- COLLEGE STATION, Texas (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.
- Fishing in Matagorda Bay (Photo courtesy
- 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,"
- 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
- "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, shes 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 worlds 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
- 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.
- "Its 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."
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