Occupational Exposure Assessment And Genetic Damage In Vinyl Chloride Monomer-exposed Workers

Vinyl chloride monomer(CH₂=CHC1,VCM) is widely used in industry,95%of them is used in polymerization to polyvinyl chloride(PVC).China is one of the important PVC production countries,and its annual production accounts for almost 25%of the global production in 2007,necessitating research regarding the health of VCM-exposed workers.VCM is a human carcinogen that has been proven to have multi-organ and multi-system effects.The mechanism of carcinogenesis was presumed to be related to the genetic damage induced by electrophilic metabolites of VCM.At present,the permissible exposure limit(PEL) of VCM in developed countries is 1 ppm (2.79mg/m³),while the TWA in China is 10mg/m³.The permissible exposure limit in China is higher than that those in developed countries,indictating that more research is needed to investigate the health effect and genetic toxicity caused by VCM-exposure under this condition for revealing mechanism of toxicology and evaluation to health risk.VCM in workplace collected by active charcoal was desorbed by carbon disulfide,then the VCM in CS₂ was analyzed by gas chromatography in this study. Personal sampling and area sampling were carried out in order to estimate current VCM exposure in three workshops.The results showed that both the STEL and TWA of VCM were lower than the Occupational Exposure Limit of VCM in China.The area sampling and measurement showed VCM concentrations were from 1.01 mg/m³ to 12.24 mg/m³.The majority of high VCM concentrations were near the units of VCM storage tanks and analytical sampling site.VCM environmental level monitored in this study was higher than that in the monitoring data of the factory.The workers were grouped in different job titles according to the conception of similar group,and the personal 8h-TWA exposures to VCM were from 0.24 mg/m³ to 3.24 mg/m³.The highest mean TWA exposure was found to be the VCM analyst.In general,the variation in personal exposures was in agreement with fluctuation in area concentration.By combining individual worker's time-activity patterns with mean area concentrations in various operational units,TWA personal VCM exposures can be indirectly calculated.A moderate agreement between VCM-measured and VCM-calculated was found for 76 pairs of simultaneously measured personal and area VCM concentrations,and the regression equation for them is Log(VCM-measured)= 0.890 Log(VCM-calculated) -0.453.The equation can only be applied in this factory in winter.The routine health examination were performed to investigate the health conditions of VCM-exposed workers and the study showed there was no significantly association between VCM exposure and the results of health examination. Cytokinesis-block micronucleus(CBMN) assay and single cell gel electrophoresis (SCGE) assay(comet assay) were used to detect the genetic damages in workers whose VCM exposure levels were lower than the national occupational health standard.The frequencies of both MN and comet in the exposed group were higher than those of the control group,and there was a dose-response relationship between VCM-exposure and the frequency of MN.Also,female and elder age were risk factors for the frequency of MN,which means the chromosomal damages.Therefore, the frequency of both MN and comet of peripheral blood lymphocyte can be used as an effective and sensitive biomarker for early health damage under low-level VCM exposure.Based on previous prevalence study,a cohort of 77 occupational VCM-exposed workers was established to explore the progress of genetic damage and its influencing factors.In 3 years' follow up,the frequencies of MN and comet detected in 2007 were significantly higher than those in 2004.Women had higher MN rates than men.The changes of both MN rates and comet rates showed the rising tendency with the increasing exposure duration,which pointed the cumulative exposure dose could increase the progress of chromosomal damage.The genotypes of CYP2E1(CG/CC) and CYP2D6(CG/GG) were risk factors and the risks were 1.29(1.02～1.63) and 1.40(1.12～1.77),respectively,which were significantly associated with the increase of chromosomal damage.No association was found between MN rates and other genetic polymorphisms,smoking and alcohol consumption.Compared with comet assay, CBMN assay was better to be used to follow up the occupational VCM-exposed workers and explore the association between genetic damage and occupational exposure dose and other factors.