Mercury levels found in waterways across the state are declining, mainly due to a single factor: the retirement of most of Georgia’s coal-fired power plants.

Over the course of an 18-year study that concluded last month, the Georgia Department of Natural Resources measured mercury levels in fish caught in lakes and streams.

The report was presented to the DNR board Tuesday by James Boylan, air branch chief of the Environmental Protection Division.

“Twenty-four coal-fired units in Georgia have either shut down or converted to firing natural gas since the beginning of this study, resulting in a 98.4% reduction of mercury emissions from coal-fired power plants between 2006 and 2020 in Georgia,” the report stated.

In its elemental form, mercury is found in the earth’s crust, including in coal deposits. It is mostly emitted into the air by the burning of coal, but also during volcanic eruptions and wildfires.

When mercury enters water bodies, microbes convert it into a highly toxic organic compound called methylmercury, which is the form in which it can contaminate fish.

Fetuses are especially sensitive to methylmercury. Exposure in the womb can impair a child’s cognitive development, research has found.

The DNR study involved annual sampling and analysis of fish tissue collected at 22 water basins across Georgia from 2006 to 2020.

When the study was commissioned, methylmercury levels at 10 of the sampling sites exceeded the federal water quality criterion of 0.3 parts per million of fish tissue, beyond which fish consumption is considered unsafe.

By the end of the study, just four of them exceeded that level.

One of those locations was on the Ocmulgee River south of Macon at Highway 96, where the 2020 mercury concentration was 0.334 ppm. The report noted that no power plants are in the vicinity of that collection site.

The other three were “blackwater” sites — swampy water bodies that are especially conducive to converting mercury to methylmercury.

Eight units are still in operation at two coal plants — Monroe County’s Plant Scherer and Bartow County’s Plant Bowen.

In addition to the shutdown of coal plants, the report also credited the decline in mercury levels to the installation of mercury pollution controls known as scrubbers at the plants that remain operational.

In hearings before the state Public Service Commission, utility company Georgia Power is seeking approval to delay the retirement of Plant Scherer beyond its planned closure date of 2028. The utility argues it will need more power generation to meet future growth.


Less testing going forward

The report recommends that, as a result of the gains it found, no further regulation be established on mercury pollution.

It also recommends that testing of fish samples only be continued at the four blackwater sites and at the other sites where mercury levels above .3 ppm were found — and that testing only occur every 10 years, rather than annually.

Rena Ann Peck, the director of the Georgia River Network, an advocacy organization, said the proposed monitoring of the blackwater sites is too infrequent.

One of the sites with elevated mercury levels is the Okefenokee Swamp, which advocates say is threatened by a controversial planned mineral mine on its eastern boundary.

 A report last year from America’s Rivers, a national nonprofit, said the Okefenokee is one of the country’s most-endangered waterways due to the mining plans.

If mining is approved, Peck said, it could affect the hydrology of the swamp and increase the chance of wildfires.

“These conditions would increase methylmercury within the Okefenokee Swamp which would increase the bioaccumulation within the swamp’s food chain,” Peck wrote.

“In lieu of increasing threats to the Okefenokee Swamp, a state, national, and global significant landscape, the Georgia River Network recommends that monitoring within the blackwater systems be conducted more frequently than every 10 years to identify critical changes in methylmercury due to changing land management.”

The Georgia Department of Public Health reports that the most common toxic chemicals in fish are mercury and PCBs. Contaminated fish may not look, smell, or taste different, but they can still be harmful if you are repeatedly exposed to certain contaminants. The department recommends that people limit consumption of fish caught in Middle Georgia to once a week.

This story comes to GPB through a reporting partnership with The Telegraph.