Pathways of exposure

70% is expected (3,18,20,29,30) when ETS is present indoors, with increases in some cases of 300% (31) to levels of 16 μg/m3 (18). To sum up, outdoor benzene provides the baseline for benzene concentrations indoors, upon which will be superimposed benzene given off from building materials and indoor artefacts. The presence of attached garages and combustion sources (especially smoking) and other human activities will be the main determinant of the concentration of benzene indoors.

Pathways of exposure

Inhalation accounts for more than 95–99% of the benzene exposure of the general population, whereas intake from food and water consumption is minimal (3,32). In the United States, daily benzene intake from ambient and indoor air has been calculated to range between 180 and 1300 μg/day, and that in food and water up to about 1.4 μg/day (2). The average daily intake for an adult in Canada was estimated to be 14 μg/day from ambient air, 140 μg/day from indoor air, 1.4 μg/day from food and drinking-water and 49 μg/day from car-related activities, giving a total of about 200 μg/day (33). Wallace (30) estimated the corresponding average intake in the United States to be 320 μg/day. Cigarette smoking has been found to contribute significantly to the amount of benzene inhaled (34). Exposure to ETS is widespread in most countries (35). A survey conducted in the United States in 2006 found that more than 40% of nonsmoking adults and almost 60% of children aged 3–11 years were exposed to ETS (36). Another survey, conducted among young people in 132 countries, found that 44% had been exposed to ETS at home and 56% in public places, while another survey found that the exposure of young people at home ranged between 30–87% and 53–98% in public places (37). Active smoking may add as much as 400–1800 μg/day (2,34), while inhalation due to passive smoking will represent an additional 14–50 μg/day to the average daily intake (2,38). Driving a car during the rush hour may give a significant additional intake of 20 μg/day (34,39). Fromme (40) calculated the relative intake from food and uptakes from ambient air, indoor air and air inside cars to be 8%, 9%, 53% and 30%, respectively. In a study carried out in Germany in the 1990s, it was found that indoor exposure to ETS and car-related activities (refuelling and time in transit) could account for 20% and 12%, respectively, of personal exposure to benzene (2). A study carried out in the United Kingdom estimated a daily dose of benzene of 70–75 μg/day for rural non-smokers and 89–95 μg/day for urban non-smokers. The daily dose rose to 116–122 μg/day for urban passive smokers and to over 500 μg/day for urban smokers. Children’s daily exposures were estimated to be 15–20 μg/day and 30–40 μg/day for infants and children, respectively, while exposure to ETS led to a daily exposure of 26 μg/day and 59 μg/day for a urban infants and children, respectively (34). Most of the children’s exposures were produced in the home (41).