Polyethylene plastic, carcinogenicity

Polyvinyl chloride can be shaped into clear, soft flexible tubing and sheets with the aid of using plasticizers such as diethylhexyl phthalate (DEHP). Polyvinyl chloride resins are used for children s toys, automobile seat covers, and for catheters used for intravenous transfusion of blood and nutrients in hospitals and homes. When DEHP was suspected of leaching out of the products, and of being a carcinogen, substitutions were developed with polyvinylacetate and polyethylene. However, these substitutes are not yet totally satisfactory, as they cannot be steam sterilized, and they are not as clear and flexible as PVC. 

Polyolefin is a generic term for polyethylene (PE) and polypropylene (PP). The burning of these plastics can generate several volatiles, including formaldehyde and acetaldehyde, both of which are suspected to be carcinogens. 

Whilst this prediction of in vivo stability is largely borne out in practice, there is some evidence that other factors are involved and that unexpected degradation mechanisms operate within the body. One of the first observations of degradation of these polymers was made by Oppenheimer" who was working on the carcinogenic properties of plastics. In attempting to elucidate the mechanisms by which plastic films induced tumours after subcutaneous implantation in rodents, certain radiolabelled polymers were employed. " C-labelled polystyrene, polyethylene and poly(methyl methacrylate) were implanted and urine, faeces and respiratory CO2 were monitored for periods over a year. With the polystyrene, nothing radioactive was excreted in the urine until 21 weeks, but some radioactivity was detected after this time. With polyethylene, radioactive species were excreted after 26 weeks and with poly(methyl methacrylate), this occurred after 54 weeks. 

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