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


VOL.: 34 (1984) (p. 65)

5. Summary of Data Reported and Evaluation

5.1 Exposures

Town gas and industrial gases derived from the destructive distillation of coal are produced in thousands of plants throughout the world. The processes are based on several gasifier designs. Substantial exposures to airborne polynuclear aromatic compounds, together with concomitant exposure to a variety of other contaminants, have been measured in retort houses. Polynuclear aromatic compounds were also measured in airborne samples and identified in surface samples from newer gasification plants.

5.2 Experimental data

Crude coal-tars from several older gas-works have been tested for carcinogenicity by skin application in mice and rabbits. All tars produced a high yield of skin papillomas and carcinomas. Various experiments have shown that the carcinogenicity of such tars cannot be attributed solely to their content of benzo[a]pyrene.

Two studies suggested that tar from horizontal retorts was more active in producing skin tumours in mice than tar from vertical retorts.

All process-stream and waste by-product samples tested which contained newer gasifier tars were mutagenic to Salmonella typhimurium. Samples of bottom ash from gasification systems did not show mutagenic activity. Several studies showed that mutagenic activity is found not only in fractions containing polynuclear aromatic compounds, but also in the more polar neutral, basic and total neutral fractions. The basic fraction of tar from one underground coal-gasification process was mutagenic and induced sister chromatid exchange in mammalian cells in vitro. No data on cell transformation were available.

5.3 Human data

Chronic bronchitis was reported to have occurred among employees in older gas-works.

Case reports of tumours of the skin (including the scrotum), bladder and respiratory tract in association with employment in industries involving the destructive distillation of coal suggested a link between that industry and human cancer. Despite their methodological shortcomings, the descriptive epidemiological studies based on death certificates corroborated these early suggestions.

A series of detailed analytical epidemiological studies of the British gas industry add further weight to the hypothesis that work in such coal gasification plants carries a risk of tumours of the lung, bladder and scrotum. Notwithstanding the limited details available on the work histories of the gas workers, there appeared to be a relationship between elevated relative risk of tumours and work in retort houses, particularly when the job entailed exposure to fume emanating from the retorts.

5.4 Evaluation

There is sufficient evidence from observations made in the first half of this century that occupational exposures to the products from the destructive distillation of coal give rise to skin cancer in humans.

The available epidemiological studies provide sufficient evidence that certain exposures in the retort houses of the older coal-gasification processes are carcinogenic to humans, giving rise to lung cancer. The likely causative agent is coal-tar fume. There is limited evidence that such occupational exposures produce bladder cancer.

There is sufficient evidence that topical application of coal-tars from several older gas-works on the skin of experimental animals produced a high yield of skin cancers.

A number of individual polynuclear aromatic compounds for which there is sufficient evidence of carcinogenicity in experimental animals have been measured at high levels in air and tar samples taken from certain areas in coal-gasification plants.

The available evidence indicates that certain exposures in retort houses of older coal-gasification processes are carcinogenic to humans. No data on carcinogenicity in experimental animals or in humans from exposures during the newer processes were available to the Working Group.

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Suppl. 7 (1987)

Last updated: 20 April 1998

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