A pharmacokinetic study of occupational and environmental benzene exposure with regard to gender

Human biomonitoring and toxicokinetics as key building blocks for next generation risk assessment

Human health risk assessment is historically built upon animal testing, often following Organisation for Economic Co-operation and Development (OECD) test guidelines and exposure assessments. Using combinations of human relevant in vitro models, chemical analysis and computational (in silico) approaches bring advantages compared to animal studies. These include a greater focus on the human species and on molecular mechanisms and kinetics, identification of Adverse Outcome Pathways and downstream Key Events as well as the possibility of addressing susceptible populations and additional endpoints. Much of the advancement and progress made in the Next Generation Risk Assessment (NGRA) have been primarily focused on new approach methodologies (NAMs) and physiologically based kinetic (PBK) modelling without incorporating human biomonitoring (HBM). The integration of toxicokinetics (TK) and PBK modelling is an essential component of NGRA. PBK models are essential for describing in quantitative terms the TK processes with a focus on the effective dose at the expected target site. Furthermore, the need for PBK models is amplified by the increasing scientific and regulatory interest in aggregate and cumulative exposure as well as interactions of chemicals in mixtures. Since incorporating HBM data strengthens approaches and reduces uncertainties in risk assessment, here we elaborate on the integrated use of TK, PBK modelling and HBM in chemical risk assessment highlighting opportunities as well as challenges and limitations. Examples are provided where HBM and TK/PBK modelling can be used in both exposure assessment and hazard characterization shifting from external exposure and animal dose/response assays to animal-free, internal exposure-based NGRA.

Human biomonitoring of low-level benzene exposures

Historically, benzene has been widely used in a large variety of applications. Occupational exposure limits (OELs) were set for benzene as it was found to be acutely toxic, causing central nervous system depression at high exposures. OELs were lowered when it was discovered that chronic exposure to benzene could cause haematotoxicity. After confirmation that benzene is a human carcinogen causing acute myeloid leukaemia and possibly other blood malignancies, OEL were further lowered. The industrial application of benzene as solvent is almost completely discontinued but it is still used as feedstock for the production of other materials, such as styrene. Occupational exposure to benzene may also occur since it is present in crude oil, natural gas condensate and a variety of petroleum products and because benzene can be formed in combustion of organic material. In the past few years, lower OELs for benzene in the range of 0.05-0.25 ppm have been proposed or were already established to protect workers from benzene-induced cancer. The skin is an important potential route of exposure and relatively more important at lower OELs. Consequently, human biomonitoring - which integrates all exposure routes - is routinely applied to control overall exposure to benzene. Several potential biomarkers have been proposed and investigated. For compliance check of the current low OELs, urinary S-phenylmercapturic acid (S-PMA), urinary benzene and blood benzene are feasible biomarkers. S-PMA appears to be the most promising biomarker but proper validation of biomarker levels corresponding to airborne benzene concentrations below 0.25 ppm are needed.

Benzene exposure and risk of benzene poisoning in Chinese workers

OBJECTIVES

Benzene is a known haematoxin and leukemogen that can cause benzene poisoning (BP), that is, a persistent reduction in white cell counts that is strongly associated with increased risk of lymphohaematopoietic malignancies. Data are needed on the exposure-response, particularly at low doses and susceptible populations for clinical and regulatory purposes.

METHODS

In a case-cohort study among 110 631 Chinese workers first employed 1949-1987 and followed up during 1972-1999, we evaluated BP risk according to benzene exposure level and investigated risk modification by subject (sex, attained age) and exposure-related factors (latency, exposure windows, age at first benzene exposure, coexposure to toluene) using excess relative risk and excess absolute risk models.

RESULTS

There were 538 BP cases and 909 benzene-exposed referents. The exposure metric with best model fit was cumulative benzene exposure during a 5-year risk window, followed by a 9-month lag period before BP diagnosis. Estimated excess absolute risk of BP at age 60 increased from 0.5% for subjects in the lowest benzene exposure category (>0 to 10 ppm-years) to 5.0% for those in the highest category (>100 ppm-years) compared with unexposed subjects. Increased risks were apparent at low cumulative exposure levels and for workers who were first exposed at <30 years of age.

CONCLUSIONS

Our data show a clear association between benzene exposure and BP, beginning at low cumulative benzene exposure levels with no threshold, and with higher risks for workers exposed at younger ages. These findings are important because BP has been linked to a strongly increased development of lymphohaematopoietic malignancies.

Sex Difference and Benzene Exposure: Does It Matter?

Sex-related biological differences might lead to different effects in women and men when they are exposed to risk factors. A scoping review was carried out to understand if sex could be a discriminant in health outcomes due to benzene. Studies on both animals and humans were collected. In vivo surveys, focusing on genotoxicity, hematotoxicity and effects on metabolism suggested a higher involvement of male animals (mice or rats) in adverse health effects. Conversely, the studies on humans, focused on the alteration of blood parameters, myeloid leukemia incidence and biomarker rates, highlighted that, overall, women had significantly higher risk for blood system effects and a metabolization of benzene 23-26% higher than men, considering a similar exposure situation. This opposite trend highlights that the extrapolation of in vivo findings to human risk assessment should be taken with caution. However, it is clear that sex is a physiological parameter to consider in benzene exposure and its health effects. The topic of sex difference linked to benzene in human exposure needs further research, with more numerous samples, to obtain a higher strength of data and more indicative findings. Sex factor, and gender, could have significant impacts on occupational exposures and their health effects, even if there are still uncertainties and gaps that need to be filled.

Gender differences in hematotoxicity of benzene-exposed workers, three cross-sectional studies on 218,061 subjects

Our aim was to analyze the effects of benzene exposure on hematotoxicity in workers, with a focus on gender differences. The study was divided into three parts, and the survey included 218,061 workers. Since 2017, some workers are selected from the total workers each year to explore the possible influencing factors (age, duration of benzene exposure, TWA (8-h time-weighted average) of benzene, SPMA (S-phenylmercapturic acid), MDA (malondialdehyde), 8-OHdG (8-hydroxy-2'-deoxyguanosine) of different hematotoxicity of different genders). The abnormal rate of WBC (white blood cell), ANC (absolute neutrophil count), and platelets of female workers in the benzene exposure group was higher than that of males in the benzene exposure group and also higher than that of the female workers in the control group. Research results in 2019 showed increased SPMA as well as increases their DNA damage including 8-OHdG and MDA in benzene-exposed female workers compared to those in the control female group (all p < 0.05. SPMA, 8-OHdG, and MDA in benzene exposure female workers increased 555%, 183%, and 33.3%, respectively). Female workers are at significantly higher risk for blood system effects of benzene exposure. Therefore, more stringent standards and guidelines may be needed to protect the changing professional population, especially for females.

A Scoping Review of Technologies and Their Applicability for Exposome-Based Risk Assessment in the Oil and Gas Industry

INTRODUCTION

Oil and gas workers have been shown to be at increased risk of chronic diseases including cancer, asthma, chronic obstructive pulmonary disease, and hearing loss, among others. Technological advances may be used to assess the external (e.g. personal sensors, smartphone apps and online platforms, exposure models) and internal exposome (e.g. physiologically based kinetic modeling (PBK), biomonitoring, omics), offering numerous possibilities for chronic disease prevention strategies and risk management measures. The objective of this study was to review the literature on these technologies, by focusing on: (i) evaluating their applicability for exposome research in the oil and gas industry, and (ii) identifying key challenges that may hamper the successful application of such technologies in the oil and gas industry.

METHOD

A scoping review was conducted by identifying peer-reviewed literature with searches in MEDLINE/PubMed and SciVerse Scopus. Two assessors trained on the search strategy screened retrieved articles on title and abstract. The inclusion criteria used for this review were: application of the aforementioned technologies at a workplace in the oil and gas industry or, application of these technologies for an exposure relevant to the oil and gas industry but in another occupational sector, English language and publication period 2005-end of 2019.

RESULTS

In total, 72 articles were included in this scoping review with most articles focused on omics and bioinformatics (N = 22), followed by biomonitoring and biomarkers (N = 20), external exposure modeling (N = 11), PBK modeling (N = 10), and personal sensors (N = 9). Several studies were identified in the oil and gas industry on the application of PBK models and biomarkers, mainly focusing on workers exposed to benzene. The application of personal sensors, new types of exposure models, and omics technology are still in their infancy with respect to the oil and gas industry. Nevertheless, applications of these technologies in other occupational sectors showed the potential for application in this sector.

DISCUSSION AND CONCLUSION

New exposome technologies offer great promise for personal monitoring of workers in the oil and gas industry, but more applied research is needed in collaboration with the industry. Current challenges hindering a successful application of such technologies include (i) the technological readiness of sensors, (ii) the availability of data, (iii) the absence of standardized and validated methods, and (iv) the need for new study designs to study the development of disease during working life.

The association of three DNA repair genes polymorphisms on the frequency of chromosomal alterations detected by fluorescence in situ hybridization

PURPOSE

Gas station workers (GSWs) are exposed to carcinogenic agents. The aim was to study the association of high somatic chromosome alterations (CAs) rates in the blood of GSWs and the polymorphisms of three genes playing a role in DNA double-strand break repair.

METHODS

This is a cross-sectional study with 114 GSWs and 115 age-matched controls. Cytogenetic analyses, blood exams, medical interviews and genotypes for RAD51/G135C (rs1801320), ATM/P1054R (rs1800057) and CHEK2/T470C (rs17879961) genes were performed.

RESULTS

The CA rate in GSWs was 9.8 CAs/1000 metaphases, and 19.1% of the workers had > 10 CAs per 1000 metaphases (group two). GSWs had decreased levels of monocytes (P = 0.024) in their blood exams. The number of variant alleles of the RAD51/G135C polymorphism was higher in GSWs (P = 0.011) compared to the controls, and were associated with enhanced number of CAs per worker (P = 0.008). No allele variant was found for CHEK2/T470C in this study.

CONCLUSION

The RAD51/G135C polymorphism appears to be related to genome instability in gas station workers. Increasing the knowledge of DNA repair gene variations involved in maintaining genomic stability in GSWs may be crucial for future cancer prevention.

Effects of inhaled combined Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX): Toward an environmental exposure model

Combined environmental exposures to the volatile organic compounds (VOCs) Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) pose clear risks to public health. Research into these risks is under-studied even as BTEX levels in the atmosphere are predicted to rise. This review focuses on the available literature using single- and combined-BTEX component inhaled solvent exposures in animal models, necessarily also drawing on findings from models of inhalant abuse and occupational exposures. Health effects of these exposures are discussed for multiple organ systems, but with particular attention on neurobehavioral outcomes such as locomotor activity, impulsivity, learning, and psychopharmacological responses. It is clear that animal models have significant differences in the concentrations, durations and patterns of exposure. Experimental evidence of the deleterious health and neurobehavioral consequences of exposures to the individual components of BTEX were found, but these effects were typically assessed using concentrations and exposure patterns not characteristic of environmental exposure. Future studies with animal models designed appropriately to explore combined BTEX will be necessary and advantageous to discovering health outcomes and more subtle neurobehavioral impacts of long-term environmental exposures.

Effect of occupational exposure to petrol and gasoline components on liver and renal biochemical parameters among gas station attendants, a review and meta-analysis

OBJECTIVES

Kidney and liver are of the most affected organs during permanent exposure to petrol and gasoline components in gas stations. This study aims to investigate the renal and liver involvements in these workers using meta-analysis.

METHODS

PubMed, Scopus, Science direct, ISI web of science, and Google scholar motor engine were searched using Mesh terms of the relevant keywords. Screening of titles, abstracts and full texts was continued until the eligible articles meeting the inclusion/exclusion criteria were selected. Quality assessment was conducted using NOS (Newcastle-Ottawa Quality score). The pooled standard mean difference of the renal and liver indices between exposed/unexposed groups was estimated using Stata ver. 11 software.

RESULTS

In this systematic review, 22 papers were entered. The pooled standard mean difference (95% confidence interval) between exposed and unexposed groups was estimated as of 0.74 (0.28, 1.21) for alkaline phosphatase (ALP), 2.44 (1.80, 3.08) for aspartate transaminase (AST), 2.06 (1.42, 2.69) for alanine transaminase (ALT), 0.10 (-0.09, 0.29) for total Bilirubin (TB), 0.74 (-0.42, -1.90) for total protein (TP), -0.49 (-0.82, -0.15) for albumin, 0.88 (-0.10, 1.87) for uric acid, 1.02 (0.45, 1.59) for creatinine and 1.44 (0.75, 2.13) for blood urea nitrogen (BUN).

CONCLUSION

Our meta-analysis showed that the serum AST, ALT, ALP, total protein, total bilirubin, BUN, uric acid and creatinine levels were higher among workers exposed to petrol and gasoline than control group, while albumin was lower in the serum of the exposed workers. Therefore, occupational exposure to gasoline stations can create adverse effects on kidney and liver function.

Spatial variation in mortality risk for hematological malignancies near a petrochemical refinery: A population-based case-control study

INTRODUCTION

The study investigated the geographic variation of mortality risk for hematological malignancies (HMs) in order to identify potential high-risk areas near an Italian petrochemical refinery.

MATERIAL AND METHODS

A population-based case-control study was conducted and residential histories for 171 cases and 338 sex- and age-matched controls were collected. Confounding factors were obtained from interviews with consenting relatives for 109 HM deaths and 267 controls. To produce risk mortality maps, two different approaches were applied and compared. We mapped (1) adaptive kernel density relative risk estimation for case-control studies which estimates a spatial relative risk function using the ratio between cases and controls' densities, and (2) estimated odds ratios for case-control study data using Generalized Additive Models (GAMs) to smooth the effect of location, a proxy for exposure, while adjusting for confounding variables.

RESULTS

No high-risk areas for HM mortality were identified among all subjects (men and women combined), by applying both approaches. Using the adaptive KDE approach, we found a significant increase in death risk only among women in a large area 2-6 km southeast of the refinery and the application of GAMs also identified a similarly-located significant high-risk area among women only (global p-value<0.025). Potential confounding risk factors we considered in the GAM did not alter the results.

CONCLUSION

Both approaches identified a high-risk area close to the refinery among women only. Those spatial methods are useful tools for public policy management to determine priority areas for intervention. Our findings suggest several directions for further research in order to identify other potential environmental exposures that may be assessed in forthcoming studies based on detailed exposure modeling.

Risk of death for hematological malignancies for residents close to an Italian petrochemical refinery: a population-based case-control study

PURPOSE

We investigated the risk of death for hematological malignancies (HMs) in the area surrounding an Italian petrochemical refinery, where atmospheric concentrations of benzene (known carcinogen) had not been adequately monitored in the past.

METHODS

We performed a population-based case-control study, using conditional logistic regression to estimate odds ratios (ORs) of HM death, with 95 % confidence intervals (CIs), and p trends, in relation to tertiles of time-weighted average residential proximity to the refinery. We identified 177 HM deaths and 349 sex- and age-matched controls from municipal files. Confounding factors were investigated from interviews with consenting relatives for 109 HM deaths and 178 matched controls.

RESULTS

For males and females combined, risk of HM death was unrelated to residential proximity. For females, ORs of HM death by increasing tertiles of proximity were 1, 2.74 (95 % CI 1.48-5.09, significant) and 1.49 (95 % CI 0.76-2.92) (p trend 0.184). For the subgroup of persons who plausibly spent most of their time at home (long-term retired, homemakers or unemployed, 53 cases, 79 controls), the ORs of leukemia plus non-Hodgkin lymphoma death (38 cases, 56 controls) by increasing tertiles of proximity were 1, 3.44 (95 % CI 1.04-11.37, significant) and 3.25 (95 % CI 0.82-12.87) (p trend 0.083).

CONCLUSIONS

No increased risk of HM death for males and females combined living close to the refinery was found. However, the findings for females and a subgroup plausibly spending most of their time at home suggest a relation between increased risk of HM death and residential proximity to the refinery.

Human risk assessment of benzene after a gasoline station fuel leak

OBJECTIVE: To assess the health risk of exposure to benzene for a community affected by a fuel leak. METHODS: Data regarding the fuel leak accident with, which occurred in the Brasilia, Federal District, were obtained from the Fuel Distributor reports provided to the environmental authority. Information about the affected population (22 individuals) was obtained from focal groups of eight individuals. Length of exposure and water benzene concentration were estimated through a groundwater flow model associated with a benzene propagation model. The risk assessment was conducted according to the Agency for Toxic Substances and Disease Registry methodology. RESULTS: A high risk perception related to the health consequences of the accident was evident in the affected community (22 individuals), probably due to the lack of assistance and a poor risk communication from government authorities and the polluting agent. The community had been exposed to unsafe levels of benzene (> 5 µg/L) since December 2001, five months before they reported the leak. The mean benzene level in drinking water (72.2 µg/L) was higher than that obtained by the Fuel Distributer using the Risk Based Corrective Action methodology (17.2 µg/L).The estimated benzene intake from the consumption of water and food reached a maximum of 0.0091 µg/kg bw/day (5 x 10-7 cancer risk per 106 individuals). The level of benzene in water vapor while showering reached 7.5 µg/m3 for children (1 per 104 cancer risk). Total cancer risk ranged from 110 to 200 per 106 individuals. CONCLUSIONS: The population affected by the fuel leak was exposed to benzene levels that might have represented a health risk. Local government authorities need to develop better strategies to respond rapidly to these types of accidents to protect the health of the affected population and the environment.

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/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.

Translational research to develop a human PBPK models tool kit-volatile organic compounds (VOCs)

Toxicity and exposure evaluations remain the two of the key components of human health assessment. While improvement in exposure assessment relies on a better understanding of human behavior patterns, toxicity assessment still relies to a great extent on animal toxicity testing and human epidemiological studies. Recent advances in computer modeling of the dose-response relationship and distribution of xenobiotics in humans to important target tissues have advanced our abilities to assess toxicity. In particular, physiologically based pharmacokinetic (PBPK) models are among the tools than can enhance toxicity assessment accuracy. Many PBPK models are available to the health assessor, but most are so difficult to use that health assessors rarely use them. To encourage their use these models need to have transparent and user-friendly formats. To this end the Agency for Toxic Substances and Disease Registry (ATSDR) is using translational research to increase PBPK model accessibility, understandability, and use in the site-specific health assessment arena. The agency has initiated development of a human PBPK tool-kit for certain high priority pollutants. The tool kit comprises a series of suitable models. The models are recoded in a single computer simulation language and evaluated for use by health assessors. While not necessarily being state-of-the-art code for each chemical, the models will be sufficiently accurate to use for screening purposes. This article presents a generic, seven-compartment PBPK model for six priority volatile organic compounds (VOCs): benzene (BEN), carbon tetrachloride (CCl(4)), dichloromethane (DCM), perchloroethylene (PCE), trichloroethylene (TCE), and vinyl chloride (VC). Limited comparisons of the generic and original model predictions to published kinetic data were conducted. A goodness of fit was determined by calculating the means of the sum of the squared differences (MSSDs) for simulation vs. experimental kinetic data using the generic and original models. Using simplified solvent exposure assumptions for oral ingestion and inhalation, steady-state blood concentrations of each solvent were simulated for exposures equivalent to the ATSDR Minimal Risk Levels (MRLs). The predicted blood levels were then compared to those reported in the National Health and Nutrition Examination Survey (NHANES). With the notable exception of BEN, simulations of combined oral and inhalation MRLs using our generic VOC model yielded blood concentrations well above those reported for the 95th percentile blood concentrations for the U.S. populations, suggesting no health concerns. When the PBPK tool kit is fully developed, risk assessors will have a readily accessible tool for evaluating human exposure to a variety of environmental pollutants.

Development of a human Physiologically Based Pharmacokinetic (PBPK) Toolkit for environmental pollutants

Physiologically Based Pharmacokinetic (PBPK) models can be used to determine the internal dose and strengthen exposure assessment. Many PBPK models are available, but they are not easily accessible for field use. The Agency for Toxic Substances and Disease Registry (ATSDR) has conducted translational research to develop a human PBPK model toolkit by recoding published PBPK models. This toolkit, when fully developed, will provide a platform that consists of a series of priority PBPK models of environmental pollutants. Presented here is work on recoded PBPK models for volatile organic compounds (VOCs) and metals. Good agreement was generally obtained between the original and the recoded models. This toolkit will be available for ATSDR scientists and public health assessors to perform simulations of exposures from contaminated environmental media at sites of concern and to help interpret biomonitoring data. It can be used as screening tools that can provide useful information for the protection of the public.

Chemical-specific screening criteria for interpretation of biomonitoring data for volatile organic compounds (VOCs)--application of steady-state PBPK model solutions

The National Health and Nutrition Examination Survey (NHANES) generates population-representative biomonitoring data for many chemicals including volatile organic compounds (VOCs) in blood. However, no health or risk-based screening values are available to evaluate these data from a health safety perspective or to use in prioritizing among chemicals for possible risk management actions. We gathered existing risk assessment-based chronic exposure reference values such as reference doses (RfDs), reference concentrations (RfCs), tolerable daily intakes (TDIs), cancer slope factors, etc. and key pharmacokinetic model parameters for 47 VOCs. Using steady-state solutions to a generic physiologically-based pharmacokinetic (PBPK) model structure, we estimated chemical-specific steady-state venous blood concentrations across chemicals associated with unit oral and inhalation exposure rates and with chronic exposure at the identified exposure reference values. The geometric means of the slopes relating modeled steady-state blood concentrations to steady-state exposure to a unit oral dose or unit inhalation concentration among 38 compounds with available pharmacokinetic parameters were 12.0 microg/L per mg/kg-d (geometric standard deviation [GSD] of 3.2) and 3.2 microg/L per mg/m(3) (GSD=1.7), respectively. Chemical-specific blood concentration screening values based on non-cancer reference values for both oral and inhalation exposure range from 0.0005 to 100 microg/L; blood concentrations associated with cancer risk-specific doses at the 1E-05 risk level ranged from 5E-06 to 6E-02 microg/L. The distribution of modeled steady-state blood concentrations associated with unit exposure levels across VOCs may provide a basis for estimating blood concentration screening values for VOCs that lack chemical-specific pharmacokinetic data. The screening blood concentrations presented here provide a tool for risk assessment-based evaluation of population biomonitoring data for VOCs and are most appropriately applied to central tendency estimates for such datasets.

Benzene risk estimation using radiation equivalent coefficients

We estimated benzene risk using a novel framework of risk assessment that employed the measurement of radiation dose equivalents to benzene metabolites and a PBPK model. The highest risks for 1 microg/m(3) and 3.2 mg/m(3) life time exposure of benzene estimated with a linear regression were 5.4 x 10(-7) and 1.3 x 10(-3), respectively. Even though these estimates were based on in vitro chromosome aberration test data, they were about one-sixth to one-fourteenth that from other studies and represent a fairly good estimate by using radiation equivalent coefficient as an "internal standard."

ATSDR evaluation of health effects of benzene and relevance to public health

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.

Whole body physiologically-based pharmacokinetic models: their use in clinical drug development

BACKGROUND

Whole-body physiologically-based pharmacokinetic (WB-PBPK) models mathematically describe an organism as a closed circulatory system consisting of compartments that represent the organs important for compound absorption, distribution, metabolism and elimination.

OBJECTIVES

To review the current state of WB-PBPK model use in the clinical phases of drug development.

METHODS

A qualitative description of the WB-PBPK model structure is included along with a review of the varying methods available for input parameterisation. Current and potential WB-PBPK model application in clinical development is discussed.

CONCLUSIONS

This modelling tool is at present used for small and large molecule drug development primarily as a means to scale pharmacokinetics from animals to humans based on physiology. The pharmaceutical industry is active in employing these models to clinical drug development although the applications in use now are narrow in comparison to the potential. Expanded integration of WB-PBPK models into the drug development process will only be achieved with staff training, managerial will, success stories and regulatory agency openness.

Physiologically-based pharmacokinetic modeling of benzene in humans: a Bayesian approach

Benzene is myelotoxic and leukemogenic in humans exposed at high doses (>1 ppm, more definitely above 10 ppm) for extended periods. However, leukemia risks at lower exposures are uncertain. Benzene occurs widely in the work environment and also indoor air, but mostly below 1 ppm, so assessing the leukemia risks at these low concentrations is important. Here, we describe a human physiologically-based pharmacokinetic (PBPK) model that quantifies tissue doses of benzene and its key metabolites, benzene oxide, phenol, and hydroquinone after inhalation and oral exposures. The model was integrated into a statistical framework that acknowledges sources of variation due to inherent intra- and interindividual variation, measurement error, and other data collection issues. A primary contribution of this work is the estimation of population distributions of key PBPK model parameters. We hypothesized that observed interindividual variability in the dosimetry of benzene and its metabolites resulted primarily from known or estimated variability in key metabolic parameters and that a statistical PBPK model that explicitly included variability in only those metabolic parameters would sufficiently describe the observed variability. We then identified parameter distributions for the PBPK model to characterize observed variability through the use of Markov chain Monte Carlo analysis applied to two data sets. The identified parameter distributions described most of the observed variability, but variability in physiological parameters such as organ weights may also be helpful to faithfully predict the observed human-population variability in benzene dosimetry.

Are there sex and gender differences in acute exposure to chemicals in the same setting?

We have little understanding of the influence that sex and gender may have on exposure to and measurement of occupational chemicals. If men and women are in the same physical environment, whether that be an occupational or an environmental setting, researchers need to question whether their acute exposure, as measured by administered and/or biologically effective dose, is the same. Not doing so may result in incorrect inferences being made about the risks associated with that exposure. Three critical questions arise specifically, do men and women differ in (1) their personal environments (immediate physical environments and personal attributes), (2) their absorption of the substance across the various biological barriers, and (3) the amount of active substance that reaches the target sites? Both contextual (e.g., smoking habits, diet, use of personal care products and jewellery, hobbies, stress, and use of medications) and biological (e.g., endocrine status) factors should be considered in answering these questions. Examples from the literature are provided to show that, depending on the chemical compound, there may be sex and gender differences in exposure to chemicals which can be manifested in sex differences in absorption, distribution, metabolism, storage, and excretion. An argument is developed to support the need to make information available, such as pharmacokinetic modeling studies in both men and women including appropriate age groups representing the spectrum of life stages and reproductive status.

Increased prevalence of primary biliary cirrhosis near Superfund toxic waste sites

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are uncommon liver diseases of unknown etiology. Reported clustering of PBC cases may be due to environmental factors. Individuals with PBC have a high prevalence of thyroid disease and thyroid disease is reportedly more prevalent near Superfund toxic waste sites (SFS). The objective of this study was to examine the prevalence and potential clustering of individuals with PBC and PSC near SFS. De-identified clinical and demographic data were used to determine the observed prevalence for each New York City zip code (n = 174) and borough (n = 5) of patients with PBC (PBC-OLT) or PSC (PSC-OLT) who were listed for liver transplantation. The expected prevalence was calculated using Organ Procurement and Transfer Network (OPTN) and U.S. Census data. Both PBC-OLT patients and patients not listed for liver transplantation (PBC-MSSM) were included in the cluster analysis. Prevalence ratios of PBC-OLT and PSC-OLT cases were compared for each zip code and for each borough with regard to the proximity or density of SFS, respectively. SaTScan software was used to identify clusters of PBC-OLT cases and PBC-MSSM cases. Prevalence ratio of PBC-OLT, not PSC-OLT, was significantly higher in zip codes containing or adjacent to SFS (1.225 vs. 0.670, respectively, P = .025). The borough of Staten Island had the highest prevalence ratio of PBC-OLT cases and density of SFS. Significant clusters of both PBC-OLT and PBC-MSSM were identified surrounding SFS. In conclusion, toxin exposure may be a risk factor influencing the clustering of PBC cases.

Biomarker Research in Occupational Health

OBJECTIVES

A variety of biomarkers have been used to study worker populations, and these studies have achieved different levels of success in the improvement of occupational health.

METHODS

Successful application of biomarker research is dependent upon several important factors: ability to identify hazardous substances from the exposure to a variety of substances, relevance to the development of disease, and usefulness for health risk assessment.

RESULTS

Besides the traditional biomarkers for exposure, biological effects, and health risk, new biomarkers for susceptibility and genome-wide responses are being used to improve our understanding of occupational health at a higher and, perhaps, more precise level.

CONCLUSIONS

In addition, there is a continued need to develop and apply biomarkers that can be used to provide real-time detection of excessive exposure to hazardous substances in the workplace, especially from unexpected fugitive emissions. These topics are discussed in the review.

Lymphohaematopoietic system cancer incidence in an urban area near a coke oven plant: an ecological investigation

AIMS

To evaluate the incidence risk of lymphohaematopoietic cancers for the 1986-94 period in Cornigliano, a district of Genoa (Italy), where a coke oven is located a few hundred metres from the residential area.

METHODS

The whole of Genoa and one of its 25 districts (Rivarolo) were selected as controls. The trend of risk around the coke oven was evaluated via Stone's method, while the geographic pattern of such risks across the Cornigliano district was evaluated by computing full Bayes estimates of standardised incidence ratio (FBE-SIR).

RESULTS

In males, elevated relative risks (RR) were observed for all lymphohaematopoietic cancers (RR 1.7 v Rivarolo and 1.6 v Genoa), for NHL (RR 2.4 v Rivarolo and 1.7 v Genoa), and for leukaemia (RR 2.4 v Rivarolo and 1.9 v Genoa). In females, statistically non-significant RR were observed. In males no excess of risk was found close to the coke oven. In females, a rising risk for NHL was observed approaching the plant, although statistical significance was not reached, while the risk for leukaemia was not evaluable due to the small number of cases. Analysis of the geographic pattern of risk suggested the presence of a cluster of NHL in both sexes in the eastern part of the district, where a foundry had been operational until the early 1980s. A cluster of leukaemia cases was observed in males in a northern part of the area, where no major sources of benzene seemed to be present.

CONCLUSIONS

The estimated risks seem to be slightly or not at all related to the distance from the coke oven. The statistically significant higher risks observed in males for NHL and leukaemia, and the clusters of leukaemia in males and of NHL in both sexes deserve further investigations in order to trace the exposures associated with such risks.

Metabolic polymorphisms and urinary biomarkers in subjects with low benzene exposure

The effect of some common metabolic polymorphisms on the rate of trans,trans-muconic acid (TMA) and S-phenylmercapturic acid (SPMA) excretion was investigated in 169 policemen exposed to low benzene levels (<10 microg/m3) during the work shift. End-shift urinary concentrations of TMA and SPMA, normalized to unmetabolized blood benzene concentration, were used as indicators of individual metabolic capacity. CYP2E1, NQO1, GSTM1, and CSTT1 polymorphisms were analyzed in all subjects by polymerase chain reaction (PCR) restriction fragment length (RFL). The results obtained show significantly elevated levels of TMA and SPMA in urine of smokers compared to nonsmokers, whereas no correlation with environmental benzene was observed. TMA/blood benzene ratio was partially modulated by glutathione S-transferase (GST) genotypes, with significantly higher values in null individuals (GSTM1 and GSTT1 combined). However, a greater fraction of total variance of TMA/blood benzene in the study population was explained by other independent variables, that is, season of sampling, smoking habits, and gender. Variance in SPMA/blood benzene ratio was only associated with smoking and occupation, whereas no significant role was observed for the metabolic polymorphisms considered. These results suggest that in a population exposed to very low benzene concentrations, urinary TMA and SPMA levels are affected to a limited extent by metabolic polymorphisms, whereas other factors, such as gender, lifestyle, or other confounders, may account for a larger fraction of the interindividual variability of these biomarkers.

Exposure to benzene in urban workers: environmental and biological monitoring of traffic police in Rome

OBJECTIVES

To evaluate the contribution of traffic fumes to exposure to benzene in urban workers, an investigation on personal exposure to benzene in traffic police from the city of Rome was carried out.

METHODS

The study was performed from December 1998 to June 1999. Diffusive Radiello personal samplers were used to measure external exposures to benzene and alkyl benzenes during the workshift in 139 policemen who controlled medium to high traffic areas and in 63 office police. Moreover, as biomarkers of internal exposure to benzene, blood benzene, and urinary trans, trans-muconic and S-phenyl mercapturic acids were measured at the beginning and at the end of the workshift in 124 traffic police and 58 office police.

RESULTS

Time weighted average (TWA) exposure to benzene was consistently higher among traffic police than among indoor workers (geometric mean 6.8 and 3.5 microg/m(3), respectively). Among the traffic police, the distribution of individual exposures was highly asymmetric, skewed toward higher values. Mean ambient benzene concentrations measured by municipal air monitoring stations during workshifts of traffic police were generally higher (geometric mean 12.6 microg/m(3)) and did not correlat with personal exposure values. In particular, no association was found between highest personal exposure scores and environmental benzene concentrations. Among the exposure biomarkers investigated, only blood benzene correlated slightly with on-shift exposure to benzene, but significant increases in both urinary trans, trans-muconic and S-phenylmercapturic acids were found in active smokers compared with non-smokers, irrespective of their job.

CONCLUSION

The exposure to traffic fumes during working activities in medium to high traffic areas in Rome may give a relatively greater contribution to personal exposure to benzene than indoor sources present in confined environments. Smoking significantly contributed to internal exposure to benzene in both indoor and outdoor workers.

Environmental and biological monitoring of benzene during self-service automobile refueling

Although automobile refueling represents the major source of benzene exposure among the nonsmoking public, few data are available regarding such exposures and the associated uptake of benzene. We repeatedly measured benzene exposure and uptake (via benzene in exhaled breath) among 39 self-service customers using self-administered monitoring, a technique rarely used to obtain measurements from the general public (130 sets of measurements were obtained). Benzene exposures averaged 2.9 mg/m(3) (SD = 5.8 mg/m(3); median duration = 3 min) with a range of < 0.076-36 mg/m(3), and postexposure breath levels averaged 160 microg/m(3) (SD = 260 microg/m(3)) with a range of < 3.2-1,400 microg/m(3). Log-transformed exposures and breath levels were significantly correlated (r = 0.77, p < 0.0001). We used mixed-effects statistical models to gauge the relative influences of environmental and subject-specific factors on benzene exposure and breath levels and to investigate the importance of various covariates obtained by questionnaire. Model fitting yielded three significant predictors of benzene exposure, namely, fuel octane grade (p = 0.0011), duration of exposure (p = 0.0054), and season of the year (p = 0.032). Likewise, another model yielded three significant predictors of benzene concentration in breath, specifically, benzene exposure (p = 0.0001), preexposure breath concentration (p = 0.0008), and duration of exposure (p = 0.038). Variability in benzene concentrations was remarkable, with 95% of the estimated values falling within a 274-fold range, and was comprised entirely of the within-person component of variance (representing exposures of the same subject at different times of refueling). The corresponding range for benzene concentrations in breath was 41-fold and was comprised primarily of the within-person variance component (74% of the total variance). Our results indicate that environmental rather than interindividual differences are primarily responsible for benzene exposure and uptake during automobile refueling. The study also demonstrates that self-administered monitoring can be efficiently used to measure environmental exposures and biomarkers among the general public.

Benzene and non-Hodgkin's lymphoma

Incidence rates for non-Hodgkin's lymphoma (NHL) have been rising throughout the world for several decades, and no convincing explanation exists for the majority of this increase. The commonest subtypes of NHL have no well-defined aetiological factors but lymphoma development has been linked with exposure to a variety of chemicals, including nitrates, pesticides, herbicides, and solvents. Benzene, a solvent and important constituent of petrochemical products, is a potent lymphomagen in experimental animals and high-dose exposure in humans is associated with both acute myeloid leukaemia and NHL. Much current interest centres on the possibility that environmental benzene exposure in the general public may underlie a proportion of the increase in NHL. Seventy per cent of benzene exposure in the environment is derived from vehicle exhaust emissions, whose increase has closely paralleled the rise in frequency of the disease. Mathematical modelling has been used to calculate an acceptable concentration of benzene in air based on risk estimates derived from industrial exposure, but the recommended target concentration in the U.K. of 1 ppb is regularly exceeded in urban locations. Detailed investigation of the health effects of low-level benzene exposure awaits an accurate assay for quantifying long-term human exposure. The (32)P post-labelling technique for the detection of toxin-specific DNA adducts is extremely sensitive and has been applied in the biomonitoring of exposure to a number of carcinogens, but benzene-DNA adducts have to date proved elusive of detection.