Studies of carcinogenicity of bitumen fume in humans
Authors: Boffetta Paolo , Burstyn Igor 
Published: December 2002

Since antiquity humans have used bitumen, either naturally occurring or derived from crude oil [Broome and Hobson, 1973], and it may have been the binding material described for bricks used in the construction of the Tower of Babel (Genesis 11, 3).Chemically, bitumen is a complex mixture of hydrocarbons consisting of both aliphatic and aromatic compounds, some of which bear nitrogen, oxygen, or sulfur functional groups [Broome and Hobson, 1973]. This material has been in widespread use since the industrial revolution. The first bituminous road was built in 1810 in Lyon, France. Large‐scale industrial use of bitumen began with the exploitation of natural bitumen deposits in Trinidad, with the first commercial shipment arriving in England in the 1840s. Bitumen's main use, in terms of volume, has been in paving, as a binder for inorganic fillers in asphalt mixes. According to conservative estimates, there are at present approximately 4000 asphalt mixing plants in western Europe. A typical mixing plant employs five to ten individuals. These plants produce approximately 275 million tons of hot and 10 million tons of cold asphalt annually. Asphalt mixes are applied to road surfaces by approximately 100,000 paving crewmen across western Europe. Other important uses of bitumen are in waterproofing and roofing. Thus, assessment of the health hazards of bitumen fumes may have far‐reaching industrial, economic, and public health implications.

Of specific concern is the potential carcinogenicity of bitumen fume inhalation. In 1985 and 1987, the International Agency for Research on Cancer [IARC, 1985, 1987] evaluated extracts of steam‐refined and air‐refined bitumen carcinogenicity in experimental animals and classified them as possible human carcinogens (IARC Group 2B), while for undiluted bitumen, the evidence of carcinogenicity in humans was inadequate (IARC Group 3).

Meta‐analysis identified and reveiwed the epidemiological studies informative of cancer hazard in asphalt workers [Partanen and Boffetta, 1994]. However, the aggregated data could not explicitly address effects of bitumen fumes. Agent‐specific exposure data were lacking, conjectured, or controversial, leaving open a number of questions with regard to the interpretation of the results. The aggregated results suggested an increased risk of cancers of the lung, (relative risk 1.8; 95% confidence interval 0.8‐1.0).

The main uncertainty in the assessment of previous epidemiological data arises from the inability to exclude the possibility of confounding by concurrent use of both coal tar a recognized carcinogen, and bitumen by pavers, roofers, and waterproofers [IARC, 1985, 1987]. The voluntary discontinuation of coal tar use by the asphalt industry in western Europe during the past few decades presented an opportunity to discover whether it is likely that bitumen exposure per se is carcinogenic [Partanen et al., 1995]. To address this question, a historical cohort of asphalt workers was assembled by IARC in eight countries (Denmark, Finland, France, Germany, the Netherlands, Norway, Sweden, and Israel) in order to obtain diverse exposure profiles and a sufficient number of cases for the main health outcome of interest: lung cancer.

Detailed results on the mortality of the workers included in the international study have been published in an IARC Internal Technical Report [Boffetta et al., 2001]. In this issue of the Journal, several papers report the key findings on cancer mortality [Boffetta et al., 2003a,b], which provide the most complete assessment of cancer hazards among workers exposed to bitumen fumes.

It is a complex task to organize and conduct international occupational cohort studies. This project was a successful example of collaboration between academic research groups, public bodies, and industrial associations. Among other challenges, it overcame the Babel of multiple languages.