International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 2B)

For definition of Groups, see Preamble Evaluation.

VOL.: 71 (1999) (p. 227)

CAS No.: 126-99-8
Chem. Abstr. Name: 2-Chloro-1,3-butadiene

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Chloroprene is a monomer used almost exclusively for the production of polychloroprene elastomers and latexes. It readily forms dimers and oxidizes at room temperature. Occupational exposures occur in the polymerization of chloroprene and possibly in the manufacture of products from polychloroprene latexes.

Although few data are available on environmental occurrence, general population exposures are expected to be very low or negligible.

5.2 Human carcinogenicity data

The risk of cancer associated with occupational exposure to chloroprene has been examined in two well conducted studies, one in the United States and one in Russia. These investigations do not indicate a consistent excess of cancer at any site.

5.3 Animal carcinogenicity data

Chloroprene was tested for carcinogenicity in two studies in mice, in two studies in rats and in one study in hamsters, all by inhalation with samples of purity > 99%. Exposure of mice to chloroprene produced lung tumours in one study in which the lung was the only organ examined. In another study in mice, chloroprene produced neoplasia in the lung, circulatory system, Harderian gland, mammary gland, liver, kidney, skin, mesentery, forestomach and Zymbal gland. In one study in rats, chloroprene caused increased incidences of tumours of the oral cavity, thyroid gland, lung, mammary gland and kidney. In another study in a different strain of rats, the incidence of mammary tumours was increased in high-dose females only when mammary tumours of all types were combined. No increase in neoplasia was seen in hamsters.

5.4 Other relevant data

The observation of excretion of mercapturates of chloroprene indicates that glutathione conjugation occurs in rats.

Genetic toxicity assays with chloroprene may often have been complicated by impurities derived either from added stabilizers or from degradation and polymerization products. Consequently, positive and negative results have been reported for most assays, and it is notable that, often, the negative results were obtained using the higher dose levels of chloroprene.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of chloroprene.

There is sufficient evidence in experimental animals for the carcinogenicity of chloroprene.

Overall evaluation

Chloroprene is possibly carcinogenic to humans (Group 2B).

Previous evaluations: Vol. 19 (1979) (Chloroprene and polychloroprene); Suppl. 7 (1987)


Last updated: 8 April 1999

    See Also:
       Toxicological Abbreviations
       Chloroprene (ICSC)