Peter J. Boogaard

Biological monitoring of exposure to benzene: a comparison between S-phenylmercapturic acid, trans,trans-muconic acid, and phenol.

OBJECTIVES--Comparison of the suitability of two minor urinary metabolites of benzene, trans,trans-muconic acid (tt-MA) and S-phenylmercapturic acid (S-PMA), as biomarkers for low levels of benzene exposure. METHODS--The sensitivity of analytical methods of measuring tt-MA and S-PMA were improved and applied to 434 urine samples collected from 188 workers in 12 studies in different petrochemical industries and from 52 control workers with no occupational exposure to benzene. In nine studies airborne benzene concentrations were assessed by personal air monitoring. RESULTS--Strong correlations were found between tt-MA and S-PMA concentrations in samples from the end of the shift and between either of these variables and airborne benzene concentrations. It was calculated that exposure to 1 ppm (8 hour time weighted average (TWA)) benzene leads to an average concentration of 1.7 mg tt-MA and 47 micrograms S-PMA/g creatinine in samples from the end of the shift. It was estimated that, on average, 3.9% (range 1.9%-7.3%) of an inhaled dose of benzene was excreted as tt-MA with an apparent elimination half life of 5.0 (SD 2.3) hours and 0.11% (range 0.05%-0.26%) as S-PMA with a half life of 9.1 (SD 3.7) hours. The mean urinary S-PMA in 14 moderate smokers and 38 non-smokers was 3.61 and 1.99 micrograms/g creatinine, respectively and the mean urinary tt-MA was 0.058 and 0.037 mg/g creatinine, respectively. S-PMA proved to be more specific and more sensitive (P = 0.030, Fishers exact test) than tt-MA. S-PMA, but not tt-MA, was always detectable in the urine of smokers who were not occupationally exposed. S-PMA was also detectable in 20 of the 38 non-smokers from the control group whereas tt-MA was detectable in only nine of these samples. The inferior specificity of tt-MA is due to relatively high background values (up to 0.71 mg/g creatinine in this study) that may be found in non-occupationally exposed people. CONCLUSIONS--Although both tt-MA and S-PMA are sensitive biomarkers, only S-PMA allows reliable determination of benzene exposures down to 0.3 ppm (8 h TWA) due to its superior specificity. Because it has a longer elimination half life S-PMA is also a more reliable biomarker than tt-MA for benzene exposures during 12 hour shifts. For biological monitoring of exposure to benzene concentrations higher than 1 ppm (8 h TWA) tt-MA is also suitable and may even be preferred due to its greater ease of measurement.

Guidelines for the communication of Biomonitoring Equivalents: Report from the Biomonitoring Equivalents Expert Workshop

Biomonitoring Equivalents (BEs) are screening tools for interpreting biomonitoring data. However, the development of BEs brings to the public a relatively novel concept in the field of health risk assessment and presents new challenges for environmental risk communication. This paper provides guidance on methods for conveying information to the general public, the health care community, regulators and other interested parties regarding how chemical-specific BEs are derived, what they mean in terms of health, and the challenges and questions related to interpretation and communication of biomonitoring data. Key communication issues include: (i) developing a definition of the BE that accurately captures the BE concept in lay terms, (ii) how to compare population biomonitoring data to BEs, (iii) interpreting biomonitoring data that exceed BEs for a specific chemical, (iv) how to best describe the confidence in chemical-specific BEs, and (v) key requirements for effective communication with health care professionals. While the risk communication literature specific to biomonitoring is sparse, many of the concepts developed for traditional risk assessments apply, including transparency and discussions of confidence and uncertainty. Communication of BEs will require outreach, education, and development of communication materials specific to several audiences including the lay public and health care providers.

Exposure to polycyclic aromatic hydrocarbons in petrochemical industries by measurement of urinary 1-hydroxypyrene.

Biological monitoring of exposure of workers to polycyclic aromatic hydrocarbons (PAHs) in petrochemical industries was performed by the measurement of urinary excretion of 1-hydroxypyrene. In 121 of the 462 workers studied (both smokers and non-smokers) who had had no recent occupational exposure to PAHs a median 1-hydroxypyrene concentration of 0.21 micrograms/g creatinine was found. The upper limit of the 95% confidence interval in these workers of 0.99 micrograms/g creatinine was used as the upper normal value for industrial workers. Urinary 1-hydroxypyrene concentrations were measured in workers involved in manufacture and maintenance operations in oil refineries (13 studies in eight different settings), in workers manufacturing or handling products containing PAHs in chemical plants (five studies in three settings) and laboratories (four studies), and in workers digging soil contaminated with PAHs (three studies). In most studies in oil refineries 1-hydroxypyrene concentrations were only marginally greater than the values measured in the 121 workers with no recent occupational exposure to PAHs. This was also the case in maintenance operations with higher potential exposure to PAHs, indicating that personal protection equipment was generally adequate to prevent excessive exposure. The studies in chemical plants also showed that exposure to PAHs is low. An exception was the workers engaged in the production of needle coke from ethylene cracker residue, where increased urinary 1-hydroxypyrene concentrations were measured. The excretion of 1-hydroxypyrene by the operators and maintenance workers of this plant was investigated in relation to potential methods of exposure to PAHs. Dermal and inhalatory exposure were both significant determinants of exposure to PAHs.

Creating context for the use of DNA adduct data in cancer risk assessment: II. Overview of methods of identification and quantitation of DNA damage

The formation of deoxyribonucleic acid (DNA) adducts can have important and adverse consequences for cellular and whole organism function. Available methods for identification of DNA damage and quantification of adducts are reviewed. Analyses can be performed on various samples including tissues, isolated cells, and intact or hydrolyzed (digested) DNA from a variety of biological samples of interest for monitoring in humans. Sensitivity and specificity are considered key factors for selecting the type of method for assessing DNA perturbation. The amount of DNA needed for analysis is dependent upon the method and ranges widely, from <1 μg to 3 mg. The methods discussed include the Comet assay, the ligation-mediated polymerase reaction, histochemical and immunologic methods, radiolabeled (14C- and 3H-) binding, 32P-postlabeling, and methods dependent on gas chromatography (GC) or high-performance liquid chromatography (HPLC) with detection by electron capture, electrochemical detection, single or tandem mass spectrometry, or accelerator mass spectrometry. Sensitivity is ranked, and ranges from ∼1 adduct in 104 to 1012 nucleotides. A brief overview of oxidatively generated DNA damage is also presented. Assay limitations are discussed along with issues that may have impact on the reliability of results, such as sample collection, processing, and storage. Although certain methodologies are mature, improving technology will continue to enhance the specificity and sensitivity of adduct analysis. Because limited guidance and recommendations exist for adduct analysis, this effort supports the HESI Committee goal of developing a framework for use of DNA adduct data in risk assessment.

Biomarkers for assessing occupational exposures to 1,3-butadiene

The overall objective of this study was to evaluate a continuum of biomarkers in blood and urine for their sensitivities as indicators of low level occupational exposures to 1,3 butadiene (BD). The study design was largely cross-sectional, with biological samples collected within a short timeframe. Personal 8-h BD exposure measures were made on several occasions over a 60-day period for each potentially exposed worker in order provide maximum accuracy for this independent variable and to accommodate the different expression intervals of the several biomarkers. Co-exposures to styrene, toluene and benzene were also measured. The study included 24 BD monomer production workers (mean BD exposure=0.642 mg/m(3)), 34 polymerization workers (mean BD exposure=1.794 mg/m(3)) and 25 controls (mean BD exposure=0.023 mg/m(3)). The several biomarkers were measured by a consortium of investigators at different locations in the US and Europe. These biomarkers included: (1) metabolic genotypes (CYP2E1, EH, GST M1, GST T1, ADH2, ADH3), determined in Prague and Burlington, VT; (2) urinary M1 and M2 metabolites (1,2-dihydroxy-4-[N-acetylcysteinyl]-butane and 1-hydroxy-2-[N-acetylcysteinyl]-3-butene, respectively), determined in Albuquerque, NM and Leiden; (3) hemoglobin adducts (N-[2-dihydroxy-3-butenyl]valine=HBVal and N-[2,3,4-trihydroxybutyl]valine=THBVal), determined in Amsterdam and Chapel Hill, NC, respectively; (4) HPRT mutations determined by autoradiographic assay in Galveston, TX, with slides re-read in Burlington, VT; (6) hypoxanthine-guanine phosphoribosyltransferase (HPRT) mutations determined by cloning assay in Leiden with mutational spectra characterized in Burlington, VT; (7) sister chromatid exchanges and chromosome aberrations determined by standard methods and FISH analysis in Prague. Urinary M1 and M2 metabolites and HBVal and THBVal hemoglobin adducts were all significantly correlated with BD exposure levels, with adducts being the most highly associated. No significant relationships were observed between BD exposures and HPRT mutations or any of the cytogenetic endpoints, regardless of method of assay.

Urinary 1-hydroxypyrene as biomarker of exposure to polycyclic aromatic hydrocarbons in workers in petrochemical industries: baseline values and dermal uptake

The suitability of urinary 1-hydroxypyrene as a biomarker for the assessment of exposure to polycyclic aromatic hydrocarbons (PAH) in petrochemical industries was evaluated in 562 workers involved in various operations in petrochemical industries. The median 1-hydroxypyrene concentration in 121 of these workers (both smokers and non-smokers) who had had no recent occupational exposure to PAH was 0.11 mumol/mol creatinine. The upper limit of the 95% confidence interval was 0.51 mumol/mol creatinine. During activities with a low potential exposure to PAH, such as loading bitumen and the handling of clarified slurry oils and furfural extracts, 1-hydroxypyrene concentrations were only marginally increased compared with the values measured in the 121 workers with no recent occupational exposure to PAH. Despite the substantially higher potential exposure to PAH during clean-out operations of various oil refinery installations, the concentrations of 1-hydroxypyrene in the workers involved were in the same range. This suggests that personal protection equipment was generally adequate to prevent excessive exposure. However, in workers digging PAH-contaminated soil and workers engaged in the production of needle coke from ethylene cracker residue, significantly increased urinary 1-hydroxypyrene concentrations were measured. A major decrease in urinary 1-hydroxypyrene following the application of dermal protective equipment in the ground workers suggested that skin absorption plays a major role in occupational exposure to PAH. The excretion of 1-hydroxypyrene by the workers of the needle coke plant was investigated in relation to potential determinants of exposure to PAH. It was indeed found that not only inhalatory but also dermal exposure was a significant determinant of occupational exposure to PAH.

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

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/m3), but greater than blood or urine concentrations relating to the air concentration at the 1 × 10−5 excess cancer risk (2.9 µg/m3). 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.

Biological effect monitoring in industrial workers following incidental exposure to high concentrations of ethylene oxide

Peripheral blood from four groups of seven workers from a chemical manufacturing plant in The Netherlands was analyzed for hemoglobin adducts in erythrocytes and for hprt mutants, micronuclei and SCEs in lymphocytes. Group I workers were incidentally exposed to acute high doses of ethylene oxide ranging from 52 to 785 mg/m3. Group II and III workers were chronically exposed to low doses of ethylene oxide for < 5 years or > 15 years respectively. Group IV workers served as unexposed controls and came from the Occupational Health Department. Hemoglobin adduct levels in group I workers were very high and ranged from 1461 to 19913 pmol HOEtVal/g Hb approximately 1 month after the accident. HOEtVal values for group II and III workers fluctuated between 0 and 190 pmol/g Hb corresponding with average EtO exposure levels in the range of < 0.01 and 0.06 mg/m3 EtO. The statistical analysis of the genetic data did not reveal any statistically significant differences between any combination of worker groups. The genetic tests for group I workers were performed on blood samples collected 89-180 days after the incidental exposure. The absence of enhanced frequencies of mutations, micronuclei and SCEs suggests that significant induction of hprt mutations in vivo did not occur and that persistent preclastogenic lesions were not present in significant amounts when the exposed lymphocytes were put in culture to visualize any induced cytogenetic damage. This finding implies that the incidental exposure to high concentrations of EtO did not cause any measurable permanent mutational/cytogenetic damage in exposed lymphocytes.

Use of haemoglobin adducts in exposure monitoring and risk assessment.

Many industrial bulk chemicals are oxiranes or alkenes that are easily metabolised to oxiranes in mammalian systems. Many oxiranes may react with DNA and are therefore mutagenic in vitro. Some oxiranes have been shown to be carcinogenic in rodents in vivo as well. Despite the very limited evidence of the carcinogenicity of oxiranes in humans, they should be considered potential human carcinogens. As a consequence, exposure to these compounds should be minimised and controlled. Twenty-five years ago, Ehrenberg and co-workers suggested that exposure to oxiranes might be determined through the measurement of the adducts they form with haemoglobin (Hb). Ten years later, a modification of the Edman degradation was developed at Stockholm University that allowed determination of adducts with the N-terminal valine of Hb by GC-MS. In our laboratory, this methodology was modified and adapted for analysis on an industrial scale. Since 1987, exposure of operators in our facilities to ethylene oxide (EO) has been routinely monitored by determination of N-(2-hydroxyethyl)valine in Hb. Biological monitoring programmes for propylene oxide (PO) and 1,3-butadiene (BD) were developed later. In this review, the methodology and its results are discussed as a tool in human risk assessment of industrial chemicals. Two major advantages of Hb adduct determinations in risk assessment are (1) the qualitative information on the structure of reactive intermediates that may be obtained through the mass spectrometry, which may provide insight in the molecular toxicology of compounds such as BD, and (2) the possibility of reliable determination of exposure over periods of several months with limited number of samples for compounds such as ethylene oxide (EO), propylene oxide (PO) and BD which form stable adducts with Hb. Since good correlations between the airborne concentrations of these chemicals with their respective adducts have been established, Hb adducts can also be used to quantitate airborne exposure which is of paramount importance as exposure assessment is usually one of the weaker parameters in risk assessment.

Comparative assessment of gastrointestinal irritant potency in man of tin(II) chloride and tin migrated from packaging.

Tin is present in low concentrations in most canned foods and beverages, the highest levels being found in products packaged in unlacquered or partially lacquered tinplate cans. A limited number of case-reports of acute gastrointestinal disorders after consumption of food containing 100-500 mg/kg tin have been reported, but these reports suffer many insufficiencies. Controlled clinical studies on acute effects of tin migrated from packaging suggest a threshold concentration for adverse effects (AEs) of >730 mg/kg. Two separate randomised, single-centre, double-blind, crossover studies, enabling comparison of the tolerability of tin added as tin(II) chloride at concentrations of <0.5, 161, 264 and 529 mg/kg in 250 ml tomato juice in 20 volunteers (Study 1) and tin migrated from packaging at concentrations of <0.5, 201 and 267 mg/kg in 250 ml tomato soup in 24 volunteers (Study 2) were carried out. Distribution studies were conducted to get insight in the acute AEs of low molecular weight (<1000 Da) tin species in the soluble fraction of food products. Results show that the chemical form of tin and not the elemental concentration per se determines the severity of AEs. A clear dose-response relationship was only observed when tin was added as tin(II) chloride in tomato juice. No clinically significant AEs were reported in Study 2 and comparison of the incidence of tin-related AEs showed no difference between the dose levels (including control). Tin species of low molecular weight in supernatant represented 31-32% of total tin in canned tomato soup versus 56-61% in juice freshly spiked with tin(II) chloride. Differences in the incidence of AEs following administration of tomato juice with 161 and 264 mg of tin per kg and tomato soup with 201 and 267 mg of tin per kg likely results from differences in the concentration of low molecular weight tin species and in the nature of tin complexes formed. The results of this work demonstrate that tin levels up to 267 mg/kg in canned food cause no AEs in healthy adults and support the currently proposed tin levels of 200 mg/kg and 250 mg/kg for canned beverages and canned foods, respectively, as safe levels for adults in the general population.