Vinyl Chloride: Still a cause for Concern

Vinyl Chloride was first used commercially in the 1920's, but id was not until the 1930's that techniques were devised to polymerize VC into stable forms of PVC. Polymerization is a batch process and takes place in a reactor under controlled conditions. Once the polymerization has ended, VC is emptied into degassing tanks. The reactor has to be cleaned periodically because a film of PVC forms on the inside wall of the reactor. Although this is now performed with solvents or high pressure jets, this task was a manual process requiring workers to use spatulas or hammers and chisels. The workers were exposed to high concentrations of VC up to 1,000 ppm and sometimes higher peak exposures.

New aspects of VC are reported in high levels in soil, ground water, aquifers, and wells near landfills and industrial disposal sites that were not located near VC/PVC production facilities. Vinyl chloride can be formed microbially, under anaerobic conditions from reductive dehalogenation of more highly chlorinated chloroethenes. Careless handling, storage, and disposal of these chemical stable compounds have made them the most frequent encountered ground water contaminants.

Exposure of the general population to VC is possible by several routes: inhalation of air polluted with VC around production plants,ingestion of food, contaminated water, medicament packed in PVC, and absorption through skin from PVC- wrapped cosmetics.

Hemangioendothelial sarcoma of the liver (ASL) is an extremely rare liver tumor and is difficult to diagnose. ASL constitutes for only 2% of all primary tumors of the liver in the general population. Cases of ASL in VC workers could be directly attributable to exposure to VC in epidemiologic studies.

The methodology of studies was a accumulation of data by epidemiologic studies on VC/PVC workers, IPCS task groups, and Pharmacokinetic model were performed to find the effects of VC in the general population. VC has been shown to be a carcinogenic and toxic in both oral and inhalation experimental reports, as well as in human epidermiologic studies. For VC, dose response analyses have been based on data of ASL because it is the most critical and sensitive effect.

Vinyl chloride is a chemical of interest in many fields of study. Even in some parts of the world workers are still being exposed to high levels, and is known as a carcinogen. ASL is correlated only to high levels over long periods of time.

The detectionof VC as a degradation product of some chlorinated solvents is an indication of the intricate problems that may be attributed to past and future chemical waste deposits. Progress in remediation processes should be able, at least in to resolve these problems.

references: Environmental Health Perspectives. volume 108.number 7, July 2000

Wikipedia encyclopedia vinyl chloride, picture of chemical structure.