Dioxins Toll On Wildlife
Monitoring the great lakes water quality agreement
When deformities in birds around the Great Lakes began to show up in great numbers in the 1970s, the cause was a mystery. Many eggs of bald eagles, double-crested cormorants, Caspian terns, black-crowned night herons, Forster's terns, red-breasted mergansers and other fish-eating birds did not hatch. Of the chicks that did hatch, many had twisted beaks, crooked legs, deformed claws and poorly formed feathers. "I could only describe the situation as catastrophic," says Michael Gilbertson, a biologist with the International Joint Commission (11C), a U.S.-Canada organization that monitors the Great Lakes Water Quality Agreement.
Suspicion turned upon the vast mix of toxic chemicals infusing the lakes from agricultural runoff and industrial waste. Gilbertson, then a biologist with the Canadian Wildlife Service, realized in 1973 that the wild birds' symptoms were nearly identical to those in domestic poultry with chick-edema disease. The outbreaks that killed millions of chickens from North Carolina to Japan began in 1957, but not until 1969 was the cause traced to a contaminant in chicken feed: dioxin.
Dioxin has been released into the Great Lakes from manufacturing plants since the 1930s, although no one realized it back then. Sediment cores from Lake Ontario show that dioxin contamination peaked in 1959. But even the most sophisticated equipment available in the early 1970s could not find a trace of dioxin in the herring gull eggs Gilbertson had collected from Lake Ontario nests. In 1974, he found the characteristic signs of chick-edema disease in herring gull embryos. "It was this awful period of time in which you knew you had a diagnosis of chick-edema disease but could not prove it," he says.
It wasn't until 1981, when dioxin turned up in Lake Ontario fish, that chemists reanalyzed the eggs Gilbertson had kept frozen since 1973. This time, the better equipment found dioxin, at more than 1,000 parts per trillion, a significant amount. The eggs may also have been contaminated with other chemicals that cause chick-edema disease; that analysis is now being conducted. In another significant study, undertaken in 1989, other researchers found a strong connection between numbers of egg deaths and amounts of dioxinlike chemicals in Great Lakes cormorant colonies.
Biochemists have discovered that some of the industrial chemicals in the lakes' waters-dioxins, certain polychlorinated biphenyls (PCBs) and dibenzofurans-act in the same ways on living cells. Dioxin is not usually the most prevalent of these chemicals in industrial waste. But because dioxin is by far the most potent of them all, scientists now call this group of chemicals and their effects "dioxinlike," and dioxin has become the standard for a rating system called toxic equivalence.
In 1989, Gilbertson and colleagues published an analysis of Great Lakes Embryo Mortality, Edema and Deformities Syndrome (GLEMEDS), making the case that dioxin and dioxinlike chemicals are the primary cause of deformities in wild birds. "Before this, scientists would only talk about potential effects," Gilbertson says. "What scientists are now saying is: 'Forget potential effects. There has been actual injury, and we know the specific causes of that injury.'"
A study released this year by the U.S. Fish and Wildlife Service (FWS) found high rates of egg mortality and deformed duckling embryos in wood duck nests near a dioxin-contaminated bayou in Arkansas. The wetland, Bayou Meto, had been contaminated by emissions from a now-closed herbicide plant. FWS scientists discovered that the wood ducks nesting closest to the plant had the highest levels of dioxin in their bodies, and the worst success at producing young. When researchers examined 10 unhatched eggs from one nest near the plant, they found six full-term embryos with twisted beaks.
In other studies, great blue heron chicks hatching from dioxin-contaminated eggs near paper mills in British Columbia had abnormal brain structures, and many had not survived. Snapping turtles in contaminated creeks near Lake Ontario have had high numbers of deformed limbs, tails, shells and skulls.
Evidence is also mounting that dioxin and dioxinlike chemicals interfere with reproduction in wildlife. Some fish downstream from paper mills develop smaller gonads or become cross-sexed, neither truly male nor female. Herring gulls in contaminated colonies often nest in female-female pairs, and the relatively scarce adult males often appear uninterested in normal mating behavior. Recent laboratory tests show that pregnant rats given single, microscopic doses of dioxin bear offspring with genital deformities and greatly reduced sperm counts. Rhesus monkeys given low doses develop endometriosis.
Even so, there is good news: "There is little doubt that levels of dioxin and dioxinlike chemicals in the environment are lower now than they were 20 or 30 years ago," says EPA toxicologist Linda Birnbaum. And after an absence of many years, two pairs of bald eagles recently nested on Michigan's Lake Erie coastline. But still, they are having trouble reproducing; last year, biologists found deformed eaglets in both nests. And the levels of dioxin and dioxinlike chemicals are "still unacceptable," according to the IJC's Gilbertson. "The way I always put it is: We've come a long way, and we've got a long way to go."