Biomonitoring during large-scale maintenance works in the chemical industry - the benzene experience

Introduction
While exposure to hazardous chemicals under regular working conditions is usually limited and well controlled, maintenance works involving a direct contact to compounds often turn out to be a relevant source of uptake. In a large-scale biomonitoring program in two chemical plants, repeated after about three years, the benzene exposure of maintenance workers was monitored to assist in the workplace safety surveillance, to enhance the safety awareness of the workers and to allow for a comparison of different biomarkers for benzene.

Methods
Several hundred workers from two chemical plants occupied between 3 - 5 weeks with shutdown and maintenance operations provided post-shift spot urine samples. Benzene was selected as a ubiquitous exposure key compound for both plants. Within the first biomonitoring program, the samples were analysed for trans,trans-muconic acid, 1-hydroxypyrene and creatinine. In the second program, additionally S-phenylmercapturic acid and unmetabolised benzene in urine were monitored. Basic information about work tasks, personal protective equipment and the individual smoker status was provided.

Results
The two studies showed that in most cases currently available biological reference or guideline values (e.g. German Exposure Equivalents for Carcinogenic Substances, ACGIH Biological Exposure Indices, or internal action values) were not exceeded. However, some specific work tasks were identified to result in a generally higher exposure with more frequent reference or guideline value excursions. The data allow for a comparison of the three biomarkers for benzene and underline the good correlation between the parameters in general and the usefulness of unmetabolised benzene in urine for a fast screening.

Discussion
The large-scale biomonitoring programs assisted in identifying relevant exposure sources for benzene during regular maintenance works in two chemical plants. The acceptance of the biomonitoring program was high and offered the opportunity to communicate health and safety issues and the potential health hazards on a solid ground.