Bitumens (IARC Summary & Evaluation, Volume 35, 1985)

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

BITUMENS

VOL.: 35 (1985) (p. 39)

5. Summary of Data Reported and Evaluation

5.1 Exposures

World usage of bitumens is estimated to be more than 60 million tonnes per year; exposures occur in a variety of applications. A total of 90-95% of bitumen is used hot (> 100 °C) in road construction, roofing and flooring. Fumes from these operations contain polynuclear aromatic compounds, although almost all of the mass of material in the fumes remains uncharacterized. Cutback bitumens, blended grades and bitumen emulsions are usually used at ambient or warm temperatures, where the potential for direct skin contact may be greater.

Blended or fluxed bitumens, which represent a relatively small percentage of the total usage, may contain aromatic oils, thermally-cracked petroleum residues or coal-tar products, which contain polynuclear aromatic compounds.

5.2 Experimental data

Steam-refined petroleum bitumens were tested by application to the skin of mice. Skin tumours were produced with undiluted bitumens, with dilutions in benzene and with a fraction of steam-refined bitumen.

When air-refined (oxidized) bitumens were applied to the skin of mice, no tumour was found with undiluted bitumens; but, in one experiment, an air-refined bitumen in solvent (toluene) produced topical skin tumours.

Two cracking-residue bitumens produced skin tumours when applied to the skin of mice.

A pooled mixture of steam- and air-blown petroleum bitumens in benzene produced tumours at the site of application on the skin of mice.

One sample of heated, air-refined bitumen injected subcutaneously into mice produced a few sarcomas at the injection sites.

A pooled mixture of steam- and air-blown petroleum bitumens produced sarcomas at the site of subcutaneous injection in mice. Steam-distilled bitumens injected intramuscularly produced local sarcomas in one experiment in rats.

Both an extract of road-surfacing bitumen and its emissions were mutagenic to Salmonella typhimurium.

Subsequent to the meeting of the Working Group, the Secretariat became aware of a study showing that solutions of the fumes from two types of roofing bitumens, generated at 232 °C or 316 °C, produced skin tumours when applied topically to mice (Thayer et al., 1983).

5.3 Human data

No epidemiological study of workers exposed only to bitumens is available. A cohort study of US roofers indicates an increased risk for cancer of the lung and suggests increased risks for cancers of the oral cavity, larynx, oesophagus, stomach, skin and bladder and for leukaemia. Some support for excess risks of lung, oral cavity and laryngeal cancers is provided by other epidemiological studies of roofers. As roofers may be exposed not only to bitumens but also to coal-tar pitches and other materials, the excess cancer risk cannot be attributed specifically to bitumens. Several case reports of skin cancer among workers exposed to bitumens are available; however, exposure to coal-tars or products derived from them cannot be ruled out.

5.4 Evaluation

There is sufficient evidence for the carcinogenicity of extracts of steam-refined bitumens, air-refined bitumens and pooled mixtures of steam- and air-refined bitumens in experimental animals.

There is limited evidence for the carcinogenicity of undiluted steam-refined bitumens and for cracking-residue bitumens in experimental animals.

There is inadequate evidence for the carcinogenicity of undiluted air-refined bitumens in experimental animals.

There is inadequate evidence that bitumens alone are carcinogenic to humans.

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Suppl. 7 (1987)

Last updated: 20 April 1998





























    See Also:
       Toxicological Abbreviations
       Bitumens  (IARC Summary & Evaluation, Supplement7, 1987)