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

(Group 3)

For definition of Groups, see Preamble Evaluation.

VOL.: 45 (1989) (p. 119)

CAS No.: 8002-05-9
Chem. Abstr. Name: Petroleum

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Crude oil, which may be broadly characterized as paraffinic or naphthenic, is a complex mixture of alkanes, cycloalkanes and aromatic hydrocarbons containing low percentages of sulfur, nitrogen and oxygen compounds and trace quantities of many other elements. Worldwide, about 500 000 workers are employed in crude oil exploration and production. Occupational exposures during drilling, pumping and transportation of crude oil, including maintenance of equipment used for these processes, may involve inhalation of volatile compounds, including hydrocarbons and hydrogen sulfide. Skin contact with crude oils, which contain polycyclic aromatic compounds, may also occur during these operations. Accidental releases of crude oil into the aquatic environment are also potential sources of human exposure.

5.2 Experimental data

N.B. - Subsequent to the meeting, the Secretariat became aware of a study in which skin tumours were reported in mice after application to the skin of East Wilmington crude oil (Clark et al., 1988).

Samples of crude oil from single sources and composite blends were tested for carcinogenicity by skin application in ten experiments in mice. Four samples of crude oil from single sources produced benign and malignant or unspecified skin tumours in two experiments. In one experiment, a composite sample produced a low incidence of skin carcinomas; in a similar experiment using the same treatment regimen but a blend of slightly different composition, no skin tumour was observed. The conduct and/or reporting of the results of six other experiments in mice were inadequate for evaluation.

Skin application to mice of fractions of two crude oil samples distilled under laboratory conditions and corresponding to various refinery streams produced skin tumours.

One sample of crude oil produced skin papillomas in rabbits in one experiment. Two other experiments were inadequate for evaluation.

5.3 Human data

In a retrospective cohort mortality study of a large group of male employees in petroleum producing and pipeline operations, mortality from all types of cancer was low, except from thyroid cancer. There was a significant deficit of lung cancer and no death from testicular cancer.

In a population-based case-control study, an elevated risk for lung cancer was observed among older men who had been employed in petroleum exploration and production. Reanalysis of the risk for lung cancer among men who had worked in the petroleum mining and refining industry showed an elevated risk for lung cancer among welders, operators, boiler makers, painters and oil-field workers taken as a group; no data were available on smoking habits.

In one of two case-control studies, an excess risk for testicular cancer was observed among petroleum and natural gas extraction workers. No such excess was found in the other study.

In a case-control study of cancer at many sites, an association was observed between exposure to crude oil and rectal and squamous-cell lung cancer. However, the association was based on small numbers and may have been confounded by life style factors.

5.4 Other relevant data

Crude oil induces dermal xenobiotic metabolizing enzymes and ornithine decarboxylase after skin application in mice.

In single studies of mice treated in vivo, crude oil induced an increase in the number of sister chromatid exchanges at the highest dose tested but did not induce micronuclei in bone-marrow cells or sperm abnormalities. Crude oil did not increase the number of sister chromatid exchanges in cultured human lymphocytes. The aromatic fractions of crude oil induced sister chromatid exchange, but not chromosomal aberrations, in cultured mammalian cells. Crude oil extracts did not induce mutation in bacteria; when fractionated, the neutral fractions of crude oil, which contain aromatic or polycyclic aromatic compounds generally had mutagenic activity in bacteria.

5.5 Evaluation

There is inadequate evidence for the carcinogenicity in humans of crude oil.

There is limited evidence for the carcinogenicity in experimental animals of crude oil.

Overall Evaluation

Crude oil is not classifiable as to its carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.


Last updated 01/21/98

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