Assessment of complete blood count variations among workers exposed to low levels of benzene

Hematological Effects and Benchmark Doses of Long-Term Co-Exposure to Benzene, Toluene, and Xylenes in a Follow-Up Study on Petrochemical Workers

Benzene, toluene, and xylenes (BTX) commonly co-exist. Exposure to individual components and BTX-rich mixtures can induce hematological effects. However, the hematological effects of long-term exposure to BTX are still unclear, and respective reference levels based on empirical evidence should be developed. We conducted a follow-up study in BTX-exposed petrochemical workers. Long-term exposure levels were quantified by measuring cumulative exposure (CE). Generalized weighted quantile sum (WQS) regression models and Benchmark Dose (BMD) Software were used to evaluate their combined effects and calculate their BMDs, respectively. Many hematologic parameters were significantly decreased at the four-year follow-up (p < 0.05). We found positive associations of CE levels of benzene, toluene, and xylene with the decline in monocyte counts, lymphocyte counts, and hematocrit, respectively (β > 0.010, Ptrend < 0.05). These associations were stronger in subjects with higher baseline parameters, males, drinkers, or overweight subjects (Pinteraction < 0.05). BTX had positive combined effects on the decline in monocyte counts, red-blood-cell counts, and hemoglobin concentrations (Ptrend for WQS indices < 0.05). The estimated BMDs for CE levels of benzene, toluene, and xylene were 2.138, 1.449, and 2.937 mg/m3 × year, respectively. Our study demonstrated the hematological effects of long-term BTX co-exposure and developed 8h-RELs of about 0.01 ppm based on their hematological effects.

Derivation of an occupational exposure limit for benzene using epidemiological study quality assessment tools

This paper derives an occupational exposure limit for benzene using quality assessed data. Seventy-seven genotoxicity and 36 haematotoxicity studies in workers were scored for study quality with an adapted tool based on that of Vlaanderen et al., 2008 (Environ Health. Perspect. 116 1700-5). These endpoints were selected as they are the most sensitive and relevant to the proposed mode of action (MOA) and protecting against these will protect against benzene carcinogenicity. Lowest and No- Adverse Effect Concentrations (LOAECs and NOAECs) were derived from the highest quality studies (i.e. those ranked in the top tertile or top half) and further assessed as being "more certain" or "less certain". Several sensitivity analyses were conducted to assess whether alternative "high quality" constructs affected conclusions. The lowest haematotoxicity LOAECs showed effects near 2 ppm (8 h TWA), and no effects at 0.59 ppm. For genotoxicity, studies also showed effects near 2 ppm and showed no effects at about 0.69 ppm. Several sensitivity analyses supported these observations. These data define a benzene LOAEC of 2 ppm (8 h TWA) and a NOAEC of 0.5 ppm (8 h TWA). Allowing for possible subclinical effects in bone marrow not apparent in studies of peripheral blood endpoints, an OEL of 0.25 ppm (8 h TWA) is proposed.

Cancer Risk Assessment for Workers Exposed to Pollution Source, a Petrochemical Company, Iran

Background:

Air pollution have led to severe problem of adverse health effect in the world. This study aimed to conduct the health risk assessment, cancer risk analysis, and non-cancer risk for exposure to volatile organic compounds (VOCs) and hydrogen sulfide (H ₂ S) in petrochemical industry.

Methods:

In this cross-sectional research, 123 samples were collected in the ambient air in Iran during winter 2016. For sampling and analysis of VOCs and H ₂ S, 3 methods (numbers 1500, 1501, and 6013) presented by the National Institute of Occupational Safety and Health (NIOSH) were used. For determination of risk assessment of chemical pollutants, semi-quantitative method presented by the Occupational Safety and Health Division, Singapore was used. Finally, for calculation of cancer risk analysis, Chronic Daily Intake (CDI) and calculation of non-cancer risk, Exposure Concentration (EC) were used.

Results:

Average concentration of benzene (2.12±0.95) in breathing zone of workers were higher than the Threshold Limit Values-Time Weighted Average (TLV-TWA) (P<0.05). Among chemical substance, benzene had very high rank of risk in petrochemical industry. Rank of risk for H ₂ S, toluene, and xylene present in the breathing zone of workers was low. The mean cancer risk for workers exposed to benzene was estimated 8.78×10^−3, in other words, 8.7 cancer per 1000 i.e. higher than the acceptable standard of 10⁻⁶. In our study, non-cancer risk for BTX was higher than the acceptable standard of 1.

Conclusion:

In particular, overall cancer and toxic risk can be associated with long term exposure to benzene.

Environmental and Health Effects of Benzene Exposure among Egyptian Taxi Drivers

Objectives

To study environmental exposure to benzene as well as hematological effects of benzene exposure in taxi drivers.

Background

Exposure to benzene has been associated with adverse health effects, including haematopoietic disorders.

Methods

A retrospective cohort study was carried out from the beginning of April 2017, through the end of June 2018, on 280 taxi drivers (the exposed group) and 120 unexposed matched individuals (controls). The tools included a predesigned self-administered questionnaire which contained questions about personal data (e.g., age, educational level, and smoking) and exposure data (e.g., duration and nature of exposure). Investigations involved complete blood count. Environmental studies for light-chain aromatic hydrocarbons (BTEX components: benzene, toluene, ethylbenzene, and xylene) were done.

Results

Mean values (ppm) of ambient concentrations of benzene, toluene, ethylbenzene, and xylene (0.81 ± 0.42, 26.69 ± 0.54, 29.36 ± 2.35, and 25.11 ± 2.06, respectively) in the stations were higher than international permissible levels (P < 0.001). On studying the clinical manifestations during the last two weeks, the prevalence of pallor, dizziness, headache, waist and back pain, fatigue, dry throat, and discomfort was significantly higher in taxi drivers (27.1%, 24.3%, 21.4%, 28.6%, 45.7%, 24.3%, and 25.7%, respectively) than among the controls (6.7%, 4.2%, 6.7%, 10%, 10%, 6.7%, 6.7%, and 9.2%, respectively). For chronic diseases, hypertension was the most prevalent chronic disease among the drivers (17.1%) than the controls (5.8%) (P=0.002). Regarding self-assessment of health status, 20.0% of taxi drivers reported poor health while 31.4% reported very good health (P < 0.001). MCH (pg), TLC (×103/μl), and platelets (×103/μl) were significantly lower among taxi drivers (26.33 ± 2.31, 6.55 ± 1.38, and 189.07 ± 53.25, respectively) (P=0.005, <0.001, and <0.001 respectively).

Conclusion

Abnormal hematological findings among taxi drivers were found on exposure to benzene. Health of taxi drivers is generally affected. Setting a clinic for periodic checkup and health education for taxi drivers is highly recommended.

The hematologic effects of BTEX exposure among elderly residents in Nanjing: a cross-sectional study

Few studies have examined the effects of environmental concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX) on the hematologic system of residents near a petrochemical complex. This study evaluated the potential effects of blood BTEX concentrations on the hematologic parameters of residents in a community near a petrochemical complex (contaminated group) and another community free of known petrochemical pollution (control group). Volunteer residents were randomly recruited. Each participant completed a questionnaire and donated blood samples to evaluate blood BTEX concentrations and hematologic parameters. We found the mean concentrations of blood BTEX of the contaminated group were 1.2 to 6.7 times higher than the control group. Multiple hematologic parameters of participants were significantly different between the two study groups. Inverse associations were found for ln-transformed blood benzene concentrations with mean corpuscular hemoglobin concentration (MCHC) (β = - 2.75) and platelet counts (β = -8.18). Several weaker associations were also observed between other compounds and multiple hematologic parameters. Our results suggest that the residents living near petrochemical complexes have higher blood BTEX concentrations. Furthermore, the increased blood BTEX levels in residents are associated with the reduction in RBC counts, hemoglobin concentration, hematocrit, MCHC, and platelet counts. This study provided particularly important information for the health risk assessment of residents living near petrochemical complexes.

Occupational health risk of working in garages: comparative study on blood pressure and hematological parameters between garage workers and Haramaya University community, Harar, eastern Ethiopia

Background

Occupational exposure to chemicals in garages causes a wide range of biological effects, depending upon the level and duration of exposure. In Ethiopia, there have been few studies conducted to assess the exposure of garage workers to chemicals. Preceding studies have not explored the effect of working in garage on blood pressure and hematological parameters. Therefore, this study aimed to assess differences in blood pressure and hematological parameters among garage workers compared to the Haramaya University community, Harar, eastern Ethiopia.

Materials and methods

A comparative cross-sectional study was conducted in Harar town, eastern Ethiopia. Thirty garage workers were selected and compared with 30 age- and sex-matched controls comprising of teachers and students. Demographic and occupational data were collected by using a structured questionnaire by a trained data collector. Blood pressure was measured using sphygmomanometry. Hematological parameters were measured with an automated hematology analyzer. Data were analyzed using Stata version 13.

Results

The majority of the garage workers did not implement effective preventive or control measures for workplace chemical exposure. Statistically significant increases were found in systolic (128.67±18.14 vs 106.33 ±9.27 mmHg, P<0.0001), diastolic blood pressure (90.33±11.29 vs 75.67 ±5.68 mmHg, P<0.0001), total white blood cells (7.9±1.51 vs 6.72±2.04×10⁹ cells/L, P=0.0138), and platelets (323.20±48.82 vs 244.1±47.3×10⁹ cells/L, P<0.0001) in garage workers compared to the control group. On the other hand, statistically significant decreases were found in red blood cells (5.13±0.38 vs 5.46±0.36×10¹² cells/L, P=0.0006), hemoglobin (14.89±0.71 vs 15.45±0.87 g/dL, P=0.0062), hematocrit (43.98%±1.99% vs 46.4%3±2.32%, P<0.0001), and mean corpuscular volume (83.19±2.93 vs 85.11±3.87 fL, P=0.0353) among garage workers compared to the control group.

Conclusion

There were significant differences in blood pressure and hematological parameters between garage workers and the control group. Therefore, appropriate and effective safety measures need to be taken by the workers to prevent possible chemical exposure during routine tasks.

Shanghai Health Study (2001-2009): What was learned about benzene health effects?

The Shanghai Health Study (SHS) was a large epidemiology study conducted as a joint effort between the University of Colorado and Fudan University in Shanghai, China. The study was funded by members of the American Petroleum Institute between 2001 and 2009 and was designed to evaluate the human health effects associated with benzene exposure. Two arms of the SHS included: an occupational-based molecular epidemiology study and several hospital-based case control studies. Consistent with historical literature, following sufficient exposure to relatively high airborne concentrations and years of exposure, the SHS concluded that exposure to benzene resulted in an increased risk of various blood and bone marrow abnormalities such as benzene poisoning, aplastic anemia (AA), myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML). Non-Hodgkin lymphoma (NHL) was not significantly increased for the exposures examined in this study. Perhaps the most important contribution of the SHS was furthering our understanding of the mechanism of benzene-induced bone marrow toxicity and the importance of identifying the proper subset of MDS relevant to benzene. Investigators found that benzene-exposed workers exhibited bone marrow morphology consistent with an immune-mediated inflammatory response. Contrary to historic reports, no consistent pattern of cytogenetic abnormalities was identified in these workers. Taken together, findings from SHS provided evidence that the mechanism for benzene-induced bone marrow damage was not initiated by chromosome abnormalities. Instead, chronic inflammation, followed by an immune-mediated response, is likely to play a more significant role in benzene-induced disease initiation and progression than previously thought.

Occupational benzene exposure from vehicular sources in India and its effect on hematology, lymphocyte subsets and platelet P-selectin expression

Benzene exposure from vehicular sources and its health impact are relatively unexplored in India. We have investigated in this study hematology and lymphocyte subsets of 25 petrol pump attendants, 25 automobile service station workers and 35 controls matched for age, sex and socioeconomic conditions. The participants were non-smoking males of Kolkata (former Calcutta) in eastern India. Compared with controls, the workers had 3.8- times more trans,trans-muconic acid in urine, suggesting higher level of benzene exposure. The exposed subjects had decreased erythrocyte, hemoglobin, lymphocyte and platelet levels, but increased neutrophil, band cells, RBC aniso-poikilocytosis and target cells. In addition, CD4+, CD8+ and CD19+ cells were decreased by 37, 20 and 47% respectively, but CD 16+ 56+ NK cells were increased by 20%. P-selectin expression on platelet surface of the workers was significantly elevated ( P < 0.05), indicating upregulation of platelet activity. In summary, the study revealed high level of benzene exposure from vehicular sources in India, and the exposed subjects had hematological and immunological alterations. Toxicology and Industrial Health 2007; 23: 167—175.

Evaluation of adverse health risks associated with antineoplastic drug exposure in nurses at two Chinese hospitals: The effects of implementing a pharmacy intravenous admixture service

OBJECTIVE

To determine the health risks of antineoplastic drugs (ADs) occupational exposure in nurses and to evaluate the effects of implementing a pharmacy intravenous admixture service (PIVAS) in two Chinese hospitals.

METHODS

The laboratory findings were collected from annual staff physical examination data. Reproductive toxicity and clinical manifestations were self-reported via a questionnaire.

RESULTS

Hematotoxicity, organ damage, reproductive toxicity, and clinical manifestations associated with AD exposure were markedly higher in oncology nurses than unexposed nurses. Application of PIVAS led to a significant restoration of the blood cell counts and kidney function, and a reduction in adverse reproductive outcomes among oncology nurses. Pronounced symptoms related to AD exposure were alleviated as well.

CONCLUSION

Oncology nurses who work with AD's experienced more adverse health outcomes than unexposed nurses. The health risks to AD were significantly alleviated by implementing a pharmacy intravenous admixture service.

Hematological effect of benzene exposure with emphasis of muconic acid as a biomarker

Human exposure to benzene in work environment is a global occupational health problem. It is established that benzene requires to be metabolized to induce its effects. Benzene has been associated with various hematotoxins and carcinogens. The aim of this study was to investigate the effect of benzene on complete blood picture, with emphasis of trans, trans-muconic acid (t,t-MA) as a biomarker of benzene in urine, considering the influence of cigarette smoke. A total of 81 workers (61 males and 20 females) have been occupationally exposed to benzene. In addition, 83 workers (55males and 28 females) were also recruited as a control group. Complete blood picture was analyzed and urinary t,t-MA was determined by liquid chromatography. In addition, creatinine in the urine samples was determined. Levels of blood elements (white blood cells, red blood cells and platelets) were decreased among exposed workers compared with the controls. The urinary level of t,t-MA/creatinine of the exposed workers was elevated especially in the smoking group compared to the controls. This study recommends that complete blood picture and t,t-MA are helpful biomarker tests that should be done to detect the early effects of benzene exposure.

Hematological Evidence of Occupational Exposure to Chemicals and Other Factors among Auto-Repair Workers in Rawalpindi, Pakistan

Objectives

Occupational exposure to aromatic solvents causes many serious health hazards to workers, especially if an ambient environment increases the exposure during routine working hours. This study was conducted on two related groups, i.e., automobile mechanics (MCs) and automobile spray painters (PNs), with an effort to analyze effects of chemical exposure on hematological parameters, keeping a focus on environmental parameters and workers’ personal behavioral characteristics that could be held responsible for increasing exposure risk.

Methods

A preliminary survey of various chemicals used in these places was done, and 78 blood samples were collected from three groups (control, n = 24; mechanics, n = 25; painters, n = 29). Demographic features of workers were recorded through a short questionnaire.

Results

Results showed that mean red blood cell (RBC) count was lower both in MCs [t(51) = 2.38, p < 0.021, r = 0.32] and in PNs [t(47) = 2.12, p < 0.03, r = 0.29], whereas mean hemoglobin (Hb) was significantly lower in MCs [t(51) = 2.5, p = 0.017, r = 0.33]. Combined data for exposed groups for smokers (SMs) versus nonsmokers (NSs) showed that SMs had a significantly lower number (RBC count: t(52) = 2.28, p < 0.027, r = 0.25; Hb count: t(52) = 2.71, p < 0.009, r = 0.30] of these parameters than NSs, even compared to the control group. Moreover, logistic regression results showed that smoking is a significant predictor of reduction in RBC and Hb counts, besides occupational exposure and work experience to a little extent among exposed workers. Mean white blood cell count [t(47) = 2.63, p < 0.01, r=0.35], mean corpuscle volume [t(47)= –2.82, p = 0.007, r = 0.29], and packed cell volume [t(47)= –2.28, p = 0.027, r = 31] were higher exclusively in painters, which could be related to exposure to benzene in addition to isocyanate.

Conclusion

It appeared that workplace exposure may be complex due to interaction of multiple factors and PNs face much more exposure to isocyanate and aromatic solvents than MCs, which had significant effects on their hematopoiesis. Smoking enhances exposure risk manifolds, and among MCs it showed combined effects along with occupational exposure. There is a need to create awareness among these workers to adopt self-safety measures during routine tasks and also of a separate study to elucidate actual occupational exposure among them, eliminating confounding factors.

Effects of environmental benzene: micronucleus frequencies and haematological values in traffic police working in an urban area

Among the toxic chemicals present in the ambient air of urban centres, benzene raises particular concern due to its haematoxicity and leukaemogenic hazards, probably related to clastogenic factors. However, little is known about the health risks associated with environmental--rather than industrial--exposure to benzene. We analysed micronucleus (MN) frequencies in peripheral lymphocytes by use of the cytokinesis-block technique, and haematological parameters among 49 traffic police and 36 indoor workers (controls) in the city of Bologna. The analysis of urban air provided by a municipal air-quality monitoring station indicated that the levels of environmental benzene were often above the recommended threshold level (10 microg/m3) whereas other pollutants--nitrogen oxides, polycyclic aromatic hydrocarbon compounds, total suspended particulate matter, carbon monoxide, sulfur dioxide--did not exceed the maximum atmospheric concentration established for air-quality standards. Mean levels of individual airborne benzene exposure--as measured by personal devices worn during 4-h morning work-shifts--were six-fold higher in the traffic police than in controls (P=0.001). While no significant difference in haematological parameters was found between the two groups, MN frequency was significantly higher among the traffic police than in indoor workers (P=0.001). Among the study population, MN frequency was found to increase with age, but no influence was observed for gender or smoking. Although it cannot be excluded that the increase of MN frequency observed in traffic police could also depend, apart from benzene, on the complex mixture of pollutants encountered in urban air, our data indicate that elevated personal benzene exposure could represent a genetic risk. The analysis of biomarkers of genetic damage in subjects particularly exposed to environmental benzene deserves careful study.

A hematology surveillance study of petrochemical workers exposed to benzene

Historically, complete blood counts (CBCs) have been recognized as an easy and readily available screen for hematotoxicity following occupational exposure to benzene. The purpose of this study is to evaluate hematology data from employees who have ever participated in the Shell Benzene Medical Surveillance Program (BMSP) compared to employees who have not participated and to examine the sensitivity of CBCs to detect hematological changes in a low-exposure occupational setting. This large study included 1200 employees who participated in the BMSP, with mean benzene exposure (TWA-8) of 0.60 ppm from 1977 to 1988 and 0.14 ppm since 1988, and 3227 comparison employees. The comparison group included employees not enrolled in either the benzene or butadiene surveillance programs. Abnormality of six CBC parameters and the adjusted mean values of these parameters in the exposed group were compared with that of the comparison group. We found no increased abnormality for any hematology parameter among exposed employees. The adjusted mean values (adjusted for age, sex, race, length of time between first and last exam, and current smoking status) of the exposed employees were similar to those in the comparison group. At current occupational exposure levels for benzene, no evidence of adverse hematological effects was observed in this study. These results raise the question of whether annual CBC surveillance for benzene-exposed workers has adequate sensitivity to detect meaningful hematological changes due to low-level exposures.

Hematological changes due to chronic exposure to natural gas leakage in polluted areas of Masjid-i-Sulaiman (Khozestan province, Iran)

An overwhelming number of studies have given consistent findings that environmental or occupational exposure to oil products results in a significant decrease in circulating erythrocytes, hemoglobin, platelets, total white blood cells, and absolute numbers of lymphocytes and neutrophils. Some parts of Masjid-i-Sulaiman (located in the southwest of Iran) are contaminated by subsurface leakage of natural gas, which contains a high level of hydrogen sulfide. The amount of all reactive sulfur compounds in air of contaminated areas of MIS was estimated as equal to 0.023+/-0.002 ppm of SO(2). In the present report the hematological findings of 99 persons from polluted areas of MIS were compared with those of 396 individuals from the general population of MIS matched by age (+/-3 years) and sex. The CBC test and the WBC differential were analyzed in one central laboratory according to standard hematological methods, by Coulter S (Biomedical). The multiple linear regression method was applied in order to detect differences among exposed and unexposed groups for hematological markers. The absolute mean number of red blood cells, percentages of hematocrit, level of hemoglobin, and absolute number of platelets were significantly higher among the exposed subjects compared with the control group. However, the absolute mean numbers of white blood cells, lymphocytes, and neutrophils were significantly decreased in the exposed group compared with the control.

Modulation of hematology changes by polymorphism of glutathione S-transferase M1 and T1

Workers in the petroleum distribution trades experience relatively low-level exposures to gasoline vapors whose consequences have not been fully elucidated. The purpose of this study was to investigate changes in the hematological parameters among filling station workers who were occupationally exposed to gasoline. The target group for the study consisted of 41 workers from eight filling stations of Shiraz (south of Iran). The control group consisted of 27 healthy subjects matched for age and sex from general population. The complete blood count analysis was done in one laboratory. Using PCR-based method, the genotypes of glutathione S-transferase T1 (GSTT1) and M1 (GSTM1) were determined. Workers were divided into three exposure groups according to employment history: duration less than 1 year, 1-5 years, and more than 5 years. Comparison was performed using Kruskal-Wallis test. In the individuals with the presence of both GSTT1 and GSTM1 functional alleles, comparison between four exposure groups revealed no significant difference for studied hematological variables. There were statistically significant differences between study groups, with only one functional allele, either GSTT1 or GSTM1, for relative number of lymphocytes (chi(2)=9.147, df=3, P=0.027) and neutrophils (chi(2)=9.951, df=3, and P=0.019), and absolute number of lymphocytes (chi(2)=9.135, df=3, and P=0.028), and RBC (chi(2)=10.586, df=3, and P=0.014). These findings could indicate the possible protective effect of concurrent presence of GSTM1 and GSTT1 enzymes on the hematopoietic system of filling station workers.

Utility of a routine medical surveillance program with benzene exposed workers

BACKGROUND

A medical surveillance program of benzene-exposed workers has to be established in such a way as to observe early signs of benzene-induced cytopenia, pancytopenia, or leukemia. This study evaluates the utility of routine medical survey applied to benzene-exposed workers by analyzing the hematological, immunological, and cytogenetic assay results.

METHODS

The results of a previous study of hematological, immunological, and cytogenetic assays in benzene-exposed workers (up to 15 ppm) are used to discuss medical surveillance program by defining the relationship between various benzene exposure concentrations and toxic endpoints.

RESULTS

Exposure to benzene concentration lower than 5 ppm does not produce any abnormal hematological measurements. For benzene cumulative exposure above 100 (ppm-years), some blood indices [mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), band neutrophils] show significant differences in comparison to the control group. The incidence of dicentric chromosomes was higher and the level of B-lymphocytes was lower even with workers exposed to 5 ppm of benzene; correlation with exposure indicators was not found.

CONCLUSIONS

The results suggest that peripheral blood indices, although not sensitive enough, are still the most suitable parameters in a health surveillance program applied to benzene-exposed workers. B-lymphocytes could be a promising indicator of the benzene-induced damage. Cytogenetic tests did not prove to be suitable. Further investigation of useful screening tests for health surveillance program of benzene-exposed workers is still required.

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.