricted in the United
States since 1972 and a declining problem for eagles, osprey, and
other predatory birds, DDT continues to show up in alarming levels
in nonmigrating songbirds. Does that spell trouble ahead for these
still-healthy species? Are humans at risk? No one knows. But one
lesson seems clear: Beware of what you put into the environment,
because it can be extraordinarily difficult to remove.
"These [findings] are reminders that our decisions are going to
affect us for decades," says Greg Butcher, a senior scientist with
the Audubon Society and author of a recent "State of the Birds"
report that showed many North American species in decline. "There
may not be a toxic effect that kills birds at these levels. But it
very well could affect their embryonic development."
Harper's findings are puzzling partly because of their
geographical specificity. Some 18 species that reside year-round
in North America have roughly 1 to 10 parts per million of DDT - 2
to 10 times the levels of those that migrate to Latin America.
Also, all 17 of the organochlorine compounds that Harper tested
for - chemical cousins to DDT - appear in each of those
nonmigrating species. In contrast, one to five of the compounds
were found in migrating birds.
Those are preliminary findings from a yet-to-be published study,
although they build upon Harper's decade of peer-reviewed research
on the same topic. His findings also parallel Canadian and US
research that show organochlorines bioaccumulating in other North
American bird species, experts say.
"These birds are the canaries in the coal mine, warning us about
what's going on in our environment," says Theo Colborn, coauthor
of "Our Stolen Future," a 1996 book that focused on developmental
problems caused by pesticides and other man-made chemicals.
Such conclusions are premature, say spokesmen for the chlorine
industry. They note that Harper's research has not been
peer-reviewed yet. "It would be a mistake to say, not knowing the
levels, how significant his findings are compared to others," says
Kip Howlett, executive director of the Chlorine Chemistry Council
(CCC), a trade association in Arlington, Va.
Since DDT was banned, bald eagles and several other species have
been rebounding, he says.
Just why North American songbirds that do not migrate have high
levels of metabolized DDT and other organochlorines in their
bodies remains a mystery, Harper says in a phone interview.
One hypothesis: The US used far more DDT than Latin America, so
there may be a lot still lingering in the soil, he says. About 1.4
billion pounds were used in the US from World War II until 1972,
the Environmental Protection Agency says.
Harper's findings suggest that any reintroduction of banned
chemicals could have "a more immediate and dramatic toxic effect
than we saw the first time around," Dr. Butcher says.
At least 50 countries ban DDT use although it is still legally
used for malaria control in 20 nations, experts say. The US and
other nations have also banned several related organochlorine
pesticides, such as chlordane and dieldrin.
such as lindane and endosulfan, are still registered for use.
So far, Harper's research has focused on detecting organochlorine
levels in birds, not on their effects. "We're not certain of the
specific impacts of these compounds on birds," he says. "We
suspect the presence of these pesticides may at least play a part
in the decline of neotropical migrants and may cause trouble for
some nonmigrants, too."
The DDT and six other organochlorine compounds that Harper found
in the birds are related to chemicals banned by international
treaty. The treaty, the Stockholm Convention, labels them as
"persistent organic pollutants," or POPs, because they remain in
animals, humans, and the environment for years.
They also tend to evaporate in warm climates and blow on the winds
to cold, northern reaches, where they concentrate.
Pesticides like DDT and lindane show up in high concentrations in
Inuit populations, seals, and polar bears, Dr. Colborn notes.
Early next month in Uruguay, more than 50 nations will discuss
rules for adding new chemicals to the POPs ban treaty, which came
into force last year.
The US chemical industry and President Bush hailed the treaty, and
the US signed it in 2001. Yet legislation to enact it is currently
stymied in Congress. Legislators disagree whether to include tough
language that would automatically ban new chemicals in the US as
they are added to the treaty list.
But until the US ratifies the treaty, it will only be an observer
and not permitted to vote on the new mechanism or on any chemicals
that may be nominated for addition to the list, observers say.
"We support the treaty itself and its implementation into US law,"
says Michael Walls, managing director of the American Chemistry
Council, an industry association in Arlington, Va. "We've been
encouraging the Bush administration and Congress to move
quickly.... The unfortunate consequences of not having ratified
the treaty is that the US won't have a vote at the first meeting."
One of the first chemicals that some say could be nominated for
addition to the list is lindane, which Harper found in most of his
songbirds in North America. It's a pesticide used to treat seeds
and also an ingredient in shampoo to combat head lice.
In California, where
lindane-based shampoo is banned, a state agency reported one
rinsing of lindane shampoo could contaminate 6 million gallons of
water, notes Kristin Schafer, program coordinator at Pesticide
Action Network, an environmental group in San Francisco. New York
is also weighing a ban, she says.
A major reason scientists worry about DDT and other
organochlorines is that they are powerful "endocrine disruptors,"
whose effects on humans and wildlife are little known. Colborn and
Harper charge that such chemicals can, even in tiny amounts in the
body, interfere with embryo development and harm reproduction and
"Every one of these chemicals has an endocrine disruptor effect
that can harm the development of the embryo by interfering with
hormones," Colborn says. She says there's growing evidence of a
link between organochlorines and learning disabilities and human
disorders, which have multiplied since such chemicals came into
But the issue is dosage, not detection, counters the American
Council on Science and Health, a nonprofit group advised by
scientists and others and created to counter activists' claims.
"Current levels of environmental chemicals in the general
population are well below those considered to be associated with
adverse effects and thus do not pose a risk to public health," it
concluded in a 2003 book.
And regulation of current pesticides already takes into account
bioaccumulation, writes a spokesman for CropLife America, a trade
group representing pesticide manufacturers, in an e-mail.
Deeper studies may be needed to settle the issue fully. Although
pesticides have been thoroughly tested, the human hormone system
is so complex that there are no generally accepted methods to
screen chemicals for adverse health effects, the CCC website says.
Glenn Wiser, a senior attorney with the Center for International
Environmental Law, disagrees: "The lesson from the songbirds is
that DDT and other POPs are still used worldwide and are still a
By Mark Clayton
ęCopyright 2005 The Christian Science Monitor. All rights