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Project Status: complete

Title: Study of vinyl chloride formation at landfill sites in California

Principal Investigator / Author(s): Molton, Peter M.

Contractor: Batelle, Pacific Northwest Laboratories

Contract Number: A4-154-32

Topic Areas: Toxic Air Contaminants


Low concentrations of vinyl chloride (VC) gas have been detected in the air above California landfills, even where no material containing it has reportedly ever been dumped. The purpose of this was to determine if vinyl chloride is produced in situ by natural processes. Review of previous work indicated that biological action on other chlorinated ethylenes present in the landfills was the most likely source of vinyl chloride. Other emission sources are possible, ranging from illegal dumping and leaching to thermal decomposition of plastics. (An evaluation of illegal dumping was beyond the scope of this study.) Experiments were performed with landfill material obtained at depths of 3-16 ft from a Northern and a Southern California landfill, and with control material presumably never exposed to chlorinated compounds (Richland, WA, anaerobic digester sewage sludge). Test materials were incubated with a range of chlorinated compounds and with 13C labeled trichloroethylene (TCE) to confirm biological production of VC from other compounds, including TCE. Pyrolysis experiments with PVC showed release of residual monomer but no VC formation. No VC was formed from ICE by photolysis or from heat and radiation sterilized landfill materials. VC formation was highest in experiments using the landfill material already containing the greatest amounts of organic compounds (and the most adapted microorganisms), and least with the "uncontaminated" sewage sludge. These experiments confirmed biological production as the most probable formation route for landfill emissions of VC and not chemical or photochemical routes of formation. Leaching from old PVC could be a minor source of VC, although there was less than 0.1% (estimated) plastic in the landfill samples containing at most, 330 ppm of VC monomer. A landfill sample known to produce vinyl chloride was used as a source of microorganisms for initiation of an anaerobic chemostat. Methanol was the only carbon supplied and carbon dioxide and methane were the main products indicating the presence of methanogenic bacteria. The enriched culture was homogeneous when grown on agar based medium under strictly anaerobic conditions in roll-tubes using methanol as the sole carbon source. Under aerobic conditions no colony growth of any kind was observed. When a sample of the enriched culture was incubated with 13C -labeled TCE in the presence of methanol 13C-labeled vinyl chloride was detected.

These experiments clearly show that microbial action on chlorinated solvents in landfills is the most probable source of observed VC formation in situ. Methods for minimizing future VC emissions from landfills are discussed.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 322-3893

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