The relationship between low-level benzene exposure and blood cell counts in Korean workers.

OBJECTIVES: Benzene is a well-known haematological toxin causing aplastic anaemia and leukaemia. Some recent studies have shown that low-level benzene exposure (<1 ppm) disturbs the haematopoietic system. However, other studies showed inconsistent results. The aim of the present study was to examine the relationship between low-level benzene exposure and blood cell counts in Korean workers. METHODS: Blood cell counts of benzene-exposed workers were extracted from a nationwide Special Health Examination Database from 2000 to 2008. If a worker did not take a blood test for benzene between 2000 and 2004, the worker was selected for analysis. In total, 8679 personal air benzene measurements were extracted from the nationwide Workplace Environment Measurement Database from 2004 to 2008. Mean benzene levels were calculated and assigned to benzene-exposed workers using various combinations of factory/industry/process codes. Mixed-effects models were used to examine dose-related associations between benzene levels and white blood cell (WBC), red blood cell (RBC), platelet, neutrophil and lymphocyte counts. RESULTS: In total, 21 140 blood samples were tested from 10 702 workers between 2005 and 2008; 40% of the workers had repeated blood tests (average, 3.4 times). RBC counts in male workers showed a significant negative association with low-level benzene exposure. WBC, platelet, neutrophil and lymphocyte counts did not show a consistent association with low-level benzene exposure. CONCLUSIONS: Our findings support the potential haematotoxicity of low-level benzene exposure (<1 ppm). A longitudinal study with direct benzene measurements for exposed workers is needed to confirm the toxicity of low-level benzene exposure.

Comparison of Grouping Schemes for Exposure to Total Dust in Cement Factories in Korea.

OBJECTIVE: The purpose of this study was to evaluate grouping schemes for exposure to total dust in cement industry workers using non-repeated measurement data. METHODS: In total, 2370 total dust measurements taken from nine Portland cement factories in 1995-2009 were analyzed. Various grouping schemes were generated based on work process, job, factory, or average exposure. To characterize variance components of each grouping scheme, we developed mixed-effects models with a B-spline time trend incorporated as fixed effects and a grouping variable incorporated as a random effect. Using the estimated variance components, elasticity was calculated. To compare the prediction performances of different grouping schemes, 10-fold cross-validation tests were conducted, and root mean squared errors and pooled correlation coefficients were calculated for each grouping scheme. RESULTS: The five exposure groups created a posteriori by ranking job and factory combinations according to average dust exposure showed the best prediction performance and highest elasticity among various grouping schemes. CONCLUSION: Our findings suggest a grouping method based on ranking of job, and factory combinations would be the optimal choice in this population. Our grouping method may aid exposure assessment efforts in similar occupational settings, minimizing the misclassification of exposures.

Cancer incidence and mortality among temporary maintenance workers in a refinery/petrochemical complex in Korea.

BACKGROUND: Petrochemical plant maintenance workers are exposed to various carcinogens such as benzene and metal fumes. In Korea, maintenance operations in petrochemical plants are typically performed by temporary employees hired as contract workers. OBJECTIVES: The purpose of this retrospective study was to evaluate cancer risk in temporary maintenance workers in a refinery/petrochemical complex in Korea. METHODS: Subjects consisted of 14 698 male workers registered in a regional petrochemical plant maintenance workers union during 2002-2007. Cancer mortality and incidence were identified by linking with the nationwide death and cancer registries during 2002-2007 and 2002-2005, respectively. Standardized mortality ratios (SMRs) and standardized incidence ratios (SIRs) were calculated for each cancer. RESULTS: Increased SMR 3·61 (six cases, 95% CI: 1·32-7·87) and SIR 3·18 (five cases, 95% CI: 1·03-7·42) were observed in oral and pharyngeal cancers. CONCLUSION: Our findings may suggest a potential association between oral and pharyngeal cancers and temporary maintenance jobs in the petrochemical industry. Future studies should include a longer follow-up period and a quantitative exposure assessment.

Dust exposure and the risk of cancer in cement industry workers in Korea.

BACKGROUND: Cement is used widely in the construction industry, though it contains hazardous chemicals such as hexavalent chromium. Several epidemiological studies have examined the association between cement dust exposure and cancer, but these associations have proved inconclusive. In the present study, we examined the association between dust exposure and cancer in cement industry workers in Korea. METHODS: Our cohort consisted of 1,324 men who worked at two Portland cement manufacturing factories between 1997 and 2005. We calculated cumulative dust exposures, then categorized workers into high and low dust exposure groups. Cancer cases were identified between 1997 and 2005 by linking with the national cancer registry. Standardized incidence ratios (SIRs) were calculated for all workers and the high and low dust exposure groups, respectively. RESULTS: The SIR for overall cancers in all workers was increased (1.35, 95% CI: 1.01-1.78). The SIR for stomach cancer in the high dust exposure group was increased (2.18, 95% CI: 1.19-3.65), but there was no increased stomach cancer risk in the low dust exposure group. The SIR for rectal cancer in all workers was increased (3.05, 95% CI: 1.32-6.02). Rectal cancer risk was similar in the high and low exposure groups. CONCLUSIONS: Our findings suggest a potential association between exposure in the cement industry and an increased risk of stomach and rectal cancers. However, due to the small number of cases, this association should be further investigated in a study with a longer follow-up period and adjustment for confounders.

Blood lead levels of Korean lead workers in 2003-2011.

OBJECTIVES: This study aimed to document the trend in blood lead levels in Korean lead workers from 2003 until 2011 and blood lead levels within each of the main industries. METHODS: Nine years (2003-2011) of blood lead level data measured during a special health examination of Korean lead workers and collected by the Korea Occupational Safety and Health Agency were analyzed. Blood lead levels were determined by year, and a geometric mean (GM) was calculated for each industry division. RESULTS: The overall GM blood lead level for all years combined (n = 365,331) was 4.35 µg/dL. The GM blood lead level decreased from 5.89 µg/dL in 2003 to 3.53 µg/dL in 2011. The proportion of the results ≥30 µg/dL decreased from 4.3% in 2003 to 0.8% in 2011. In the "Manufacture of Electrical Equipment" division, the GM blood lead level was 7.80 µg/dL, which was the highest among the industry divisions. The GM blood lead levels were 7.35 µg/dL and 6.77 µg/dL in the "Manufacturers of Rubber and Plastic Products" and the "Manufacture of Basic Metal Products" division, respectively. CONCLUSIONS: The blood lead levels in Korean lead workers decreased from 2003 to 2011 and were similar to those in the US and UK. Moreover, workers in industries conventionally considered to have a high risk of lead exposure also tended to have relatively high blood lead levels compared to those in other industries.

Cancer mortality and incidence in cement industry workers in Korea.

OBJECTIVES: Cement contains hexavalent chromium, which is a human carcinogen. However, its effect on cancer seems inconclusive in epidemiologic studies. The aim of this retrospective cohort study was to elucidate the association between dust exposure in the cement industry and cancer occurrence. METHODS: The cohorts consisted of male workers in 6 Portland cement factories in Korea. Study subjects were classified into five groups by job: quarry, production, maintenance, laboratory, and office work. Cancer mortality and incidence in workers were observed from 1992 to 2007 and 1997-2005, respectively. Standardized mortality ratios and standardized incidence ratios were calculated according to the five job classifications. RESULTS: There was an increased standardized incidence ratio for stomach cancer of 1.56 (27/17.36, 95% confidence interval: 1.02-2.26) in production workers. The standardized mortality ratio for lung cancer increased in production workers. However, was not statistically significant. CONCLUSION: Our result suggests a potential association between cement exposure and stomach cancer. Hexavalent chromium contained in cement might be a causative carcinogen.