Poisoning the Imperiled
Three decades after DDT was banned, pesticides still take a toll on the nation's most vulnerable species
Copyright Jessica Snyder Sachs (first published in National Wildlife)
THE BALD EAGLE on Richard Stroud's autopsy table showed the all-too-familiar signs of carbofuran poisoning: talons knotted into fists, legs cocked back against its body, but no signs of traumatic injury or disease. "Basically, the mechanism was death by convulsion," explains Stroud, a veterinary pathologist with the National Fish and Wildlife Forensics Lab in Ashland, Oregon.
Ironically, deadly but short-lived poisons such as carbofuran have come into use largely to replace less acutely toxic but lingering pesticides such as DDT. The devastating effect those earlier pesticides had on birds—especially predatory species such as the bald eagle—inspired Rachel Carson's 1962 manifesto Silent Spring, which in turn helped spur creation of the U.S. Environmental Protection Agency (EPA) in 1970 and passage of the Endangered Species Act three years later.
Yet today, three decades after the act was passed, pesticides remain a threat to the recovery of the nation's endangered plants and animals. The crueler irony, perhaps, is that EPA, the agency charged with assessing pesticide hazards, has no estimate of how many of more than 700 pesticides it has registered pose a hazard to more than 1,260 species listed as threatened or endangered.
By its own admission, the agency has not even tackled a backlog of pesticides that initial studies red-flagged as potentially harmful; these chemicals remain in use pending further evaluation. The number of pesticide victims is equally unknown. "We don't come close to having a handle on all the mortality," says Stroud. "While a dead eagle dropping in a barnyard is hard to miss, most pesticide victims simply disappear."
Toxic by design, the hundreds of pesticides on the U.S. market today include insecticides, rodenticides, herbicides, fungicides and disinfectants. Beneficial, even essential, under some circumstances—protecting an important food crop, for example—their use extends far beyond agriculture to nearly every home, business, school, hospital, park and roadside. Recent studies of major rivers and streams document that virtually all surface waters in the country contain detectable levels of one or more pesticides.
Protecting endangered species from these products is getting more complex: As manufacturers keep bringing new pesticides to market, studies continue to uncover unexpected hazards from those already in widespread use.
Modern pesticides threaten nontarget plants and animals differently than those that caused a public uproar three decades ago."Where once we had a problem with organochlorine pesticides that produced eggshell thinning, today we have poisons that acutely and fatally affect the nervous system by blocking nerve transmission," says Stroud. One example is a class of pesticides, including carbofuran, called cholinesterase inhibitors.
Even more problematic may be the widespread use of herbicides and insecticides known as endocrine disrupters. These compounds work by blocking crucial biochemical pathways such as those used by plants and fungi to form waxy cuticles or by molting insects to form hard chitin skin. In vertebrates from frogs to humans, however, these chemicals interfere with the development of reproductive organs, leading to gross deformities and, in humans at least, cancer.
Some pesticides have killed endangered species outright. In central California, for example, Stroud has seen several San Joaquin kit foxes die of internal hemorrhages after eating poisoned rats. Stands of Texas poppy mallow and neces river rose mallow are occasionally razed when landowners clear brush with herbicides that target broad-leaved plants. And scores of piping plovers have died from seizures over the past few years after their habitat was sprayed with the insecticide fenthion in an effort to eradicate mosquitoes.
Even sublethal pesticide doses take a toll. "When life is a fight for survival, imagine how something as simple as a tremendous headache will set you up for increased predation," notes Stroud. "Because we only see the acute deaths, we don't pick up the chronic problems associated with pesticide exposure." Scientists have discovered endangered animals that suffer abnormal development, deformities, lowered fertility, impaired senses or increased susceptibility to predation and disease when they're exposed to even trace amounts of certain pesticides or their residues.
Take the mysterious global decline of amphibians. Though the problem likely stems from several factors, including habitat loss, Gary Fellers, a research biologist with the U.S. Geological Survey (USGS), and his colleagues have linked reduced tadpole survival and frog deformities to organophosphate insecticides such as diazinon, chlorpyrifos and malathion. In follow-up lab studies, another USGS researcher, Deborah Cowman, found that these insecticides cause genetic damage, which likely results in the increased incidence of death and deformities such as absent or extra hind limbs. Other research has shown that endocrine-disrupter pesticides, such as the widely used herbicide atrazine, cause sexual abnormalities in frogs exposed to trace amounts as low as one part per 10 billion.
Even amphibians in apparently pristine areas have suffered. In California's snow-capped Sierra Nevada, for example, Fellers has spent more than a decade studying crashing populations of frogs and toads. "We're finding high levels of a lot of pesticides," he says of habitat on the western slope. Fellers believes the contaminants are carried in by wind from the central valley, where farmers apply roughly 156 million pounds of pesticides a year. Victims include the mountain yellow-legged frog and the California red-legged frog. The largest native frogs west of the Continental Divide, redlegs were so common in the early 1900s that they featured prominently on restaurant menus and in jumping contests such as that made famous by Mark Twain's "The Celebrated Jumping Frog of Calaveras County." Today few people have witnessed the frog's spectacular leap, and the species continues to decline.
Not surprisingly, frogs and other amphibians show a special vulnerability to any poison dissolved in their watery habitats. "They're like environmental sponges," says Fellers. A similar vulnerability can be seen in fish such as the Northwest's 26 threatened and endangered populations of Pacific salmon, a group that includes migrating coho, chinook, chum, sockeye and steelhead.
"While we sometimes see pesticides kill these fish outright, I'd say most of our scientific concerns point to sublethal effects," says research zoologist Nat Scholz of the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center. As an example, Scholz describes a remarkable behavior normally seen when a predator such as a kingfisher strikes a juvenile Pacific salmon: Young salmon downstream of the attack instinctively stop feeding and drop motionless to the bottom to avoid the same fate. They're detecting a special alarm scent, or pheromone, released from the wounded animal's skin cells, Scholz explains.
That doesn't happen, though, when trace amounts of copper-based fungicides and algaecides leach into stream waters from pressure-treated wood pilings, irrigation canals or crop fields. Laboratory studies by Scholz and others have shown that copper impairs the salmon's olfactory nervous system, or sense of smell. In addition to avoiding predators, salmon rely on their keen noses to navigate home to their spawning grounds and to successfully time the laying and fertilization of their eggs. And copper pesticides, though widespread, account for just a handful of more than 50 pesticides found in Northwestern salmon streams.
Indirect harm, sometimes missed by EPA tests, is another problem. Endangered plants, for example, can be devastated not only by direct contact with an herbicide, but also indirectly by insecticides that wipe out local populations of pollinators. "A lot of endangered plants depend on specific species of pollinators," notes botanist Jackie Poole of the Texas Parks and Wildlife Department. Animals can likewise suffer indirect harm. In addition to poisoned kit foxes, Stroud has seen multiple instances of bald eagles that died after feasting on famphur-poisoned starlings.
Another regulatory weakness stems from the unknown effects of hundreds of so-called inert ingredients contained in commercial pesticide formulas. EPA requires manufacturers to safety test only "active" ingredients—the chemicals directly responsible for killing the targeted insect, plant, fungus or microbe—but not the emulsifiers, binders, spreading agents and other chemicals that contribute to the pesticide's effectiveness. Of special concern are additives known as adjuvants or synergists, which boost the active ingredient's toxicity.
"While a variety of pesticide products share the same active ingredient, these other ingredients give them different actions and potencies," explains Peter deFur, an environmental toxicologist with Virginia Commonwealth University's Center for Environmental Studies and a scientific advisor on federal committees looking at endocrine-disrupter pesticides. "Our message has been loud and clear," says deFur. "The EPA needs to look at pesticides as they are used—as chemical mixtures." Exposure to combinations of different pesticides with similar active ingredients is a similar often overlooked danger.
New research also shows that certain pesticides become harmful at ultralow doses, far below the levels where toxicologists normally stop testing. "If you stop testing when you see no mortality or only test for a few days, you'll entirely miss these effects," says deFur. Yet short-term tests for deadly effects remain the standard for pesticide registration.
DeFur's own research explores the impact of pesticide-contaminated farm runoff on Virginia's many endangered freshwater invertebrates, including fist-sized pearly mussels and "pig toes." He has found that endocrine-disrupting pesticides such as atrazine and dimlin can directly interfere with the formation of the animals' shells. Worsening the problem, other pesticides kill local populations of fish that harbor the mussels' free-swimming larvae inside their gills.
To prevent harm to such vulnerable plants and animals, EPA is required by law to consult with federal wildlife agencies—NOAA Fisheries for marine and anadromous species and the U.S. Fish and Wildlife Service (FWS) for others—on the potential impact of pesticides on endangered and threatened species. Yet the agency faces a large and growing backlog of products awaiting such consultations, including more than 50 that scientists have identified as potentially harmful to listed plants and animals. For their part, the federal wildlife services seldom clamor to fulfill their own legal obligation under the act: to ensure that no action by a federal agency (including pesticide approval) hampers endangered species recovery. NOAA Fisheries oversees 55 listed species, including all endangered salmon, while FWS manages more than a thousand.
To help slash the backlog, the administration has proposed a rule change that would limit EPA's requirement to consult with wildlife services to only those pesticides that the agency has deemed "likely" to adversely affect listed plants and animals. In effect, the move would shield from the agencies' scrutiny any product EPA deems a "possible but not likely" hazard.
When federal agencies released the proposal for public comment in early 2003, they received a flood of responses. Overwhelmingly, pesticide, industry and farming groups voiced support. Citing EPA's poor track record at enforcing endangered species protections, conservationists, water boards and biologists objected. "This proposed rulemaking change is clearly de-signed to put pesticide approvals on a fast track, with less time to look for impacts on wildlife," says NWF senior counsel John Kostyack. "Historically, EPA has always given short shrift to wildlife," he adds.
Worsening this crisis of trust, advocacy groups have caught EPA consulting with pesticide manufacturers behind closed doors, says veterinarian Patti Bright, director of the American Bird Conservancy's pesticides campaign. Through Freedom of Information Act requests, the conservancy garnered memos and e-mail showing a pattern of industry making changes in the agency's initial assessments, she says. "In one instance, the industry had the agency scrub anything that referred to eagles in an assessment of rat poisons that had been shown to kill threatened bald eagles and golden eagles, as well as endangered San Joaquin kit foxes."
Bright also cites a pattern of EPA routinely granting "emergency exemptions" allowing growers to use highly toxic pesticides such as carbofuran in situations known to kill wildlife, including endangered songbirds. "When we see these emergency exemptions being granted year after year going back to 1995, it forces us to conclude that these are not emergency situations at all," she argues. Bright and others point to the wisdom of the Endangered Species Act and its clearly stated requirement that EPA, with its staff of pesticide specialists, consult with wildlife biologists at FWS and NOAA Fisheries.
The real issue, say observers on both sides of the argument, is woefully inadequate funding. "Right now, no agency or service has the kind of resources needed to do these crucial endangered species assessments," says Kostyack. "We have limited staff," agrees EPA's Arthur-Jean Williams with deadpan understatement. Responsible for running the endangered species program under the agency's pesticide office, Williams recently received permission to double her staff of scientists—from three to six. Such limitations continue to slow progress on endangered species protections.
As a veteran of EPA's scientific advisory panels, deFur recalls the years of "hemming and hawing" over the use of just one particularly troublesome pesticide formula—the granular form of the insecticide carbofuran, which resulted in widespread deaths of endangered songbirds and their predators. "Nothing happened until, one day, a carbofuran-poisoned bald eagle turned up on Senator John Warner's doorstep," deFur recalls. Virtually overnight, the pesticide's granular form was pulled from the market.
"Unfortunately," says deFur, "we're not always going to have such a charismatic victim to grab attention."
Jessica Snyder Sachs is the author of Corpse: Nature, Forensics, and the Struggle to Pinpoint Time of Death (Perseus, 2001).