To clarify the effect of lead exposure on peripheral hemodynamics, acceleration plethysmography (APG) was performed for 48 male subjects occupationally exposed to lead (exposure group) and 43 male subjects with no history of occupational exposure to lead (control group). In the exposure group, the blood lead concentration (Pb-B) was also measured. Each APG parameter was assessed by comparing measured data with the standard aging curves. A significant negative correlation was obtained between the parameter - b/a and Pb-B. The exposure group showed significantly lower values of parameters - b/a (p<0.01) and d/a (p<0.05) than the control group. The parameter - b/a in the exposure group dose-dependently decreased with increases in length of working career (duration of exposure to lead) and Pb-B. The parameter - b/a significantly (p<0.05) decreased in subjects with working careers of 5 years or more and in subjects whose Pb-B was 40μg/100ml or more. These results suggest that lead exposure affects peripheral hemodynamics as evaluated by APG.
To investigate the risks of developing asbestos-related diseases we conducted a historical cohort mortality study on 249 ship repair workers (90 laggers and 159 boiler repairers) in a single U.S. Navy shipyard in Japan. We successfully identified the vital status of 87 (96.7%) laggers and 150 (94.3%) boiler repairers, and, of these, 49 (56.3%) and 65 (43.3%) died, respectively, during the follow-up period from 1947 till the end of 1996. Our in-person interviews with some of the subjects clarified that asbestos exposure was considered to be substantially high in the 1950-60s, decreased thereafter gradually but remained till 1979 in the shipyard. The laggers, who had handled asbestos materials directly, showed a significantly elevated SMR of 2.75 (95% C.I.:1.08-6.48) for lung cancer. The risk developing the disease was greater in the laggers after a 20-year latency (SMR=3.42). Pancreatic cancer yielded a greater SMR than unity (7.78, 90% C.I.: 2.07-25.19) in a longer working years group. Four laggers died from asbestosis. The boiler repairers, who had many chances for secondary exposure to asbestos and a few for direct exposure, showed no elevation of the SMR of lung cancer overall, but there was a borderline statistically significant SMR of 2.41 (90% C.I.:1.05-5.45) in a longer working years group. One boiler repairer died from mesothelioma and four from asbestosis.
In order to ascertain whether PVA fibers can produce cancer in humans or not, we have conducted a retrospective cohort study of workers exposed to PVA fibers. A total of 447 exposed and 2416 non-exposed male workers who were engaged before 1980 were followed up until the end of 1996. The SMR for all causes was 0.57 (observed 38, 95%CI: 0.41-0.78) for the exposed, and 0.66 (observed 210, 95%CI: 0.58-0.75). As for lung cancer, its SMR was 0.77 (observed 3, 95%CI: 0.15-2.24) for the exposed workers and 0.67 (12 observed, 95%CI: 0.34-1.16) for the non-exposed workers. Lung cancer SMR was 0.86 (observed 2, 95%CI: 0.10-3.11) for the workers with 20 or more years' employment. This study showed no difference in lung cancer risk between the workers exposed to PVA fibers and the non-exposed workers.
The correlations of lethal doses of various industrial chemicals for rats and mice with occupational exposure limit values were investigated. 50% lethal dose (LD50) values obtained by oral (p.o.) and intraperitoneal (i.p.) injection and 50% lethal concentration (LC50) values obtained by inhalation exposure were collected from Registry of Toxic Effects of Chemical Substances (RTECS). Threshold Limit Value (Time-Weighted Average) (TLVs-TWA) and Threshold Limit Value (Short Term Exposure Limit) (TLVs-STEL) recommended by American Conference of Governmental Industrial Hygienists (ACGIH) were used as exposure limits. TLVs-TWA or TLVs-STEL and LD50 or LC50 values obtained for the rats were plotted on logarithmic scales on the ordinate and abscissa, respectively. High correlations were obtained between these parameters. The order of correlations was: TLVs-STEL vs. LC50s>TLVs-TWA vs. LC50s>TLVs-TWA vs. LD50s i.p.>TLVs vs. LD50s p.o. The same calculations for the relationship between TLVs and lethal doses in mice were also performed. The order of the three types of correlations was same as that of the rats; however, correlation coefficients for TLVs-STEL vs. LC50s and for TLVs-TWA vs. LC50s obtained in mice were smaller than those in rats. TLVs-TWA are, therefore, well correlated with LC50 values rather than LD50 values, particularly with those in rats. High correlations between TLVs-STEL vs. LC50s were also obtained, as had been expected before calculation. The equation: TLV-TWA=10b×(LC50)a can be obtained from these plottings, where the values a and b are taken from each linear regression line. TLV-TWA for each chemical can be calculated by using LC50 and the equation. The upper and lower 95% confidence limits for calculated TLV-TWA were TLV-TWA (calculated from LC50)×22.9 and TLV-TWA (calculated)/22.9, respectively, where LC50 for rats expressed in ppm×hr was used.
To understand the basic characteristics of the human body vibration induced by low frequency noise and to use it to evaluate the effects on health, we designed a measuring method with a miniature accelerometer and carried out preliminary measurements. Vibration was measured on the chest and abdomen of 6male subjects who were exposed to pure tones in the frequency range of 20 to 50Hz, where the method we designed was proved to be sensitive enough to detect vibration on the body surface. The level and rate of increase with frequency of the vibration turned out to be higher on the chest than on the abdomen. This difference was considered to be due to the mechanical structure of the human body. It also turned out that the measured noise-induced vibration negatively correlated with the subject's BMI (Body mass Index), which suggested that the health effects of low frequency noise depended not only on the mechanical structure but also on the physical constitution of the human body.
Lung toxicity of chromium fumes (Cr fumes) was examined by a single intratracheal instillation into rats of 10.6mg and 21.3mg Cr fumes/kg body weight and by repeated (3 times) instillations of 10.8mg and 21.7mg Cr fumes/kg. The pathological changes were compared with those induced by single administrations of 3.2mg and 19.2mg Na2CO3 solution-insoluble fraction of Cr fumes (Cr-Fr)/kg and 20.8mg commercially available chromium (III) oxide powder (Cr (III) oxide)/kg. Single and repeated administrations of Cr fumes suppressed growth rate in a dose-dependent manner, but administrations of Cr-Fr and Cr (III) oxide did not. A single administration of Cr fumes produced granulomas in the entire airways and alveoli with progressive fibrotic changes, as well as severe mobilization and destruction of macrophages and foamy cells. Those histopathological changes were aggravated by the repeated administration of Cr fumes. On the other hand, single administrations of Cr-Fr and Cr (III) oxide produced no remarkable histopathological changes. Cr fumes were found to be composed of 73.5% chromium (III) oxide and 26.5% chromium (VI) oxide. The primary particles of Cr fumes and Cr-Fr were similar, 0.02μm in size (σg: 1.25), and Cr (III) oxide particles were 0.30μm in size (σg: 1.53), measured by analytical electron microscopy (ATEM). Diffuse clusters of the primary particles in Cr fumes were identified as Cr (VI) oxide. The present results suggested that the lung toxicity of Cr fumes was mainly caused by these Cr (VI) oxide (CrO3) particles in Cr fumes.
The aim of the present study was to establish a useful animal model that simulates humans sensitive to inhaled particulate matter (PM). We have developed a new rat model of acute bronchiolitis (Br) by exposuring animals to NiCl2 (Ni) aerosols for five days. Three days following the Ni exposure, the animals developed signs of tachypnea, mucous hypersecretion, and bronchiolar inflammation which seemed to progress quickly during the fourth to fifth day. They recovered from lesions after four weeks in clean air. To assess the sensitivity of the Br rats to inhaled particles, two kinds of PM of respirable size were tested with doses similar to or a little higher to the recommended threshold limit values (TLVs) for the working environment in Japan. Titanium dioxide (TiO2=Ti) was chosen as an inert and insoluble particles and vanadium pentoxide (V2O5=V), as a representative soluble and toxic airborne material. The Br rats exposed to either Ti or V were compared the pathological changes in the lungs and the clearance of particles to those in normal control or Br rats kept in clean air. The following significant differences were observed in Br rats: 1. delayed recovery from preexisting lesions or exacerbated inflammation, 2. reductions in deposition and clearance rate of inhaled particles with the progress of lesions. The present results suggest that Br rats are more susceptible to inhaled particles than control rats. Therefore, concentrations of particulate matter lower than the TLVs for Japan, which have no harmful effects on normal lungs, may not always be safe in the case of pre-existing lung inflammation.
A field survey of 147 engineers (23-49 years) in an electronics manufacturing company was conducted to investigate the effect of working hours on cardiovascular-autonomic nervous functions (urinary catecholamines, heart rate variability and blood pressure). The subjects were divided into 3 groups by age: 23-29 (n=49), 30-39 (n=74) and 40-49 (n=24) year groups. Subjects in each age group were further divided into shorter (SWH) and longer (LWH) working hour subgroups according to the median of weekly working hours. In the 30-39 year group, urinary noradrenaline in the afternoon for LWH was significantly lower than that for SWH and a similar tendency was found in the LF/HF ratio of heart rate variability at rest. Because these two autonomic nervous indices are related to sympathetic nervous activity, the findings suggested that sympathetic nervous activity for LWH was lower than that for SWH in the 30-39 year group. Furthermore, there were significant relationships both between long working hours and short sleeping hours, and between short sleeping hours and high complaint rates of “drowsiness and dullness” in the morning in this age group. Summarizing these results, it appeared that long working hours might lower sympathetic nervous activity due to chronic sleep deprivation.
10 types of standard mineral fiber samples (JFM fibers) were tested for their cytotoxicity in alveolar macrophages (AM) in vitro experiments, in which UICC chrysotile B was used as a positive control. The cytotoxicity included the production of superoxide anion radical and hydrogen peroxide, depletion of glutathione (GSH) and increase of intracellular free calcium. The results showed that chrysotile and most of the 10 mineral fibers could increase the production of superoxide anion and hydrogen peroxide, deplete the concentration of GSH and increase the level of free intracellular Ca2+ in AM. But all the effects of JFM fibers were lower than that induced by UICC chrysotile B. Although the cytotoxicity of JFM fibers were lower than that of asbestos, these mineral fibers should be used with highly care for workers in industries.
An autoregressive spectral analysis of heart rate variability (HRV) was used to analyze the differences in autonomic functions during graded head up tilt (HUT) between young and elderly men. After recording at the 0° position, the table was rotated to an upright position. The incline of the table was increased progressively to 15°, 30° and 60°. The data obtained from seven young subjects (mean age of 20.0 years) and nine elderly subjects (mean age of 63.3 years) were analyzed. The high frequency components expressed by normalized units (HFnu) were used as the parasympathetic indicators, and HFnu decreased with tilt angle in both age groups. These results suggested that parasympathetic withdrawal have an important role in adaptation to an upright posture in both age groups. However, mean HF amplitude at the 0° position in elderly men was not significantly different from that of young men at 60° tilt. A significant interaction effect (age group ×tilt angle) was found for mean HF amplitude. The increase of the low frequency components expressed by normalized units (LFnu) and the LF-to-HF ratio in elderly subjects from 0° to 15° seemed to be larger than that in young subjects. Sympathetic activities may be sensitive to lower levels of orthostatic stress in the elderly, and the elderly workers are easily affected by a change in workload. Therefore, keeping the workload lower and constant may be recommended to avoid excessive sympathetic activation among the elderly.
High hematocrit (Ht) level has been reported to be a correlating factor of hypertension in aged people, but has not been examined in younger generation. To investigate the association between Ht and blood pressure (BP) in healthy young workers, statistical analysis was performed for 646 male employees, using cross-sectional health-check data. Ht was positively correlated with systolic blood pressure (SBP) and with diastolic blood pressure (DBP) by Pearson's simple correlation analysis. Multiple regression analysis for SBP and DBP was conducted by stepwise procedure, using Ht, age, body mass index (BMI), and drinking and smoking habits as independent variables. It was revealed that Ht was a significant independent variable for DBP (p<0.001), as well as age and BMI, but not for SBP. These findings suggest that increased Ht is an important variable for assessing risk for cardiovascular disorders, especially diastolic hypertension, in young male office workers.
Various aerosol generators have been developed for animal inhalation experiments and the performance tests of measuring instruments and respirators. It has been, however, difficult to generate aerosols from an aqueous solution or suspension keeping the concentration and particle size distribution constant for a long time. Resolving such difficulties, the present study developed an animal exposure system that generates well-controlled and stable aerosols from liquids. The exposure system consists of an aerosol generator using ultrasonic nebulizer, a mixing chamber and an exposure chamber. The validity of this system was confirmed in the generation of NiCl2 and TiO2 aerosol from solution and suspension, respectively. The concentration levels of NiCl2 aerosol were kept at 3.2mg/m3 and 0.89mg/m3 for 5 hours with good coefficients of variation (CVs) of 2.5% and 1.7%, respectively. For TiO2 aerosol, the concentration levels of 1.59mg/m3 and 0.90mg/m3 were kept for 5 hours with small CVs of 1.3% and 2.0%, respectively. This exposure system could be sufficiently used for inhalation experiments with even high toxic aerosols such as NiCl2 because a momentary high concentration possibly affects results and an extremely stable concentration is required.
No method has yet been established to evaluate the exposure to tobacco smoke in passive smoking (PS). We therefore conducted a study on the possibility that the levels of urinary trans, trans-muconic acid (MA) and the exhaled carbon monoxide (CO) could be indices of the passive exposure to tobacco smoke. The moderate correlation was observed between urinary MA levels and the number of consumed cigarettes per day in smokers. The mean urinary MA level of the PS (+) group was significantly higher than that with the PS (-) group. Among the PS (+) group, the mean MA level in the urine obtained in the afternoon was higher than that obtained in the morning. A high correlation was observed between the exhaled CO levels and the number of consumed cigarettes per day in smokers. Like the urinary MA level, the mean exhaled CO level in the PS (+) group, too, gave a significantly higher level than in the PS (-) group. Because the biological half life of MA (7.5 ±0.85h) was longer than that of CO (3.0±0.36h), the measurement of urinary MA level is recommended for evaluating the exposure of passive smoking. The measurement of exhaled CO levels is useful only for chain smokers and nonsmokers with PS just before measurement.
Micronuclei is induced in cytoplasm as a consequence of the formation of chromosomal fragments or remaining chromosomes during cell division by the cause of clastogens or spindle poisons, and is used as an indicator of genotoxicity screening tests. There are few short-term genotoxicity screening tests using brain cells. We attempted to establish a new in vitro micronucleus test (MN test) system by use of central nervous system cells. Primary cultured astrocytes were prepared from newborn male Sprague-Dawley (SD) rats. In growth curve of astrocytes, doubling time was determined to be 31h. In time study, the highest frequency of micronuclei was observed at 48h, 72h and 6h-exposure-66h-recovery by vincristine (VCR), mitomycin C (MMC) without metabolic activation system and cyclophosphamide (CPM) with metabolic activation system, respectively. Dose-response relationships between micronucleus frequency and concentrations of MMC, VCR and CPM were observed, respectively. It is suggested that the in vitro MN test using new born rat-astrocytes could be used as a screening test of environmental and occupational genotoxic chemicals in the central nervous system cells.
A clearance model of inhaled man-made fibers (MMFs) was developed, and the calculated fiber numbers and dimensions were compared with the experimental ones using a glass fiber (GF), ceramic fiber (RF1) and two potassium octatitanate whiskers (PT1, TW). If the translocation rate by macrophages is constant and the effect of dissolution and disintegration can be ignored, the fiber number is expected to decrease exponentially with time. In the experimental study, however, the fiber number did not always decrease exponentially. In the case of RF1, the fiber number decreased almost exponentially and the diameter decreased linearly with the time. The clearance rate constant of GF during 3 to 6 months after the end of one-month exposure was greater than that during 1 to 3 months. On the contrary, the clearance rate constants of PT1 and TW during 1 to 6 months were greater than next six months. The diameter and the length of GF did not change significantly. The fiber length of PT1 tends to become longer with time although the diameter did not change significantly. Our theoretical model gives a satisfactory fit to these experimental results.
We are at a time when reform in the special medical examination program in keeping with the changing times is desperately needed because the common perception of workers, employers, and medical examination facilities is “special medical examination is merely ritualistic and unproductive.” Therefore, we have tried to set forth the basic structure for reforming the special medical examination program by taking a close look at the management status of the current program and analyzing its problems. The specifics of the special medical examination program reform proposal consist of three parts such as the types, health evaluation based on occupational medicine, and the interval, subject selection, items and procedure. Pre-placement medical examination and non-periodic medical examinations-as-necessary are introduced newly. Health evaluation based on occupational medicine consists of classification of health status, evaluation of work suitability, and post-examination measure. Details regarding the medical examination interval, subject selection, items and procedure were changed.
Bangladesh is a relatively young and developing country. At the present time, like in most developing countries, a clear demarcation between occupational health care and general medical care is difficult to be recognized in Bangladesh. Occupational health is a fairly new field, as the country is undergoing industrialization and Occupational health activities are operated by several ministries, such as Labour, Health, Industry and Transport. Legal foundations of the occupational health-care system based on British India and Pakistani era, were adopted and amended by the Government of Bangladesh after the liberation of the country in 1971. Most of the Labour laws have been rectified by the Government of Bangladesh according to the ILO Conventions. Reconsideration of the occupational health service system avoiding duplication for the ‘occupational health’ component in several ministries might be helpful to achieve the successful provision of an occupational health service in the developing Bangladesh.