Introduction

1. Benzene is a chemical consisting of six atoms each of carbon and hydrogen, arranged in a ring structure. At normal ambient temperatures it is a liquid, but it readily evaporates and small amounts are detectable in the atmosphere. Almost all of the benzene found at ground level in the northern hemisphere is likely to have resulted from human activities, in particular the combustion of petroleum fuels by motor vehicle engines. Other sources, of which cigarette smoking is the major one, make important contributions to the exposure of individuals.
2. Benzene is naturally broken down by chemical reactions in the atmosphere, but these reactions take several days. Thus, in common with inhabitants of other industrial and industrialising nations, people living in the United Kingdom are exposed to benzene in the air they breathe.
3. Benzene is a chemical that people may also be exposed to in certain industrial workplaces, and studies of several such groups of workers exposed in the past have shown that those most heavily exposed have run a small, but definite, increase in risk of developing certain types of leukaemia. Studies in laboratory animals have shown similar effects, and have suggested moreover that benzene exerts its effect by damaging the genetic make-up of cells - in other words it is a genotoxic carcinogen. This means that it is impossible to determine a concentration to which people might be exposed at which there is no risk detectable by existing methods. Having said this, it should be recognised that leukaemia is a relatively rare group of diseases, affecting about one adult in 6000 each year, and we believe that it is feasible to recommend an air quality standard for benzene which, for all practical purposes, presents a risk to the population of the United Kingdom which is exceedingly small and unlikely to be detectable by any practicable method.
4. In this document, the Panel discuss briefly the sources and methods of monitoring of atmospheric benzene and the evidence for its harmful effects on health. We then make recommendations for an Air Quality Standard for the United Kingdom. In doing so, we accept that absolute safety cannot be guaranteed and we therefore recommend that steps are taken to reduce concentrations below this Standard, and that the Government set a target date by which this be achieved.