Bacteria Can Clean Up PCBs Without Dredging

Bacteria Can Clean Up PCBs Without Dredging

May 2007 -   Researchers have identified a group 
of bacteria that can detoxify a common type of polychlorinated biphenyls, 
PCBs. These carcinogenic compounds, once used as coolants and lubricants, 
have contaminated more than 250 U.S. sites, including lake and river 
sediments. 
The discovery is a first step toward a bioremediation strategy that would 
naturally detoxify the PCBs without risky removal of the sediments in 
which they persist. 
Development of bioremediation technologies for PCB cleanup would offer an 
alternative to sediment dredging and disposal in landfills, which is the 
most commonly used method for removing PCBs used today. Dredging is 
controversial because of the invasive nature of this technology and the 
risk of spreading contaminants. 
Researchers have known for more than 20 years that naturally occurring 
microorganisms could slowly dechlorinate PCBs, which were once commonly 
used by industry. The compounds were banned from production in the United 
States in 1977 because of their toxicity to humans and animals. 
In research funded by the National Science Foundation and General 
Electric, PCB expert Donna Bedard, a biology professor at Renssalaer 
Polytechnic Institute, analyzed sediments from the Housatonic River in 
Massachusetts. 
One of several sections of the Housatonic River contaminated with PCBs 

This area is contaminated with PCBs that were used by the General Electric 
Company in its transformer and capacitor divisions in Pittsfield. GE 
released the chemicals into the river between 1929 and the passage of the 
Clean Water Act in 1977. Dredging to remove the Housatonic PCBs is now 
underway and is expected be complete on one section of the river this 
year. 
Bedard collaborated with microbiologists at the Georgia Institute of 
Technology to study microbial degradation in Aroclor 1260, a common, 
highly chlorinated PCB mixture. 
Working with sediment samples from the Housatonic, the team was able to 
determine that bacteria in the Dehalococcoides, Dhc, group were 
responsible for the dechlorination of Aroclor 1260. 
These microbes replace the chlorine atoms in Aroclor 1260 with hydrogen, 
which fuels their growth and initiates the PCB degradation process, 
explained Frank Loeffler, an associate professor in the Georgia Tech 
School of Civil and Environmental Engineering and the School of Biology. 
Once Dhc bacteria dechlorinate Aroclor 1260 to a certain level, other 
microbes will degrade it further and completely detoxify PCBs, Loeffler 
said. 
"Identifying the bacteria responsible for Aroclor degradation represents a 
crucial step. Now we can start to design tools to look for these microbes 
in sediments and then develop engineering approaches to stimulate their 
growth and activity in river or lake sediments," Loeffler said. 
"Then the decontamination will occur more rapidly. Instead of taking 
decades, the microbes might be able to degrade the PCBs in a few years," 
he said. 
Professor Frank Loeffler adds bacteria to a bioreactor in his lab at 
Georgia Tech. 
The research results were published April 15 in the journal "Applied and 
Environmental Microbiology." 
Loeffler is optimistic about a bioremediation strategy for PCBs because of 
his lab’s earlier success in identifying microbes that degrade the common 
solvents tetrachloroethene, PCE, and trichloroethene, TCE. These toxic 
compounds, which contaminated subsurface environments and groundwater 
decades ago when their use was unregulated, are used in dry cleaning 
operations and degreasing of metal components. 
After Loeffler’s discovery, it took less than five years for scientists 
and engineers to develop and implement bioremediation strategies that use 
these microbes to detoxify PCE and TCE. 
"The situation with PCBs is a little more complicated because they are in 
river and lake sediments instead of groundwater and subsurface 
environments, but in principle, the same sequence of events could occur," 
Loeffler said. "We need industry, engineers and scientists to work 
together to develop a bioremediation approach for PCBs." 
Loeffler predicts that bioremediation technologies for addressing PCB 
detoxification will be developed first for lakes, such as Lake Hartwell in 
South Carolina. Then it will be refined to clean up river sediments, where 
the flow rate is greater and bioremediation may be more difficult to 
implement. 
Polychlorinated biphenyls are mixtures of up to 209 individual chlorinated 
compounds. 
PCBs have been used as coolants and lubricants in transformers, 
capacitors, and other electrical equipment because they do not burn easily 
and are good insulators. 
The manufacture of PCBs was stopped in the United States in 1977 because 
of evidence they build up in the environment and can cause harmful health 
effects. Old fluorescent lighting fixtures and electrical devices and old 
microscope and hydraulic oils may still contain PCBs. 
PCBs entered the air, water, and soil during their manufacture, use, and 
disposal; from accidental spills and leaks during their transport; and 
from leaks or fires in products containing PCBs. 
An excavator digs up Housatonic River sediment contaminated with PCBs. 

PCBs can still be released to the environment from hazardous waste sites, 
illegal or improper disposal of industrial wastes and consumer products, 
leaks from old electrical transformers containing PCBs, and burning of 
some wastes in incinerators. 
These compounds do not readily break down in the environment. They can 
travel long distances in the air and be deposited in areas far away from 
where they were released. On land, PCBs bind strongly to soil. 
In water, a small amount of PCBs may remain dissolved, but most stick to 
organic particles and bottom sediments. 
PCBs are taken up by small organisms and fish in water. They are also 
taken up by other animals that eat these aquatic animals as food. PCBs 
accumulate in fish and marine mammals, reaching levels that may be many 
thousands of times higher than in water. 
The main dietary sources of PCBs are fish, especially sportfish caught in 
contaminated lakes or rivers, meat, and dairy products. 
The Department of Health and Human Services has concluded that PCBs may 
reasonably be anticipated to be carcinogens. The U.S. Environmental 
Protection Agency and the International Agency for Research on Cancer have 
determined that PCBs are probably carcinogenic to humans.    

       
      

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