|Benzene occurs naturally in crude oil and is a natural constituent of petrol. It is also formed during incomplete combustion of fossil fuels and it is an important intermediate in the manufacture of many chemicals.|
Petrol is the only product marketed to the general public in the UK in which benzene is present in more than trace amounts.
Vapour inhalation is the most important pathway for human exposure (95% of daily intake). The US Total Exposure Assessment Methodology (TEAM) studies found that the overwhelming source of benzene exposure for smokers was cigarette smoke; (smokers bodies have average benzene levels 6 – 10 times that of non-smokers). Non-smokers exposure will primarily occur from indoor air, and during driving and refuelling at petrol stations. Smokers will have a much higher exposure to benzene than non-smokers.
The major health risk associated with low-level exposure to benzene is leukaemia and the strongest link in humans is with acute non-lymphocytic leukaemia (ANLL). The lowest level for an increased incidence of ANLL among occupationally exposed workers appears to be in the range of 32 – 80 mg m-3 (10-25 ppm), although some studies have suggested that effects may occur at lower levels.
Based on data from the Institute for Environment and Health (1) estimated exposure to benzene for the general population is three times less than the lowest exposures reported to be associated with adverse effects.
In the Review of the National Air Quality Strategy (January 1999) the Government has proposed a new hourly mean objective for benzene of 16.25 mg/m3 (5 ppb) as a running annual mean to be achieved by 2003. These objectives apply in non-occupational, near-ground level, outdoor locations where people might reasonably be expected to be exposed over the relevant averaging period.
BENZENE IN CORNWALL
The map below (2) is taken from the NETCEN website (www.aeat.co.uk/netcen/airqual/welcome.html) and shows the estimated annual mean background benzene concentration for 1996 (ppb).
|At present there is no data available from benzene monitoring in Cornwall. Real-time benzene monitoring is being undertaken in Falmouth during the summer of 2000 and the results from that survey will be made available as soon as possible.
1. IEH (1999) Report on benzene in the environment. (Report R12). Leicester, UK, MRC Institute for Environment and Health.
2. Stedman JR (1998). Revised High Resolution Maps of Background Air Pollutant Concentrations in the UK. AEA Technology NETCEN.