Certain people may be exposed to benzene through their work e.g. those working in the petrochemical industry. Benzene concentrations in outdoor air are highest next to busyurban roads and lowest at remote rural locations. Benzene concentrations are greatest in the winter and lowest in the summer months. Sources of Benzene The majority of benzene found at ground level inthe northern hemisphere is likely to have resulted from human activities:
Air quality standard The level recommended by the Expert Panel on Air Quality Standards for benzene is 50 parts perbillion (ppb) measured as a running annual average. The running annual average is calculated by taking the recorded benzene level each day for the past year, adding these together and dividing by 365.The panel also recommended that this Standard should be reduced to 1 ppb running annual average and that the Government set a target date by which this should be achieved
What is Benzene? Benzeneis an organic (carbon based) chemical consisting of six carbon atoms each associated with a hydrogen atom arranged in a ring structure. At normal temperatures it is a liquid. This evaporates easilyand small amounts can be detected in the atmosphere. Benzene is broken down by chemical reactions which occur naturally in the atmosphere, but the reactions take several days.
motorvehicles’ exhaust fumes petrol evaporation from vehicles and at filling stations petrol refining and distribution burning of oil, wood etc. gas leakage other industrial processes cigarette smoking (themajor exposure source for tobacco smokers).
Health effects of Benzene Benzene is easily absorbed by the body when breathed into the lungs, with about one half of it being retained, in the body’sfatty tissues, the brain and bone marrow. Benzene is eliminated by chemical breakdown in the body and excretion in the urine. 80% is eliminated by the body within about two days.