ORNL Explores New Ways to Tackle Mercury Cleanup

Jun 27, 2019

Post-doctoral research associate Grace Schwartz checks slime growth on donut-shaped ceramic disks Oak Ridge National Laboratory uses to see how mercury moves through streams like East Fork Poplar Creek.
Credit Heather Duncan

Close your eyes and hear the water, bubbling like a creek over smoothed rocks. 

But open them, and you’ll see no trees overhead, no mossy banks. The light reflecting off this water comes not from the sun, but from fluorescent bulbs above long, straight fiberglass chutes.

 

This is a facility where Oak Ridge National Laboratory scientists study and try to understand how mercury moves through a meandering stream environment in the real world -- specifically, the environment of East Fork Poplar Creek. It’s the polluted stream that flows right through the middle of town.

 

“We can simulate a creek environment under a variety of different conditions, and look at how mercury behaves under all those different conditions,” said research staff scientist Scott Brooks.

 

An expansion to the Aquatic Ecology Lab in the next few months will enable researchers to conduct better experiments using larger amounts of actual creek water, complete with the tiny bacteria and microorganisms that live in the water. 

 

Currently, experiments can be conducted only with small creek samples or with deionized water “made” in the lab, says senior staff scientist Melanie Mayes. Some long-term tests won’t work with these substitutes. 

 

“Mercury forms strong chemical complexes with dissolved organic matter… and different streams have different characteristics,” Mayes said. “So working with some other creek water doesn’t get you to that place where you can understand how mercury in East Fork water actually reacts with something.”

 

East Fork Poplar Creek starts within the Y-12 nuclear complex, but the mercury pollution is worse in the urban stretches downstream. There, the creek contains 8 to 20 times the legal limit of the neurotoxin. The heavy metal can travel up the food chain once it contacts natural bacteria in the creek. 

 

“There’s a focus right now at the lab in figuring out how we can break that chain and eliminate that transfer from water to fish to people,” said David Adler, a director with the Department of Energy at Oak RIdge. He coordinates with state and federal regulators on the mercury cleanup.

 

Having grown up in Oak Ridge, Adler knows firsthand how central the stream is to the town.

“I’m certain that there are kids that romp around in that stream,” he said. “I actually did that as a kid myself. We thought it was fun to take packing crates from businesses in Oak Ridge, throw them in the creek, and wallow our way down the stream.”

 

The stream contamination is only a health hazard to someone who eats fish from the stream on a regular basis. Mercury can cause developmental problems in children whose mothers ate contaminated fish during pregnancy.

 

Y12 imported more than 20 million pounds of mercury for lithium purification in the 1950s and ‘60s. About 700,000 pounds of it escaped, either into equipment or the soil beneath the buildings. Some of it eventually eroded into the creek. 

 

“Mercury is one of the larger environmental challenges we face as part of the cleanup program at Oak Ridge, because of the amount used, the amount discharged, and the amount that still needs to be cleaned up, primarily in these oldest processing buildings,” Adler said.

 

Two big construction projects are underway to handle both old and new mercury contamination. One is the aquatics lab expansion, with a price tag of about $2 million, to improve cleanup of existing mercury. The other is a $200 million treatment plant to prevent more.

 

That plant will probably be ready in around 5 to 8 years, Adler says. It will back up the stream at its headwaters and pipe most of the water into a plant that can treat up to 3,000 gallons a minute. The Department of Energy calculates that it will reduce mercury concentrations in water leaving Y-12 by 84 percent.

 

When the plant comes online, the Department of Energy will be able to demolish some of the huge old Y-12 buildings. These have hardly been used since the 1960s, but the federal government had to keep pouring money into maintaining them -- it even just replaced their roofs -- because their destruction might further contaminate the creek, Adler said.

 

Most demolition debris will be put in a lined landfill at the site, he said. Anything especially contaminated with mercury will be placed in a special mercury storage facility. The United States is currently looking for a site for a national repository to store mercury waste, he noted.

 

“Our basic objective is to take material currently down in the lower area of the valley, (which is) in some cases in contact with groundwater and proximate to streams, dig it all up, separate out the mercury, take what’s left, and put it in a well-engineered landfill up out of the floodplain and away from groundwater,” Adler said.

 

The most common way to remove mercury from a stream is to dig up the banks and haul the dirt to a landfill, Brooks said. That’s very expensive and disrupts both the ecology and the neighbors. 

 

The aquatics lab is trying to better understand how natural processes might remove mercury. This could lead to simpler, cheaper cleanup just by managing the watershed differently.

For example, bacteria in creek algae turn mercury into its more dangerous form. Post-doctoral research associate Grace Schwartz is studying how changes in light and temperature might slow that process. 

 

Schwartz has a chute full of algae growing on rocks and ceramic disks. These can be exposed to mercury to see how they cycle it. Schwartz also conducts experiments to see how the bacteria are affected by compounds in the water that enter the stream through a sewage treatment plant’s output. What she learns could lead to different treatment requirements from plants on mercury-polluted streams. 

 

Scientists also want to find ways to use the natural water filtering process of native mussels. The Southeast United States has some of the most diverse populations of these filter feeders in the world. However, in East Fork Poplar Creek and elsewhere, few remain because of pollution and competition from invasive species. 

 

Research associate Amber Hills is studying how much mercury native mussel species could remove from the water, with the possibility of re-introducing native mussels to the creek. In the lab, the aquarium containing mussels and clams is clear, while the one next door is so full of algae it’s hard to see through.

 

“We have a few species of native mussels in the lab so that we can measure how fast they clear the water,” she said. “How fast they filter will of course affect how much mercury they can remove from the stream.”

 

Other scientists are capitalizing on carbon fiber technology being developed by another division in the national lab. Melanie Mayes is experimenting with ways to make a matting, perhaps made of carbon fiber, coated with a material that binds with mercury. This could be placed in “hot spots” along the creek bank. Mayes is testing different materials to see what attracts the most mercury.

 

“It needs to have physical properties to where it can stabilize the creek bank, it needs to have good chemical properties to where it can take up the mercury, and it needs to be cheap,” she said. 

 

Oak Ridge might be the only place that could work on this project, Brooks said: “I’m not aware of another research group in the world that has at their fingertips the ability to research those kind of materials.”

 

The research could have a wide impact because mercury pollution is so common. In Tennessee alone, 25 water bodies have fishing advisories because of mercury, including Fort Loudon Lake and the Holston River. 

 

“While the techniques and technologies we’re looking at might be specific for mercury in Oak Ridge, a lot of these are likely to be applicable in many other regions across the country as well as across the world,” Brooks said.