A Moment of Science

Are Indiana’s Fish Contaminated By Mercury?

There are lots of good reasons to make fish a regular part of your diet. But rising mercury levels in aquatic ecosystems are worrying scientists.

Sign warning fishermen to not eat fish caught in area due to mercury contamination

Photo: Joey Rozier (Flickr)

Signs such as this one warn fishermen that their catches could be contaminated.

The dangers of eating fish containing high levels of mercury have been well publicized in recent years.  Mercury that is ingested via fish consumption is a neurotoxicant, this means that it can cause damage to your central nervous system.

Pregnant women, nursing mothers, and very small children are especially at risk. In 2005, the PBS program NOW determined that a small child can exceed the Environmental Protection Agency’s (EPA) recommended monthly dose of mercury simply by eating 6 ounces of chunk white tuna (canned).

So where is all of this mercury coming from? Why is it present in such high amounts in fish?

Sources Of Mercury

Mercury is a naturally occurring element that is found in the air, water, and soil.  Coal also contains mercury and smoke from coal-burning power plants and other industrial sites releases this mercury into the atmosphere.

Since the beginning of the industrial revolution, in the late 18th century, the levels of atmospheric mercury have tripled. A new study supported and conducted by Indiana University – Purdue University Indianapolis (IUPUI) has shown that mercury deposited in urban areas by local coal-burning power plants is being quickly spread far afield.

Once the mercury is in the air it easily enters nearby soil and from there watershed carries the mercury to water sources such as rivers.

Additionally, IUPUI researchers have shown that wind carries mercury-contaminated soil far afield, ultimately depositing the chemical into waterways far from the coal-burning power plant where it originated.

Bioaccumulation Of Mercury In Fish

IUPUI researches have good reason to investigate mercury contamination. According to the U.S. Geological Survey, one in seven fish in Indiana contain unsafe levels of mercury. But how does the mercury get from the water into the fish?

The most toxic kind of mercury, methylmercury, is the result of bacteria in streams and lake sediment transforming mercury deposited by watershed from pollution sources. Methylmercury is absorbed more readily than non-methylated mercury.

Fish in streams and lakes are exposed to this easily-absorbed mercury and accumulate it faster than their bodies can process it out (this is called bioaccumulation).

This highly toxic form of mercury is then transferred to our bodies when we eat the contaminated fish and then we begin to bioaccumulate methylmercury. The EPA has determined that unborn babies are the most at risk from methylmercury in the bloodstream.

How To Avoid Contaminated Fish

  • Pay attention to fishing advisories in your state
  • Restrict the fish consumption of pregnant women, nursing mothers, and small children
  • Eat younger fish (older fish have had more time to bioaccumulate more mercury)
  • Eat fewer predatory fish, such as shark, swordfish, and marlin (older fish that eat other fish have higher levels of mercury)
  • Use the EPA’s table “Mercury Levels in Commercial Fish and Shellfish”

Read More:

Erin Sweany

Erin is a graduate student at Indiana University studying early English medical texts. Erin has studied both science and literature throughout her academic career. She loves science for what it tells us about our world and literature for what it tells us about our culture. Erin combines these interests in her scholarship and writing as much as possible.

View all posts by this author »

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science