Old culprit hits birds - maybe people
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.Skip to next paragraph
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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."