Occupational Health Risk Assessment Of Exposure To Benzene At Low Levels

Objective:This study is aims to describe the distribution of benzene exposure of mainly districts and to clarify top 5 of industries in China.And risk assessment model is used to evaluate health hazards of workers that exposed to benzene at low level.Methods:1.The distribution of benzene in six districtsSix districts(Tianjin,Shandong,Jiangsu,Sichuan,Fujian and Guangdong province)with large production and consumption of benzene are selected.Distribution of industries and concentration of air benzene in each of 6 districts are analyzed.Blood cell counts of benzene-exposed workers from 2 typical districts(Tianjin and Jiangsu)are analyzed.2.Occupational health risk assessment of benzene2.1 Concentration monitoringAll benzene-exposed workers from 3 factories in Tianjin and Shandong province are selected to have field investigation and concentration monitoring.Passive air samplings are wear by benzene-exposed workers for a whole shift,and post-shift urine was collected.Gas chromatography is used to analysis concentration of air benzene.The concentration of urinary S-phenylmercapturic acid(S-PMA)and trans,trans-muconic acid(t,t-MA)concentration are analyzed by Ultra performance liquid chromatography tandem triple quadrupole mass spectrometry.2.2 Linearized multistage model is established based on the Chinese benzene cohort studyThe maximum likelihood estimation methods(MLEs)was used to analyze the leukemia incidence data of the Chinese benzene cohort study,and the external-dose based linearized multistage(ELMS)model was obtained.The internal-dose based linearized multistage(ILMS)model is derived after establishing the linearized regression relationship(adjusting for smoking,SMO)between urinary S-PMA and t,t-MA and air benzene of 98 workers from two factories of Shandong.2.3.Carcinogenic risk assessment of benzeneThe United States Environmental Protection Agency(EPA)carcinogenic inhalation risk assessment model and the ELMS model are used to assess the carcinogenic risk of benzene-exposed workers in both of benzene-exposed industries(top five industries)of six districts and the 3 factories in Shandong and Tianjin province.2.4.Non-carcinogenic risk assessment of benzeneThe Singapore semi-quantitative risk assessment model and the EPA non-carcinogenic inhalation risk assessment model are used to assess the non-carcinogenic risks of two companies in Shandong Province.Results:1.Benzene exposure in ChinaManufacturing industry is the main benzene exposure industry in 3111 enterprises from 6 districts.Time-weighted average(TWA)of air benzene in most of enterprises are less than 2 mg/m3.The average concentration of air benzene in top 5 of industries is 0.6 mg/m3.Few of workers in some industries(automobile manufacturing,ferrous metal smelting and rolling processing industry,and general equipment manufacturing industry)are still expose to a higher concentration(≥6 mg/m3)of benzene exposure.The proportions of benzene-exposed workers from top 5 of industries in Tianjin and Jiangsu province whose white blood cell counts are less than 4×109/L(lower limit of normal white blood cell count)are 4.9%and 3.3%,respectively.And their proportion of declined neutrophil counts(less than 2×109/L)are 5.4%and 3.1%,respectively.Workers with a white blood cell count<4×109/L are mainly work in local factories from one of top 5 of industry;for workers in Tianjin are the petroleum,coal and other fuel processing industries;while workers in Jiangsu are chemical raw materials and chemical product manufacturing industries.The platelet count or white blood cell count of benzene-exposed workers in Tianjin and Jiangsu province are decreased with the increasing of working duration(P<0.001).2.Occupational health risk assessment of benzene2.1 Results of concentration monitoringTwo times of benzene concentration monitoring were carried out on 20 benzene workers in benzene enterprises in Tianjin,and the results were 0.48±0.75 mg/m3 and 1.60±3.36 mg/m3.In the first monitoring,the concentration of air benzene of 10 workers was lower than the detection limit(0.05 mg/m3).There was no significant difference in the concentration of urinary metabolites among the 10 workers(P value larger than 0.05).The concentration of 98 benzene workers in two factories in Shandong province was measured for three times,and the concentration of benzene in 73.5%of air samples are less than 6 mg/m3.The average concentration of air benzene of 98 workers is 11.81±33.09 mg/m3.The concentration of urinary S-PMA and t,t-MA of 98 workers are linearly correlated with the TWA concentration of air benzene,the correlation coefficients are 0.65 and 0.62,respectively(P<0.001).2.2 The linearized multistage model based on the Chinese benzene cohort study was obtainedThe leukemia data from the Chinese benzene cohort study was used to fit the linearized multistage model,and the external-dose based linearized multistage model is expressed as:P(d)=2.65×10-4+(1-2.65×10-4)[1-exp(-2.51×10-6CTWA×T).In which CTWA represents concentration of air benzene,T for working duration and P(d)represents cancer risk.The internal dose and external dose are linearly correlated(adjusted for smoking,SMO,R2 is 0.44 and 0.38 respectively),and the internal-dose based linearized multistage model is obtained.2.3 Carcinogenic risk assessment of benzeneAccording to the ELMS model,workers from top 5 industries in six districts have a lifetime carcinogenic risk of 3.11-3.32×10-4 after 40 years of continuous exposure to air benzene at<1 mg/m3.The lifetime cancer risk of benzene-exposed workers in two factories in Shandong ranges from 2.75 to 7.15×10-4.For 10 workers in Tianjin whose concentration of air benzene was measured under the limit of detection,the carcinogenic risks of theses 10 workers calculated by the ILMS model based on S-PMA and t,t-MA were 3.35×10-4 and 3.33×10-4,respectively.The above two models assessed that the carcinogenic risks of top 5 benzene industries and 3 factories are all exceed the acceptable carcinogenic risk of 1×10-5.2.4 Non-carcinogenic risk assessment of benzeneThe results of EPA non-carcinogenic risk assessment model and Singapore semi-quantitively risk assessment model showed that the health risk of workers in two factories of Shandong are all at medium risk and above.Conclusion:Most of workers are exposing to benzene at low level in China,while few of workers are exposing to benzene at high level.The carcinogenic risk of exposure to benzene at<1 mg/m3 for 40 years is still unacceptable.Internal-dose of benzene is more suitable for evaluating occupational health risks at low levels.