Warning the public about mercury-contaminated fish

Consumption of mercury-contaminated fish is the primary pathway of human exposure to methylmercury. In the U.S., state agencies are responsible for surveying fish populations in public water bodies and issuing fish consumption advisories that inform the public about hazardous levels of methylmercury in recreationally-caught game fish. Usually, state agencies issue fish consumption advisories on a site-specific basis for large water bodies with public access. These state fish consumption advisories for the south central U.S. can be found on state websites.

The U.S. EPA suggests issuing a fish consumption advisory when concentrations of methylmercury in fish exceed a human health screening value of 300 parts per billion (ppb). However, states have the authority to develop their own systems for issuing fish consumption advisories for methylmercury. Five states in the south central United States (Arkansas, Louisiana, Mississippi, Oklahoma, and Texas) issue advisories for the general human population when concentrations of methylmercury exceed 700 to 1000 ppb.

We conducted a study in 2015 of site-specific fish consumption advisories for largemouth bass to examine the effects of states using higher screening value than recommended by U.S. EPA. Largemouth bass is a widely distributed and economically important species of freshwater game fish. Adult largemouth bass are top predators that have high methylmercury concentrations relative to other fish species.   Like other fish, as largemouth bass increase in length, they become more contaminated with mercury.

We found that the five states in the south central U.S. have issued fish consumption advisories for fewer than one-half of the water bodies that would have advisories if U.S. EPA recommendations were followed. For example, for 15-inch largemouth bass, we found that 478 sites in the database that would have advisories if states followed U.S. EPA recommendations. Only 177 sites currently have state-issued advisories following state guidelines, resulting in 301 sites that would need new advisories if states followed U.S. EPA recommendations.

Site-specific Advisory All Sizes Bass 3 column

This study demonstrates that when states set screening values higher than recommended by U.S. EPA, they dramatically reduce the number of fish consumption advisories. This means that consumers may not be warned about mercury in fish from water bodies when their levels exceed 300 ppb.


Sources of Information

For more information about our mercury research, go to our Aquatic Ecology Lab website.