It remains controversial whether silica is a human lung carcinogen. In this study, we estimated the relative risks of lung cancer due to silica and silicosis by meta-analysis. We collected papers published from 1966-2001 which epidemiologically reported on the relationship between silica/silicosis and lung cancer. We removed papers which did not exclude the effects of asbestos and radioactive materials including radon. We selected the most recent one if some papers were based on the same cohort. Based on the selected papers, we summarized the lung cancer risks from silica, silicosis and non-silicosis with exposure to silica, by meta-analysis using a random effects model. The pooled relative risks were 1.32 (95% confidence interval (CI), 1.23-1.41) for silica, 2.37 (95% CI, 1.98-2.84) for silicosis and 0.96 (95% CI, 0.81-1.15) for non-silicosis with exposure to silica. Since some papers on silica did not exclude silicosis, the risk due to silica itself may be smaller than 1.32. It was less possible that silica exposure directly increases lung cancer risk. On the other hand, the relative risk, 2.37 for silicosis suggested that silicosis increases lung cancer risk. Meta-analysis also revealed that cigarette smoking strongly increased the lung cancer risk in silicotic patients (relative risk, 4.47; 95% CI, 3.17-6.30). Thus, the present study suggested the great importance of preventing silicosis and smoking cessation in reducing lung cancer incidence in silica-exposed workers.
This study is performed to detect changes of gene expression in substantia nigra (SN) and striatum in manganese (Mn)-exposed mice brain. The cDNA array is a recently developed molecular biological method that can detect the differential expression of several hundreds of genes simultaneously and is therefore advantageous in the study of trace metal intoxication effect at the genetic level. Using this technology, we discovered 5 genes in the mouse striatum and 9 genes in SN changed by more than 50% following Mn exposure. Depression were observed in two genes (neural cell adhesion protein BIG2, heavy neurofilament subunit genes) in striatum and three genes (light neurofilament subunit, brain acyl-CoA synthetase II, heavy neurofilament subunit genes) in the SN. However three genes (N-acetylglucosaminyltransferase I, S100β, and synaptonemal complex protein I genes) in striatum and six genes (noggin, striatin, Ost oncogene, S100β, calcium/calmodulindependent protein kinase kinase beta, and N-acetylglucosaminyltransferase I genes) in SN were elevated following Mn exposure. Immunohistochemical study revealed that protein levels of S100β also increased following Mn treatment. Activated astrocytes overexpressing S100β are invariably and intimately associated with decreased expression of heavy and light neurofilament subunits which is a distinguishing feature of neurodegeneration by Mn exposure. All our findings suggested that neuronal degenerations occur in SN as well as striatum of mice exposed to Mn.
The primary purpose is to do cancer risk assessment of toxaphene by using four steps of risk assessment proposed by the United States National Academy of Sciences/National Research Council (NAS/NRC). Four steps of risk assessment including hazard identification, dose-response relationship, exposure assessment, and risk characterization were used to evaluate cancer risk of toxaphene. Toxaphene was the most heavily used insecticide in many parts of the world before it was banned in 1982. It increased incidence of neoplasms of liver and uterus in mice and increased incidence of neoplasms of endocrine organs, thyroid, pituitary, adrenal, mammary glands, and reproductive systems in rats. From mice's and rats' study, slope factor for toxaphene is 0.8557 (mg/kg/day)-1. Lifetime average daily dose (LADD) of toxaphene from ambient air, surface water, soil, and fish were 1.08 × 10-6, 5.71 × 10-6, 3.43 × 10-7, and 7.96 × 10-5 mg/kg/day, respectively. Cancer risk of toxaphene for average exposure is 7.42 × 10-5. From this study, toxaphene might have carcinogenic risk among humans.
It is assumed that differences in the mortality rates of occupational groups are explained by work-related factors, socioeconomic status, and health practices, etc. The present study focuses on the common factors contributing to differences in the mortality rates from all and major specific causes among Japanese male occupational groups. With respect to mortality rates, the following conditions were adopted as major specific causes of death: cerebrovascular disease (CVD), ischemic heart disease (IHD), stomach cancer (Stomach CA), lung cancer (Lung CA) and suicide. Occupations were classified into eight groups. Age-adjusted mortality rates due to each specific cause of death were calculated, using the age-specific population in 1985 as a standard, for every five years of census from 1965 until 1995. The number of significant correlation coefficients and their magnitude between mortality rates due to major specific causes, among the eight occupational groups, increased with advancing census year. Namely, the order of mortality rates for the major causes in Japanese male occupational groups became more similar over the recent 30 yr period. According to the principal component analysis of mortality rates due to major specific causes, the first main factor contributed 57.9% of the commonality in 1965, 76.5% in 1980, and 86.0% in 1995, respectively.
The microdialysis technique was applied to detect the changes in the activity of acetylcholine (ACh) neurons in the rat brain. The effects of intraperitoneal (i.p.) injection of toluene on the amount of ACh release from the nerve terminals of the brain cholinergic neurons were investigated in freely moving rats. In the striatum, injection of toluene decreased the extracellular concentration of ACh in a dose dependent manner in the range 200 to 2, 000 mg/kg. Similar effects of toluene on ACh release were observed in the hippocampus after i.p. administration. The increases in ACh content in brain homogenate after i.p. injection of toluene seemed to be caused by the decreased release of ACh from cholinergic nerve endings. Injection of toluene at doses higher than 200 mg/kg decreased ACh release and a similar decrease was suggested to occur in 8-h inhalation exposure to toluene at 1, 000 ppm or higher concentrations.
To monitor smoking status among workers, we improved the colorimetric method to detect cotinine and other nicotine metabolites in urine. In adding ethanol in the reaction mixture, the quantitative measurable time defined as the duration with more than 95% of the peak absorbance, extended to 80 min in contrast to 16 min in the original method. As the analytical condition, a aliquot of urine sample (0.5 ml) was mixed with 0.5 ml of ethanol, with 0.2 ml of 4 M acetate buffer (pH: 4.7), with 0.1 ml of 150 mM KCN, with 0.1 ml of 0.44 M chloramin and then with 0.5 ml of 78 mM barbituric acid. A linear relationship was observed between cotinine concentration up to 80 μM and absorbance at 508 nm (r=0.998, p<0.01). Mean levels of nicotine metabolites among non smokers a nd smokers were 4.9 and 47.4 μM cotinine equivalent, respectively. Sensitivity and specificity were 96.1% and 96.7%, respectively for nicotine metabolites concentration among workers (n=385) when adopting 6.9 μM cotinine equivalent as a cut off value and the area under the ROC curve was 0.982. This method can be applicable to quantitative detection of smoking status.
We performed a hospital based case-control study in the southeast region of Korea to clarify the role of occupational exposure, especially manganese (Mn), in the etiology of Parkinson's disease (PD) and to discover the association between any occupation and PD. 105 outpatients with PD and 129 neurological disease controls and 101 healthy controls were interviewed. We employed occupational and industrial categories as defined by Section (the most broad category) and Division (sub-category) of the Korea Standard Industry Code and the Korea Standard Classification of Occupations. There was not a significant association between exposure to hazardous materials, especially Mn and PD. There were not any occupations listed under the Section of Industry Classification as a significant risk factor or protective factor for PD. However, the 'clerk' occupation [Section] was positively associated with PD. There is a decreased risk for PD with a subject ever having worked in the 'agriculture, forestry and fishery' occupational group. Ever having worked in 'sales' also was negatively associated with PD. There were not any Divisions of Industry found as a significant risk factor or protective factor for PD. However, ever having worked in an 'agriculture' Division of Occupation was negatively associated with PD.
To examine age-related change in the strength of the association of white blood cell count (WBC) with features of the metabolic syndrome (MS), body mass index, blood pressure, total cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, fasting plasma glucose, and uric acid were assessed as the components of the MS in 5, 218 Japanese male office workers aged 23-59 yr. The subjects were stratified by age into three groups of 23-39, 40-49, and 50-59 yr. WBC count showed a positive crude correlation with the components of the MS, except for HDL cholesterol (negative), in all three age groups. With an increase in age, an association between WBC count and each component of the MS declined, and an interaction with age weakened. After controlling for potential confounders, the largest differences of WBC count for each categorized feature of the MS were found among those aged 23-39 yr. Stratified analyses by smoking status and age showed that in both non-smokers and current smokers the adjusted WBC count increased as the number of features of the MS increased in all three age groups. In each category of the number of clustered features of the MS, differences of WBC count compared with the presence of no features of the MS were the largest in those aged 23-39 yr in both non-smokers and current smokers. The adjusted odds ratios of ≥3 features of the MS also increased with an increase in WBC count in all three age groups in both non-smokers and current smokers. The adjusted odds ratios of ≥3 features of the MS across quartiles of WBC count (lowest to highest) were the largest in the youngest age group. Our results indicate that a variety of features of the MS are associated with WBC count and that these tendencies are more pronounced in younger individuals in both non-smokers and current smokers.
This study recruited seven height-matched healthy males to examine their maximum isometric lifting strengths across 13 exertion heights, ranging from 25 cm to 133 cm in increment of 9 cm. The results showed a nonlinear (increasing-decreasing-increasing) strength-height relationship for all subjects. The subjects' lifting strength was strongest (mean 1253.2 N) at the exertion height of 61 cm and weakest (mean 454.1 N) at the exertion height of 115 cm. Due to a large variability of strength ratio for the weakest individual strength to the strongest individual strength across the 13 exertion heights, ranging from 59.6% to 83.7%, practitioners should be cautious when assessing workers' lifting capacity based on strength testing.
A cross-sectional survey of semiconductor factories was conducted to identify the ergonomic risk factors in the work processes, the prevalence of body pain among workers, and the relationship between body pain and work processes. A total of 906 women semiconductor workers took part in the study. In wafer preparation and polishing, a combination of lifting weights and prolonged standing might have led to high pain prevalences in the low back (35.0% wafer preparation, 41.7% wafer polishing) and lower limbs (90.0% wafer preparation, 66.7% wafer polishing). Semiconductor front of line workers, who mostly walked around to operate machines in clean rooms, had the lowest prevalences of body pain. Semiconductor assembly middle of line workers, especially the molding workers, who did frequent lifting, had high pain prevalences in the neck/shoulders (54.8%) and upper back (43.5%). In the semiconductor assembly end of line work section, chip inspection workers who were exposed to prolonged sitting without back support had high prevalences of neck/shoulder (62.2%) and upper back pain (50.0%), while chip testing workers who had to climb steps to load units had a high prevalence of lower limb pain (68.0%). Workers in the assembly of electronic components, carrying out repetitive tasks with hands and fingers, and standing in awkward postures had high pain prevalences in the neck/shoulders (61.5%), arms (38.5%), and hands/wrists (30.8%).
The aim of this study was to determine the specific agent responsible for eczema on the forearms of 2 electronic assemblers who cleaned out a flux-spraying unit once a week. Soldering flux can be a source of skin irritation as well as allergy. Patch test with dried flux residue (as is) and rosin in dilution series of 20%, 10%, and 1% in olive oil was performed. Readings were taken on day 2 and day 3. The rosin in dilution series was negative; however, the flux residue gave a + reaction on day 2, and by day 3 the reaction had weakened (+?). Similar results were obtained in 2 unexposed controls. Patch tests results in our cases indicate that the flux used in the soldering process caused irritant contact dermatitis.
Two female workers, aged 23 and 24, engaged in cleaning metal straps with trichloroethylene (TCE) in a watch manufacturing plant, experienced generalized eruption, mucosal lesion, fever and hepatitis. The first case suffered fulminant hepatitis and died from liver failure in two weeks after the first symptom appearance. The second case, whose onset of generalized eruption, mucosal lesion and hepatitis without jaundice was nine days after that of the first case, however, recovered in 2 wk. Because the result of working environment measurement suggested heavy exposure to TCE, we deemed that there would be a causal relationship between TCE exposure and the illness. Although there have been considerable number of papers describing the above-mentioned relationship, the fact is not well recognized even among medical personnel in Thailand. Taking the wide use of TCE into account, the prevention of this illness would be very important especially in rapidly industrializing countries.