- Air Quality Standards for Benzene
The UK National Air Quality Strategy Consultation Draft8 has set an Air Quality Standard (AQS) for benzene of 5 ppb as a running annual mean. The standard was formulated on the basis of the recommendation made by the Expert Panel on Air Quality Standards (EPAQS) 1. The EPAQS recommended standard was based upon a study of occupational data which estimated that exposure to a mean benzene concentration of 500 ppb over a working lifetime would lead to an increased risk of leukaemia which would be too small to detect. On the basis that a chronological lifetime is about 10 times a working lifetime it was considered that this should be reduced to 50 ppb for the general population. Furthermore, since occupational studies are based on healthy workers a further safety factor of 10 was incorporated to produce a value of 5 ppb, to allow for exposure to other groups of the population which might be more sensitive.
In recommending an AQS of 5 ppb EPAQS 'recognised that the current average concentrations of benzene to which the general public are exposed in the United Kingdom's air (which rarely exceed this concentration) present an exceedingly small risk to health'. In recognition that benzene is a known carcinogen EPAQS also recommended the AQS 'be reduced to the lower level of 1 ppb'. This recommendation 'will ensure that ambient air is no longer the main source of individual exposure, even for non-smokers'.
The World Health Organisation (WHO) have interpreted the occupational data in a different way in providing their air quality guidelines, by stating that there is no known threshold for benzene effects and hence no basis for setting a guideline. WHO also conducted a formal risk calculation which estimated the lifetime risk of leukaemia from exposure to 1 ppb to be about 12 x 10-6, that is there will be 12 cancers (incidences of leukaemia) per million people per 1 ppb benzene over a 70 year life time exposure.
Report prepared by Stanger Science and Environment
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