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Birds On the Brink

The pesticide DDT continues to show up in alarming levels in nonmigrating songbirds.
 
 
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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 migrating species.

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. Others, 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 survival.

"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 common use.

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 problem."

Mark Clayton is a staff writer for the Christian Science Monitor.