The use of biomonitoring data in exposure and human health risk assessment: benzene case study

Abstract

Abstract A framework of "Common Criteria" (i.e. a series of questions) has been developed to inform the use and evaluation of biomonitoring data in the context of human exposure and risk assessment. The data-rich chemical benzene was selected for use in a case study to assess whether refinement of the Common Criteria framework was necessary, and to gain additional perspective on approaches for integrating biomonitoring data into a risk-based context. The available data for benzene satisfied most of the Common Criteria and allowed for a risk-based evaluation of the benzene biomonitoring data. In general, biomarker (blood benzene, urinary benzene and urinary S-phenylmercapturic acid) central tendency (i.e. mean, median and geometric mean) concentrations for non-smokers are at or below the predicted blood or urine concentrations that would correspond to exposure at the US Environmental Protection Agency reference concentration (30 µg/m(3)), but greater than blood or urine concentrations relating to the air concentration at the 1 × 10(-5) excess cancer risk (2.9 µg/m(3)). Smokers clearly have higher levels of benzene exposure, and biomarker levels of benzene for non-smokers are generally consistent with ambient air monitoring results. While some biomarkers of benzene are specific indicators of exposure, the interpretation of benzene biomonitoring levels in a health-risk context are complicated by issues associated with short half-lives and gaps in knowledge regarding the relationship between the biomarkers and subsequent toxic effects.

Figure 1.

(A) Benzene ambient air concentrations in the USA, HEI (2007). Reprinted with permission from the Health Effects Institute, Boston, MA. (B) Benzene ambient air concentrations in European metropolitan areas. Adapted from Bruinen de Bruin et al. (2008) with kind permission from Springer Science + Business Media.

Figure 2.

A schematic of liver metabolism of benzene. From Boogaard (2009); reproduced with permission of John Wiley & Sons Ltd. EH, epoxide hydrolase; GSH, glutathione; GST, glutathione-S-transferase; DHDH, dihydrodiol dehydrogenase; MPO, myeloperoxidase; NQO1, NADPH quinone oxidoreductase 1.

Figure 3.

Reported blood benzene concentrations (central tendency) for the general population compared to the benzene biomonitoring equivalent value based upon USEPA non-cancer and cancer benchmarks. Each bar represents a separate exposure population.

Figure 4.

Reported urinary benzene concentrations (central tendency) for the general population compared to the urinary concentration related to USEPA non-cancer and cancer benchmarks. Each bar represents a separate exposure population.

Figure 5.

Reported urinary SPMA concentrations (central tendency) for the general population compared to the urinary concentration related to USEPA non-cancer and cancer benchmarks. Each bar represents a separate exposure population. NA = North America and ND = not defined.

Figure 6.

Reported urinary SPMA concentrations (central tendency) for urban workers compared to the ACGIH BEI. Each bar represents a separate exposure population. ND = not definded.

Figure 7.

Reported urinary ttMA concentrations (central tendency) for urban workers compared to the ACGIH BEI. Each bar represents a separate exposure population. ND = not definded.