Benzene exposure: An overview of monitoring methods and their findings
Introduction
Human exposure characterization is a necessary component of environmental and occupational epidemiological studies, risk characterizations and risk management. Exposure science links emissions of a toxicant with dose and public health [1], [2]. Adverse health effects of benzene, in particular blood diseases such as leukemia and aplastic anemia, were initially noted in occupational settings in which the benzene air concentrations were tens to hundreds of ppm [3], [4]. That observation, along with toxicological studies of benzene in animals resulted in the establishment of workplace standards in many countries limiting the air concentrations that workers can be exposed to (Table 1). Current epidemiological studies are still investigating what level of benzene exposure leads to blood diseases and other adverse effects in healthy workers, how to extrapolate health effects to environmental exposures and to provide evidence for risk characterization and management of benzene exposure to the public. The assessment of exposure is often the weakest portion of epidemiological studies and improved methods for extrapolation to environmental exposures based on direct inhalation and dermal exposure assessment and biomarker data are needed to be properly ascertain what health outcomes identified in occupational setting are relevant to the general population for current environmental exposures. This manuscript reviews benzene air concentrations and exposures in both occupational and environmental settings along with methodologies for sample collection and analysis. The impact of air concentrations outdoors, indoors and in transit along with activity patterns on personal exposure is discussed. The applicability of different biomarkers of benzene exposure across different magnitude of exposure is also evaluated.
Occupational exposures occur within the petrochemical industry and in manufacturing that require aromatic solvents or glues that contain benzene such as rubber production, shoe manufacturing, and printing [5], [6], [7], [8]. Environmental exposures to the general population are predominantly through inhalation due to benzene's volatility. Benzene is a component of gasoline, thus emissions from mobile sources are major contributors to the benzene air concentrations where gasoline engines are prevalent [9], [10], [11]. Benzene is also present in cigarette smoke so smokers and individuals who inhale environmental tobacco smoke (ETS) or second hand smoke (SHS) are exposed to benzene above background ambient air levels. A key to determining exposure is the understanding of activities of workers and populations at risk. The benzene levels in the microenvironment encountered and the activities and behaviors that lead to contact change with time [12], [13]. These parameters, combined with biomarker measurements can help define the exposure to dose relationships and lead to approaches that can define how best to reduce benzene exposures.
Section snippets
Air samples
To determine benzene and other non-polar volatile organic compounds (VOCs) air concentrations, the major pathway for benzene exposure, samples are collected from the air on either an adsorbent or by trapping whole air in a container. Passive vapor monitors or badges which collect VOCs based on diffusion are commonly used in occupational settings to measure ppm concentration levels present within the personal or breathing zone air as they present little burden to the wearer [14], [15]. Passive
Biomarkers
The measurement of benzene in blood, breath or urine definitively documents a benzene exposure. However, the biological resident time of benzene in the body is minutes to hours [102] so it is difficult to determine the actual and in some cases even the relative exposures across individuals from a single benzene measurement in blood or breath unless details of when the sample was collected relative to the exposure are known.
Discussion
Benzene exposures still commonly occur within both occupational and environmental settings, though they have been declining over the last several decades. Occupational exposures are now typically below the regulatory standard of 1 ppm and often below 0.1 ppm. However, identifying higher exposures, exceeding 10's of ppm exist in small, unregulated workplaces is an important data gap. Environmental exposures among the general population are much lower than occupational exposures, ranging from <1 to
Conflicts of interest
None declared.
Acknowledgement
The author is supported in part by the NIEHS sponsored UMDNJ Center for Environmental Exposures and Disease, Grant #: NIEHS P30ES005022.
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