Benzene Concentrations In Air Research Articles

Assessment of the correlation between exposure to benzene and urinary excretion of t, t-muconic acid in workers from a petrochemical plant.

The investigation covered 148 workers from three plants with different levels of benzene exposure. The aim of the study was to assess the correlation between workers' personal exposure and urinary excretion of t, t-muconic acid (TTMA). The personal exposure to benzene was measured by the sampling of the workplace air on sorbent tubes with active charcoal followed by elution with carbon disulphide and gas chromatographic determination. The individual internal exposure was assessed by determination of TTMA in urine by a liquid chromatographic method. The urine samples were collected at the beginning (t(0)) and end (t(1)) of the work shift. The individual whole-shift concentrations of benzene in workplace air in the three studied facilities varied from 0.1 to 67.53 mg/m(3). The concentration of TTMA at the beginning of the shift (t(0)) was from 0.02 to 2.53 mg/l and at the end of the shift (t(1)) was from 0.02 to 9.96 mg/l. Significant correlation was found between benzene level in workplace air and TTMA concentration in urine at the end of the work shift, with a correlation coefficient r=0.425 ( P=0.01). The analysis of the obtained results shows that TTMA can be used as a biological indicator for benzene exposure. The registered single cases of workers with unexpectedly high results for t, t-muconic acid are explained by their consumption of canned foods containing sorbic acid as a preservative. The subjects involved in similar studies should be advised not to consume canned foods 12 h before the examination.

Use of expert judgment in exposure assessment. Part I. Characterization of personal exposure to benzene.

This paper presents the results of the first phase of a study, conducted as an element of the National Human Exposure Assessment Survey (NHEXAS), to demonstrate the use of expert subjective judgment elicitation techniques to characterize the magnitude of and uncertainty in environmental exposure to benzene. In decisions about the value of exposure research or of regulatory controls, the characterization of uncertainty can play an influential role. Classical methods for characterizing uncertainty may be sufficient when adequate amounts of relevant data are available. Frequently, however, data are neither abundant nor directly relevant, making it necessary to rely to varying degrees on subjective judgment. Since the 1950s, methods to elicit and quantify subjective judgments have been explored but have rarely been applied to the field of environmental exposure assessment. In this phase of the project, seven experts in benzene exposure assessment were selected through a peer nomination process, participated in a 2-day workshop, and were interviewed individually to elicit their judgments about the distributions of residential ambient, residential indoor, and personal air benzene concentrations (6-day integrated average) experienced by both the non-smoking, non-occupationally exposed target and study populations of the US EPA Region V pilot study. Specifically, each expert was asked to characterize, in probabilistic form, the arithmetic means and the 90th percentiles of these distributions. This paper presents the experts' judgments about the concentrations of benzene encountered by the target population. The experts' judgments about levels of benzene in personal air were demonstrative of patterns observed in the judgments about the other distributions. They were in closest agreement about their predictions of the mean; with one exception, their best estimates of the mean fell within 7-11 microg/m(3) although they exhibited striking differences in the degree of uncertainty expressed. Their estimates of the 90th percentile were more varied with the best estimates ranging from 12 to 26 microg/m(3) for all but one expert. However, their predictions of the 90th percentile were far more uncertain. The paper demonstrates that coherent subjective judgments can be elicited from exposure assessment scientists and critically examines the challenges and potential benefits of a subjective judgment approach. The results of the second phase of the project, in which measurements from the NHEXAS field study in Region V are used to calibrate the experts' judgments about the benzene exposures in the study population, will be presented in a second paper.

Reductions in human benzene exposure in the California South Coast Air Basin

Benzene typically contributes a significant fraction of the human cancer risk associated with exposure to urban air pollutants. In recent years, concentrations of benzene in ambient air have declined in many urban areas due to the use of reformulated gasolines, lower vehicle emissions, and other control measures. In the California South Coast Air Basin (SoCAB) ambient benzene concentrations have been reduced by more than 70% since 1989. To estimate the resulting effect on human exposures, the Regional Human Exposure (REHEX) model was used to calculate benzene exposures in the SoCAB for the years 1989 and 1997. Benzene concentration distributions in 14 microenvironments (e.g. outdoor, home, vehicle, work) were combined with California time-activity patterns and census data to calculate exposure distributions for 11 demographic groups in the SoCAB. For 1997, the calculated average benzene exposure for nonsmoking adults in the SoCAB was 2 ppb, compared to 6 ppb for 1989. For nonsmokers, about half of the 1997 exposure was due to ambient air concentrations (including their contributions to other microenvironments), but only 4% for smokers. Passive tobacco smoke contributed about one-fourth of all exposure for adult nonsmokers. In-transit microenvironments and attached garages contributed approximately 15 and 10%, respectively. From 1989 to 1997, decreases in passive smoke exposure accounted for about one-sixth of the decrease in exposure for nonsmoking adults, with the remainder due to decreases in ambient concentrations. The reductions in exposure during this time period indicate the effectiveness of reformulated fuels, more stringent emission standards, and smoking restrictions in significantly reducing exposure to benzene.

Penetration of Evaporative Emissions into a Home from an M85-Fueled Vehicle Parked in an Attached Garage

ABSTRACT The use of both oxygenated fuels in carbon monoxide (CO) nonattainment areas and reformulated gasoline in ozone nonattainment areas has been mandated by the 1990 Clean Air Act Amendments. Methanol has been proposed as an alternative fuel for CO nonattainment areas. Its use will potentially increase indoor methanol inhalation exposure resulting from the evaporation of metha-nol vapor from methanol-fueled vehicles parked in residential garages. Indoor air concentrations of metha-nol, benzene, and toluene were measured in a residential home with an attached garage. The effects of vehicle emission control devices (charcoal canister hose connection); home heating, ventilation, and air conditioning (HVAC) fans; ambient air, garage, and fuel tank temperatures; and wind speed were examined. The disconnection of the charcoal canister hose, which simulates a spent evaporative emission control device, resulted in elevated benzene, toluene, and metha-nol concentrations in the garage and attached home. Higher fuel tank temperatures resulted in higher benzene and toluene concentrations in the garage, but not methanol. The concentrations for all compounds in the garage and concentrations of benzene and toluene in the adjacent room were lower when the HVAC fan was on than when it was off, while the concentrations of all three compounds in the rest of the house were higher, although these differences were not statistically significant. Thus, the portion of the population that parks cars in garages attached to homes will experience increased methanol exposures if methanol is used as an automotive fuel.

Monitoring and Assessment of Exhaust Emission in Bangkok Street Air

Measurement of the exhaust emission from gasoline-powered motor vehicles in Bangkok were performed on chassis dynamometer. A fleet of 10 vehicles of different model, years and manufacturers were selected to measure the air pollutants in the exhaust effluent. The study revealed that the carbon monoxide and hydrocarbon emissions averaged 32.3–64.2 and 1.82–2.98 g km−1, respectively, for 1990–1992 cars and decreased to 17.8–40.71 and 0.75–1.88 g km−1, respectively, for 1994–1995 cars. A monitoring program for air pollutant concentrations in ambient air was also conducted to evaluate the air pollution problems in Bangkok arising from vehicle exhaust emission. Four air sampling stations were strategically established to cover the Bangkok Metropolitan Region (BMR). Composite air samples in this study area were collected during the day/night times and weekday/weekend. The average concentrations of suspended particulate matter, carbon monoxide, and nitrogen dioxide in Bangkok street air were found to be 0.65 mg/m3 (24 hr ave.), 19.02 mg/m3 (8 hr ave.) and 0.021 mg/m3 (1 hr ave.), respectively. The average concentrations of benzene and toluene in the ambient air of the study area were found to be 15.07–50.20 and 25.76–130.95 μg/mf3, respectively, for 8 hr average. These results indicated that there was a significant increase in air pollutant emissions with increasing car mileage and model year. Subsequent analysis of data showed that there were only 20% of the test vehicles complied to approved emission standard. The finding also revealed that there was a correlation between the average air pollutant concentrations with average traffic speed in each traffic zone of the Bangkok Metropolitan Region (BMR).

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.

An optimized sampling and GC–MS analysis method for benzene in exhaled breath, as a biomarker for occupational exposure

Benzene is known to be toxic and carcinogenic: therefore, in case of exposure to benzene vapours, a reliable biological monitoring procedure is needed, particularly in the field of occupational hygiene. The determination of the concentration of benzene in the exhaled air 8 h after the exposure has been demonstrated to be a significant biomarker, even for low concentrations of airborne benzene vapours. This work presents a sampling and analysis method that optimizes previously described procedures: in the sampling phase, a double-step sample collection in Tedlar bags is used, in order to remove the breath moisture and to standardise the sample volumes. The analytical phase uses a cryogenic trap for the concentration of the air samples to be injected in the GC–MS, without the need for trapping materials, significantly reducing time and costs of the analysis and improving sensitivity. The presented method has been successfully applied to the biological monitoring of a mixed population (occupationally exposed and not exposed subjects, smokers and non-smokers), with a lower detection limit of 1.5 ng of benzene per litre of exhaled air, that is 1/200 of the biological exposure index recommended by the American Conference of Governmental Hygienists.

Investigation of a cluster of leukaemia in the Illawarra region of New South Wales, 1989-1996.

To investigate a cluster of leukaemia among young people and assess the plausibility of a disease-exposure relationship. Descriptive analysis of population-based leukaemia incidence data, review of evidence related to the causation of leukaemia, assessment of environmental exposures to known leukaemogens, and resulting risks of leukaemia. Illawarra region of New South Wales, Australia, focusing on suburbs between the Port Kembla industrial complex and Lake Illawarra (the Warrawong area). Standardised incidence ratios (SIRs) for leukaemia; current measured and past estimated ambient air benzene concentrations; and expected leukaemia cases attributable to estimates of ambient air benzene concentrations. In 1989-1996, 12 leukaemia cases among Warrawong residents aged less than 50 years were observed, more than the 3.49 cases expected from the rate in the rest of the Illawarra region (SIR, 343.8; 99% CI, 141.6-691.7). These people lived in suburbs immediately to the south-southwest of a coke byproducts plant (a major industrial source of benzene, one of the few known leukaemogens). The greatest excess was among 15-24-year-olds (SIR, 1085.6; 99% CI, 234.1-3072.4). In 1996, ambient air concentrations of benzene averaged less than 1 part per billion (ppb). Since 1970, ambient air concentrations of benzene were estimated to have averaged up to 3 ppb, about one-thousandth of the level at which leukaemia risk has been identified in occupational epidemiological studies. Using the risk assessment model developed by the US Environmental Protection Agency, we estimate that past benzene levels in the Warrawong area could have resulted in 0.4 additional cases of leukaemia in 1989-1996. The excess occurrence of leukaemia in the Warrawong area in 1989-1996 is highly unusual. Current environmental benzene exposure and the reconstructed past environmental benzene exposure level are too low to explain the large excess of leukaemia. The cause of the cluster is uncertain.

Environmental exposure to benzene: an update.

During the 1990s, several large-scale studies of benzene concentrations in air, food, and blood have added to our knowledge of its environmental occurrence. In general, the new studies have confirmed the earlier findings of the U.S. Environmental Protection Agency Total Exposure Assessment Methodology (TEAM) studies and other large-scale studies in Germany and the Netherlands concerning the levels of exposure and major sources. For example, the new studies found that personal exposures exceeded indoor concentrations of benzene, which in turn exceeded outdoor concentrations. The new studies of food concentrations have confirmed earlier indications that food is not an important pathway for benzene exposure. The results of the National Health and Nutrition Examination Survey on blood levels in a nationwide sample of 883 persons are in good agreement with the concentrations in exhaled breath measured in about 800 persons a decade earlier in the TEAM studies. Major sources of exposure continue to be active and passive smoking, auto exhaust, and driving or riding in automobiles. New methods in breath and blood sampling and analysis offer opportunities to investigate short-term peak exposures and resulting body burden under almost any conceivable field conditions.

On-line monitoring of benzene air concentrations while driving in traffic by means of isotopic dilution gas chromatography/mass spectrometry.

There is no shortage of information about the average benzene concentrations in urban air, but there is very little about microenvironmental exposure, such as in-vehicle concentrations while driving in various traffic conditions, while refuelling, or while in a parking garage. The main reason for this lack of data is that no analytical instrumentation has been available to measure on-line trace amounts of benzene in such situations. We have recently proposed a highly accurate, high-speed cryofocusing gas chromatography/mass spectrometry (GC/MS) system for monitoring benzene concentrations in air. Accuracy of the analytical data is achieved by enrichment of the air sample before trapping, with a stable isotope permeation tube system. The same principles have been applied to a new instrument, specifically designed for operation on an electric vehicle (Ducato Elettra, Fiat). The zero emission vehicle and the fully transportable, battery-operated GC/MS system provide a unique possibility of monitoring benzene exposure in real everyday situations such as while driving, refuelling, or repairing a car. All power consumptions have been reduced so as to achieve a battery-operated GC/MS system. Liquid nitrogen cryofocusing has been replaced by a packed, inductively heated, graphitized charcoal microtrap. The instrument has been mounted on shock absorbers and installed in the van. The whole system has been tested in both fixed and mobile conditions. The maximum monitoring period without external power supply is 6 h. The full analytical cycle is 4 min, allowing close to real-time monitoring, and the minimum detectable level is 1 microgram/m3 for benzene. In-vehicle monitoring showed that, when recirculation was off and ventilation on, i.e., air from outside the vehicle was blown inside, concentrations varied widely in different driving conditions: moving from a parking lot into normal traffic on an urban traffic condition roadway yielded an increase in benzene concentration from 17 to 62.3 micrograms/m3 even if the actual distance was small. A larger increase was observed when a car was left with the engine running at a distance 2 m from the zero emission vehicle: We measured an increment of benzene concentrations from 15.2 to 174.4 micrograms/m3 with a car equipped with a catalytic converter, and from 19.1 to 386.3 micrograms/m3 with a car without such a converter.

On-line monitoring of benzene air concentrations while driving in traffic by means of isotopic dilution gas chromatography/mass spectrometry

On-line monitoring of benzene air concentrations while driving in traffic by means of isotopic dilution gas chromatography/mass spectrometry

Ambient Air Benzene Concentrations in Canada (1989-1993): Seasonal and Day of Week Variations, Trends, and Source Influences

Abstract Since 1987, the Pollution Measurement Division of the Environmental Protection Service, Environment Canada, has operated a field program for measuring benzene in ambient air. With the cooperation of provincial and municipal environmental agencies, samples have been collected at over 30 urban and rural monitoring sites across the country. Samples are collected in evacuated canisters and analyzed by gas chromatography with a mass-selective detector. Using data from all sites, the composite average benzene concentration for Canada over the years 1989 to 1993 was 3.6 μg/m3 and the composite median was found to be 2.6 μ/m3. Benzene concentrations are highest at urban sites near major streets and at sites influenced by industrial sources. For eighteen urban and suburban trend sites (those with no nearby industrial sources), composite annual median benzene concentrations decreased by 20% between 1989 and 1993. For the same period, median benzene concentrations decreased by 33% at four trend sites with n...

Contamination of indoor air by toxic soil vapours: a screening risk assessment model

A simple steady-state model is derived for estimating the concentration of vapour-phase contaminants in indoor air, given the contaminant concentration in the soil. The model includes the key mechanisms of transport and dispersion—contaminant partitioning into the soil-vapour phase, molecular diffusion, suction flow, and ventilation rate. It is shown that indoor air concentrations are largely controlled by two variables: soil permeability, and the half-life for contaminant removal from soil. A worked example shows the effect of these two variables on the concentration of benzene in soil that would give rise to a concentration of benzene in indoor air of 5 ppb (the recently proposed U.K. Air Quality Standard).

Volatile organic compounds (VOCs) and air mutagenicity: Results of one year monitoring at an urban site

The concentrations of four volatile organic compounds (VOCs: benzene, toluene, ethylbenzene and xylenes) and the levels of inhalable (< 10 μm) airborne particles were monitored during 1 year at a site with intense vehicular traffic in the city of Rome. VOCs as well as airborne particulate matter were sampled every alternate day and pooled in fortnightly samples representative of the first and second half of each month. Some meteorological parameters (mean temperature, heliophany, air pressure and relative humidity) were concurrently recorded. Air particulate extracts were tested for mutagenicity in the Salmonella reversion system with tester strain TA98. Air mutagenicity levels were compared to air concentrations of benzene and alkylbenzenes, putative indicators of vehicular traffic, in order to elucidate their interrelationships. The results of multivariate statistical analyses show that seasonal variations in air mutagenicity are mainly dependent on the increased content of organic matter in airborne pa...

Concentrations of benzene in blood and S-phenylmercapturic and t,t-muconic acid in urine in car mechanics.

Different parameters of biological monitoring were applied to 26 benzene-exposed car mechanics. Twenty car mechanics worked in a work environment with probably high benzene exposures (exposed workers); six car mechanics primarily involved in work organization were classified as non-exposed. The maximum air benzene concentration at the work places of exposed mechanics was 13 mg/m3 (mean 2.6 mg/m3). Elevated benzene exposure was associated with job tasks involving work on fuel injections, petrol tanks, cylinder blocks, gasoline pipes, fuel filters, fuel pumps and valves. The mean blood benzene level in the exposed workers was 3.3 micrograms/l (range 0.7-13.6 micrograms/l). Phenol proved to be an inadequate monitoring parameter within the exposure ranges investigated. The muconic and S-phenylmercapturic acid concentrations in urine showed a marked increase during the work shift. Both also showed significant correlations with benzene concentrations in air or in blood. The best correlations between the benzene air level and the mercapturic and muconic acid concentrations in urine were found at the end of the work shift (phenylmercapturic acid concentration: r = 0.81, P < 0.0001; muconic acid concentration: r = 0.54, P < 0.05). In conclusion, the concentrations of benzene in blood and mercapturic and muconic acid in urine proved to be good parameters for monitoring benzene exposure at the workplace even at benzene air levels below the current exposure limits. Today working as a car mechanic seems to be one of the occupations typically associated with benzene exposure.

Urinary excretion of unmetabolized benzene as an indicator of benzene exposure.

Benzene concentrations in urine samples (Cu, ng/L) from 110 workers exposed to benzene in chemical plants and gasoline pumps were determined by injecting urine supernate into a gas chromatograph. The urine was saturated with anhydrous N2SO4 to facilitate the passage of benzene in the air over the urine. The solvent was stripped from the urine surface and concentrated on an adsorbent substrate (Carbotrap tube) by means of a suction pump (flow rate 150 ml/m). Wash-up of the head space was achieved by simultaneous intake of filtered air through charcoal. Benzene was thermically desorbed and injected in a column (thermal tube disorder, Supelco; 370 degrees C thermal flash; borosilicate capillary glass column SPB-1, 60 m length, 0.75 mm ID, 1 microns film thickness; GC Dani 8580-FID). Benzene concentrations in the urine from 40 non-exposed subjects (20 smokers > 20 cigarette/d and 20 nonsmokers) were also determined [median value of 790 ng/L (10.17 nmol/L) and 131 ng/L (1.70 nmol/L), respectively]. The 8-h time-weighted exposure intensity (Cl, micrograms/m3) of individual workers was monitored by means of charcoal tubes. The median value for exposure to benzene was 736 micrograms/m3 (9.42 mumol/m3) [geometric standard deviation (GSD) = 2.99; range 64 micrograms/m3 (0.82 mumol/m3) to 13,387 micrograms/m3) (171.30 mumol/m3)]. The following linear correlation was found between benzene concentrations in urine (Cu, ng/L) and benzene concentrations in the breathing zone (Cl, micrograms/m3): log(Cu) = 0.645 x log(Cl) + 1.399 r = .559, n = 110, p < .0001 With exclusion of workers who smoked from the study, the correlation between air benzene concentration and benzene measured in urine was: log(Cu) = 0.872 x log(Cl) + 0.6 r = .763, n = 63, p < .0001 The study results indicate that the urinary level of benzene is an indicator of occupational exposure to benzene.

Chromosome aberrations in lymphocytes of mice after sub-acute low-level inhalation exposure to benzene

Male and female CD-1 mice were exposed to near ambient air concentrations of benzene by inhalation for 22 h per day, 7 days per week for 6 weeks. The concentrations were 0, 40, 100 and 1000 ppb. Significant increases in chromosome aberrations in spleen lymphocytes were observed in exposed compared with control mice except in the high-dose group ( p < 0.05 for female mice in 2 experiments and for male mice in 1 experiment; p < 0.15 for male mice in the second experiment). A lack of increase in aberrations among mice of the high-dose group may be due to an induction of detoxifying enzymes as observed by us in a previous study (Au et al., 1988b). We also found that the female mice were more sensitive to the clastogenic activity of benzene than male mice under our experimental conditions. Our study serves to emphasize the need to conduct subchronic, low-dose in vivo genotoxicity studies using exposure conditions similar to those of humans, for evaluation of potential hazards. Our data suggest that the current occupational exposure concentrations for benzene (< 1000 ppb) may still be hazardous to humans.

Urinary t,t-muconic acid as an indicator of exposure to benzene.

A method for rapidly determining t,t-muconic acid (MA) by high performance liquid chromatography was developed and successfully applied to urine samples from 152 workers exposed to benzene (64 men, 88 women) and 213 non-exposed controls (113 men, 100 women). The MA concentrations in urine correlated linearly with time weighted average benzene concentrations in the breath zone air of workers. A cross sectional balance study showed that about 2% of benzene inhaled is excreted into the urine as MA. The MA concentrations in the urine of the non-exposed was below the detection limit (less than 0.1 mg/l) in most cases, and the 95% lower confidence limit of MA for those exposed to benzene at 5 ppm (5.0 mg/l as a non-corrected value) was higher than the 97.5%-tile values for the non-exposed (1.4 mg/l). In practice, it was possible to separate those exposed to 6-7 ppm benzene from the non-exposed by means of urine analysis for MA. The urinary MA concentration was suppressed by coexposure to toluene.

Determination of benzene, toluene and 1,3-butadiene in cigarette smoke by GC-MSD

An analytical procedure was devised for the determination of selected gas phase constituents in cigarette smoke utilizing capillary gas chromatography and mass selective detection (GC-MSD); the MSD was used in the selective ion monitoring mode (SIM). The gas of freshly generated mainstream smoke was analyzed via a 10-port gas sampling valve on a puff-by-puff basis. Benzene, toluene, and 1,3-butadiene were found in the range of 6–73, 5–88, and 16–75 μg/cigarette, respectively. The gas phase of sidestream smoke was trapped in methanol using 3 midget impingers at −78°C. Benzene in sidestream smoke was found in the range of 490–840 μg/cigarette; toluene and 1,3-butadiene levels were 1,090–1,690 and 300–470 μg/ cigarette, respectively. Environmental tobacco smoke (ETS), sampled in a smoke-filled bar, was analyzed using the cold trap method. The concentrations of benzene and toluene in this indoor air were found to be 26–36 and 41–80 μg/m 3, respectively, while 1,3-butadiene was present at 3.3–4.5 μg/m 3.

Determination of catechol and quinol in the urine of workers exposed to benzene.

Time weighted average concentrations of benzene in breathing zone air (measured by diffusive sampling coupled with FID gas chromatography) and concentrations of catechol and quinol in the urine (collected at about 1500 in the second half of a working week and analysed by high performance liquid chromatography) were compared in 152 workers who were exposed to benzene (64 men, 88 women). The concentration of urinary metabolites was also determined in 131 non-exposed subjects (43 men, 88 women). There was a linear relation between the benzene concentrations in the breathing zone and the urinary concentrations of catechol and quinol (with or without correction for urine density) in both sexes. Neither catechol nor quinol concentration was able to separate those exposed to benzene at 10 ppm from those without exposure. The data indicated that when workers were exposed to benzene at 100 ppm about 25% of benzene absorbed was excreted into the urine as phenolic metabolites, of which 13.2%, 1.6%, and 10.2% are phenol, catechol, and quinol, respectively.