Toxic Breakdown:

Microbes in a bio-wall may help degrade chemical contaminants into less harmful products, writes SESYNC summer intern

by COLINE BODENREIDER

Imagine this: You’re a journalist looking for your next story when you get hear rumors of toxic chemicals in a neighborhood called Love Canal in Niagara Falls, New York. There’s a good chance it could be nothing, but you take a chance and jump on a flight to Niagara Falls. After going door to door talking to neighbors, you start hearing odd stories of black sludge seeping into basement walls, of sick and dying plants in the yard, and, more tragically, of children in the neighborhood being born with physical deformities.

This was the case with journalist Michael Brown. It was 1978, and he just uncovered what is now known as "one of the most appalling environmental tragedies in American history."

As he and other journalists would later discover, the neighborhood of Love Canal was built on top of a site containing more than 20,000 tons of toxic chemical waste, dumped there 40 years ago by Hooker Chemical Company.

In the wake of the Love Canal disaster, the US Environmental Protection Agency (EPA) established its Superfund program, designed to clean up toxic chemical waste sites. Today, a staggering 1,836 Superfund sites exist in the United States. One of those sites in particular, a landfill at the Beltsville Agricultural Research Center (BARC) in Beltsville, MD, is the subject of the research I’ve been helping to conduct as a SESYNC intern at the University of Maryland’s Persistent Organic Pollutants (POPs) lab this summer.

The BARC landfill, open from the 1940s to the 1980s, held vegetative waste from agricultural practices that occurred on the site. Trichloroethylene (TCE), used commonly as a degreaser of metal parts, likely found its way to the landfill through illegal dumping. Land site investigations found TCE levels 60 times the amount allowed in drinking water, and the site was placed under the Superfund program to be cleaned up. 

Though any toxic chemical is hazardous to human health, TCE’s chemical properties make it especially dangerous. TCE, an organic compound, is more readily absorbed into fat than water. This means that when animals or humans ingest TCE, it gets deposited in fat tissue where accumulates in the body in a process called bioaccumulation. The resulting concentrations of TCE can cause numerous health problems, like cancer, problems with the nervous and immune function, and liver and kidney damage. 

TCE is made even more dangerous because concentrations of TCE increase with every step up the food chain, or trophic level, so that by the time large predators feed on their prey, they ingest fats that contain extremely high levels of TCE. It’s because of this process, called biomagnification, that the Bald Eagle population began declining shortly after the introduction of DDT after World War II. Bald Eagles preyed upon fish that absorbed the DDT, a pesticide, resulting in Bald Eagles ingesting copious amounts of DDT that interfered with their ability to produce resistant eggshells and produce offspring.

The same characteristics that make TCE dangerous to ecosystems makes it rather difficult to remove from the environment. Because it isn’t volatile (i.e. it doesn’t evaporate into the air) and because it’s not soluble in water, it’s difficult for it to disperse and become diluted to safer levels. Instead, they remain in high concentrations in the soil they were dumped in, posing a potent threat to the ecological community.

So how do you get TCE out of the environment if it’s so dangerous and won’t degrade on its own? One commonly used solution, “Pump & Treat,” removes contaminated groundwater by pumping it up to the surface, treating it, and pumping the cleaned water back in. However, this method is expensive, disrupts the ecosystem by introducing heavy machinery, and is potentially ineffective as a long-term solution. Another less common solution is bioremediation, where microbes in the soil and water break down chemical contaminants into harmless products. The BARC site is currently being cleaned up using a specific type of bioremediation where the microbes are placed downstream of the site in a trench that intercepts the groundwater flow, instead of applied directly to the entire contaminated area. This trench filled with soil and microbes is commonly called a Permeable Reactive Barrier, or “bio-wall.” With the bio-wall now in place, the contaminated groundwater can flow through it, be cleaned by the microbes in the bio-wall, and come out of the other side clean. This method is better for the ecosystem because it only disrupts a single strip of land within the site, whereas conventional methods would cut off water access to a wide area of plants, as well as require the installation of invasive large pipes.

(Photo from the Environmental Protection Agency)

Despite being a potentially more viable cleanup, or remediation, technique, implementation of bio-wall remediation techniques is made difficult because not enough research has done on how they best function. My work this summer focuses on finding out what kind of soil produces the most favorable environmental conditions for growing microbes, which we tested by simulating mini groundwater systems, with each hosting different types of soil conditions. This will help future bio-wall projects determine the soil material needed to fill the trench for the bio-wall, as well as if the bacteria need any extra nutrients or modifications to be able to better survive in it. Though data has yet to be released on the effectiveness of the bio-wall at degrading TCE at the BARC site, results released on similar bio-walls are promising, showing that they were successful in breaking down TCE into less harmful components.

Remediation efforts have come a long way since Love Canal, and the questions we answer in this research problem will take us one step further in being able to clean up toxic chemical waste and keep our environment safe.

The BARC Superfund Site Bio-wall, marked by two stakes on either side of a monitoring well. (Photo by Coline Bodenreider)

References:

Agency for Toxic Substances and Disease Registry (ATSDR). 2014. Toxicological profile for Trichloroethylene (TCE) (Draft for Public Comment). Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

Brown, M. H. (1979, December). Love Canal and the Poisoning of America. Retrieved August 01, 2016, from http://www.theatlantic.com/magazine/archive/1979/12/love-canal-and-the-p...

Fact Sheet: Natural History, Ecology, and History of Recovery. (2015, April 20). Retrieved August 01, 2016, from https://www.fws.gov/midwest/eagle/recovery/biologue.html

Groundwater Pump and Treat Systems: Summary of Selected Cost and Performance Information at Superfund-financed Sites. (2001, December). Retrieved August 1, 2016, from https://clu-in.org/download/remed/542r01021b.pdf

Lu X, Wilson JT, Shen H, Henry BM, Kampbell DH (2008) Remediation of TCE-contaminated groundwater by a permeable reactive barrier filled with plant mulch (Biowall). J. Environ. Sci Health Part A Toxichazardous Subst. Environ. Eng. 43:24–35

Persistent Organic Pollutants: A Global Issue, A Global Response. (2015, December 11). Retrieved August 01, 2016, from https://www.epa.gov/international-cooperation/persistent-organic-polluta...

United States Department of Agriculture (UDSA). 2005. Beltsville Agricultural Research Center: Remedial Investigation, BARC 27: Beaver Dam Road Landfill.