Toxic Avengers: Pollution Drove Fish Evolution Tomcod fish found in rivers in New York and New Jersey evolved to handle dangerous chemicals that were dumped in the river between 1947 and 1976, a study finds. The fish aren't mutants, though — some had genetic resistance that allowed them to tolerate the PCBs and dioxins that entered the water.
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Toxic Avengers: Pollution Drove Fish Evolution

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Toxic Avengers: Pollution Drove Fish Evolution

Toxic Avengers: Pollution Drove Fish Evolution

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Scientists have discovered a strange fish that lives in a soup of some of the industry's worst pollutants. The fish are found in rivers in New York and New Jersey.

As NPR's Christopher Joyce reports, it turns out that the fish can survive because they've evolved to cope with dangerous chemicals.

CHRISTOPHER JOYCE: From Godzilla to the Toxic Avenger, film and television have run with the idea that radiation or toxic waste can create weird new species. Just take it from Leela, the one-eyed mutant girl dreamt up by "The Simpsons" creator Matt Groening in the cartoon series "Futurama."


KATEY SAGAL: (As Leela) Look at that lake. One dip in that toxic muck and your DNA will be permanently mutated. Jump in and go for a swim.

JOYCE: In New York and New Jersey, it's not a lake full of toxic muck, but the Hudson and nearby rivers. The weird fish in question are called tomcod. They look like a regular cod but smaller. These tomcod are up to their eyeballs in dangerous chemicals - PCBs and dioxins that General Electric companies dumped into the Hudson from 1947 to 1976. By the 1980s, about 95 percent of those fish in some areas had liver tumors.

But toxicologist Isaac Wirgin at New York University found that some populations of the exposed fish were doing OK.

ISAAC WIRGIN: And it turns out that the more we were dealing with these things, it became apparent that they actually were very resistant to PCB and dioxin.

JOYCE: Here's what had happened. In some fish, pollutants entered the nucleus of cells, where they distorted the DNA instructions from one particular gene. The fish got sick. But some tomcod, just by chance, had a version of that gene that tolerates PCBs and dioxin. So over time, fish with the resistant gene did better than fish without it, and pretty much took over.

Technically they're not mutants - the chemicals just gave one genetic group an advantage over the rest. So, some survived. But Wirgin says there's a downside to that.

WIRGIN: Normally, these levels of PCBs or dioxins would kill these types of organisms, but here they survive and they're prime prey.

JOYCE: Prey for bigger fish, which absorb the pollutants in the tomcods and pass them up to whatever, or whoever, eats them.

The research appears in the journal Science. And a toxicologist who studies fish says it makes an important point.

RICHARD DI GIULIO: That pollution has driven evolution.

JOYCE: That's Richard Di Giulio at Duke University. He says it's happened in North Carolina, too, with something called killifish. They evolved resistance to another pollutant, polycyclic aromatic hydrocarbons, from wood preservatives that seeped into the Elizabeth River.

Di Giulio points out another drawback to the evolution of chemical hardiness.

DI GIULIO: While they have evolved resistance to the pollution, they have lost some ability to cope with natural stressors.

JOYCE: Stressors like low oxygen in the water or abnormally high water temperatures. So, survivors these peculiar fish may be, but a success story they are not.

Christopher Joyce, NPR News.

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