Death came abruptly to the plump seals basking on the tiny Danish isle of Anholt.
First the pups, then the adults could barely swim and refused to eat. Lungs clogged with fluid, skin became mottled with ulcerous sores, and fevers soared.
Within days, almost 300 carcasses piled up along the shore of this sparsely populated retreat in an arm of the North Sea. With the virulence of a hurricane, the mysterious killer jumped south, then north, then west, until it had ambushed nearly every seal colony of Northern Europe. When the outbreak ended six months later, in the fall of 1988, 20,000 harbor seals had perished--more than half the continent’s population.
Europeans were horrified. It was an ecological disaster of epic proportions--orders of magnitude worse than any oil spill--and they wondered what had gone dreadfully wrong along their cherished coasts. Speculation raged: Poisonous algae. Global warming. A chemical spill.
When, months later, the culprit was identified as a newly discovered distemper virus, Europeans were relieved that the seals’ deaths could be chalked up to “natural causes.”
But scientists now suspect that this traditional and simplistic explanation for mass epidemics that periodically plague the world’s animals masks an underlying man-made cause: Immune-altering pollution.
Immune systems are under global assault from chronic buildup of chemical pollution. And experts in this emerging science are amassing compelling new evidence that wildlife, especially sea mammals, that feed in contaminated waters have weakened defenses that leave them easy victims of deadly disease.
The Times reviewed nearly 200 scientific reports, including some as-yet unpublished findings, and interviewed 70 of the world’s leading experts to investigate the environmental threat to the immune systems of animals and humans.
Toxicologists have documented that an array of contaminants in water, air and food can deplete immune cells and exacerbate disease. In tests on laboratory animals and some wildlife, exposure to chemicals--often in amounts mimicking real-world conditions--suppresses the crucial T cells, B cells and “natural killer” cells that protect the body from invading viruses, bacteria and tumors.
In study after study, the most potent immune-suppressor has proven to be PCBs--the banned but still ubiquitous industrial lubricants that contaminate most of the world’s waters. Others include mercury, lead, dioxins and pesticides such as DDT. Oil spills, especially the massive fouling of Alaska’s Prince William Sound, also show some signs of damaging the immune systems of otters and other sea creatures.
But are these chemicals disarming natural defenses so severely that disease turns deadly? The evidence of human harm is less clear, but for wild animals, most experts believe that it is a question of degree--not whether pollution is weakening their immunity and contributing to their deaths, but by how much.
The prevailing wisdom is that many exposed creatures have become the animal kingdom’s version of AIDS patients--they die from infections they could have fended off if their immune system hadn’t been compromised.
“There is very strong evidence that animals in the wild are immunosuppressed,” said Peter Ross, a biologist in Holland who conducted a groundbreaking study of seals feeding on PCBs-contaminated fish.
“I believe if those harbor seals in the North Sea were uncontaminated, you would not have seen the severity of mortality we saw. Without contamination, it might have been like the common cold. But instead of the common cold, you got a killer disease.”
Worldwide, viral epidemics among wild animals are spreading farther and faster than ever, especially among dolphins, seals, birds and other fish-eating animals that top the food chain and carry high body burdens of immune-damaging chemicals.
The distemper outbreak that decimated Europe’s seals actually began a year earlier thousands of miles away, first striking Siberia, then the East Coast of the United States. A record number of dolphins washed ashore between New Jersey and Florida in 1987. As much as half of the near-shore population of bottlenose dolphins was wiped out.
Three years later, the distemper plague struck the scenic beaches of Spain, France and Greece, with more than 1,000 striped dolphins piling up on the shores of the Mediterranean. In 1994, along the gulf shore of Texas, bottlenose dolphins again died in record numbers.
Scientists found that the dead animals shared a common bond beyond the virus--their bodies carried high amounts of industrial compounds, especially polychlorinated biphenyls, or PCBs.
The dolphins that perished in the Mediterranean had an average of three times more PCBs in their tissue than dolphins that survived, according to research by University of Barcelona animal biologist Alex Aguilar. In Northern Europe, seals in the least polluted waters survived the virus at a greater rate.
Can it be mere coincidence that in many cases, marine animals whose tissue carry large amounts of chemicals succumb to infectious disease, while the survivors are far less contaminated? Scientists suspect not.
“You don’t get that magnitude of a die-off--20,000 seals in Europe--without a contributing factor from the environment,” said David Ferrick, a UC Davis immunologist who is studying California sea otters, dolphins and seals. “They seemed healthy, but when they were introduced to [a virus], it just decimated them. That is condemning evidence that immune impairment is one of the few rational explanations.”
Other sea animals have dropped dead en masse in mysterious ways recently, including some species that hover near extinction. Wildlife investigators are probing for clues to a plague that has killed more than 150 manatees in South Florida since March, the largest epidemic to strike any U.S. endangered species.
Also, in Monterey during a single week last July, 11 sea otters, a threatened species, died mysteriously.
Although sea mammals are most susceptible because they feed their entire lives in polluted oceans or estuaries, humans could be at risk too. The immune system of human beings is virtually identical to those of other mammals, and they encounter smaller amounts of the same immune-suppressing chemicals in their food, water and air.
“What’s going to hurt a marine mammal,” Ferrick said, “is probably going to hurt us too.”
After focusing for decades on chemicals’ ability to inflict more obvious and direct injuries such as cancer, scientists in government, academia and industry have begun to explore the insidious effects on bodily systems from immunity to sex hormones to brain function.
Because many of the man-made organochlorines that are considered the worse offenders--PCBs, dioxins and DDT--are so persistent in the environment, governments led by the United States, the European Union and Canada have recently begun the long, thorny task of negotiating pacts to limit them, especially in developing nations.
When it comes to most synthetic chemicals, the most sensitive part of the body--whether seal, fish, bird or human--is the immune system. Minute levels of contamination--too small to poison, maim or mutate--seem to suppress the volumes and efficiency of animals’ immune cells.
Only recently, though, have scientists developed tools--many borrowed from AIDS research--that are sophisticated enough to go beyond simple counts of white blood cells. The detectives in this rapidly growing field, called immunotoxicology, now can measure the exact and subtle changes in individual immune cells and functions.
“Are certain pollutants at certain levels causing effects on the immune system? Absolutely,” said Judith Zelikoff, a New York University Medical Center immunotoxicologist. “We know they are bringing about changes. And there is a strong suspicion, and strong evidence, suggesting that it plays a major role in increased incidence of wildlife morbidity and mortality.”
Still, definitive proof linking pollution to die-offs in real-life conditions may forever elude these experts because in nature many confounding factors, such as poor nutrition and weather, also can increase an epidemic’s severity.
“None of the studies in and of itself proves it,” said Garet Lavhis, an immunologist at the University of Maryland School of Medicine, “but as a picture, they are all saying something very, very well.”
Canadian biologist Peter Ross was studying harbor seals in Nova Scotia when he heard the stunning news that a viral plague had claimed six of 10 seals in the North Sea.
Why, Ross wondered, were the seals he was seeing in eastern Canada healthy and thriving? Tests of their antibodies showed that they had been exposed to the distemper virus that had devastated the European seals. But, for some reason, the Canadian seals fended off the disease.
Marine biologists suspected immune suppression, but they had no proof. What they needed were measurements of seals’ immunity under real-life conditions. But unlike the usual test animals such as mice and rats, seals live in the wild, not in a laboratory. Such an experiment had never been tried under natural conditions.
Three years later, under the auspices of the Dutch government, Ross moved to Holland and embarked on a landmark study that culminated in the most compelling evidence that environmental pollution is severely suppressing marine animals’ ability to fight disease.
Seal pups were caught in the relatively clean waters off Scotland and divided into two groups kept in separate pens. One group was fed herring from the heavily contaminated Baltic Sea, while the other ate herring from the cleaner Atlantic. The difference in PCBs intake was tenfold.
After two years, Ross and his colleagues compared the groups’ immune cells. The differences, reported in 1995, were far greater than anyone had predicted.
Seals fed the Baltic fish developed 25% fewer “natural killer” cells--the first line of defense against viruses--and 35% fewer T cells, the white blood cells essential to clearing infections and ordering production of antibodies.
Such a severe loss of immunity is comparable to what is seen in some AIDS patients. But the scientists, for ethical reasons, did not take the logical next step and expose their subjects to disease. The seals, Ross suspects, all would have died.
In wild seals, the immune damage is probably even worse than what Ross found.
The captive seals were fed Baltic herring for only two years, while wild ones live 30 to 40 years. The captives’ blubber contained 17 parts per million of PCBs, compared with hundreds, sometimes thousands, of parts per million found in wild seals and dolphins that died from distemper. And they were born in fairly clean waters, so their mothers did not pass chemicals to the womb during the fragile stage of immune system development.
The most disturbing implications reach even further. The fish the seals ate had come from Holland’s commercial markets. The same Baltic Sea herring is served at the dinner tables of most Dutch households.
“The harbor seal is the canary in the gold mine,” Ross said. “When 60% of a population dies, it means there is something wrong. Some people say, ‘Who cares about cute, cuddly seals?’ But what it indicates is the state of the world’s oceans, and the commercial fisheries too.”
In the St. Lawrence estuary near Quebec, snow-colored whales called belugas contain so many chemicals that when they die, their carcasses are considered hazardous waste. Their hearses are specially equipped trucks; their burial grounds are toxic waste incinerators.
Over the last 12 years, each autopsy of more than 100 St. Lawrence belugas has found a highly concentrated mix of toxic substances in their blubber and organs. The whales are believed to be the most polluted animals on Earth.
Unlike other whales that migrate, the belugas stay in the St. Lawrence, feeding on bottom-dwelling creatures that swim in waters containing a toxic soup of PCBs, DDT, dioxins and mercury. Many of the eels they eat come from the Great Lakes, where PCB contamination is severe. Quebec’s aluminum plants also release mercury and other immune-suppressing compounds into the estuary.
For years, these “river whales,” an endangered species in Canada, have been dying at an inordinate rate with cancerous tumors filling their bladders and other organs. Fifteen to 20 of the St. Lawrence’s remaining population of 500 belugas die each year.
“These whales are among the most sick I’ve ever seen on the planet,” said Sylvain De Guise, a University of Quebec marine mammal immunotoxicologist. “None of the wild whales examined anywhere seem to be in as bad condition as these. Other whales seem to be able to fight [disease] sufficiently.”
Bacteria that bring a mild response in whales living in less polluted waters cause lethal infections and cancers in these whales. Nearly half have tumors, while autopsies of arctic whales from other areas show no such tumors and lesions.
Laboratory tests, although preliminary, confirm that the pollutants involved can damage immune cells. Whale cells exposed to the concentrations of PCBs, mercury and metals found in the belugas have weak immune response.
At their current death rate, the small, toothed whales of the St. Lawrence, which have swum these waters for 10,000 years, may become extinct.
“Over the long term,” De Guise said, “it would be hard to have a rate of births high enough to sustain a stable or growing population.”
Great Lakes Birds
Wearing a hard hat and rain slicker as protection against thousands of flapping and pecking seabirds, Keith Grasman, a biologist at Ohio’s Wright State University, visits the Great Lakes islands where Caspian terns and herring gulls breed each spring.
Gingerly removing 3-week-old chicks from their nests, he takes blood samples and exposes the birds to mild skin irritants to measure their immune system response.
In four years of testing, Grasman found that birds born in the areas most contaminated with PCBs developed 30% to 45% fewer T cells compared to those in the least contaminated sites. Eggs in Lake Huron’s Saginaw Bay, western Lake Erie and Lake Ontario’s Hamilton Harbor contain the highest concentrations of PCBs.
“We’re certainly seeing suppression of immune function. We’ve been able to replicate that in two species, and enough times,” Grasman said. “The question is, what is the effect on the population? We don’t have that link yet.”
Unlike many marine mammals, the Great Lakes birds have not been stricken with obvious, massive die-offs. There are signs of trouble, though, in the Caspian terns, which have been designated a threatened species in Michigan. Terns normally return to breed on the island where they were born, but in the most contaminated areas of the Great Lakes, only 20% are returning.
“Something is happening that these birds are dropping out of the population,” Grasman said. “We’re seeing significant population-level problems at highly contaminated sites. Is that because their immune systems are suppressed? You certainly do see dying chicks in these colonies, but these are migrating birds, and it is hard to track what happens to them.”
In the 1970s, the Great Lakes were called “dead lakes” because of severe pollution. The main culprits, PCBs and DDT, declined considerably in the 1970s when they were banned in the United States. But in the Great Lakes they have remained constant for more than a decade, apparently frozen at levels that can still weaken a bird’s immunity.
“You can’t deny the fact that there have been significant improvements in the Great Lakes,” Grasman said. “But what we’re left with is a legacy of toxic pollutants which in many ways is invisible.”
Chesapeake Bay Marine Life
Chesapeake Bay is one of the richest--and most troubled--marine resources in the nation.
More than 32 million pounds of oysters were harvested annually until 1959. Now the catch has dipped to almost zero, with much of the blame going to an outbreak of parasitic disease. Fish in the bay’s tributaries have cataracts and swollen underbellies, sometimes with tumors that fill half their livers.
Investigations by toxicologists show that the fish and oyster diseases could be aggravated by pollutants. When researchers compared the immune functions of fish from the Elizabeth River, which drains into Chesapeake Bay, with fish from a nearby clean river, they found “huge immune suppression,” said Mohammed Faisal, an associate professor at the Virginia Institute of Marine Sciences at the College of William and Mary. Numbers of T cells in the Elizabeth River fish were down by half.
Faisal concludes that creosote, a wood preservative produced on the banks of the river, is the source of the problem.
Similar studies show that a compound named tributyltin, used to kill barnacles on ship hulls, could explain the oyster epidemic.
In his laboratory, Bob Anderson of University of Maryland’s Center for Environmental and Estuarine Studies exposed oysters to amounts of the compound comparable to those found in the bay and discovered that parasitic disease progresses much more rapidly when contamination is present.
Anderson, though, cautioned that his work does not prove what is happening in the bay itself, because the Chesapeake has an array of ills--such as fertilizer-fed algae--that also could play a role in die-offs.
Turning the theories into fact is virtually impossible, because the scientists cannot treat the world’s resources like their living chemistry experiment.
“It’s always difficult to show cause and effect,” Anderson said. “You can’t go out and pour a pollutant in an estuary to see what happens.”
Still, laboratories worldwide are sending the same disturbing message: Death due to “natural causes” often has more to do with the acts of man than nature.
“Disease is an expression of an environment out of balance,” said Milton Friend, director of the National Wildlife Health Center, the federal laboratory that investigates animal epidemics. “And nothing is natural out there anymore.”
NEXT: The impact on human immune systems.
(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)
A Deadly Toll
In recent years, die-offs and disease outbreaks among marine animals have increased in severity and scope. Toxicologists suspect that chronic buildup of contamination is supressing animals’ immune systems and increasing vulnerability to disease and infection. Here are some recent problems in the wild:
1) California sea lions / San Francisco Bay Islands
* High cancer rate found in necropsies, including one out of every five in Bay Area. Could be linked to high amounts of DDT, PCBs.
2) Sea otters / Monterey Bay
* 11 found dead in one week in 1995
* The cause is unknown, but large numbers of other otters have died from valley fever and parasitic diseases.
3) Caspian terns / Great Lakes
* No known die-off, but depleted numbers return to breed at the most contaminated spots: Saginaw Bay and western Lake Ontario. Amounts of PCBs are linked to severe immune suppression found in their eggs.
4) Oysters / Chesapeake Bay
* Nearly entire population wiped out by parasitic disease. Tributyltin, used on boat hulls to kill marine growth, seems to spread the disease more rapidly. Fish here also have huge tumors linked to creosote.
5) Common dolphins
Santa Barbara, San Luis Obispo counties
* At least 73 deaths in 1994
* Carcasses found on beaches on the two counties. They had liver and lung lesions of unknown cause. High PCBs and DDT are found in Central California marine life.
Orange, L.A. counties
* At least 37 deaths in 1995
* Cause unknown. High PCBs and DDT are found in Palos Verdes area.
6) Striped dolphins / Mediterranean Sea
* At least 1,000 deaths in 1990-92
* Most of the carcasses were found in Spain. Many more are believed to have died. Distemper virus was the cause, but the dead dolphins contained three times more PCBs than survivors.
7) Beluga whales / St. Lawrence Estuary, Canada
* 15-20 annual deaths
* 3% to 4% of the estuary’s 500 belugas die annually, half with cancer. They are the most contaminated wild animals on Earth. Their bodies contain two dozen contaminants, including PCBs and mercury.
8, 9, 10) Harbor seals
* 20,000 deaths in 1988
* 60% of northern Europe’s population died in the worst wildlife epidemic in history. The cause was a distemper virus, but high amounts of PCBs aggravated the mass die-off.
Cape Cod, Mass.
* At least 400 deaths in 1979
* Recent evidence points to distemper virus. Contaminants are unidentified.
Lake Baikal, Siberia
* Several thousand died from distemper virus in 1987. The contaminants are unknown.
11) Manatees / Gulf Coast of Florida
* At least 157 deaths this year
* Die-off since March in Sarasota area, about 10% of the population, is the worst ever for this endangered species. The cause is unknown, but red tide or disease is suspected.
12, 13) Bottlenose dolphins
U.S. Atlantic coast
* At least 750 deaths in 1987-88
* Number of deaths probably exceeded the 750 carcasses found. An estimated half of the entire East Coast population died. Distemper virus was the cause. The carcasses contained a variety of contaminants.
Gulf of Mexico, Texas
* At least 220 deaths in 1994
* Distemper virus was the cause. Carcasses contained many contaminants.
Other sites highly contaminated with immune suppressors
14) Puget Sound, Washington
15) Lower Columbia River, Oregon
16) Battle Sea, Europe
17) Hudson Bay, Arctic Canada
Some immune-suppressing agents
benzo (a) pyrene
ultraviolet B radiation