Vinyl Chloride is the key component for polymerization to polyvinyl chloride (PVC), a $19 billion/year industry. It has a rich history that dates back to 1835 however it is over the past 50 years that we have identified just how dangeous it is. Classified a a known human carcinogen, vinyl chloride is strictly monitored for airborne and waterborne exposures in the workplace and general public.
The major metabolic pathway for vinyl chloride cytochrom P-450 and the two major metabolites are choroethylene oxide and chloroacetaldehyde. Both are excreted in urine through saturable processes. Vinyl chloride must be metabolized to produce carcinogenicity and appears to be dose dependent.
The first carcinogenic effects published was from experimental research in 1971 to rats exposed to vinyl chloride. Numerous studies have followed, all focused on inhalation exposure with high positive findings from those exposed to industrial processes with high concentrations for prolonged periods of time. Most cases resulted in angiosarcoma of the liver (which is rare in the general population). In the years to follow, the International Agency for Research on Cancer (IARC) established an international study to investigate dose-response relations between liver cancer and vinyl chloride exposure. The result was increased liver cancer was clearly associated with exposure to vinyl chloride during normal time frames and unrestricted levels.
In 1981, one of the most comprehensive bioassay's was conducte targeting the ingestion of vinyl chloride. A group of 80 Sprague-Dawley rats were studied (40 male/40 female). Varying doses of vinyl chloride was administered four to five times per day for 52 weeks via gastric intubation tube and at 136 weeks, 27 liver angiosarcomas were identified in only the rats administered vinyl chloride at the 16 and 50 mg/kg body weight rate.
Another study was one ment for the silver screen. Though studies were underway identifying the possible and later confirmed health risks associated with exposure to vinyl chloride, it wasn't until 1974 the public was made aware of this. Then 10 years in what can only be coined a political move, the Chemical Manufacturers Association pushed the lead researchers to withdraw some of their findings due to a failure to obtain permission from the sponsor.
Currently, it is suggested exposure to vinyl chloride is associated with certain brain cancers. In 2000, there was a fourth study opened and the conclusion was it remains unclear. That said, vinyl chloride is one of the few chemicals listed as a known human carcinogen. The EPA requires the amount of vinyl chloride in drinking water to not exceed 0.002 mg/L of water. OSHA has set a limit of 1ppm vinyl chloride (air) in the workplace. The Food and Drug Administration monitors and regulates the amount of vinyl chloride contained in various plastics that carry food and liquids.
References:
Agency for Toxic Substances and Disease Registry (ATSDR). 2006. Toxicological Profile for Vinyl Chloride. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. http://www.atsdr.cdc.gov/tfacts20.htm
Environmental Health Perspectives (Vol 113/No 7). July 2005. Vinyl Chloride: A Case Study of Data Suppression and Misrepresentation. http://dx.doi.org
Environmental and Workplace Health, Vinyl Chloride. 1992. http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/vinyl_chloride/index-eng.php
Vinyl Chloride. Winkipedia. 2009. http://en.wikipedia.org/wiki/Vinyl_chloride
Carcinogenicity Bioassay of Vinyl Chloride Monomer. A model of Risk Assessment on an experimental basis. C. Maltoni. www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1568874
No comments:
Post a Comment