Invasive Species and Toxic Chemicals

  • The round goby is an invader in the Great Lakes... and now scientists are discovering that toxins called PCBs are accumulating in round gobies... and then those toxins are getting into fish that we eat. (Photo by David Jude)

Invasive species and toxic chemicals…

This is The Environment Report. I’m Rebecca Williams.

There are these chemicals called PCBs or polychlorinated biphenyls. They were found to be toxic decades ago. The Environmental Protection Agency considers them to be probable human carcinogens. They were banned in the 1970s, but they’re still all around us. They’re buried in the sediment at the bottom of some of our rivers and lakes. Now researchers are finding invasive species are passing these old, toxic chemicals up the food web.

David Jude is a research scientist and a fish biologist at the University of Michigan.

So you found that zebra mussels and round gobies are driving this problem. How so?


“Well, the zebra mussels and the quagga mussels, which is a cousin of the zebra mussels, are filtering the water of algae and sometimes other detrital material and PCBs will absorb to that material. Therefore, they accumulate high concentrations of toxic substances including PCBs. So any organism that eats those organisms are going to accumulate PCBs in their bodies.”

RW: So the zebra mussels and quagga mussels are accumulating the PCBs…the round gobies are eating them and they’re stockpiling the PCBs in their bodies (DJ: “Exactly.”) and then here come the walleye and they eat the round gobies (“Exactly.”):

DJ: “So any walleyes that spend a lot of time in the Saginaw River eating round gobies are going to pick up a lot of PCBs because those fish are contaminated.”

RW: You studied Saginaw Bay in particular. Is this same zebra mussel, round goby, walleye connection happening in other parts of the Great Lakes?

“Yes, sometimes there may be a different top predator involved but all the Great Lakes have places where this particular food web is in operation, except for Lake Superior. And, the other point I think I should make is that, again, this study was done in a highly contaminated area. In other areas of the Great Lakes, for example in Lake Michigan, you would not see this sort of uptake of PCBs. It’s only in these contaminated areas of concern across the Great Lakes that we’re seeing this sort of a pattern.”

RW: So what does this mean for people who like to catch and eat walleye?

“The bigger the fish, which we found in this study, the more contaminants that they’re going to have. So you should be eating smaller fish and you should do everything you can to get rid of the fat.”

RW: And that’s because PCBs collect in fat, right?

DJ: “Yes, exactly right.”

RW: So this applies, what you’re finding applies to other kinds of fish as well?

“Well, I would think so. You could, by analogy, suggest that other fatty fish are probably picking up a lot higher levels than what we’re seeing in the walleyes.”

RW: So if I’m at the fish market, what kinds of Great Lakes fish would I be best off buying?

“Well, small fish. I’d get small fish first and then I would get yellow perch if I could do that. They would probably be the lowest contamination level of the ones that are there. Lake whitefish probably would be another good one for you to eat. They’re fairly low on the food chain and unfortunately they are starting to eat a lot of quagga and zebra mussels, but again, they’re eating them in areas where they’re not as highly contaminated as they would be in an area of concern. So, you possibly could get some that were eating these zebra mussels and quagga mussels in an area of concern so they could be contaminated but in general, I would say lake whitefish might be a good species to eat.”

RW: David Jude is a research scientist and a fish biologist at the University of Michigan. Thank you so much for coming in.

“My pleasure.”

That’s The Environment Report. I’m Rebecca Williams.