Grantee Research Project Results
1999 Progress Report: Biological Markers of Exposure to Benzene
EPA Grant Number: R826249Title: Biological Markers of Exposure to Benzene
Investigators:
Institution: Lovelace Biomedical & Environmental Research Institute
EPA Project Officer: Chung, Serena
Project Period: March 20, 1998 through March 19, 2001
Project Period Covered by this Report: March 20, 1998 through March 19, 1999
Project Amount: $471,696
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The objective of the research is to develop a panel of biological markers of exposure to benzene that can be used to relate the level of markers in the body in a quantitative manner to both recent and earlier exposures. The hypothesis is that by using a battery of benzene-specific biomarkers of varying half-lives in the body, one can more readily describe the type of exposure to benzene that has occurred in the past than with a single biomarker. For example, one should be able to distinguish between a person who has had a continuous low level of exposure to benzne (as in someone exposed to environmental tobacco smoke) from someone who has had a single high level exposure to benzene in a hobby project. In the former case, one would expect to find a build-up of longer half-life markers and only a low level of shorter half-life markers, while in the latter case, one would detect high levels of short half-life markers and very little of the longer half-life markers. An empirically based mathematical model will be used to relate the current levels of biomarkers of varying half-lives to prior exposures to benzene. A variety of exposure regimens will be conducted in mice to determine if the markers can distinguish between the different regimens. Lastly, limited studies in petroleum workers will explore the usefulness of the battery of markers in assessing exposures in an occupational setting.Progress Summary:
The following benzene-specific markers of exposure were chosen: urinary phenyl mercapturic acid (PMA), t,t-muconic acid, blood S-phenyl cyteine adducts on albumin and hemoglobin, and benzene in exhaled air. Sensitive assays for the urinary metabolites (relatively short half-lifes) have been developed and assays for the longer half-life blood metabolites are being developed. Methods were developed for the combined extraction, derivatization, and analysis of S-PMA and t,t MA from urine via liquid extraction, followed by derivatization using hydrochloric acid/methanol and GC/MS analysis. Using ethyl acetate for liquid extraction, recoveries of the analytes from 1 mL of acidified synthetic urine were 98 ? 6.2 percent and 101 ? 4.2 percent for t,tMA and S-PMA, respectively. The Limit of Quantification was 40 hg/mL for t,tMA and 60 hg/mL for S-PMA. The Limit of Detection was 10 hg/mL for t,tMA and 20 hg/mL for S-PMA. The Coefficient of Variation was less than 10 percent for both t,tMA and S-PMA. The best sensitivity for the combined analytes was obtained using positive ionization, although negative ionization was more sensitive for t,tMA alone.An empirical mathematical model has been developed based on a battery of biomarkers from blood, exhaled air, and urine. The logic of the model is that equations describing the concentration-time relationships for multiple markers can be used to solve for the concentration and the time since exposure to benzene. Based on preliminary results for the short-term markers, a generalized negative exponential function has been fit to the data. Curve fits for a hypothetical longer term marker also have been generated to assess the ability of the model to distinguish among different exposure patterns. The results suggest that the proposed empirical model will be capable of distinguishing between different time-concentration patterns of benzene exposure. Furthermore, because of the empirical basis of the underlying model structure, it may be easily extended to model different compounds.
Future Activities:
We are currently completing the assays for the blood biomarkers of benzene exposure. When these are complete, the full empirical model equations will be fit. To validate the model, an experiment will be performed in which mice will be exposed to benzene by a variety of regimens, and urine and blood sampled at varying times after the exposures. It will be critical that the assays of the markers be done blind to the analyst and the results be given blindly to the modeler on the project. That is, neither the analyst nor the modeler will be aware of the exposure conditions. The objective will be to determine if the blinded results can be used to describe the prior exposure regimen. Following successful validation of the model in mice, the model will be extended to humans. Samples will be taken from petroleum workers with known exposures to benzene and the equations will be fit.Journal Articles:
No journal articles submitted with this report: View all 7 publications for this projectSupplemental Keywords:
ambient air, exposure, toxics, mathematics, measurement methods, petroleum, benzene, toxicokinetics., Health, Scientific Discipline, Air, Toxics, air toxics, Environmental Chemistry, Health Risk Assessment, Epidemiology, HAPS, Risk Assessments, Biochemistry, Atmospheric Sciences, risk assessment, ambient air quality, monitoring, blood samples, animal model, air sampling, ambient monitoring, benzene, inhalation, human exposure, urine and blood samples, biocontaminants, half-life markers, biological markers, human health, Volatile Organic Compounds (VOCs), Benzene (including benzene from gasoline)Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.