| ObjectivePurpose of this study was to evaluate the correlation between risk of ischemic heart disease and jobs and occupational hazards among foundry workers.MethodsA foundry factory of a large-scale automobile company in Shiyan city, Hubei province was chosen as study site, data of occupational hazads workers exposed in foundry during the past years were collected, means and geometric means of the concentrations of occupational hazards were calculated, characteristics of occupational hazards were elaborated, and levels of cumulative silica exposure for foundry workers were estimated.Nested case-control study was used, following-up foundry workers employed for more than one year during January 1,1980 to December 31,1996 as cohort members. In total,30 years were followed to December 31,2009. Ischemic heart disease related data among foundry workers were collected, as well as case and control groups were matched on the basis of gender, age, smoking, alcohol drinking and observational start-point. In cohort study, person-year incidence and relative risk (RR) and its 95% confidence intervals for ischemic heart disease were estimated, and the correlation between risk of ischemic heart disease and jobs and occupational hazards and relative ratio (RR) and its 95% confidence intervals were analyzed with cox regression model using SPSS software. In matched case-control study, the correlation between risk of ischemic heart disease and jobs and occupational hazards and OR and its 95% confidence intervals were analyzed with cox regression model using SPSS software.Results1 Occupational hazards workers exposed in foundryVariety of dust, chemical and physical occupational hazards workers exposed were co-existed in foundry, and the main ones were silica, noise and heat stress. Dust, mainly silica, widely existed in all aspects of foundry. Concentrations of silica were high and exceeded permissible exposure limits stipulated by the national occupational hygienic standards. Silica concentrationas among jobs were significantly different, with higher level in cast shakeout and finishing, sand preparation, overhead crane operation, pouring, and melting. Concentrations of respirable dust were low, not exceeding permissible exposure limits stipulated by the national occupational hygienic standards. Risk of grinding wheel dust and welding fume were high, with levels exceeding permissible exposure limits stipulated by the national occupational hygienic standards. Coal dust mainly existed in melting and cast shakeout and finishing, with higher risk in latter.Main chemical occupational hazard workers exposed in foundry was formaldehyde, with concentrations of 1.23 mg/m3, exceeding permissible exposure limits stipulated by the national occupational hygienic standards. All of ammonia, phenol, metal fume, sulfur dioxide, hydrogen sulfide, phosphine in foundry were in low level. Geometric mean of concentration of polycyclic aromatic hydrocarbons(PAHs) was 0.1405μg/m3, with higher level in pouring(0.2394μg/m3).Main physical occupational hazards workers exposed in foundry were noise and heat stress. High-intensity of noise were widely distributed, mainly steady noise, with levels of 85.1 db(A). Noise level among jobs were significantly different, with higher level in cast shakeout and finishing(89.3 db(A)) and moulding(85.4 db(A)). Heat stress mainly existed in pouring(33.3℃), melting(32.8℃), and overhead crane operation(35.1℃).2 Risk factors for ischemic heart disease among foundry workersTotally,1817 workers were followed-up for 45553.05 person-years during 30 years, with 156 cases of ischemic heart disease and incidence of 342.46 per 100 000 person-years. In cases, the average age at onset was 51.46 years and duration of employment at onset was 17.06 years, with total of 23 strata of matched case-control groups.In cohort study, results showed that male, smoking and alcohol drinking were risk factors for ischemic heart disease. Compared with women workers, risk of ischemic heart disease among men workers increased by 57.1 percent(RR= 1.571, 95%CI=1.054-2.340). Compared with non-smokers, risk of ischemic heart disease among smokers increased by 70.3 percent (RR=1.703,95%CI=1.205-2.406). Compared with non-drinkers, risk of ischemic heart disease among drinkers increased by 55.3 percent (RR=1.553,95%CI=1.129-2.135). Compared with wokers aged 30-39, risk of ischemic heart disease among workers aged 40-49,50-59 and 60 and older increased by 7.275 folds(RR=8.275,95%CI=2.008-34.103),13.650 folds(RR=14.650, 95%CI=3.602-59.594) and 4.647 folds(RR=5.647,95%CI=1.340-23.803), respectively. Compared with wokers with 10 years and less years of employment, risk of ischemic heart disease among workers with 20 to 29 and 30 years and more year increased by 1.315 folds(RR=2.315,95%CI=1.454-3.685) and 1.228 folds(RR=2.228, 95%CI=1.264-3.927), respectively.In cohort study, results of multiple cox analysis showed that risk of ischemic heart disease increased by 75.8 percent(RR=1.758,95%CI=1.221-2.532) with comulative silica exposure of 1 mg/m3·year, adjusted for smoking. In matched case-control study, risk of ischemic heart disease increased by 66.4 percent (OR=1.664,95%CI=1.129-2.454) with comulative silica exposure of 1 mg/m3·year, adjusted for gender, age, smoking, alcohol drinking and observational start-point.In cohort study, compared with control groups, risk of ischemic heart disease among exposed groups increased by 45.8 percent (RR=1.458,95%CI=1.020-2.084), with incidence of 383.71 per 100 000 person-years. Risk of ischemic heart disease varies by job, and compared with auxiliary workers, risk of ischemic heart disease among workers exposed to sand preparation increased by 82.1 percent (RR= 1.821, 95%CI= 1.084-3.060), with incidence of 479.19 per 100 000 person-years. In cohort study, results of multiple cox analysis showed that risk of ischemic heart disease increased by 80.3 percent (RR=1.803,95%CI=1.255-2.589) among exposed groups, adjusted for smoking. And compared with auxiliary workers, risk of ischemic heart disease increased by 1.048 folds(RR=2.048,95%CI=1.203-3.486),1.395 folds(RR=2.395,95%CI=1.444-3.973),70.4 percent (RR=1.704, 95%CI=1.040-2.792),97.0 percent (RR=1.970,95%CI=1.151-3.370) and 1.270 folds(RR=2.270,95%CI= 1.229-4.196) among workers exposed to sand preparation, cast shakeout and finishing, melting, moulding and core-making, respectively, adjusted for smoking.In matched case-control study, results of cox analysis showed that compared with control groups, risk of ischemic heart disease among exposed groups increased by 74.5 percent (OR=1.745,95%CI=1.211-2.515), adjusted for gender, age, smoking, alcohol drinking and observational start-point. And compared with auxiliary workers, risk of ischemic heart disease increased by 1.343 folds(OR=2.343, 95%CI=1.364-4.023),1.062 folds(OR=2.062,95%CI=1.233-3.448),99.0 percent (OR=1.990,95%CI=1.153-3.433) and 1.507 folds(OR=2.507, 95%CI=1.332-4.719)among workers exposed to sand preparation, cast shakeout and finishing, moulding and core-making, respectively, adjusted for gender, age, smoking, alcohol drinking and observational start-point.Conclusions1 Variety of dust, chemical and physical occupational hazards workers exposed are co-existed in foundry. High concentrations of dust are widely distributed with the downward trend in concentration, chemical occupational hazards including ammonia, phenol, hydrogen sulfide, metal fume are complex with low- concentraions, high-intensity of noise are widely distributed both from foundry process and the collision and operating of foundry parts, and high-intensity of heat stress mainly exist in jobs of pouring, melting and overhead crane operation.2 Workers exposed to occupational hazards lead to high risk of ischemic heart diseas in foundry. Risk of ischemic heart disease varies by job, which is higher in workers exposed to sand preparation, cast shakeout and finishing, moulding and core-making. Risk of ischemic heart disease increased by 66.4 percent with comulative silica exposure of 1 mg/m·year, adjusted for gender, age, smoking, alcohol drinking and observational start-point. |
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