Superfund Research Program
Research Points to Need for Reassessment of PCB Volatility
For decades, conventional wisdom has led many environmental scientists and engineers to believe that once polychlorinated biphenyl compounds (PCBs) are sorbed to soils and sediments, the compounds are relatively immobile in these media. Because PCBs are considered hydrophobic and practically insoluble in water, many current remediation technologies also assume that water hinders the movement of PCBs in the environment. Until recently, few have questioned these beliefs.
A commentary in the February 1998 issue of Environmental Health Perspectives argues that under select conditions "semivolatile" PCBs are much more volatile and mobile in the environment than generally recognized. Researchers at SUNY-Oswego and the University at Albany challenge some of the commonly held tenets of PCB behavior based on the results of a series of laboratory experiments conducted on microbially degraded sediments collected from the St. Lawrence River.
In the series of bench scale experiments, PCB volatility was strongly correlated with evaporative losses of water. More than 75 percent of the total PCBs in samples collected from St. Lawrence River sediments were lost through volatilization when the contaminated sediments were maintained underneath a layer of water over a five to seven day period. Most of the losses occurred when the water overlying the contaminated sediments evaporated. The contaminated sediments were particularly susceptible to volatile losses of PCBs because the PCBs had been extensively modified by reductive, microbial dechlorination. This microbial activity resulted in the production of more volatile, as well as more water soluble compounds.
Additional field experiments, not reported in the commentary, provide supplementary evidence that PCBs exhibit a high degree of volatility. A field experiment conducted by SUNY-Oswego researchers at a New York State Superfund site suggests that PCB volatilization occurred at depths of several centimeters below the land surface. Volatilization not only decreased the total PCB concentrations in contaminated industrial casting sands at this site, but also resulted in significantly altered congener patterns. Specifically, the congener patterns showed a reduction in the lower chlorinated congeners which tend to be more water soluble and mobile in the environment.
What is now clear is that PCBs, particularly microbially altered PCBs, are highly susceptible to volatilization in the environment. Large quantities of these compounds may be transferred to the atmosphere as the water overlying contaminated sediments evaporates and when moisture laden, contaminated sediments dry. The potential releases resulting from large scale removal of PCB-contaminated sediments in the Hudson and St. Lawrence Rivers of New York, and other contaminated areas of the world, could be responsible for redistributing large quantities of semivolatile compounds to the atmosphere.
These studies provide evidence for a potential redistribution of large quantities of PCBs and other semivolatile compounds. Atmospheric redistribution of a variety of semivolatile contaminants - including polyaromatic hydrocarbons, some pesticides, and other chemicals - is likely responsible for the increasing concentrations of chemical contaminants in remote areas of the world. Ironically, several commonly used remediation technologies may be contributing to the global redistribution of semivolatile compounds. There is a possibility that select aerobic biodegradation remedial technologies - including land farming, composting, and other processes which employ cultivation, mixing and watering - may be redistributing contaminants to the atmosphere.
Many scientists do not yet recognize the volatile potential of PCBs. A review of recent bioremediation journal and proceedings articles indicates that the majority of reported experiments did not control for volatile losses. Reductions in contaminant concentrations in the experimental systems were attributed solely to microbial processes. However, in the case of PCBs, not only would the total contaminant concentration change through volatile loss, but the congener pattern would also be altered. Beginning in the laboratory and proceeding to the design and implementation of remedial protocols, volatile losses have typically not been distinguished from microbial processes.
The findings discussed in the Environmental Health Perspectives commentary are likely to have a significant impact on the remediation processes of PCBs. This compelling commentary suggests that volatility should be integrated into all experimental and remedial protocols in which atmospheric redistribution of contaminants is possible.
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To learn more about this research, please refer to the following sources:
- Chiarenzelli J, Scrudato RJ, Bush B, Carpenter DO, Bushart S. 1998. Do large-scale remedial and dredging events have the potential to release significant amounts of semi-volatile compounds to the atmosphere?. Environ Health Perspect 106(2):47-49.
- Chiarenzelli J, Scrudato RJ, Wunderlich M. 1997. Volatile loss of PCB Aroclors from subaqueous sand. Environ Sci Technol 31(2):597-602.
- Chiarenzelli J, Scrudato RJ, Wunderlich M, Oenga G, Lashko O. 1997. PCB volatile loss and the moisture content of sediment during drying. Chemosphere 34:2429-2436.
- Chiarenzelli J, Scrudato RJ, Arnold GJ, Wunderlich M, Rafferty D. 1996. Volatization of polychlorinated biphenyls from sediments during drying at ambient conditions. Chemosphere 33:899-911.
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