Biomonitoring for benzene exposure: from occupational exposure to environmental pollutant

摘要

Aim. This work is aimed at reviewing the use of biomonitoring of benzene exposure focusing on those changes in the occupational limit values and in air pollution that have prompted the research of new biomarkers. Methods. A bibliographic review on biomedical databases has focused on papers dealing with biomonitoring of benzene in the last 40 years. Results. In the forties of the last century occupational limit values for benzene were in the order of hundreds of ppm; one of the outcome of the epidemiological studies conducted on the Pliofilm Goodyear cohort in the eighties, was that benzene was recognised as leukemogenic to human and the limits were lowered to about 1 ppm. Until that time the biological monitoring of the exposure to benzene was performed by measuring urinary phenol, accounting for about 70% of the adsorbed dose; however a major drawback was its poor specificity. Industrial toxicologists were forced to identify new bioindices to assess the lower occupational exposure: in the early nineties, urinary t,t-muconic acid (MA, 3 -18 % of the absorbed dose), urinary S-phenylmercapturic acid (SPMA, < 1%), blood benzene (< 1%), and urinary benzene (<0.1%) were introduced and biological limit values were proposed. These indices were first applied to assess exposure in petrochemical workers, coke oven workers, shoe makers, and rubber workers. Almost in the same years, in Europe and US a new blended petrol, enriched with a mixture of aromatic hydrocarbons, including benzene, was introduced. Airborne benzene level increased, mostly due to auto vehicle exhaust fumes, and it became a pollutant of the living environment and a chemical of public concern. New biomarkers were then used to assess exposure to low levels of benzene in petrol station attendants, traffic policemen, bus and taxi drivers and in the general population; studies investigated the specificity and sensibility, practical and ethical implications, analytical issues, and optimal application ranges of these biomarkers. The results highlighted that MA is increased by sorbic acid in diet, so that it is not useful to assess low exposure; on the other hand blood benzene, although specific, requires an invasive sampling; urinary benzene and SPMA are non-invasive biomarkers, they are specific and useful to trace the lowest exposures. Conclusions. Biomonitoring of benzene has been challenged by several changes toward low exposures; for this reason, it is ready to face upcoming lower occupational exposure limits as well as biomonitoring programme in the general population.