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Mercury Contamination in Fish Nationwide

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Mercury contamination was detected in every fish sampled in 291 streams across the country. About a quarter of these fish were found to contain mercury at levels exceeding the criterion for the protection of people who consume average amounts of fish, established by the U.S. Environmental Protection Agency.

We talked to Lia Chasar, lead ecologist on the USGS study.




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Jennifer LaVista: Mercury contamination was found in every fish studied in rivers and streams across the country. I'm Jennifer LaVista, and joining me on the phone is Lia Chasar to tell us more about this US Geological Survey study. Lia, thanks for joining us.

Lia Chasar: Well you're very welcome. Thanks for having me.

Jennifer LaVista: Sure thing. What were the major findings?

Lia Chasar: This study is very important because it’s the most comprehensive study to date of mercury in streams and rivers. We sampled water, stream sediment and fish in nearly 300 streams across the country and we found mercury in all of the fish that we sampled. In fact, fish from 27% of our sites actually contained mercury levels that exceed the U.S. EPA criterion, which is 0.3 ppm.

Jennifer LaVista: Wow.

Lia Chasar: They set this criterion for the protection of people who eat fish, an average amount of fish, which is about two meals a week of fish with the levels of mercury.

So, we also found that there are specific geographic patterns in mercury levels in water and fish across the U.S. So while the most important factor in mercury contamination would be the delivery of mercury onto the landscape, there are these watersheds that seem to be more sensitive in terms of mercury stimulation in fish. And these sensitive ecosystems we found tend to be watersheds with evergreen forests and abundant wetlands.

Jennifer LaVista: With all that being said, is it still safe to eat fish?

Lia Chasar: Well, mercury is a neurotoxin. In babies and children it causes impaired neurological development, and in everyone it can adversely affect things like memory and language and attention and even motor skills. So right now, 48 out of 50 states have fish consumption advisories for mercury, so that means that 48 out of 50 states have at least one commonly consumed kind of fish that exceeds the mercury level of 0.3 ppm which is considered safe for eating.

Both EPA and the FDA recommend that we include fish as a part of our healthy diet, so they provide guidelines for us so that we can make informed decisions about which fish we should eat. And they urge us to choose fish that are lowest in mercury.

Jennifer LaVista: So how do we know which fish are safe to eat?

Lia Chasar: For the fish that we studied, which would be fish in rivers and streams, that would be what people call "pan fish" or small sunfish. And also other fish that depend more on things like plants and aquatic insects for their diet. So that would be mullet and some perch, things like that.

And then FDA and EPA instruct us to eat less or avoid fish that are big, longer-lived  predatory fish. So those would be like the basses, the black basses.

Jennifer LaVista: OK.

Lia Chasar: Largemouth, smallmouth bass. Things like pickerel, walleye,  and some of the bigger predatory catfish. So if you go to EPA's advisory website, you can link to all of the state advisories, the national advisories, and the guidelines for eating fish in your area.

Jennifer LaVista: Great. Where are the highest levels of mercury in fish found?

Lia Chasar: Well, like I said earlier, we found sensitive systems that have lots of forests and wetlands, and these areas are typically in the East and the Southeast. So we found the highest levels in mercury in fish in water in the coastal plain streams in Louisiana, Georgia, Florida, and North and South Carolina.

And we also found high levels in areas of New England and the Midwest that have a lot of wetlands. And we even found high mercury in fish in some areas that are mined in the West.

Jennifer LaVista: Did this study also cover saltwater fish?

Lia Chasar: No. We did not address saltwater fish. The same websites that I talked about with EPA that gives the advisories for freshwater fish also gives advisories and consumption guidelines for saltwater fish.

Jennifer LaVista: OK. How did fish become contaminated?

Lia Chasar: Well, mercury is actually a naturally occurring element. Human activities are responsible for releasing and distributing mercury over the landscape, and it gets changed into forms that are more toxic and get into the foods we eat, which for us is principally fish and shellfish.

The most of the mercury in our waters come from atmospheric deposition. That's mercury that gets emitted from coal-fire power plants and waste incineration and as a by-product of the production of cement and chlorine. And then it can get rained out from the atmosphere in rain, snow, or sometimes just as dry particles.

Some of this mercury gets deposited locally but some of it ends up being transported for really long distances, so it can become a global problem. It is a global problem. In some areas of the western U.S., it's not atmospheric deposition, but there are areas that have been highly contaminated from past mercury or gold mining.

Jennifer LaVista: OK.

Lia Chasar: So anyway, once this mercury gets onto the landscape, especially in places that have wetlands or are seasonally inundated or wetted, there are these bacteria that can convert these mercury into the toxic form that we talked about, the methylmercury, and this is the form that gets in the aquatic organisms and ends up in the fish, and the fish-consuming wildlife, and then us.

Jennifer LaVista: Is this affecting species that share environments with these fish?

Lia Chasar: Yes. There's a lot of research being done now about how mercury affects wildlife, wildlife that eats aquatic insects and fish, and that includes birds and mammals. And there are areas across the country where this wildlife is exposed to sub-lethal levels of this contaminant. That means levels that don't cause them to die right away but that can influence their reproduction, their feeding, their behavior, and their long-term health and fitness.

In our city we found that concentrations at 71% of our almost 300 sites exceeded 0.1 ppm guidelines for the protection of fish-eating wildlife.

Jennifer LaVista: Is anything being done about this problem?

Lia Chasar: Well, yes, with studies like ours, it helps us understand how mercury, how it cycles in the environment and how it gets in the fish so we can predict how fish mercury levels will respond to the management of mercury sources. And recently, in February of 2009, the EPA announced that it's going to be working towards controlling mercury emissions from coal-fire power plants by issuing a rule under the Clean Air Act. So, there is work being done now.

Jennifer LaVista: So Lia, how can our listeners learn more?

Lia Chasar: Well, as I said, the US EPA has a great website. So if you go to, that's where you can find all those links that I talked about. There's also a great USGS website on mercury research which has links to summaries on mercury in the environment and lots of links to these studies and others. And that's 

Jennifer LaVista: Great. Well, Lia, is there anything else you would like to add?

Lia Chasar: No. Thank you, Jen. It's been great.

Jennifer LaVista: Thank you so much for joining us. And thanks to all of you for listening. CoreCast is a product of the US Geological Survey, Department of the Interior. I'm Jennifer LaVista.

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