USFWS/Lusk

U.S. Fish and Wildlife Service officials caught fish to analyze mercury levels on the Navajo Nation.

A key part of any fishing trip is checking Arizona’s fish consumption advisory map to see if elevated mercury levels could keep you from safely eating your catch.

KJZZ listener Greg wanted to know if coal power plants in the state are to blame for the elevated mercury levels in some Arizona fish, so he asked via KJZZ’s Q&AZ reporting project.

A Global Issue

Mercury is a naturally occurring element, and volcanoes and forest fire release mercury gas into the atmosphere.

However, that only accounts for a portion of atmospheric mercury. Coal-fired power plants, vehicle emissions and mining activities release far more mercury into the atmosphere than natural sources.

“Asian countries emit a lot of mercury into the air and it travel across the pacific ocean and deposits in North America and when we burn coal and other fossil fuel we emit a lot of mercury that goes into Europe and when Europe burns it it goes into Asia,” said Joel Lusk, a biologist with the U.S. Fish and Wildlife Service who worked with the Navajo Nation to set its first mercury advisories in 2005.

Lusk says while closing a coal-fired power plant in one state would help, “It’s a ‘if we all do a little we all do a lot’ kind of idea,” he said. “It’s not a regional cause and effect.”

While the phrase holds true for atmospheric mercury, there are sources of mercury that originate in Arizona and effect Arizona wildlife.

“In Arizona, abandoned mines that were established prior to the development of modern mining practices can be major contributors to mercury in the environment,” according to an Arizona Department of Environmental Quality advisory.

USFWS/Lusk

Scientists tested various fish in the lake and analyzed their levels of mercury.

In The Food Chain

Atmospheric mercury eventually falls back to earth in rain, snow and even solid deposits. Whether it comes from the sky or a mine, it leaches into the ground or runs into rivers, lakes and fish.

“It gets into the wetlands the the plants take it up, then the invertebrates eat the plants and the mercury gets into their tissue, then the fish eat the plants and the bugs and then bigger fish eat smaller fish and so on,” said Carrie Marr, a biologist with the U.S. Fish and Wildlife Service who works in Arizona.

It’s a process called biomagnification, where animals higher up the food chain have higher mercury levels from the combined mercury levels in their various food sources.

Biomagnification can happen with many elements, but scientists pay particular attention to mercury due to the health effect.

“There’s no known benefit to fish or other wildlife,” Marr said. “At high concentrations mercury can affect neurological function, disrupt organism development and effect reproduction in fish and birds of prey that eat a lot of fish, like the eagles and the osprey.”

In Arizona, catfish, largemouth bass and striped bass are high up the food chain and therefore have higher mercury levels. Which is the same reason humans, considered to be at the top of the chain, should make use of a resource fish can't: food advisory warnings.

Mercury is toxic, and can wreak havoc on your nervous system. Many advisories recommend pregnant women limit how much fish they eat, since the EPA estimates  every year more than 75,000 newborns may have increased risk of learning disabilities due to in-utero mercury exposure.

Danger In Arizona

On a global scale, mercury levels in seafood are increasing, but here in Arizona they’re relatively stable.

There’s only been one new advisory since late 2017, and Lusk said the state and tribes in the region have been “proactive” about reducing mercury exposure. Their efforts include stocking lakes with trout, a fish with lower mercury levels thanks to its size and omnivorous diet.

Even so, there are still some areas where officials cannot say any amount of certain fish species are safe for consumption.