Gasoline vapor exposures at a high volume service station

Gasoline vapor concentrations were measured at a high volume service station for one week in May, 1983, for service station attendants, self-service customers and for various area locations. To facilitate the retention of highly volatile, low-molecular weight gasoline vapor components, 100/50 mg charcoal adsorption tubes were used with flow rates of 100 cc/min for long-term exposure samples and 900 cc/min for short-term exposures. Methylene chloride was selected as the desorption solvent. Desorbed hydrocarbons were analyzed and quantitated by capillary column gas chromatography using a flame ionization detector and a 0-100 degrees C temperature program. The data proved that the predominant ambient air hydrocarbons are those of C4 and C5 compounds. Monitoring results showed that the total gasoline vapor TWA exposures for service station attendants ranged from 0.6 to 4.8 ppm with a geometric mean of 1.5 ppm. Short-term personal samples collected while refueling ranged from not detectable to 38.8 ppm with a geometric mean of 5.8 ppm.     

Characterizing historical industrial hygiene data: a case study involving benzene exposures at a chemical manufacturing facility (1976-1987)

This article describes how nearly 3700 air samples of benzene collected in a typical chemical manufacturing (acetic acid) facility in the United States from 1976 to 1987 were used to characterize daily time-weighted average (TWA) exposure levels. We found that those workers directly involved in manufacturing operations had likely TWA exposures to benzene of about 2.0 ppm from 1976-1981 and about 1.0 ppm from 1982-1987. These results are consistent with the improved industrial hygiene programs at chemical facilities, which often occurred following the adoption of stricter occupational exposure limits. Additionally, about 97% of all personal TWA samples had reported benzene concentrations less than 10 ppm, which was the permissible exposure limit in place prior to 1987. Because one of the primary objectives of historical workplace air sampling efforts was to understand the source of release of contaminants, a large number of short-term (typically about 1 min) area samples were also collected. Although these types of samples are often not useful for predicting human exposure without time-motion information, airborne benzene concentrations were about five- to tenfold higher for many of the short-term area samples than for the personal TWA measurements. The methodology presented here should be useful for evaluating industrial hygiene data collected after the early 1970s (after the promulgation of OSHA), and our findings support prior reports that large corporations in the United States have tended to reduce workplace exposures to airborne contaminants consistent with historical changes in occupational exposure limits.     

A control technology evaluation of state-of-the-art,perchloroethylene dry-cleaning machines

NIOSH researchers evaluated the ability of fifth-generation dry-cleaning machines to control occupational exposure to perchloroethylene (PERC). Use of these machines is mandated in some countries; however, less than 1 percent of all U.S. shops have them. A study was conducted at a U.S. dry-cleaning shop where two fifth-generation machines were used. Both machines had a refrigerated condenser as a primary control and a carbon adsorber as a secondary control to recover PERC vapors during the dry cycle. These machines were designed to lower the PERC concentration in the cylinder at the end of the dry cycle to below 290 ppm. A single-beam infrared photometer continuously monitors the PERC concentration in the machine cylinder, and a door interlock prevents opening until the concentration is below 290 ppm. Personal breathing zone air samples were measured for the machine operator and presser. The operator had time-weighted average (TWA) PERC exposures that were less than 2 ppm. Highest exposures occurred during loading and unloading the machine and when performing routine machine maintenance. All presser samples were below the limit of detection. Real-time video exposure monitoring showed that the operator had peak exposures near 160 ppm during loading and unloading the machine (below the OSHA maximum of 300 ppm). This exposure (160 ppm) is an order of magnitude lower than exposures with more traditional machines that are widely used in the United States. The evaluated machines were very effective at reducing TWA PERC exposures as well as peak exposures that occur during machine loading and unloading. State-of-the-art dry-cleaning machines equipped with refrigerated condensers, carbon adsorbers, drum monitors, and door interlocks can provide substantially better protection than more traditional machines that are widely used in the United States.     

Estimating airborne benzene exposures from air monitoring data for mineral spirits

"Low aromatics" vs. "regular" mineral spirits differ substantially in their aromatic hydrocarbon content. Mineral spirits contain benzene and other compounds that boil at temperatures below the cited boiling point range of 300 ° to 415 °F. Available published information shows that until at least 2000, the benzene content of regular mineral spirits was typically 0.1% wt/wt and at times could have been 1.0% wt/wt. The present analysis accounts for benzene's higher volatility compared to mineral spirits as a whole and applies thermodynamic principles to estimate benzene vapor exposure as a subset of measured exposure to total hydrocarbons generated by the evaporation of mineral spirits. For a scenario in which the bulk mineral spirits only partially evaporate, this analysis explains the error in assuming that the mole fraction of benzene to "everything else" is the same in the vapor and liquid phases. It is shown that for a given concentration of total hydrocarbon vapor, the benzene vapor concentration can be more than 65-fold greater during mineral spirits evaporation compared to after all the mineral spirits has evaporated. In turn, it is reasonable to expect that during the use of regular mineral spirits, containing benzene typically at 0.1% wt/wt (as applies to usage prior to 2000), benzene vapor exposures could have exceeded 1 ppm even though the mineral spirits vapor exposure did not exceed 100 ppm, the ACGIH? TLV? time-weighted average (TWA) value for mineral spirits. The same analysis can be applied to current petrochemical products, such as toluene, that contain benzene and for which the required physico-chemical information is available. The analysis provides evidence that the material safety data sheet (MSDS) for a petrochemical product containing benzene at less than 0.1% wt/wt should, pursuant to Hazard Communication Standard requirements, identify the benzene as a hazardous ingredient.     

An evaluation of retrofit engineering control interventions to reduce perchloroethylene exposures in commercial dry-cleaning shops

Real-time monitoring was used to evaluate the ability of engineering control devices retrofitted on two existing dry-cleaning machines to reduce worker exposures to perchloroethylene. In one dry-cleaning shop, a refrigerated condenser was installed on a machine that had a water-cooled condenser to reduce the air temperature, improve vapor recovery, and lower exposures. In a second shop, a carbon adsorber was retrofitted on a machine to adsorb residual perchloroethylene not collected by the existing refrigerated condenser to improve vapor recovery and reduce exposures. Both controls were successful at reducing the perchloroethylene exposures of the dry-cleaning machine operator. Real-time monitoring was performed to evaluate how the engineering controls affected exposures during loading and unloading the dry-cleaning machine, a task generally considered to account for the highest exposures. The real-time monitoring showed that dramatic reductions occurred in exposures during loading and unloading of the dry-cleaning machine due to the engineering controls. Peak operator exposures during loading and unloading were reduced by 60 percent in the shop that had a refrigerated condenser installed on the dry-cleaning machine and 92 percent in the shop that had a carbon adsorber installed. Although loading and unloading exposures were dramatically reduced, drops in full-shift time-weighted average (TWA) exposures were less dramatic. TWA exposures to perchloroethylene, as measured by conventional air sampling, showed smaller reductions in operator exposures of 28 percent or less. Differences between exposure results from real-time and conventional air sampling very likely resulted from other uncontrolled sources of exposure, differences in shop general ventilation before and after the control was installed, relatively small sample sizes, and experimental variability inherent in field research. Although there were some difficulties and complications with installation and maintenance of the engineering controls, this study showed that retrofitting engineering controls may be a feasible option for some dry-cleaning shop owners to reduce worker exposures to perchloroethylene. By installing retrofit controls, a dry-cleaning facility can reduce exposures, in some cases dramatically, and bring operators into compliance with the Occupational Safety and Health Administration (OSHA) peak exposure limit of 300 ppm. Retrofit engineering controls are also likely to enable many dry-cleaning workers to lower their overall personal TWA exposures to perchloroethylene.     

Respiratory exposure of grain inspection workers to carbon tetrachloride fumigant

Carbon tetrachloride (often mixed with carbon disulfide or ethylene dichloride) is a common constituent of liquid grain fumigants. Applied as liquids, these mixtures volatilize and achieve vapor concentrations sufficient to control insect infestations in stored grains. Absorbed grain desorbs fumigant components after the fumigation period, and it then becomes a source of exposure to workers who handle fumigated grain. Carbon tetrachloride meets the EPA's risk criteria for hepatotoxicity, nephrotoxicity and oncogenicity, and it has been under regulatory review since 15 October 1980. Present OSHA standards for CCl4 are a time-weighted average (TWA) of 10 ppm and an acceptable ceiling of 25 ppm. ACGIH and NIOSH have recommended lowering the OSHA standard. The point at which peak exposure occurs during the grain inspection process has been identified as the off odor test in which the inspector smells the grain sample for rancidity, sourness, etc. Ambient concentrations of CCl4 in 7750 grain samples submitted for inspection were determined by colorimetric tube, and these concentrations were an estimate of peak grain inspector exposure to CCl4. The average ambient concentration of CCl4 per grain sample was 1.69 ppm +/- 8.35. Approximately 380 TWA CCl4 exposures for grain inspection workers were determined by using passive dosimeters. All TWA exposures were less than 2 ppm. Variables are examined, such as location of work, grain type, time of year and grain transportation vehicle--all of which are known to the sampler or inspector before performing their job functions and which affect potential exposure.     

Gasoline vapor exposures. Part I. Characterization of workplace exposures

Monitoring surveys of gasoline vapor exposures were conducted on truck drivers and terminal operators from five terminal loading facilities, on dockmen and seamen at two tanker/barge loading facilities, and on attendants at a single expressway service plaza. Results revealed wide variations in total C6+ hydrocarbon exposures for each location, with overall 8-hr time-weighted averaged (TWA) geometric means of 5.7 mg/m3 (1.4 ppm) for the terminals, and 4.0 mg/m3 (1.0 ppm) for the service plaza, respectively. The exposures ranged from 0.8 to 120.8 mg/m3 (0.2-30.1 ppm) for the terminals, and from 1.1 to 130.3 mg/m3 (0.3-32.5 ppm) for the service plaza. For the terminals, exposures were not significantly different regardless of loading method or the presence or absence of vapor recovery systems. Comprehensive chemical analyses of terminal employee exposure samples revealed that the C4 and C5 hydrocarbon components constituted 74.8 +/- 9.2% of the total exposure sample on a microgram/sample basis. The C6, C7, and C8+ components constituted 13.0 +/- 1.9, 6.2 +/- 3.0, and 5.9 +/- 7.2% of the total samples, respectively. Comprehensive analyses of the marine employee exposure samples resulted in a similar distribution of components; that is, 66.6 +/- 7.9, 17.5 +/- 4.7, 9.2 +/- 3.1, and 6.4 +/- 1.9% for the C4/C5, C6, C7, and C8+ components, respectively. The composition of the exposures, however, was weighted more toward the C5, C6 and C7 components when compared to the bulk terminal employee exposures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Customer exposure to MTBE, TAME, C6 alkyl methyl ethers, and benzene during gasoline refueling.

We studied customer exposure during refueling by collecting air samples from customers' breathing zone. The measurements were carried out during 4 days in summer 1996 at two Finnish self-service gasoline stations with "stage I" vapor recovery systems. The 95-RON (research octane number) gasoline contained approximately 2.7% methyl tert-butyl ether (MTBE), approximately 8.5% tert-amyl methyl ether (TAME), approximately 3.2% C6 alkyl methyl ethers (C6 AMEs), and 0.75% benzene. The individual exposure concentrations showed a wide log-normal distribution, with low exposures being the most frequent. In over 90% of the samples, the concentration of MTBE was higher (range <0.02-51 mg/m3) than that of TAME. The MTBE values were well below the short-term (15 min) threshold limits set for occupational exposure (250-360 mg/m3). At station A, the geometric mean concentrations in individual samples were 3.9 mg/m3 MTBE and 2. 2 mg/m3 TAME. The corresponding values at station B were 2.4 and 1.7 mg/m3, respectively. The average refueling (sampling) time was 63 sec at station A and 74 sec at station B. No statistically significant difference was observed in customer exposures between the two service stations. The overall geometric means (n = 167) for an adjusted 1-min refueling time were 3.3 mg/m3 MTBE and 1.9 mg/m3 TAME. Each day an integrated breathing zone sample was also collected, corresponding to an arithmetic mean of 20-21 refuelings. The overall arithmetic mean concentrations in the integrated samples (n = 8) were 0.90 mg/m3 for benzene and 0.56 mg/m3 for C6 AMEs calculated as a group. Mean MTBE concentrations in ambient air (a stationary point in the middle of the pump island) were 0.16 mg/m3 for station A and 0.07 mg/m3 for station B. The mean ambient concentrations of TAME, C6 AMEs, and benzene were 0.031 mg/m3, approximately 0.005 mg/m3, and approximately 0.01 mg/m3, respectively, at both stations. The mean wind speed was 1.4 m/sec and mean air temperature was 21 degreesC. Of the gasoline refueled during the study, 75% was 95 grade and 25% was 98/99 grade, with an oxygenate (MTBE) content of 12.2%.     

The MTBE air concentrations in the cabin of automobiles while fueling.

Methyl tertiary-butyl ether (MTBE) is the most commonly used oxygenated compound added to gasoline to reduce ambient carbon monoxide levels. Complaints about perceived MTBE exposures and adverse health symptoms have been registered in several states, including New Jersey (NJ). Fueling automobiles is the activity thought to cause the highest environmental MTBE exposures. The current study was conducted to determine the MTBE concentrations inside automobile cabins during fueling, which represents the peak exposure that can occur at full service gasoline service stations, such as those that exist in NJ. Air samples were collected at service stations located on the NJ and PA turnpikes from March 1996 to July 1997 during which the MTBE content in gasoline varied. A bimodal distribution of MTBE concentrations was found in the cabin of the cars while fueling. The median MTBE, benzene and toluene in cabin concentrations were 100, 5.5 and 18 ppb, respectively, with the upper concentrations of the distribution exceeding 1 ppm for MTBE and 0.1 ppm for benzene and toluene. The highest in cabin concentrations occurred in a car that had a malfunctioning vapor recovery system and in a series of cars sampled on an unusually warm, calm winter day when the fuel volatility was high, the evaporation maximal and the dispersion by wind minimal. The in-cabin concentrations were typically higher when the car window was opened during the entire fueling process. Thus, exposure to MTBE during fueling can be reduced by properly maintaining the integrity of the fuel system and keeping the windows closed during fueling.     

Benzene: standards, occurrence, and exposure

The national occupational standard values for benzene are 10 ppm for Australia, 10 ppm for Denmark, 10 ppm for Finland, 10 ppm for Japan, 10 ppm for The Netherlands, 10 ppm for the United States, and 5 ppm for Sweden; in the Federal Republic of Germany the technical guideline value is 8 ppm. Crude mineral oil contains benzene as a natural constituent of approximately 0.1%. Gasoline in Sweden may contain 4-5% benzene by volume. The 8-hour time-weighted average (TWA) exposure levels of Swedish petroleum refinery workers vary between 0.1 to 1 mg benzene/m3 in air. The exposures of benzene in various other occupations were measured and described. Other environmental exposures to benzene may have their origin in pyrolysis, such as tobacco smoking and burning of substances such as polyvinylchloride.     

Benzene toxicokinetics in humans: exposure of bone marrow to metabolites.

A three compartment physiologically based toxicokinetic model was fitted to human data on benzene disposition. Two separate groups of model parameter derivations were obtained, depending on which data sets were being fitted. The model was then used to simulate five environmental or occupational exposures. Predicted values of the total bone marrow exposure to benzene and cumulative quantity of metabolites produced by the bone marrow were generated for each scenario. The relation between cumulative quantity of metabolites produced by the bone marrow and continuous benzene exposure was also investigated in detail for simulated inhalation exposure concentrations ranging from 0.0039 ppm to 150 ppm. At the level of environmental exposures, no dose rate effect was found for either model. The occupational exposures led to only slight dose rate effects. A 32 ppm exposure for 15 minutes predicted consistently higher values than a 1 ppm exposure for eight hours for the total exposure of bone marrow to benzene and the cumulative quantity of metabolites produced by the bone marrow. The general relation between the cumulative quantity of metabolites produced by the bone marrow and the inhalation concentration of benzene is not linear. An inflection point exists in some cases leading to a slightly S shaped curve. At environmental levels (0.0039-10 ppm) the curve bends upward, and it saturates at high experimental exposures (greater than 100 ppm).     

Occupational exposures associated with petroleum-derived products containing trace levels of benzene

Benzene may be present as a trace impurity or residual component of mixed petroleum products due to refining processes. In this article, the authors review the historical benzene content of various petroleum-derived products and characterize the airborne concentrations of benzene associated with the typical handling or use of these products in the United States, based on indoor exposure modeling and industrial hygiene air monitoring data collected since the late 1970s. Analysis showed that products that normally contained less than 0.1% v/v benzene, such as paints and paint solvents, printing solvents and inks, cutting and honing oils, adhesives, mineral spirits and degreasers, and jet fuel typically have yielded time-weighted average (TWA) airborne concentrations of benzene in the breathing zone and surrounding air ranging on average from <0.01 to 0.3 ppm. Except for a limited number of studies where the benzene content of the product was not confirmed to be <0.1% v/v, airborne benzene concentrations were also less than current occupational exposure limits (e.g., threshold limit value of 0.5 ppm and permissible exposure limit of 1.0 ppm) based on exceedance fraction calculations. Exposure modeling using Monte Carlo techniques also predicted 8-hr TWA near field airborne benzene concentrations ranging from 0.002 to 0.4 ppm under three hypothetical solvent use scenarios involving mineral spirits. The overall weight-of-evidence indicates that the vast majority of products manufactured in the United States after about 1978 contained <0.1% v/v benzene, and 8-hr TWA airborne concentrations of benzene in the workplace during the use of these products would not have been expected to exceed 0.5 ppm under most product use scenarios. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a document containing exposure modeling scenarios and results, historical benzene content of petroleum-derived products, and air monitoring results.].     

Worker exposure to perchloroethylene in the commercial dry cleaning industry

The National Institute for Occupational Safety and Health (NIOSH) conducted industrial hygiene surveys at 44 commercial dry cleaning facilities in five states as part of an industry wide study to assess the health effects of long-term, low-level exposure to perchloroethylene (PCE). Time-weighted average (TWA) and peak exposures to PCE were determined by collecting personal air samples using activated charcoal tubes and battery-operated pumps. TWA exposures of the machine operators ranged from 4.0 to 149.0 ppm PCE. The geometric mean PCE exposure of the machine operators (22 ppm) differed significantly from the mean exposures of the pressers (3.3 ppm), seamstresses (3.0 ppm), and the concentrations in the front counter areas of the facilities (3.1 ppm). Te geometric mean 5-minute peak PCE exposure during textile transfer was 44 ppm while the mean 15-minute exposure was 33 ppm. No significant differences were found between exposures when either the TWA or the peak data were grouped by geographic location (i.e., state), or by the type of processing equipment used (i.e., "Combination" units vs. separate washing and drying units). Recommendations for work practices, ventilation, maintenance, plant layout and personal protective equipment are presented to reduce PCE exposures to lowest achievable levels.     

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

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

Muconic acid in urine: A reliable indicator of occupational exposure to benzene

In male subjects not occupationally exposed to benzene, the concentration of muconic acid (MA) in urine is usually below 0.5 mg/g creatinine. At ambient levels of benzene exposure (below 0.01 ppm), the mean MA level was greater in 21 smokers than in 14 nonsmokers. In 38 male subjects employed in garages and coke ovens, a statistically significant correlation was found between the airborne concentration of benzene measured with passive monitors and MA in postshift urine. The mean postshift MA concentrations corresponding to a benzene 8-hour time-weighted average exposure (TWA) of 0.5 and 1 ppm were 0.8 and 1.4 mg/g creatinine, respectively. © 1994 Wiley-Liss, Inc.     

The development of a revolving personal sampler.

The American Conference of Governmental Industrial Hygienists recommends the use of threshold limit value-short-term exposure limit (TLV-STEL) and ceiling limit (TLV-C) as guide-lines to prevent workers from irritation, chronic or irreversible tissue damage, and narcosis caused by intense exposures to hazardous substances for short periods. To evaluate whether a worker's exposure level is within the specified limit, it is desirable to measure every 15-min time-weighted average concentration (15-min TWA) during a workday. The authors developed a revolving personal sampler that can collect consecutive short-term exposure samples. A recovery test of toluene of various concentrations was conducted by using this sampler. Toluene concentrations in the test atmosphere were 10, 50, 100, 200, and 400 ppm. The test results showed that the mean recovery at each concentration was 97.7% to 100.0%, and the coefficient of variation was 0.008 to 0.015. The revolving personal sampler can be used to monitor every 15-min TWA of a worker.     

Evaluation of biomarkers for occupational exposure to benzene.

OBJECTIVE--To evaluate the relations between environmental benzene concentrations and various biomarkers of exposure to benzene. METHODS--Analyses were carried out on environmental air, unmetabolised benzene in urine, trans, trans-muconic acid (ttMA), and three major phenolic metabolites of benzene; catechol, hydroquinone, and phenol, in two field studies on 64 workers exposed to benzene concentrations from 0.12 to 68 ppm, the time weighted average (TWA). Forty nonexposed subjects were also investigated. RESULTS--Among the five urinary biomarkers studied, ttMA correlated best with environmental benzene concentration (correlation coefficient, r = 0.87). When urinary phenolic metabolites were compared with environmental benzene, hydroquinone correlated best with benzene in air. No correlation was found between unmetabolised benzene in urine and environmental benzene concentrations. The correlation coefficients for environmental benzene and end of shift catechol, hydroquinone, and phenol were 0.30, 0.70, and 0.66, respectively. Detailed analysis, however, suggests that urinary phenol was not a specific biomarker for exposure below 5 ppm. In contrast, ttMA and hydroquinone seemed to be specific and sensitive even at concentrations of below 1 ppm. Although unmetabolised benzene in urine showed good correlation with atmospheric benzene (r = 0.50, P < 0.05), data were insufficient to suggest that it is a useful biomarker for exposure to low concentrations of benzene. The results from the present study also showed that both ttMA and hydroquinone were able to differentiate the background level found in subjects not occupationally exposed and those exposed to less than 1 ppm of benzene. This suggests that these two biomarkers are useful indices for monitoring low concentrations of benzene. Furthermore, these two metabolites are known to be involved in bone marrow leukaemogenesis, their applications in biological monitoring could thus be important in risk assessment. CONCLUSION--The good correlations between ttMA, hydroquinone, and atmospheric benzene, even at concentrations of less than 1 ppm, suggest that they are sensitive and specific biomarkers for benzene exposure.     

Hematological changes among Chinese workers with a broad range of benzene exposures

BACKGROUND: Depression of peripheral blood cells is a well-known indicator of benzene hematotoxicity. Previous studies of its effects on specific types of blood cells have yielded inconsistent results. We examine hematological findings and their possible relations with exposure markers validated in a recent biomarker project conducted in Tianjin, China. METHODS: Personal benzene exposures were sampled with 3-M organic vapor monitors, and analyzed by gas chromatography. The peripheral blood cells were counted by a cell counter. The WBC differential was manually counted on a total of 900 cells by a US commercial laboratory. RESULTS: A total of 130 exposed workers and 51 age- and gender-matched unexposed subjects were recruited in this study. Benzene exposure levels monitored on the day of biological sample collection for exposed workers ranged from 0.06 to 122 ppm. Their 4-week average and cumulative benzene exposure levels were 0.08-54.5 ppm and 6.1-623.2 ppm-years, respectively. Significant decreases of red blood cells (RBC), white blood cells (WBC), and neutrophils were observed and correlated with both personal benzene exposures and levels of urinary metabolites (S-phenylmercapuric acid and t,t-muconic acid) and albumin adducts of benzene oxide and 1,4-benzeoquinone. CONCLUSIONS: The depressions in RBC, WBC, and neutrophils observed in this study are not only exposure dependent, but also significantly different in the lowest exposed group (at or below 0.25 ppm) compared with unexposed subjects. The results of the present study appear to suggest that lymphocytes may not be more sensitive to chronic benzene exposure than neutrophils.     

Occupational exposures to noise resulting from the workplace use of personal media players at a manufacturing facility

This study examined the contribution of noise exposures from personal media player (PMP) use in the workplace to overall employee noise exposures at a Colorado manufacturing facility. A total of 24 workers' PMP and background noise exposures were measured. Twelve PMP users worked in high-background-noise exposure (HBNE) areas, and 12 worked in low-background-noise exposure (LBNE) areas. The self-selected PMP listening level of each worker was measured using an ear simulator, and the background noise of each employee workstation was measured using a sound level meter. Workers' self-reported PMP duration of use, PMP listening exposure levels, and background noise levels were used to estimate the daily occupational noise exposures. Measured background noise levels averaged 81 dBA for HBNE workers and 59 dBA for LBNE workers. Measured, free-field equivalent listening exposure levels were significantly greater for HBNE workers (85 dBA) compared with LBNE workers (75 dBA) (p = 0.0006). Estimated mean daily noise exposures for both groups were below the ACGIH threshold limit value for noise of 85 dBA8-hr time weighted average (TWA), specifically 84 dBA TWA for HBNE workers and 72 dBA TWA for LBNE workers. Three of 12 (25%) HBNE workers had estimated exposures greater than 85 dBA TWA when only background noise was considered, yet when PMP use was also considered, 6 of 12 (50%) had estimated exposures greater than 85 dBA TWA, suggesting that PMP use doubled the number of overexposed workers. None of the LBNE workers had estimated exposures greater than 85 dBA TWA. The contribution of PMP use to overall noise exposures was substantially less among HBNE workers than LBNE workers due to the disproportionate selection of noise-attenuating headsets among HBNE workers compared with LBNE workers. It is recommended that the facility management either restrict workplace PMP use among HBNE workers or require output-limiting technology to prevent occupational noise-induced hearing loss.     

Benzene exposures during gasoline loading at bulk marketing terminals.

A study was conducted at 20 gasoline bulk marketing terminals to determine benzene exposure levels to both Gulf and outside carrier personnel operating at these facilities. Emphasis was placed on breathing zone samples of short duration during loading of trucks at the rack. Racks utilizing various methods of product transfer were surveyed. From the results of the study, it can be seen that the largest employee exposure to benzene occurs at facilities utilizing top loading without vapor recovery. Exposures during loading can exceed 0.5 ppm for an eight-hour time-weighted average.