Reflections on the OECD guidelines for in vitro skin absorption studies.

At the 8th conference of Occupational and Environmental Exposure of the Skin to Chemicals (OEESC) (16-18 September 2019) in Dublin, Ireland, several researchers performing skin permeation assays convened to discuss in vitro skin permeability experiments. We, along with other colleagues, all of us hands-on skin permeation researchers, present here the results from our discussions on the available OECD guidelines. The discussions were especially focused on three OECD skin absorption documents, including a recent revision of one: i) OECD Guidance Document 28 (GD28) for the conduct of skin absorption studies (OECD, 2004), ii) Test Guideline 428 (TGD428) for measuring skin absorption of chemical in vitro (OECD, 2004), and iii) OECD Guidance Notes 156 (GN156) on dermal absorption issued in 2011 (OECD, 2011). GN156 (OECD, 2019) is currently under review but not finalized. A mutual concern was that these guidance documents do not comprehensively address methodological issues or the performance of the test, which might be partially due to the years needed to finalize and update OECD documents with new skin research evidence. Here, we summarize the numerous factors that can influence skin permeation and its measurement, and where guidance on several of these are omitted and often not discussed in published articles. We propose several improvements of these guidelines, which would contribute in harmonizing future in vitro skin permeation experiments.

Washout kinetics of ethanol from the airways following inhalation of ethanol vapors and use of mouthwash.

Introduction: Breath analyzers are commonly used to test for alcohol intoxication, i.e., elevated systemic levels of ethanol, at workplaces and among vehicle drivers. However, local low-dose exposure to ethanol in the mouth or airways may temporarily increase the breath-alcohol concentration (BrAC) without the systemic ethanol level being affected, leading to false positive test results. The aim of this study was to assess the impact of local ethanol exposure on the BrAC.Methods: Eleven healthy adults (six women) were exposed to on average 856 mg/m3 ethanol vapor for 15 min, followed by repeat collection of exhaled breath in Tedlar bags. One hour later, the subjects washed their mouth for 30 s with a typical mouthwash containing 22% ethanol and post-exposure breaths were again collected repeatedly. Negligible systemic uptake of ethanol was confirmed by analysis of blood sampled before, between and after the exposures. Ethanol in breath and blood was analyzed by gas chromatography.Results: No or very low levels (less than 0.002 mg/g) of ethanol were detected in blood at any time point, indicating negligible systemic uptake. The decline in breath was mono-exponential after both exposures with average half times of 0.4 (range 0.3-0.8) min after inhalation exposure and 1.9 (1.1-3.0) min after mouthwash. BrAC levels in the first sample, collected a few seconds after exposure, were 0.14 (0.07-0.13) mg/L after inhalation and 4.4 (2.7-6.0) mg/L after mouth wash. On average, it took 0.5 (0.06-0.7) min and 11 (6-15) min, respectively, for the BrAC to fall below the Swedish statutory limit of 0.1 mg/L air.Conclusion: In practice, use of breath analysis should not be a problem even if the subject inhaled ethanol vapors before the test. In contrast, use of ethanol-containing mouthwash results in a false positive test if sampling is done within 15 min.

Chloroanisoles may explain mold odor and represent a major indoor environment problem in Sweden.

Indoor mold odor is associated with adverse health effects, but the microbial volatiles underlying mold odor are poorly described. Here, chloroanisoles were studied as potential key players, being formed by microbial metabolism of chlorophenols in wood preservatives. Using a three-stage approach, we (i) investigated the occurrence of chloroanisoles in buildings with indoor air quality problems, (ii) estimated their frequency in Sweden, and (iii) evaluated the toxicological risk of observed chloroanisole concentrations. Analyses of 499 building materials revealed several chloroanisole congeners in various types of buildings from the 1950s to 1970s. Evaluation of Swedish records from this time period revealed three coinciding factors, namely an unprecedented nationwide building boom, national regulations promoting wood preservatives instead of moisture prevention, and use of chlorophenols in these preservatives. Chlorophenols were banned in 1978, yet analysis of 457 indoor air samples revealed several chloroanisole congeners, but at median air levels generally below 15 ng/m(3) . Our toxicological evaluation suggests that these concentrations are not detrimental to human health per se, but sufficiently high to cause malodor. Thereby, one may speculate that chloroanisoles in buildings contribute to adverse health effects by evoking odor which, enhanced by belief of the exposure being hazardous, induces stress-related and inflammatory symptoms.

The Global Landscape of Occupational Exposure Limits--Implementation of Harmonization Principles to Guide Limit Selection.

Occupational exposure limits (OELs) serve as health-based benchmarks against which measured or estimated workplace exposures can be compared. In the years since the introduction of OELs to public health practice, both developed and developing countries have established processes for deriving, setting, and using OELs to protect workers exposed to hazardous chemicals. These processes vary widely, however, and have thus resulted in a confusing international landscape for identifying and applying such limits in workplaces. The occupational hygienist will encounter significant overlap in coverage among organizations for many chemicals, while other important chemicals have OELs developed by few, if any, organizations. Where multiple organizations have published an OEL, the derived value often varies considerably-reflecting differences in both risk policy and risk assessment methodology as well as access to available pertinent data. This article explores the underlying reasons for variability in OELs, and recommends the harmonization of risk-based methods used by OEL-deriving organizations. A framework is also proposed for the identification and systematic evaluation of OEL resources, which occupational hygienists can use to support risk characterization and risk management decisions in situations where multiple potentially relevant OELs exist.

Neurobehavioral performance in volunteers after inhalation of white spirits with high and low aromatic content.

The content of aromatic hydrocarbons in solvent mixtures, such as white spirits (WS), has been assumed a major contributor to the neurotoxic effects of these compounds. Hence, dearomatized WS have been introduced to the market rapidly in the last decade. Studies investigating other aromatic hydrocarbons (toluene) and animal models have supported the aforementioned assumption, but the current study is the first one to compare acute neurobehavioral effects of exposure to aromatic and dearomatized WS (aWS, daWS) content in human volunteers at current occupational exposure limit values. In a pseudo-randomized crossover design, six female and six male healthy volunteers were exposed to aWS and daWS at two concentrations (100 and 300 mg/m(3)) and to clean air for 4 h at rest. During each of the five exposure conditions, volunteers performed five neurobehavioral tasks that were selected following a multidisciplinary approach that accounted for findings from the cognitive neurosciences and mechanisms of solvent toxicity. Two of the tasks indicated performance changes during aromatic WS exposure, the working memory (WM) and the response shifting task, but both effects are difficult to interpret due to low mean accuracy in the WM task and due to a lack of dose-response relationship in the response shifting task. Healthy human volunteers showed weak and inconsistent neurobehavioral impairment after 4-h exposures to 100 and 300 mg/m(3) aromatic or dearomatized WS. Our multidisciplinary approach of selecting neurobehavioral test methods may guide the test selection strategies in future studies.

Acute effects of exposure to vapors of 3-methyl-1-butanol in humans.

UNLABELLED: The secondary alcohol 3-methyl-1-butanol (3MB, isoamyl alcohol) is used, for example, as a solvent in a variety of applications and as a fragrance ingredient. It is also one of the microbial volatile organic compounds (MVOCs) found in indoor air. There are little data on acute effects. The aim of the study was to assess the acute effects of 3MB in humans. Thirty healthy volunteers (16 men and 14 women) were exposed in random order to 1 mg/m(3) 3MB or clean air for 2 h at controlled conditions. Ratings with visual analogue scales revealed slightly increased perceptions of eye irritation (P = 0.048, Wilcoxon) and smell (P < 0.0001) compared with control exposure. The other ratings were not significantly affected (irritation in nose and throat, dyspnea, headache, fatigue, dizziness, nausea, and intoxication). No significant exposure-related effects were found in blinking frequency, tear film break-up time, vital staining of the eye, nasal lavage biomarkers, lung function, and nasal swelling. In conclusion, this study suggests that 3MB is not a causative factor for health effects in damp and moldy buildings. PRACTICAL IMPLICATIONS: 3-Methyl-1-butanol (3MB) is one of the most commonly reported MVOCs in damp and moldy buildings and in occupational settings related to agriculture and composting. Our study revealed no irritation effects at 1 mg/m3, a concentration higher than typically found in damp and moldy buildings. Our study thus suggests that 3MB is not a causative factor for health effects in damp and moldy buildings.

Acute effects of exposure to 1 mg/m(3) of vaporized 2-ethyl-1-hexanol in humans.

The objective was to assess acute effects from controlled exposure of volunteers to 2-ethyl-1-hexanol, a volatile organic compound that is often found in indoor air. Sixteen males and fourteen females were in random order exposed to 1 mg/m(3) of vapors of 2-ethyl-1-hexanol or to clean air (control exposure) in an exposure chamber during 2 h at rest. The subjects performed symptom ratings on Visual Analog Scales. During exposure to 2-ethyl-1-hexanol subjective ratings of smell and eye discomfort were minimally but significantly increased. Ratings of nasal irritation, throat irritation, headache, dyspnoea, fatigue, dizziness, nausea, and intoxication were not significantly affected. No exposure-related effects on measurement of blinking frequency by electromyography, measurement of the eye break-up time, vital staining of the eye, nasal lavage biomarkers, transfer tests, spirometric and rhinometric measures were seen. No differences in response were seen between sexes or between atopics and non-atopics. Practical Implications It is important to assess acute effects in volatile organic compounds like 2-ethyl-1-hexanol. 2-ethyl-1-hexanol is often found in indoor air generated by degradation of plastic building materials or in new buildings. There are associations between 2-ethyl-1-hexanol in indoor air and respiratory effects, eye irritation, headache, and blurred vision. A controlled chamber exposure study in acute effects was performed. In conclusion, this study showed weak subjective symptom of irritation in the eyes.

The 2008 ICOH Workshop on Skin Notation.

BACKGROUND: On 29 March 2008 the International Commission on Occupational Health (ICOH) Scientific Committee on Occupational and Environmental Dermatoses organized a Skin Notation Workshop hosted by the 11th International Percutaneous Penetration Perspectives Conference (La Grande Motte, France). Skin notation (S) was chosen as a topic for discussion because this is the only example of existing regulation in the field of dermal risk assessment. The issue was discussed in a previous workshop held in Siena, Italy in 2006 with the objective of focussing on the problems related to S, the different assignment criteria and the attempts to improve the S system made by various international and governmental agencies. A position paper was subsequently published. OBJECTIVES: The workshop in France was a continuation of this activity with the aim of evaluating how the different strategies can improve S. METHODS AND DISCUSSION: The Workshop was divided into two sessions. The first was dedicated to lectures focused on different aspects of S. In the second session participants discussed key issues with the aim of exploring the actions needed to improve international S. systems.

Acute effects of exposure to vapours of dioxane in humans.

Information on the acute effects associated with the handling of 1,4-dioxane is sparse. Our aim was to evaluate the acute effects of 1,4-dioxane vapours. In a screening study, six healthy volunteers rated symptoms on a visual analogue scale (VAS), while exposed to stepwise increasing levels of 1,4-dioxane, from 1 to 20 ppm. The initial study indicated no increased ratings at any of the exposure levels; we decided to use 20 ppm (72 mg/m3) as a tentative no observed adverse effect level (NOAEL). In the main study, six female and six male healthy volunteers were exposed to 0 (control exposure) and 20 ppm 1,4-dioxane vapour, for 2 hours at rest. The volunteers rated 10 symptoms on VAS before, during, and after the exposure. Blink frequency was monitored during exposure. Pulmonary function, and nasal swelling, was measured before, and at 0 and 3 hours after exposure. Inflammatory markers in plasma (C-reactive protein, and interleukin-6) were measured before and at 3 hours after exposure. In conclusion, exposure to 20 ppm 1,4-dioxane for 2 hours did not significantly affect symptom ratings, blink frequency, pulmonary function, nasal swelling, or inflammatory markers in the plasma of the 12 volunteers in our study.

Are women more sensitive than men to 2-propanol and m-xylene vapours?

AIMS: To evaluate possible differences between men and women in acute health effects after controlled short term chamber exposure to vapours of two common organic solvents. METHODS: Fifty six healthy volunteers (28 per sex) were exposed to 150 ppm 2-propanol, 50 ppm m-xylene, and clean air for two hours at rest. The subjects rated symptoms on a visual analogue scale before, during, and after the exposure. Blinking frequency was measured continuously during exposure. Pulmonary function, nasal swelling, inflammatory markers (lysozyme, eosinophilic cationic protein, myeloperoxidase, albumin) in nasal lavage and colour vision (Lanthony D-15 desaturated panel) were measured before and at 0 and 3 hours after the exposure. RESULTS: There were no significant sex differences in response to solvent exposure with respect to blinking frequency, lung diffusing capacity, nasal area and volume, inflammatory markers in nasal lavage, and colour vision. Increased symptoms were rated by both sexes for nearly all 10 questions during exposure to 2-propanol or m-xylene, most increases being significant at one time point at least. The rating of "discomfort in the throat or airways" increased more in women during exposure to 2-propanol or m-xylene. During exposure to 2-propanol the rating of "fatigue" was more increased in men after one hour, but more increased in women after two hours of exposure. With regard to pulmonary function, women had small but significant decreases in FVC, FEV(1)/FVC, and FEF(75) three hours after exposure to m-xylene, but only the decrease in FVC was significantly different from that in men. CONCLUSION: Our results suggest that women are slightly more sensitive than men to the acute irritative effects of 2-propanol and m-xylene vapours.

Procedures for health risk assessment in Europe.

This report compares cancer classification systems, health risk assessment approaches, and procedures used for establishing occupational exposure limits (OELs), in various European countries and scientific organizations. The objectives were to highlight and compare key aspects of these processes and to identify the basis for differences in cancer classifications and OELs between various scientific organizations and countries. Differences in cancer classification exist in part due to differences in the ultimate purpose of classification and to the relative importance of different types of data (i.e., animal vs human data, mechanistic data, and data from benign vs malignant tumors). In general, the groups surveyed tend to agree on classification of chemicals with good evidence of carcinogenicity in humans, and agree less on classification of chemicals with positive evidence in animals and inadequate or limited evidence in humans. Most entities surveyed distinguish between genotoxic and nongenotoxic chemicals when conducting risk assessments. Although the risk assessment approach used for nongenotoxic chemicals is fairly similar among groups, risk assessment approaches for genotoxic carcinogens vary widely. In addition to risk assessment approaches, other factors which can affect OELs include selection of the critical effect, use of health-based vs technology-based exposure limits, and consideration of technological feasibility and socioeconomic factors.

Development and validation of the Theoretical Orientation Scale for Clinicians: reflecting solution-focused principles.

This article describes the development and validation of the 40-item Theoretical Orientation Scale for Clinicians (TOSCsF), an instrument designed to (a) operationalize attitudes towards the principles of solution-focused brief therapy (SFBT), and (b) assess clinicians' endorsement of this therapeutic approach. Participants (N=284) were members of the National Association of Alcoholism and Drug Abuse Counselors (NAADAC) who responded (63%) to a mail questionnaire containing the TOSCsF. Reliability (Cronbach's alpha = .82) and validity of scores on the TOSCsF are examined in light of the detection of an acquiescent response pattern in 40 respondents. A subsequent three-factor structure derived from a principal components analysis (accounting for 28% of the variance) suggests modest, but positive, support for the construct validity of the TOSCsF. Recommendations for further refinement of the instrument are discussed.

Assessing the reliability of PBPK models using data from methyl chloride-exposed, non-conjugating human subjects.

Physiologically based pharmacokinetic (PBPK) models are often optimized by adjusting metabolic parameters so as to fit experimental toxicokinetic data. The estimates of the metabolic parameters are then conditional on the assumed values for all other parameters. Meanwhile, the reliability of other parameters, or the structural model, is usually not questioned. Inhalation exposures with human volunteers in our laboratory show that non-conjugators lack metabolic capacity for methyl chloride entirely, and that elimination in these subjects takes place via exhalation only. Therefore, data from these methyl chloride exposures provide an excellent opportunity to assess the general reliability of standard inhalation PBPK models for humans. A hierarchical population PBPK model for methyl chloride was developed. The model was fit to the experimental data in a Bayesian framework using Markov chain Monte Carlo (MCMC) simulation. In a Bayesian analysis, it is possible to merge a priori knowledge of the physiological, anatomical and physicochemical parameters with the information embedded in the experimental toxicokinetic data obtained in vivo. The resulting estimates are both statistically and physiologically plausible. Model deviations suggest that a pulmonary sub-compartment may be needed in order to describe the inhalation and exhalation of volatile adequately. The results also indicate that there may be significant intra-individual variability in the model parameters. To our knowledge, this is the first time that the toxicokinetics of a non-metabolized chemical is used to assess population PBPK parameters. This approach holds promise for more elaborate experiments in order to assess the reliability of PBPK models in general.

A Bayesian analysis of the influence of GSTT1 polymorphism on the cancer risk estimate for dichloromethane.

The carcinogenicity of dichloromethane (DCM) is related to metabolic activation mediated by glutathione transferase theta 1 (GSTT1), whereas oxidation serves as a detoxification pathway. The aim of this study was to calculate the excess cancer risk from DCM, using Bayesian statistics. In a first step, a previously developed population physiologically based pharmacokinetic (PBPK) model for DCM was simultaneously fitted to extensive human toxicokinetic data from 27 male volunteers exposed to 250-1000 ppm DCM (Astrand et al. Scand. J. Work Environ. Health 1, 78-94, 1975; Engström and Bjurström, Scand. J. Work Environ. Health 7, 215-224, 1977) using Markov chain Monte Carlo simulation. Improved population estimates were obtained for the PBPK model parameters. In a second step, excess cancer risk was calculated for lifelong exposure to 1-1000 ppm DCM by Monte Carlo simulation. Data on GSTT1 gene frequencies in the Swedish population were used, including all three genotypes. Estimated mean and median excess risks were in general agreement with those previously derived (El-Masri et al. Toxicol. Appl. Pharmacol. 158, 221-230, 1999). However, we estimate higher excess risks at the upper confidence limits. Furthermore, our simulations suggest that 1% of the Swedish population is not covered by a factor 4.2-7.1 away from the mean target dose. The majority of the fraction of the population not covered was classified as GSTT1 homozygote. This indicates that a higher uncertainty factor than the commonly used 3.16 should be considered in noncancer risk assessment for substances with polymorphic bioactivation.

Acute health effects common during graffiti removal.

OBJECTIVE: The aim of this study was to identify possible health effects caused by different cleaning agents used in graffiti removal. METHODS: In 38 graffiti removers working 8-h shifts in the Stockholm underground system, the exposure to organic solvents was assessed by active air sampling, biological monitoring, and by interviews and a questionnaire. Health effects were registered, by physical examinations, porta7ble spirometers and self-administered questionnaires. The prevalence of symptoms was compared with 49 controls working at the underground depots, and with 177 population controls. RESULTS: The 8-h time-weighted average exposures (TWA) were low, below 20% of the Swedish permissible exposure limit value (PEL) for all solvents. The short-term exposures occasionally exceeded the Swedish short-term exposure limit values (STEL), especially during work in poorly ventilated spaces, e.g. in elevators. The graffiti removers reported significantly higher prevalence of tiredness and upper airway symptoms compared with the depot controls, and significantly more tiredness, headaches and symptoms affecting airways, eyes and skin than the population controls. Among the graffiti removers, some of the symptoms increased during the working day. On a group basis, the lung function registrations showed normal values. However, seven workers displayed a clear reduction of peak expiratory flow (PEF) over the working shift. CONCLUSIONS: Though their average exposure to organic solvents was low, the graffiti removers reported significantly higher prevalence of unspecific symptoms such as fatigue and headache as well as irritative symptoms from the eyes and respiratory tract, compared with the controls. To prevent adverse health effects it is important to inform the workers about the health risks, and to restrict use of the most hazardous chemicals. Furthermore, it is important to develop good working practices and to encourage the use of personal protective equipment.

Physiologically based pharmacokinetic modeling of inhalation exposure of humans to dichloromethane during moderate to heavy exercise.

Dichloromethane (methylene chloride, DCM) is metabolized via two pathways in humans: mixed-function oxidases (MFO) and glutathione-S:-transferase (GST). Most likely, the carcinogenicity for DCM is related to metabolic activation of DCM via the GST pathway. However, as the two pathways are competing, the metabolic capacity for the MFO pathway in vivo is also of interest in risk assessment for DCM. Past estimates of MFO metabolism are based on the in vitro activity of tissue samples. The aim of the present study was to develop a population model for DCM in order to gain more knowledge on the variability of DCM inhalation toxicokinetics in humans, with main emphasis on the MFO metabolic pathway. This was done by merging published in vitro data on DCM metabolism and partitioning with inhalation toxicokinetic data (Astrand et al., 1975, Scand. J. Work.Environ. Health 1, 78-94) from five human volunteers, using the MCMC technique within a population PBPK model. Our results indicate that the metabolic capacity for the MFO pathway in humans is slightly larger than previously estimated from four human liver samples. Furthermore, the interindividual variability of the MFO pathway in vivo is smaller among our five subjects than indicated by the in vitro samples. We also derive a Bayesian estimate of the population distribution of the MFO metabolism (median maximum metabolic rate 28, 95% confidence interval 12-66 micromol/min) that is a compromise between the information from the in vitro data and the toxicokinetic information present in the experimental data.

Bayesian estimation of variability in adipose tissue blood flow in man by physiologically based pharmacokinetic modeling of inhalation exposure to toluene.

Due to the lipophilicity of many xenobiotics, the perfusion of fat tissue is of special interest in physiologically based pharmacokinetic (PBPK) modeling. In order to estimate inter- and intra-individual variability in fat tissue blood flow with exercise, a population PBPK model for toluene was fitted to experimental data from subjects exposed to toluene vapors (Carlsson, A., 1982. Exposure to toluene: uptake, distribution and elimination in man. Scand. J. Work Environ. Health 8, 43-55). Six male volunteers were exposed to 80 ppm toluene for two hours during rest and moderate to heavy exercise (50-150 W). Extensive data collection was made, including sampling of arterial blood, exhaled breath and subcutaneous fat tissue. The model was simultaneously fitted to the time courses of toluene in arterial blood, exhaled breath, and subcutaneous fat in the six individuals by Markov chain Monte Carlo (MCMC) simulation. In order to describe the experimental observations in subcutaneous fat accurately, the fat compartment was split in two. According to the analysis, the increased perfusion of perirenal fat associated with physical workload was best described if it was set to the same, elevated, level during all exercise levels, rather than scaled directly to the increase in oxygen uptake. No increase in subcutaneous fat perfusion could be detected at these exposure conditions.

Air and biological monitoring of solvent exposure during graffiti removal.

OBJECTIVE: The principal aim of the study was to estimate the level of exposure to organic solvents of graffiti removers, and to identify the chemicals used in different cleaning agents. A secondary objective was to inform about the toxicity of various products and to optimise working procedures. METHODS: Exposure to organic solvents was determined by active air sampling and biological monitoring among 38 graffiti removers during an 8-h work shift in the Stockholm underground system. The air samples and biological samples were analysed by gas chromatography. Exposure to organic solvents was also assessed by a questionnaire and interviews. RESULTS: Solvents identified were N-methylpyrrolidone (NMP), dipropylene glycol monomethyl ether (DPGME), propylene glycol monomethyl ether (PGME), diethylene glycol monoethyl ether (DEGEE), toluene, xylene, pseudocumene, hemimellitine, mesitylene, ethylbenzene, limonene, nonane, decane, undecane, hexandecane and gamma-butyrolactone. The 8-h average exposures [time-weighted average (TWA)] were below 20% of the Swedish permissible exposure limit value (PEL) for all solvents identified. In poorly ventilated spaces, e.g. in elevators etc., the short-term exposures exceeded occasionally the Swedish short-term exposure limit values (STEL). The blood and urine concentrations of NMP and its metabolites were low. Glycol ethers and their metabolites (2-methoxypropionic acid (MPA), ethoxy acetic acid (EAA), butoxy acetic acid (BAA), and 2-(2-methoxyethoxy) acetic acid (MEAA)) were found in low concentrations in urine. There were significant correlation between the concentrations of NMP in air and levels of NMP and its metabolites in blood and urine. The use of personal protective equipment, i.e. gloves and respirators, was generally high. CONCLUSIONS: Many different cleaning agents were used. The average exposure to solvents was low, but some working tasks included relatively high short-term exposure. To prevent adverse health effects, it is important to inform workers about the health risks and to restrict the use of the most toxic chemicals. Furthermore, it is important to develop good working procedures and to encourage the use of personal protection equipment.

Glutathione transferase T1 phenotype affects the toxicokinetics of inhaled methyl chloride in human volunteers.

The aim of the present study was to investigate how the genetic polymorphism in glutathione transferase T1 (GSTT1) affects the metabolism and disposition of methyl chloride in humans in vivo. The 24 volunteers (13 males and 11 females) who participated in the study were recruited from a group of 208 individuals previously phenotyped for GSTT1 by measuring the glutathione transferase activity with methyl chloride in lysed erythrocytes ex vivo. Eight individuals with high (+/+), eight with medium (+/0) and eight with no (0/0) GSTT1 activity were exposed to methyl chloride gas (10 p.p.m.) in an exposure chamber for 2 h. Uptake and disposition was studied by measuring the concentration of methyl chloride in inhaled air, exhaled air and blood. A two-compartment model with two elimination pathways corresponding to exhalation and metabolism was fitted to experimental data. The average net respiratory uptake of methyl chloride was 243, 158, and 44 micromol in individuals with high, intermediate and no GSTT1 activity, respectively. Metabolic clearance was high (4.6 l/min) in the +/+ group, intermediate (2.4 l/min) in the +/0 group, and close to zero in 0/0 individuals, while the exhalation clearance was similar in the three groups. No exposure related increase in urinary S-methyl cysteine was detected. However, gender and the GSTTl phenotype seemed to affect the background levels. In conclusion, GSTT1 appears to be the sole determinant of methyl chloride metabolism in humans. Thus, individuals with nonfunctional GSTT1 entirely lack the capacity to metabolize methyl chloride.

Styrene oxide in blood, hemoglobin adducts, and urinary metabolites in human volunteers exposed to (13)C(8)-styrene vapors.

Styrene is used in the manufacture of plastics and polymers and in the boat-building industry. The major metabolic route for styrene in rats, mice, and humans involves conversion to styrene-7,8-oxide (SO). The purpose of this study was to evaluate blood SO, SO-hemoglobin (SO-Hb) adducts, and urinary metabolites in styrene-exposed human volunteers and to compare these results with data previously obtained for rodents. Four healthy male volunteers were exposed for 2 h during light physical exercise to 50 ppm (13)C(8)-styrene vapor via a face mask. Levels and time profiles of styrene in exhaled air, blood, and urine (analyzed by GC) and urinary excretion patterns of mandelic acid and phenylglyoxylic acid in urine (analyzed by HPLC) were comparable to previously published volunteer studies. Maximum levels of SO in blood (measured by GC-MS) of 2.5-12.2 (average 6.7) nM were seen after 2 h, i.e., in the first sample collected after exposure had ended. The styrene blood level in humans was about 1.5 to 2 times higher than in rats and 4 times higher than in mice for equivalent styrene exposures. In contrast the SO levels in human blood was approximately fourfold lower than in mice. The level of hydroxyphenethylvaline (determined by GC-MS-MS) in pooled blood collected after exposure was estimated as 0.3 pmol/g globin corresponding to a SO-Hb adduct increment of about 0.003 pmol/g and ppmh. NMR analyses of urine showed that a major portion (> 95%) of the excreted (13)C-derived metabolites was derived from hydrolysis of SO, while only a small percentage of the excreted metabolites (< 5%) was derived from metabolism via phenylacetaldehyde. Signals consistent with metabolites derived from other pathways of styrene metabolism in rodents (such as glutathione conjugation with SO or ring epoxidation) were not detected.