| Dioxins (polychlorinated dibenzo-p-dioxins and of polychlorinated dibenzofurans, PCDD/Fs) are persistent organic pollutants (PoPs). They have persistent, bioaccumulative, semi-volatile and highly toxic characteristics. The common dioxins are at least the 2,3,7,8 chlorinated dioxins and furans, referring to seven dioxin congeners and ten furan congeners. The most toxic congener was 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD), which is known as the "poison of the century".Dioxins are generated almost entirely from industrial activities. The industries involving combustion and high temperature can generate dioxins. Common industries are impurities and byproducts of chemical production (PCBs, chlor-alkali industry, pentachlorophenol and dye industry, etc.); waste burning, including garbage and medical waste; metal smelting and processing (steel production and metal heat treatment); disassembly of electronic waste; paper and pulp bleaching process; vehicle exhaust emissions; rice straw burning, and so on. Today in our country, dioxins emissions are mainly from metal smelting industries.Previous studies indicated that dioxins may produce a wide spectrum of adverse health effects, including toxicity and carcinogenicity to multiple organs and tissues. Among dioxins,2,3,7,8-TCDD, the most toxic congener of dioxins had been designated as a Group 1 carcinogen by IARC in 1997. The studies on dioxins related with human adverse health effects have caught widespread concern. To protect human health, many countries all over the world had developed a control standard for dioxins, namely tolerable daily intake (TDI). The TDI for dioxins was newly revised at l-4pgTEQkg-1d-1 by WHO in 2005. However, the results of current researches showed that cancers from dioxins on human beings were very limited and need further evaluation.So far, the detection methods for dioxins have also been improved continuously, such as the biological method, enzyme-linked immunosorbent assay and chemical analysis. Each method has its own advantages and disadvantages, which provide more choices to meet different detection needs. However, there is no standard method to determine dioxins in work sites in our country.The foundry process is considered to be one of the main dioxin emissions sources from industrial production in our country, but researches on dioxins emissions from such processes are still limited. The objectives of this study were to (1) develop and regulate the methods to determine dioxins in foundry process, to analyze the concentrations and characteristics of dioxins; (2) to estimate personal dioxins for exposure workers and surrounding residents;, and (3) to explore association between dioxins exposure and cancer mortality among workers. There are the following three parts in this study.Partâ… Determination and analysis of dioxins in production environment of one automobile foundry factorySection I HRGC/HRMS method for determining dioxins in production environment of the foundry factoryThis objective of this section was to determine and analysis the concentrations and characteristics of dioxins generated from foundry process by collecting air and dust samples in and outside the foundry workshop, and to evaluate dioxins levels in the foundry factory and their contaminations on surrounding environment.Air and settling dust samples were collected from front-line job categories including melting, casting, modeling and assistant job categories including technical and administrative staff and entrance guard. After adding internal standard, extraction, purification and concentration, the extracts were analyzed by HRGC/HRMS qualitatively and quantitatively. The dioxins concentrations of air in workplace ranged 0.36-2.25 pg WHO-TEQ Nm-3 (average 1.01pg WHO-TEQ Nm-3), which were 1.16-7.26 times higher than those outside the factory. The dioxins concentrations of settling dust in workplace ranged 3.34-18.64 pg WHO-TEQ g-1 (average 8.25 pg WHO-TEQ g-1), which were lower than those just outside the factory (average 16.13 pg WHO-TEQ g-1). For concentrations, higher chlorinated congeners prevailed in dioxins, especially furans congeners; for TEQs, 2,3,4,7,8-PeCDF was the main characteristic factor of dioxins in foundry process.The results showed that the dioxins generated from foundry production process contaminated surrounding environment, and the melting furnaces were the main source of dioxins emissions in foundry process.Sectionâ…¡EROD method for determining dioxins in production environment of the foundry factoryThis objective of this section was to determine and analyze dioxins generated in foundry process by biological method of EROD.Dust samples were collected at melting furnaces, casting, modeling, fettling and core making in several main job categories in the foundry production workshops, and two sites of air samples were collected at melting furnaces and casting. Samples were extracted by Soxhlet extractions, purified through multi-layer chromatography column, and then determined by EROD method after enrichment and constant volume. EROD method was based on the principle that dioxins can stimulate EROD activity of fixed cell particularly, and the risk level of dioxins was reflected by measuring the EROD activity.For settling dust samples, high concentrations of dioxins were in melting furnaces and casting (28.79pgTEQ/g and 13.58pgTEQ/g, respectively), followed by modeling and fettling; the concentration of dioxins in core making process was below the detection limit; the concentration of dioxins in ventilation dust collectors was higher than those at above five job categories. For air samples, the concentrations of dioxins at melting furnaces and casting were 3.89pgTEQ/m3 and 2.19pgTEQ/m3, respectively. The results also showed that melting furnaces was the main source of dioxins emissions in foundry process, and compared with chemical method, the EROD method was more applicable to screen dioxins in occupational and environmental samples rapidly. Section III Comparison of the results between EROD and HRGC/HRMS methodsThe objective of this section was to discuss the applicability of EROD and HRGC/HRMS methods by comparing the results of dioxins. Data of dust and air samples collected in melting and casting job categories were analyzed. The results showed that the concentrations of dioxins determined by EROD method were generally higher than those by HRGC/HRMS method, showing a good correlation (R2=0.94), which manifested there was a certain comparability between two methods.And these two methods combined can meet different inspection requirements for occupational health.Part II Personal exposure assessment of dioxins for foundry workers and nearby residentsThe objective of this part was to assess personal external exposure levels of dioxins for foundry workers and nearby residents preliminarily on the basis of air concentrations of dioxins inside and outside the factory.Among melting, casting and modeling job categories, intake of dioxins via respiratory pathway during working time one day for melting workers was the highest. Intake of dioxins via respiratory pathway during working time one day for front-line workers were 1.14-9.43 times for those for residents all day long. Moreover, total daily intake of dioxins for residents showed that intake of dioxins for children per kilogram body weight was about twice that for adults, and had exceeded the upper limit value of TDI established by WHO for dioxins.The results of this part suggested that dioxins generated from this foundry factory pose threats to the foundry workers and nearby residents, therefore, the protection measures for workers should be strengthened and dioxins emissions should be controlled strictly.Partâ…¢Nested case-control study of cancer mortality among foundry workers The objective of this part was to evaluate the relation between dioxins exposure and cancer mortalities among workers by a cohort study of foundry workers.A retrospective study with a cohort of 3529 subjects employed during 1980 to 1985 and had worked for more than one year in this foundry factory was conducted. The cohort was followed from beginning of 1980 up till the end of 2005. The causes of death information was collected from medical and funeral records in hospitals. The occupational history was recorded from registers of the factory. The SMRs and 95%CI were calculated for the first cause of death by using 1980-2005 Chinese national age-specific mortality rates as reference.Cancer was the leading cause of death among foundry workers. When compared with the national average mortality, mortality from all cancers (SMR=1.70,95%CI=1.35-2.13), especially from lung cancer (SMR=2.13,95%=1.58-2.88) and liver cancer (SMR=1.71,95%CI=1.21-2.42) was significantly increased. A nested case-control study of 121 cancer deaths (male,95 cases) and 363 controls was initiated from the cohort study. According to the air concentrations of dioxins, job categories in foundry process were divided into high, medium, and low (or no) dioxins exposure levels. Cox proportional hazards model results showed that there was a dose-response relation between cancer mortality risk for workers and dioxins exposure with statistically significant (P<0.01), and cancer mortality for high dioxins exposure group was 2.44 times more than that for low (or no) dioxins exposure group (95% CI:1.38-4.32).The results of this part showed that dioxins generated from in foundry process were the main occupational carcinogens, and long-term dioxins exposure may have relation with high cancer mortality among workers.In summary, this study detected and analyzed the concentrations and fingerprint characteristics of dioxins generated from one automobile foundry production process by biological methods (EROD) and chemical methods (HRGC/HRMS). The dioxins generated from producing processes also polluted the surrounding environment. We established a cohort to evaluate adverse health effects from occupational dioxins expoaure among workers. A dose-response relationhisp between dioxins exposure and cancer mortality among foundry workers was observed by a nested case-control study in this foundry. Although we conducted determination twice in the foundry factory, more sampling would be help to evaluate dioxin concentrations and changes in different work sites. Moreover, other confounding factors that may cause cancer should be studied in future. |
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