For definition of Groups, see Preamble Evaluation.
VOL.: 60 (1994) (p. 45)
Chem. Abstr. Name: Ethene
Ethylene, the petrochemical manufactured in largest volume worldwide, is produced primarily by the steam-cracking of hydrocarbons. It is used mainly as a chemical intermediate in the production of polymers and other industrial chemicals; small amounts are used to promote the ripening of fruits and vegetables. Ethylene is introduced into the environment from both natural and man-made sources, including emissions from vegetation, as a product of burning of organic material (such as cigarettes) and of incomplete combustion of fossil fuels, and in its production and use. Few data are available on levels of occupational exposure.
The available data did not allow the Working Group to evaluate the carcinogenicity of ethylene to humans.
Ethylene was tested for carcinogenicity in one experiment in rats exposed by inhalation. No increase in tumour incidence was reported.
Endogenous but unidentified sources of ethylene exist in man and experimental animals. Steady-state alveolar retention of ethylene is less than 10% in both man and rat. The biological half-time of ethylene in humans is about 0.65 h. In rats and man, the processes of uptake, exhalation and metabolism are described by first-order kinetics, at least up to 50 ppm; in rats, ethylene metabolism follows first-order kinetics up to about 80 ppm. The maximal rate of metabolism in rats is reached at about 1000 ppm, the initial metabolite being ethylene oxide; hydroxyethyl cysteine is a urinary metabolite in mice. Because ethylene metabolism can be saturated, the maximal possible concentration of ethylene oxide in rat tissues is about 0.34 nmol/ml (15 ng/g bw). Exposure to ethylene results in the formation of adducts with proteins. In nonsmokers, the background concentrations of the hydroxyethyl valine adduct of haemoglobin were 12-188 pmol/g haemoglobin. Environmental ethylene contributes to these concentrations; the endogenous contribution was calculated to be about 12 pmol/g haemoglobin in nonsmoking control subjects. The increment of N-terminal hydroxyethyl valine formed during a 40-h work week has been estimated as 100-120 pmol/g haemoglobin per part per million of ethylene. Tobacco smoke contributes to formation of this adduct: smoking 10-30 cigarettes/day was reported to result in 600-690 pmol/g haemoglobin. Background concentrations of 7-hydroxyethyl guanine were 8.5 nmol/g DNA in one study of human peripheral lymphocytes and ranged from 2 to 6 nmol/g DNA in various tissues of rats and mice. A single exposure of mice to 50 ppm ethylene for 1 h resulted in 0.1-0.2 nmol/g DNA. No data were available on the genetic and related effects of ethylene in exposed humans. In a single study, no micronuclei were induced in bone-marrow cells of mice and rats exposed in vivo. Gene mutation was not induced in Salmonella typhimurium. Although the genetic effects of ethylene have not been well studied, its metabolite, ethylene oxide, is genotoxic in a broad range of assays.
There is inadequate evidence in humans for the carcinogenicity of ethylene.
There is inadequate evidence in experimental animals for the carcinogenicity of ethylene.
Ethylene is not classifiable as to its carcinogenicity to humans (Group 3).
For definition of the italicized terms, see Preamble Evaluation.
Previous evaluation: Suppl. 7 (1987) (p. 63)
See Also: Toxicological Abbreviations Ethylene (ICSC)