Mercury levels in Nolichucky fish are here to stay, expert says

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TDEC's advisory says mercury levels rise in Nolichucky fish

TRI-CITIES, Tenn. (WJHL) – Mercury levels in Nolichucky fish are here for the foreseeable future, a local biologist said after the state issued an expanded consumption advisory last week.

The Tennessee Department of Environment and Conservation issued the first fish consumption advisory in 2018 for smallmouth bass and channel catfish in the Nolichucky River.

Further data prompted the department to extend the advisory last week to include all species of black bass across the entirety of the Nolichucky, from the Douglas Reservoir to the North Carolina border.

TDEC declared the cause of the mercury to be “atmospheric.”

According to Dr. Joe Bidwell, chairman and professor at East Tennessee State University’s Department of Biological Services, burning coal, usually from power plants, releases mercury into the atmosphere.

From there, the mercury gets carried by rain and snow from high elevations to streams and rivers like the Nolichucky.

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He said he doesn’t expect the advisory to change any time soon.

“The only way to reduce the amount of uptake is to stop the input, and then you would have to allow the existing metal in the sediments in the river to be covered over and become, basically, locked in place, and that can take a long time,” he said.

The advisory says the “trigger” measurement of mercury levels is .3 milligrams per kilogram (parts per million), and fish samples along the Nolichucky exceeded that trigger number.

“It’s a precautionary situation,” Bidwell said. “If the levels in the fish were above 1 mg/kg then they would have issued a ‘do not consume’ (warning), but this is just an advisory so people can make choices about what kind of risks they want to take.”

TDEC said not enough data was collected on walleye to include the species on the advisory. Additionally, catfish in the upper parts of the Nolichucky did not exceed the trigger.

TDEC said in its advisory that researchers tested fish at river miles 8.5 (Hurley Island), 20.9 (Conway Bridge) 68 (Davy Crockett Birthplace State Park and 83.9 (off Charlie Carson Road).

Bidwell said mercury levels tend to rise as it makes its way up the food chain in a process called biomagnification. The mercury makes its way into the muscle tissues of the fish, and then are consumed by humans.

Catfish and black bass (which includes smallmouth, largemouth and spotted bass) are considered the predatory fish of the Nolichucky, and stand to have the largest mercury levels, Bidwell said.

When humans eat the fish, they consume that mercury and can cause problems over time.

“Mercury is one of those metals that’s got no biological function in the body,” he said. “It’s called a non-essential metal. It’s bad because it can accumulate in neurological tissues, and it can cause nervous system effects in humans.”

The advisory says pregnant people should take extra steps to be careful as mercury could harm the developing nervous system of a fetus.

TDEC said activities such as boating, swimming, wading and catch-and-release fishing don’t carry a risk. The advisory suggests eating the flagged fish no more than once per month. Pregnant people and children should avoid the noted fish altogether, according to the release.

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