Risk assessment of leukaemia and occupational exposure to benzene.

Experimental toxicological studies have offered clear evidence that benzene induces haematopoietic neoplasms, and it is generally accepted that exposure to benzene is a risk factor for leukaemia, in particular for acute non-lymphatic leukaemia. Quantitative aspects of benzene risk assessment are still a matter of controversy, however. In several risk assessments an estimated 50 deaths from leukaemia per 1000 deaths would arise from exposures to benzene of 10 ppm during a working life of 30 years. The assessment presented in this paper leads to lower estimates, which are more in agreement with the weak toxicological data. Furthermore, an approach is presented to incorporate the results of low exposure epidemiological studies into the process of quantitative risk assessment.     

Risk assessment of leukaemia and occupational exposure to benzene

Experimental toxicological studies have offered clear evidence that benzene induces haematopoietic neoplasms, and it is generally accepted that exposure to benzene is a risk factor for leukaemia, in particular for acute non-lymphatic leukaemia. Quantitative aspects of benzene risk assessment are still a matter of controversy, however. In several risk assessments an estimated 50 deaths from leukaemia per 1000 deaths would arise from exposures to benzene of 10 ppm during a working life of 30 years. The assessment presented in this paper leads to lower estimates, which are more in agreement with the weak toxicological data. Furthermore, an approach is presented to incorporate the results of low exposure epidemiological studies into the process of quantitative risk assessment.     

Malignancies due to occupational exposure to benzene

There is no doubt about the leukemogenic effect of benzene in man. The evidence is as follows: (1) The incidence of leukemia in shoeworkers exposed to benzene in a period of 8 years in Istanbul was 13.6/100,000, which is significantly higher than that for leukemia in the general population. (2) Following the phase-out of benzene in Istanbul, the number of leukemic workers decreased and none were reported in the subsequent 3 years. (3) The development of leukemia in pancytopenic patients with benzene exposure was observed in 13 out of 51 patients. (4) The differences in the distribution of the types of leukemia in individuals exposed and in nonexposed groups were as follows: acute leukemia 96.1% in the former group, and 46% in the latter group. The high percentages of acute erythroleukemia and preleukemia were other interesting findings in the exposed group. (5) Two cases of leukemia were observed in a 6-year period at a tire cord manufacturing plant with 550 workers. At one location in the plant the concentration of benzene measured by gas chromatography was nearly 110 ppm. Additionally, we have studied 12 cases of malignant lymphoma, four cases of multiple myeloma, and six cases of lung cancer, all of whom were chronically exposed to benzene. The possible role of benzene in the etiology of these malignancies is discussed.     

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.     

Biological monitoring of occupational exposure to benzene and toluene

This study was carried out to evaluate the biological monitoring of occupational exposure to benzene and toluene in a total number of 31 male exposed workers and 30 control subjects. The present study showed a statistically significant higher level of biological indices of exposure (p < 0.01) of phenol and hippuric acid in urine of workers exposed to benzene and toluene than control subjects. Significant changes (p < 0.05, 0.01) in the levels of hematological and biochemical findings have been observed among exposed workers and control group. In addition, statistically significant higher levels of Mg, Mn and Ca were found among workers exposed to benzene and toluene while statistically significant lower levels of serum iron (p < 0.05) have been observed. No significant variations could be detected in the level of Zn and Cu between exposed and control subjects.     

Evaluation of occupational exposure to benzene by urinalysis

Urinary phenol determinations have traditionally been used to monitor high levels of occupational benzene exposure. However, urinary phenol cannot be used to monitor low-level exposures. New biological indexes for exposure to low levels of benzene are thus needed. The aim of this study was to investigate the relations between exposure to benzene (Abenzene, ppm), as measured by personal air sampling, and the excretion of benzene (U-benzene, ng/l),trans,trans-muconic acid (MA, mg/g creatinine), andS-phenylmercapturic acid (PMA, g/g creatinine) in urine. The subjects of the study were 145 workers exposed to benzene in a chemical plant. The geometric mean exposure level was 0.1 ppm (geometric standard deviation = 4.16). After logarithmic transformation of the data the following linear regressions were found: log (U-benzene, ng/l) = 0.681 log (A-benzene ppm) + 4.018; log (MA, mg/g creatinine) = 0.429 log (A-benzen ppm) – 0.304; and log (PMA, g/g creatinine) = 0.712 log (A-benzene ppm) + 1.664. The correlation coefficients were, respectively, 0.66, 0.58, and 0.74. On the basis of the equations it was possible to establish tentative biological limit values corresponding to the respective occupational exposure limit values. In conclusion, the concentrations of benzene, mercapturic acid, and muconic acid in urine proved to be good parameters for monitoring low benzene exposure at the workplace.     

职业苯暴露生物标志物研究进展

苯是一种广泛存在于工业和生活环境中的化学污染物。长期、较大剂量接触苯可引起人体外周血白细胞减少、骨髓造血功能抑制,甚至导致白血病。1982年国际癌症研究中心（IARC）将苯列为确定的人类致癌物。基于苯对人体的危害性,世界诸多发达国家均制订了工作场所相应的职业卫生标准以保护职业苯接触工人的身体健康,但由于作业环境苯浓度的监测数据并不能完全客观地反映个体接触的实际情况和个体易感性,尤其不能反映机体体内蓄积作用（内暴露剂量）,用于对长期低剂量职业苯接触工人的危险度评价有一定的局限性。苯的生物标志物因其灵敏度高,特异性强,更能客观、全面、准确反映工人的实际接苯状况,因此更适合作为职业苯接触工人暴露水平检测、健康监护、暴露危害性评价。生物标志物根据性质不同可分为接触标志物、效应标志物和易感性标志物。     

Biological monitoring of occupational exposure to low levels of benzene.

To obtain reference values for the biological monitoring of benzene, the kinetics of benzene were studied in volunteers. Benzene in blood and expired air could easily be followed until the next morning after a 4-h exposure to a benzene concentration of 10 cm3.m-3. Even after exposure to 1.7 cm3.m-3 the benzene levels in the morning blood and expired air samples differed from those in unexposed subjects. One hour after exposure to 10 and 1.7 cm3.m-3 the mean levels of benzene were 238 and 25 nmol.l-1 in blood and 13.2 and 2.5 mumol.m-3 in exhaled air, respectively. It was concluded that, at high benzene levels (approximately 10 cm3.m-3), samples collected 16 h after exposure reflect the body burden of benzene, while at low exposure (< 1 cm3.m-3) samples collected 1 h after exposure may be used to estimate the exposure over the preceding few hours. Exposure to benzene from smoking is a potential confounder in estimating occupational exposure to low levels of benzene.     

Environmental and occupational exposure to benzene by analysis of breath and blood.

Benzene exposure of chemical workers was studied, during the entire workshift, by continuous monitoring of workplace benzene concentration, and 16 hours after the end of the workshift by the measurement of alveolar and blood benzene concentrations and excretion of urinary phenol. Exposure of hospital staff was studied by measuring benzene concentrations in the alveolar and blood samples collected during the hospital workshift. Instantaneous environmental air samples were also collected, at the moment of the biological sampling, for all the subjects tested. A group of 34 chemical workers showed an eight hour exposure to benzene, as a geometric mean, of 1.12 micrograms/l which corresponded, 16 hours after the end of the workshift, to a geometric mean benzene concentration of 70 ng/l in the alveolar air and 597 ng/l in the blood. Another group of 27 chemical workers (group A) turned out to be exposed to an indeterminable eight hour exposure to benzene that corresponded, the morning after, to a geometric mean benzene concentration of 28 ng/l in the alveolar air and 256 ng/l in the blood. The group of hospital staff (group B) had a benzene concentration of 14 ng/l in the alveolar air and 269 ng/l in the blood. Instantaneous environmental samples showed that in the infirmaries the geometric mean benzene concentration was 58 ng/l during the examination of the 34 chemical workers, 36 ng/l during the examination of the 27 chemical workers (group A), and 5 ng/l during the examination of the 19 subjects of the hospital staff (group B). Statistical analysis showed that the alveolar and blood benzene concentrations in the 34 workers exposed to 1.12 microgram/l of benzene differed significantly from those in groups A and B. It was found, moreover, that the alveolar and blood benzene concentrations were higher in the smokers in groups A and B but not in the smokers in the group of 34 chemical workers. The slope of the linear correlation between the alveolar and the instantaneous environmental benzene concentrations suggested a benzene alveolar retention of about 55%. Blood and alveolar benzene concentrations showed a highly significant correlation and the blood/air partition coefficient, obtained from the slope of the regression line, was 7.4. In the group of the 34 chemical workers no correlation was found between the TWA benzene exposure and the urinary phenol excretion.     

New PBPK model applied to old occupational exposure to benzene

An intensive program of benzene monitoring using new techniques was undertaken in Western Europe in the late 1960s and early 1970s. Significant exposure was found in the transport of benzene and gasoline, particularly during the loading of barges, and during the loading and operation of sea-going vessels. The ceiling threshold limit value of 25 ppm recommended at that time generated problems in assessing exposure, so alternative criteria were proposed. During that period some shore-based exposures were reported, and their significance was discussed in several articles. The information gained at that time is reexamined by physiologically based pharmacokinetic (PBPK) modeling and is used to help validate an improved PBPK model, which is described and tested on results from experimental exposure in a companion article. The old field data, comprising five specific studies, confirm the relevance of modeling to assessment of occupational exposure, and demonstrate its value for interpretation of field data, which is seldom as complete, systematic, or accurate as that obtained in experimental work. The model suggests that metabolism of benzene in humans may not be restricted to the liver. Sites and processes of metabolism merit further investigation.     

职业苯暴露生物标志物的研究现状

苯作为有机化学生产过程中广泛使用的原料,在生产环境中多以蒸气形式由呼吸系统进入人体,主要分布在含类脂质较多的组织和器官,如骨髓、脑髓、脂肪组织和肝脏[1],体内苯主要在肝脏代谢,在肝微粒体上的细胞色素P450(CYP)介导下苯被氧化成环氧化苯.通过对DNA的直接损伤作用,而引起造血系统的损害[2].苯已被国际癌症研究机构定为Ⅰ类化学致癌物[3].发达国家现将苯接触阈值限值-时间加权平均浓度(TLV-TWA)降至32 mg/m3以下,美国则降至0.32 mg/m3,我国现行GBZ2-2002<工作场所有害因素职业接触限值>中规定生产环境空气中苯的时间加权平均容许浓度为6 mg/m3,而短时间接触容许浓度(PC-STEL)为10 mg/m3[4].1989年至2000年国内期刊报道有28例苯白血病[5].Stockstad等[6]报道在鞋厂工作的工人接触1 mg/m3的苯浓度仍可引起人体白细胞和淋巴细胞减少.Lan Q等[7]认为40 mg/m3以下苯作业工人易罹患骨髓瘤.苯还可诱导血清活性氧水平,引起细胞成分包括DNA氧化损伤[8].     

Projections of leukemia risk associated with occupational exposure to benzene

In 1982, White et al published an assessment of quantitative leukemia risk associated with lifetime occupational exposure to benzene. At about the same time, IARC (1982) published estimates of quantitative cancer risk associated with industrial chemicals. Benzene was one of the two chemicals selected by IARC for its risk estimation. This paper presents a summary of these assessments along with new study results demonstrating adverse effects on bone marrow and peripheral blood cells as a result of low-level benzene exposure. Mathematical extrapolations based on epidemiologic studies are consistent with a finding of significant risk of dying from leukemia under the current occupational permissible exposure limit of 10 ppm. Although a significant reduction of risk could be expected to be achieved by reducing exposure to 1 ppm, a significant risk may still remain. The uncertainty of the dose-response projections rests on the underlying estimates of relative risk of death from leukemia, the estimates of benzene exposure (dose), and the appropriateness of the mathematical model. Recent findings in experimental animals demonstrate chromosomal damage to bone marrow cells, significant depression of the bone marrow, and disturbances of immune system function as a result of less than 1 week of exposure to the current permissible benzene exposure limit of 10 ppm. This was the lowest dose tested. These experimental findings provide further evidence of a potentially significant risk of bone marrow proliferative cancer (leukemia) as a result of low-dose benzene exposure.     

Environmental and occupational exposure to benzene by analysis of breath and blood

Benzene exposure of chemical workers was studied, during the entire workshift, by continuous monitoring of workplace benzene concentration, and 16 hours after the end of the workshift by the measurement of alveolar and blood benzene concentrations and excretion of urinary phenol. Exposure of hospital staff was studied by measuring benzene concentrations in the alveolar and blood samples collected during the hospital workshift. Instantaneous environmental air samples were also collected, at the moment of the biological sampling, for all the subjects tested. A group of 34 chemical workers showed an eight hour exposure to benzene, as a geometric mean, of 1.12 micrograms/l which corresponded, 16 hours after the end of the workshift, to a geometric mean benzene concentration of 70 ng/l in the alveolar air and 597 ng/l in the blood. Another group of 27 chemical workers (group A) turned out to be exposed to an indeterminable eight hour exposure to benzene that corresponded, the morning after, to a geometric mean benzene concentration of 28 ng/l in the alveolar air and 256 ng/l in the blood. The group of hospital staff (group B) had a benzene concentration of 14 ng/l in the alveolar air and 269 ng/l in the blood. Instantaneous environmental samples showed that in the infirmaries the geometric mean benzene concentration was 58 ng/l during the examination of the 34 chemical workers, 36 ng/l during the examination of the 27 chemical workers (group A), and 5 ng/l during the examination of the 19 subjects of the hospital staff (group B). Statistical analysis showed that the alveolar and blood benzene concentrations in the 34 workers exposed to 1.12 microgram/l of benzene differed significantly from those in groups A and B. It was found, moreover, that the alveolar and blood benzene concentrations were higher in the smokers in groups A and B but not in the smokers in the group of 34 chemical workers. The slope of the linear correlation between the alveolar and the instantaneous environmental benzene concentrations suggested a benzene alveolar retention of about 55%. Blood and alveolar benzene concentrations showed a highly significant correlation and the blood/air partition coefficient, obtained from the slope of the regression line, was 7.4. In the group of the 34 chemical workers no correlation was found between the TWA benzene exposure and the urinary phenol excretion.     

Urinary phenylmercapturic acid as a marker of occupational exposure to benzene

A hand-saving HPLC method to measure urinary phenylmercapturic acid (PMA) was developed which allows about 35 PMA determinations per day. The method involves conversion of pre-PMA to PMA by the addition of sulfuric acid to a urine sample, extraction into an ether-methanol mixture followed by condensation under a nitrogen stream. The condensate was introduced to a ODS-3 column in a HPLC system, and PMA in the column was eluted into a mobile phase of acetonitrile: methanol: perchloric acid: water. The elution of PMA was monitored at 205 nm. One determination will be completed in 40 min. The method was applied to analysis of end-of-shift urine samples from 152 workers exposed up to 210 ppm benzene, 66 workers exposed to a mixture of benzene (up to 116 ppm) and toluene + xylenes (up to 118 ppm), and 131 non-exposed controls of both sexes. A linear regression was established between time-weighted average intensity of exposure to benzene and urinary PMA. From the regression, it was calculated that urinary PMA level will be about 6.4 mg/l after 8-hour exposure to benzene at 100 ppm, and that PMA in urine accounted for about 0.1% of benzene absorbed. No effects of sex, age, and smoking habit of individuals were detected, and the effect of co-exposure to toluene + xylenes at the levels comparable to that of benzene was essentially nil, which indicates an advantage of PMA as a benzene exposure marker over monoto tri-phenolic metabolites or t,t-muconic acid.