Destroying the Balance of Nature

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The Times reviewed nearly 200 scientific reports, including some as-yet unpublished findings, and interviewed 70 of the world's leading experts to investigate the environmental threat to the immune systems of animals and humans.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.