PCBs in Texas Dolphins a Warning to Humans

PCBs in Texas Dolphins a Warning to Humans

COLLEGE STATION, Texas, February 19, 1999 (ENS) - A study of bottlenose dolphins that stranded and died in Texas’ Matagorda Bay has found toxic levels of polychlorinated biphenyls (PCBs) in their tissues. Scientists wondering what effects these pollutants might have on dolphins and people living in the area.

As part of a study funded by Texas Sea Grant, Texas A&M University toxicologist David Busbee analyzed tissue samples taken from the blubber of 10 of the dolphins that stranded in the winter of 1990. He tested them for a variety of pesticides and pollutants, including PCBs, and calculated the amounts and toxic equivalencies required for specific chemicals to prove dangerous to animals.

PCBs are a family of compounds produced commercially by directly chlorinating biphenyl. Many different combinations are possible. In chemical terminology, phenyl means a ring structure of six carbon atoms attached to something else. Biphenyl results when two such rings are attached to each other. And polychlorinated biphenyl (PCB) is any molecule having multiple chlorine atoms attached to the carbon atoms of a biphenyl nucleus. Chlorine atoms can be placed at any or all of ten available sites, with 209 PCB mixtures theoretically possible.

While dolphin researchers found many forms of 209 different PCBs at low levels, the 10 dolphins carried an extremely toxic amount of a form known as non-ortho, coplanar PCBs. The non-ortho coplanar forms of PCBs are so toxic that even extremely small amounts can threaten animals, Busbee said.

The toxic equivalency levels he found in the 10 dolphins studied were 200 times those known to cause birth defects in rats and developmental defects in birds.

"Some of these animals had, over their lifetimes, accumulated fairly large concentrations of these compounds," Busbee said.

No one had previously identified non-ortho PCB levels in the stranded dolphins because scientists do not routinely measure some of the very rare, but potentially toxic, forms when they study PCB levels. But even with this additional information, Busbee said, scientists still do not know what killed the 10 dolphins.

"We think the cold weather and food scarcity put the animals in a lot of stress," he said. "Because they were stressed and using up their normal blubber reserves, they were releasing chemicals stored in the blubber, exposing themselves to extremely high levels of compounds."

This finding raises questions about whether people living near the bay or eating seafood are also accumulating high levels of potentially poisonous PCBs. Research suggests that humans may be even more vulnerable to PCBs and related chemicals than dolphins, Busbee said.

"Dolphins eat fish," he said. "People eat fish. People accumulate these compounds in their body fat just like dolphins."

A happy Matagorda Bay fisherman

Matagorda offers some of the finest saltwater fishing on the entire Texas Gulf Coast. Its coastlines stretch for over 50 miles, from Sargent in the east, to the Port O'Conner Jetties in the west, and north to Palacios. The historic town of Matagorda is in the center of the coastline on the Colorado River. The entire area supports a thriving recreational fishing industry.

In view of Busbee's dolphin studies, scientists want to know whether people who live along the Texas Gulf Coast and eat fish on a regular basis would also accumulate high levels of the compounds, Busbee said. They just do not know yet.

If present in stored fat, the toxic PCBs could pose a particular threat to women, especially those who are pregnant or nursing. Women draw on their fat reserves, where PCB compounds are stored, to produce milk, just as dolphins do.

"When a female dolphin is making milk, she’s using up blubber," Busbee said. "As she uses up that blubber to make milk, all of those compounds that have been stored in the blubber get offloaded into the milk. These baby dolphins are being exposed to tremendously high levels of lipid-soluble compounds. This has been documented in a number of studies."

If the scientists are able to attribute the dolphins’ cause of death to PCBs, Busbee said, their finding might also help explain the world’s shrinking dolphin population, which in some places has fallen by 50 percent in the past 10 to 15 years.

Chemist, not Busbee, works on PCB analysis (Photo courtesy Hudsonwatch)

Viruses have killed off large numbers of the marine mammals, he said, but some scientists believe pollutants are more likely the underlying cause of those deaths. PCBs and other environmental pollutants suppress the immune system in animals, including humans, making it tougher for them to fight off infectious agents such as viruses and bacteria.

Scientists have already linked pollution to birth defects among seals in the heavily polluted Baltic Sea and other areas around the world. Scientists would not necessarily observe these same defects among dolphins as the defective dolphins may die in infancy or be eaten by predators.

Busbee and his researchers will continue to examine the biochemistry behind how dolphins respond to poisonous chemicals in coastal waters.

"It’s a cause for concern," he said. "These dolphins live on our coast. They live in Matagorda Bay. They eat the same fish that we catch in the Gulf and eat ourselves."