Migration and Degradation Patterns of Volatile Organic Compounds

Abstract

The mobility and persistence of volatile, chlorinated priority pollutants has been documented at sites across the country. Examples of commonly used solvents include 1,1,1-trichloroethane, trichloroethene, tetrachloroethene and methylene chloride. At some facilities, other volatile chlorinated compounds, which were never handled or disposed at these same facilities, have been detected in significant concentrations. These other compounds include dichloroethanes, dichloroethenes, chloroethane and vinyl chloride. Recent research shows that these less commonly used solvents can be present as a result of anaerobic degradation of major contaminants (commonly used solvents) within the groundwater system.

This paper presents data to help clarify the conditions under which one may anticipate finding degradation products and discusses their distribution trends. Data are presented from studies conducted at solvent recovery facilities, solid/hazardous waste landfills and solvent contamination near an industrial facility. When degradation occurs, the parent solvent compounds are at highest concentrations near the source. With distance from the source, increasing proportions of degradation products are present. Degradation products are most frequently found near a source containing high concentrations of other biodegradable organic compounds. Standard analytical protocols for measurement of volatile organic priority pollutants by GC/MS do not distinguish between trans-1,2-dichlorethene, a highly-toxic priority pollutant, and the cis isomer which is a significantly less hazardous non-priority pollutant degradation product and is the dominant degradation contaminant present at these sites.