The general population is exposed to methylmercury (MeHg) through a diet, especially fishes. The ability of MeHg to easily pass through the biological membranes seems to be responsible for easily passing of MeHg through the blood brain barrier and the placental barrier. Thus, the accumulation of MeHg in the brain and in the fetus results in neurological disturbances and fetal impairments. The neuronal damage caused by MeHg is almost exclusively limited to the central nervous system in the adult human. Furthermore, the areas of damage to the brain are highly localized. Little is known about the mechanism of the selective damage caused by MeHg in the nervous system. In this paper, many studies on the adverse effects of MeHg at the biochemical level were cited. The ability to accumulate MeHg and a low level of intracellular glutathione seem to make neuronal cells to susceptible to MeHg. By considering the high affinity of MeHg cations to SH groups, it appeares reasonable that a large number of cellular functions are being affected. Effects of MeHg on protein synthesis, membrane functions and cytoskeletons are discussed. Recent evidence suggests that oxidative stress and/or apoptosis are involved in the neurotoxicity of MeHg. Cumulative data indicate that functions of microtubules and neuronal transmission are highly susceptible toward MeHg exposure in vivo and in vitro. In prenatal exposure, a possible mechanism of MeHg toxicity is that MeHg alters the brain architecture and decreases the brain size due to the depression of cell division and neuronal migration, perhaps through inhibition of the microtuble functions.

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Pesticide concentration in serum must be measured in order to determine the proper treatment for patients with pesticide poisoning. We previously investigated the effectiveness of a screening method for fat-soluble pesticides by HPLC equipped with photo-diode-array detection (HPLC-DAD) and found that the method was effective in emergency medical units. In the present study, we investigated the effectiveness of a method for quantitative analysis for these fat-soluble pesticides. The concentrations of all pesticides were proportional to the peak area up to 100 μg/ml (injection amount : 1 μg), and the recovery ratio was excellent. This method was applied to three actual cases of acute poisoning, and we were able to give important advice to the doctor according to the concentration of the pesticides in the serum. The screening of pesticides by HPLC-DAD was confirmed by GC-MS.

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We developed a method to analyze tritium activity in the individual components of Japanese rice wine (Sake), i.e., aqueous and organic (alcohol). This method consists of a series of analytical procedures including fractionation, alcohol-oxidation, tritium enrichment and radioactivity measurement. Specialized fractionation and oxidation systems were designed and the operation conditions were determined. The enrichment system and measurement method contained an electrolysis method using multiplate cells and liquid scintillation analysis as previously described. In the first step of the pre-examination using ethylalcohol, the tritium content was measured within ±5%. In subsequent analyses, the tritium contetn was measured in Sake produced in 1990-1996. The tritium concentration in the aqueous component was consistently higher in Sake produced in the northern regions (Hokkaido and Tohoku) than in the southern regions (Kyushu) and also higher in Sake produced in the regions on the side of the Sea of Japan than that of the Pacific Ocean. However, this trend became less apparent with time. The tritium concentraton in the organic component showed no relation to the area of production. In general, the tritium level in this component was twice the aqueous component.

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Isocyanuric acid (H₃Cy) has been used in outdoor pools as a chlorine stabilizer. For the evaluation of the influence of H₃Cy on the disinfection with chlorine, the inactivation rates for poliovirus (Lsc, 2ab strain) with sodium hypochlorite and dichloroisocyanuric acid (Cl₂HCy) (0.1-2.0 mg/l as available chlorine) containing various concentrations of H₃Cy (0.7-30 mg/l) were determined at pH 7 and 20°C. Two types of virus suspensions, one in a cell maintenance medium (MEM) and the other in phosphate buffered saline (PBS), were used to compare the effects of H₃Cy on the chloramine formation and its virus inactivation efficacy. The residual chlorine in the test solutions was determined simultaneously by the DPD method. The addition of H₃Cy had few effects on the chloramine formation and on the chlorine consumption. The chloramine formed in the test solutions showed less virus inactivation efficacy. The influence of H₃Cy on the virus inactivation rates was observed when free residual chlorine was determined in the test solutions. In the experiments of a virus suspension in PBS with chlorine at 0.4 mg/l as available chlorine, the rates decreased with an increase in H₃Cy concentrations, although the amounts of free residual chlorine in the test solutions were the same. The plots of survival ratios at each contact time against the H₃Cy/chlorine ratios showed good linearity. The product of the contact time and the slope of each line became nearly constant. These results suggest that the inactivation rates were dependent on the H₃Cy/chlorine ratios and the contact time, and also suggest that the change of the H₃Cy/chlorine ratio might shift the hydrolysis equilibrium between hypochlorite and chlorinated isocyanuric acid.

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In order to know the photochemical behaviors of pesticides in natural water and on the surface of solids such as agricultural leaves and clay particles, the degradation patterns of 35 organophosphorus, 28 organonitrogens, 9 organochlorines and 7 pyrethroid pesticides in distilled water and on the silica gel plate during exposure to UV light (365 nm) for four hours were investigated. The percentages of the degradation of pyrethroid and organophosphorus pesticides were higher than those of organochlorine and organonitrogen pesticides under photoexposure in distilled water and on the silica gel plate. The percentages of degradation of all the pyrethroid pesticides were higher than 36%. Besides, the photochemical degradation on the thioether groups in disulfoton and fenthion were beyond 70%. Photochemical degradation products derived from disulfoton and fenthion were confirmed to be disulfoton sulfoxide and fenthion sulfoxide by GC-MS. The percentages of degradation of hormothion, disulfoton, fenthion, vamidothion, edifenfos and pyridafenthion on the silica gel plate were superior to those in distilled water. These findings suggested that those pesticides described above on the surface of solids such as agricultural leaves and clay particles were readily degradated as compared with those in natural water.

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