Assessing environmental carcinogens: review of an approach adopted by the expert groups of the World Health Organization Regional Office for Europe.

The World Health Organization Regional Office for Europe has adopted the viewpoint that it is necessary to attempt to evaluate potential human carcinogens in such a way so that the risk they present can be compared and used in general consideration of protecting the public from toxic substances found in various environments. In order to demonstrate this process, the evaluations for a number of criteria air pollutants as presented in the volume Air Quality Guidelines for Europe are summarized and reviewed. The basic method used is that involving the estimation of risk based on lifetime exposures to airborne carcinogens by a linear extrapolation from known data using no threshold, with the carcinogenic potency expressed as the incremental unit risk estimate. This unit risk is defined as the average expected for a hypothetical population exposed for a lifetime to a concentration of one microgram per cubic meter of the agent in the air they breathe. The advantages and disadvantages of the method are reviewed, and background information for actual environmental conditions and risks leading up to the consensus guidelines adopted are presented for those 17 of the initial 28 criteria air pollutants treated which have IARC classifications of carcinogenicity.