In order to analyse writing work which was considered to be continuous burdens of the hand-arm-shoulder system, the electromyogram (EMG) of the shoulder and the arm on the writing hand side using surface electrodes and the writing pressure were observed during writing performance. Factors associated with writing such as writing tools (a ball-point pen and a pencil of hardness of HB) diameters of pen-holder (7 mm and 11 mm), number of sheets of paper (1 and 3) and sex difference were analysed quantitatively with the experimental design method. Above all, the muscular tension and the writing pressure during a 20 min writing were examined. The subjects were asked to write, through hearing from a loud-speaker, one Japanese "kana" leter per 1 sec under the usual writing pressure or the writing pressure above the given minimum value of 0.13 kg. It can be concluded that the burden of muscles of the arm and the shoulder caused by the pencil is lighter than that by the ball-point pen and the burden of shoulder muscles indicates spectrum change in the low frequency components of EMG below 20 Hz even in 20 min continuous writing. The larger diameter pen-holder and the thicker sheets of paper promote increase of muscular tension which may induce muscular fatigue. The writing pressure which shows spectrum of 1-7 Hz also endorses these findings.
Through a fled survey of about 300 female checkers of cash-registers at some supermarket, it was found that notwithstanding improvement of a key pushing force of electronic cash-register (ECR) which was quite lighter than that of me-chanical cash-register (MCR), the checkers had complained of stiff-shoulder, although complaints associated with the arms had decreased. Through preliminary experi-ments in our laboratory, it was revealed that at the end of continuous key pushing experiment an increase of muscular tension and an increase of the low frequency components in the electromyogram (EMG) on the arms and shoulders could not be recognised clearly, on the contrary, both of them were observed in the experiment of writing performance mentioned in Part 1. The muscular tension in key pushing was kept constant or decreased plainly. Using the observed values of the EMG on trapezius, forearm flexor, forearm extensor and triceps and the key pushing force, the following five factors with two levels were assigned with an orthogonal array table L16(215) to make variance analysis: types of cash-registers (MCR and ECR), heights of key-board, registering items (a numerical table for training of the checkers or practical merchandise as a matter to be registered), physical posture (sitting or standing) and experience of subjects. It was concluded that muscular burden for operating of ECR was lighter than that for the MCR except that both the cash-registers had the same effect on the shoulder. The effect of the height of the key-board appeared on the shoulder and the lower position was better from the view-point of the muscular burden. The sitting posture also increased muscular burden on the shoulder. On the correlation matrix calculated, the values to explain the relation between the muscles and the key pushing force, called contribution rate, indicated to be larger on the muscles except the trapezius and those corresponding to correlation between mutual muscles, called cooperation rate, indicated to be larger on the ant-agonistic muscles (flexor and extensor) and the cooperative muscles (flexor and triceps).
Twenty-three workers who had occupationally been exposed to lead were ex-amined for blood and urinary lead contents (bPb, uPb), urinary delta-aminolevulinic acid and coproporphyrin contents (δ-ALA, Copro), erythrocyte δ-ALA dehydratase activities (ALA-D), hemoglobin concentration (Hb), and 2-hr and 24-hr urinary lead excretions since the start of 1-hr intravenous infusion of 20 mg CaEDTA per kilo-gram of body weight (uPb2-hr mob., uPb24-hr mob.). The blood lead value (μg/100g) ranged from 4 to 73 with an average of 24. By factor analysis, the parameters were classified to three groups. The first group consisted of uPb24-hr mob., uPh2-hr mob., bPb, uPb and ALA-D; the second group, δ-ALA and Copro; and the third group, Hb. There were found highly significant linear relationships between all pairs of bPb, uPb, ALA-D, uPb2-hr mob, and uPb24-hr mob, on a log scale. Δ-ALA, Copro and Hb had less in extent, but significant correlations with five parameters mentioned above. BPb, uPb, Hb and uPb2-hr mob. had the closest correlations with uPb24-hr mob.;ALA-D, with bPb; and δ-ALA, Copro. The criteria for the mobilization yield were estimated from the viewpoint of acceptable limit in lead absorption. Practical usefulness of "2-hr method (uPb2-hr mob.)" was indicated as a simplified diagnostic mobilization test.
Erythrocyte δ-aminolevulinic acid dehydratase (ALA-D) activity in blood speci-mens from normal and lead-exposed workers was simultaneously determined accord-ing to two methods with different principle. In one method, erythrocyte ALA-D activity is calculated from the amount of porphobilinogen (PBG) formed by enzyme assay. In the other method, the ALA-D activity is calculated from the amount of substrate δ-aminolevulinic acid (ALA) consumed during incubation. The value of erythrocyte ALA-D activity (micromols ALA/min/liter RBC) ob-tained from the amount of ALA consumed was more nearly accurate than the value (micromols PBG/min/liter RBC) obtained from information on the amount of PBG formed. In addition, in the workers occupationally exposed to lead, the blood lead levels tended to more inversely correlate with the value of erythrocyte ALA-D activity calculated from ALA consumed than that from PBG formed.
Blood lead concentration and erythrocyte protoporphyrin (PROTO) levels were determined in workers with a occupational exposure to lead. The exposure time of the workers was from 3 to 18 years. n the lead workers, the concentration of blood lead was 32±13μg/100ml and the erythrocyte PROTO levels were 147±102μg/100ml RBC. On the other hand, the normal levels obtained from healthy men with no history of lead exposure were 10±3μg/100ml for the blood lead and 43±17μg/100ml RBC for the erythrocyte PROTO. In the lead-exposed workers, there were a significant positive correlation be-tween the logarithm of erythrocyte PROTO and blood lead levels (r=0.6263, P< 0.001). In addition, the equation of the regression line was as follows: Log10 PROTO=0.0127 Blood lead+1.6808 From this investigation, it will be demonstrated that the measurement of ery-throcyte PROTO together with the test of δ-aminolevulinate dehydratase which had often been carried out is available for detecting the degree of lead absorption in workers occupationally exposed to lead.
The cadmium accumulation with a single injection was studied in rabbits. In-jected dose of cadmium was 3 mg per kg of body weight. The cadmium conentra-tions in liver and kidney were measured after 3 hours to 24 months. The liver cadmium reached the maximum concentration at the early stage (3 days-2 weeks), and then it decreased slowly. The kidney cadmium increased up to one year. Then, it retained a certain level (approximate 100 μg per g) for one more year. More than 80 per cent of the organ cadmium were found in the metallothionein fraction on Sephadex G-75 gel filtration.
The permeabilities of methylmercury and inorganic mercury chloride across human red cell membranes were compared using Hg203 compounds. Methylmercury incorporation reached maximum even at 37° and 0°C in 3 min in the range from 80 to 90%. Methylmercury incorporation at concentrations of 10-8, 10-6 and 10-4M was the same, but mercury chloride incorporation at 10-6 and 10-8 was lower. Cysteine inhibited the incorporation of methylmercury and mercury chloride, but DTT was not so effective. Plasma proteins inhibited the incorporation of methyl-mercury only slightly, but that of mercury chloride strongly. EDTA did not in-hibit the methylmercury incorporation in contrast to mercury chloride. Methyl-cobalamine did not affect the incorporation of methylmercury and mercury chloride even at 37° and 0°C, with or without plasma proteins for at least 60 min. After the incubation of mercury chloride with methylcobalamine the Hg203 mercury chloride was nearly completely changed into methylmercury in the absence of red cells. Binding of methylmercury to cell membranes was estimated. The values were slightly but significantly larger than that to hemoglobin on the basis of protein weight.
Repeated dermal application of thorium nitrate in different concentrations in-duced mild histopathological changes in the skin and testes of experimental rats. Liver and kidney, however, did not show any pathological damage. The mild degenerative changes observed are attributed to the poor absorption of thorium nitrate through intact skin.
The percutaneous absorption of 8 chlorinated solvents were studied. The ex-perimental method consisted of the application of the solvent to the abdominal mouse skin and quantitating its absorption through the skin by its presence in whole body and its appearance in expiration. Determination of the solvent in tissues and expiration was carried out by gas chromatographic methods. There was a great diversity of ability among solvents to penetrate the mouse skin. Dichloromethane was absorbed to an amount which was 53 times as large as the amount of tetrachloroethyene. Among tested solvents, those which had the highest solubility in water showed the greatest absorption rate, while those having the lowest solubility in water gave the smallest absorption rate from skin. The linear relationship between the absorption rate from skin and the solubility in water was found: in case of X ?? 16, Y=30.8+2.13X, r=0.87; in case of X ?? 16, Y= -52.8+6.59X, r=1.00; where Y is the percutaneous absorption rate (nM/min/cm2 of skin) and X is the solubility in water of solvent (mM at 25°C).
To clarify chronic nitroglycol intoxication upon the cerebral activity, electro-encephalographic examinations of nine subjects working in a dynamite factory were conducted. There were only slight and little positive findings in the workers on the sub-jective symptoms and objective examinations except for EEG. Seven subjects out of nine indicated abnormal EEG records both in cases experienced anginal attack and not yet experienced such sign. It can be seen from the EEG findings in workers exposed to nitroglycol that fast activity in all areas was dominant particularly. Based on these findings, it may be concluded that chronic nitroglycol exposure seemed to influence upon the cerebral activity of factory workers.
The author tried a series of experiments for the purpose of capturing mercury vapor in air. Mercury was captured with various types of impingers containing a solution of potassium permanganate (KMnO4) in sulphuric acid (H2SO4) as sampling solutions. Though the mechanism of reaction between mercury and sampling solu-tion is complicate, all the types of impingers used had a very excellent sampling efficiency. This solution is unstable: dissolved potassium permanganate in the sam-pling solution changes to manganese dioxide, and granules of manganese dioxide educes out gradually. The greater part of captured mercury was adsorbed on educed manganese dioxide, and mercury captured in liquid phase was rather little in amount. Potassium permanganate played a great part in capture of mercury, and sulphuric acid was necessary for the adsorption of mercury on manganese dioxide.