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

COAL-TARS AND DERIVED PRODUCTS

VOL.: 35 (1985) (p. 83)

5. Summary of Data Reported and Evaluation

5.1 Exposures

Large quantities of crude coal-tars, which contain polynuclear aromatic compounds as major components, are formed as by-products of the destructive distillation of coal, coke-ovens being the major source. The distillate fractions of crude coal-tars alone or in combination with coal-tar pitch, both of which contain polynuclear aromatic compounds, are mixed to produce various products, such as creosote. Most human exposure to crude coal-tars and derived products takes place during the destructive distillation of coal in foundries and in aluminium production, on which monographs have already been prepared. Members of the general population use topical pharmaceutical coal-tar preparations.

Exposure to polynuclear aromatic compounds in other occupations is especially heavy among workers applying hot coal-tar pitch, such as in roofing, paving, surface coatings and in the production of refractory bricks. There is also potential exposure in coal-tar distillation plants.

Creosote has world-wide use as a wood preservative. In addition to possible inhalation exposures, cutaneous exposure may be considerable.

5.2 Experimental data

Three high-temperature tars, one undiluted and two as benzene extracts, all produced skin tumours, including carcinomas, when applied to the skin of mice. Each of five blast-furnace tars and two extracts of blast-furnace tars produced skin tumours, including carcinomas, after topical application to mice.

Each of five pharmaceutical coal-tar preparations caused skin tumours, including carcinomas, when applied to the skin of mice.

Two unspecified coal-tars both caused skin tumours, including carcinomas, after application to the skin of mice. Lung tumours but no skin tumour were produced in rats after application of a coal-tar to the skin. A fourth, unspecified coal-tar produced tumours when applied to the ears of rabbits.

Intramuscular administration of a coal-tar fume condensate to mice in one experiment gave evidence of sarcoma formation.

Five creosotes or creosote oils all produced skin tumours, including carcinomas, when applied to the skin of mice. One of the creosotes also produced lung tumours in mice after skin application. In two limited studies, a basic fraction of creosote oil was not carcinogenic for the skin of mice.

In two experiments, anthracene oils produced skin tumours (and, in one experiment, carcinomas) when applied to the skin of mice.

Six coal-tar pitches and three extracts of coal-tar pitches all produced skin tumours, including carcinomas, when applied to the skin of mice. An extract of roofing-tar pitch had both initiating and promoting activity in separate experiments.

In one experiment, mice developed skin tumours, including carcinomas, after whole-body exposure to pitch powder.

No data were available to the Working Group on the carcinogenicity of distillation fractions of low-temperature tars or of products derived from them.

Samples of therapeutic coal-tar and extracts of coal-tar shampoos were mutagenic in Salmonella typhimurium in the presence of an exogenous metabolic system. Extracts of urine from patients undergoing combined treatment with coal-tar preparations and ultraviolet light were mutagenic in S. typhimurium.

Extracts of coal-tar pitch were mutagenic in S. typhimurium in the presence of an exogenous metabolic system.

Extracts of roofing-tar emissions were mutagenic in S. typhimurium in the presence of an exogenous metabolic system and were mutagenic in two mutation assays and induced sister chromatid exchanges in cultured mammalian cells, both in the presence and absence of an exogenous metabolic system. Viral transformation was enhanced in Syrian hamster embryo cells. A statistically non-significant increase in the number of morphologically transformed foci was observed in BALB/c 3T3 cells. The material did not cause DNA fragmentation in cultured Syrian hamster embryo cells.

Creosote and a coal-tar-creosote mixture were mutagenic in S. typhimurium and were positive in the mouse lymphoma L5178Y system, in the presence of an exogenous metabolic system. The urine from rats administered creosote was mutagenic in S. typhimurium in the presence of an exogenous metabolic system.

5.3 Human data

A mortality analysis in the UK from 1946 showed a greatly increased scrotal cancer risk for patent-fuel workers exposed to pitch. Furthermore, a large number of case reports describing the development of skin (including the scrotum) cancer in workers occupationally exposed to coal-tar and/or to pitch have been published.

A cohort study of US roofers indicated an increased risk for cancer of the lung and suggested increased risks for cancers of the oral cavity, larynx, oesophagus, stomach, skin and bladder and for leukaemia. Some support for excess risks of lung, laryngeal and oral-cavity cancer is provided by other epidemiological studies of roofers. Roofers may be exposed not only to a mixture of pitches but also to bitumens and other materials.

One study showed a small excess of bladder cancer in tar distillers and in patent-fuel workers. An elevated risk of cancer of the renal pelvis was also seen in workers exposed to 'petroleum or tar or pitch'.

There have been a number of case reports of skin cancer developing in patients using tar ointments to treat a variety of skin diseases.

A mortality analysis of many occupations indicated an increased risk of mortality from scrotal cancer for creosote-exposed brickmakers. Malignant epitheliomas, about a third of which were of the scrotum, have been reported in several case reports of workers exposed to creosote. The only available cohort study suffered from limitations of size.

5.4 Evaluation

There is sufficient evidence for the carcinogenicity in experimental animals of coal-tars, creosotes, creosote oils, anthracene oils and coal-tar pitches.

There is sufficient evidence that occupational exposure to coal-tars as it occurs during the destructive distillation of coal is causally associated with the occurrence of skin cancer in humans (IARC, 1984a). The findings of the few studies available on other occupational exposures to coal-tars are consistent with that evaluation.

There is sufficient evidence that coal-tar pitches are carcinogenic in humans.

There is limited evidence that coal-tar-derived creosotes are carcinogenic in humans.

Taken together, the data indicate that coal-tars and coal-tar pitches are causally associated with cancer in humans and that creosotes derived from coal-tars are probably carcinogenic in humans.

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Suppl. 7 (1987)


Last updated: 20 April 1998






















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