VICKSBURG, Miss. – Researchers with the U.S. Army Engineer Research and Development Center (ERDC) are experimenting on the phytostabilization potential and biomonitoring of heavy metals, specifically selenium and arsenic that come from contaminated soil and groundwater at coal combustion residuals (CCRs) storage sites.
The burning of coal produces CCRs, which can contain contaminants like mercury, cadmium and arsenic. If not disposed of properly, these contaminants can pollute the air, as well as nearby waterways, groundwater and drinking water. The goal of the project, funded by the Department of Energy’s Office of Fossil Energy and Carbon Management (FECM), is to seek advancements that will aid in a cost-effective, long-term monitoring of various types of chemical plumes and/or treat or stabilize contaminated soil and groundwater at CCR storage sites.
Dr. Afrachanna Butler, a research physical scientist with the ERDC’s Environmental Laboratory (EL), and Kortland Almore, an EL intern from Alcorn State University, are collaborating with ERDC’s Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, New Hampshire.
“There are two tasks for this study. It started as a literature review in fiscal year 2022, and it has expanded into an experimental greenhouse approach,” Butler said. “CRREL has a task where they are doing biomonitoring, and I am looking at phytostabilization.”
The phytostabilization process utilizes metal-tolerant plants to contain heavy metals within their roots, reducing the chance of them entering the ecosystem.
The FECM is working toward the Biden-Harris administration’s goal of being a fully decarbonized power sector by 2035 and net-zero U.S. greenhouse gas emissions by 2050, and remediation of contaminated soils is an essential part of meeting those goals. Butler thinks certain plants may be one component of an effective solution.
“There's been a lot of research on remediation of heavy metals, fly ash contaminants or CCR compounds,” she said. “But there's limited research out there for doing phytostabilization on Department of Energy sites with plants, particularly of selenium and arsenic, and how these plants can be used as bioindicators or sentinels to indicate an elevated risk potential from these two metals present in CCR impoundments.”
The actual experimentation at ERDC-EL is just beginning, and Butler has high hopes that four specific plants may have potential to stabilize soils contaminated with arsenic and selenium.
“Right now, we're in the initial phase,” said Butler. “Our goal in the next month is to expose the sand with selenium and arsenic and verify results. Hopefully, the plants are able to survive the various concentrations, because we would like to make a recommendation that red fescue, switchgrass, perennial ryegrass or bahia grass can be used to stabilize these contaminants. But, we don't know until we try.”
Butler’s team is utilizing visible and near-infrared light to determine plant health in a technique called Normalized Difference Vegetation Index (NDVI). NDVI uses the measured difference between near-infrared, which vegetation reflects, and red light, which vegetation absorbs, for fast, remote sensing of ecological problems.
“We're hoping in my part of the study, as well as CRREL, that these plants can be used as bioindicators,” said Butler. “Especially with using visible and near-infrared imagery and converting it into a NDVI, which can determine plant health and identify stress indicators.”
In a best-case scenario, the plants will not only signal that the heavy metals are present, but they will also immobilize the heavy metals within their structures.
“If the plant can be used to stabilize the arsenic and selenium in the soil with its roots and shoots, it will be even better,” said Butler.