by Tracy Hampton
Beneath the waters of the New Bedford Harbor lies one of the most highly
PCB contaminated sites in the nation. PCBs, or polychlorinated
biphenyls, were dumped there as a byproduct of manufacturing plants
that operated from the 1940s to the1970s. The harbor has been declared
a Superfund site because PCB levels are over four times higher than what
the Environmental Protection Agency says is biologically safe.
Surprisingly enough, a species of fish is thriving there despite long-term
exposure to high levels of these toxic chemicals.
Mark Hahn of the Woods Hole Oceanographic Institution enjoys showing
off his collection of killifish. His lab is like a small aquarium -in each
tank, there's a different group of fish on display.
Mark Hahn: "This is Fundulus heteroclitis, which is the Atlantic
killifish, sometimes called the mummichog. And when the males are
mature, they have this beautiful yellow color that you might see in some of
these guys, whereas the females are more of a dull, but pretty,
Hahn gets his killifish from nearby estuaries and marshes, and he brings
them back to his lab where he breeds them and studies their genetic
makeup. One of his research interests is how these little fish - as
well as other vertebrates " are affected by pollution.
Mark Hahn: "It's a very interesting ecological question.
What happens when animals are exposed for generations to very high
levels of contaminants. One thing that could happen is that the population
could be eliminated, but another thing that could happen is that the
population is able to adapt through genetic changes to the high levels of
And that's just what Hahn has found at the New Bedford Harbor.
There're plenty of killifish living there, and they seem to be eating and
reproducing without any trouble. But upon closer examination, he noticed
there was something abnormal about a particular genetic pathway in
these fish that acts in response to chemicals like PCBs. Say a fish takes
PCBs into its body. Normally, the PCBs are metabolized and broken
down, and the resulting chemicals are even more toxic to the fish than the
original PCBs themselves. The fish in the New Bedford Harbor have
somehow managed to shut down this pathway, and they're able to
survive because the toxic breakdown products aren't formed. Other
species of fish in the New Bedford Harbor weren't as adaptive as the
killifish. Diane Nacci of the EPA:
Diane Nacci: "The whole story about the genetic adaptation, well
does that mean it's really ok, well, no, it doesn't mean it's
ok. Because one species happened to have sufficient genetic variation
that it was able to evolve. There probably were many fish species that
were unable to evolve, were unable to live there as the PCBs moved in,
and are unable to live there now. It is one of the most highly PCB
contaminated sites in the nation."
And just because killifish have been able to adapt, that doesn't mean
they're perfectly healthy. Sarah Cohen is a population geneticist at
Harvard University, and she says these fish may now be even more
susceptible to the toxic effects of other chemicals.
SarahCohen: "There's a cost for that kind of alteration. And it
can be a severe cost. For example, we see that if there's other kinds
of dangerous compounds in the environment, if the organism has shut
down the pathway, then it can't metabolize other harmful things. So
there's a tradeoff to adapting to these extreme situations. You
can't have it all."
Another cost is the effect these fish are having on other animals. The
PCBs build up in the fish's bodily tissue and are passed along up
the food chain. So far, scientists don't know the full implications of
that. Cohen and Hahn are also interested in seeing how their fish studies
can apply to other areas of research and medicine.
Mark Hahn: "There's a field called pharmicogenetics, which
looks at variability among humans in their sensitivity to chemicals and
drugs. There are genetic differences in humans that determine this
sensitivity. So we're using these fish to give us two populations that
are very different in sensitivity that might serve as examples of the two
ends of the spectrum in humans in their sensitivity to a
Cohen also says studying fish is much simpler than trying to study
Sarah Cohen: "Because humans do so many different things
-their behavior is so much more complex. For example, smoking
might be something that might interact with immunogenetics or
compounds and these fish don't smoke - we happen to know.
So that allows us to partition out what kinds of effects are
The researchers are also curious about what will happen to these fish
when the New Bedford Harbor is finally cleaned up - something the
EPA plans to do in the near future. The question is, will they be so well
- adapted to an extreme environment that they'll no longer be
able to live in a healthy one.
Tracy Hampton is a reporter for WCAI-WNAN.