Large quantities of herbicides are used in paddy fields, so that there is much concerned about contamination of herbicides in water. The contamination of eight different compounds of herbicides was investigated in run-off waters from paddy fields and drainager river located around the southern basin of Lake Biwa.
Adsorption of the herbicides on suspended solids was found to increase with decrease in solubility of them in water. It is confirmed that the run-off of herbicides from paddy fields is influenced by the time of scattering herbicides, rainfall after scattering and inappropriate control of water in the paddy fields.
Although water in the paddy fields was not intentionally discharged during application of herbicides, the run-off of herbicides was found to frequently occur by rainfalls and inappropriate control of water in the paddy fields.
High peaks of concentration of herbicides that decreased rapidly in water were detected in the drainage river waters during application of the herbicides in paddy fields.
On the other hand, herbicides that could remain in paddy fields for a long time, were detected even after a long time in the drainage river waters.

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An analytical method for total mercury and alkylmercury (methylmercury chloride and ethyimercury chloride) in water by GC/MS was developed.
In the analysis of total mercury, mercury compounds in 500 ml of water sample were oxidized to divalent mercury (Hg(II)) with nitric acid and sodium persulfate, and the generated Hg(II) was adsorbed on a chelating resin in the pH range from 5 to 7. After elution with 25 ml of 6N HCI, Hg(II) was phenylated with sodium tetraphenylborate in the pH range from 3 to 10. The generated diphenyimercury was extracted with n-hexane and was analysed by GC/MS.
In the analysis of alkylmercury, alkylmercurys were concentrated and purified by extraction with toluene and reverse extraction with L-cysteine-sodium acetate solution. Methylmercury chloride and ethylmercury chloride were changed to methylpheylmercury and ethylpheylmercury respectively by the phenylation method mentioned above, and these compounds were analysed by GC/MS in the same way as the analysis of total mercury.
Using the methods described above, 1.0 μg Hg·l^-1 of total mercury and 0.5 μg Hg·l^-1 of each alkylmercury in water could be analyzed.

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Fly ash from a municipal solid waste incinerator is regulated under the hazardous waste regulation “Waste under Special Control”, according to the Amendment of the Waste Disposal and Public Cleaning Law in Japan, because it contains high concentrations of heavy metals which are available for leaching.
To evaluate the toxicity of fly ash, at first, a fly ash leachate was prepared according to the Japanese standard leaching procedure. The chemical analysis of the leachate showed that one of the possibly most toxic substances was cadmium. The toxicity of the leachate and cadmium was determined by algal assay and Daphnia acute toxicity test. The results showed that the leachate was about 10 times more toxic to the growth of algae, and 20 to 30 times more toxic to the survival of Daphnia than expected from its cadmium concentration.
The toxicity interaction between cadmium and the other constituents in the leachate was also examined. The toxicity of cadmium showed additive effect with the other constituents in the leachate in algal assay. In Daphnia test, however, cadmium showed antagonistic effect.

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The adhesion of biofilm to the microscopic part, or the thermal microhabitat on the heated media was studied to establish an effective water purification process at low water temperature. The circular tube was used as filter media for simplicity of both the experimental operation and the theoretical development to which the theory of the convection heat transfer at laminar flow was applied. Major conclusions obtained in this study were as follows : (1) The rise of water temperature by the heated media was a function of the surface area of media, the heat flux from media surface and the flow rate. (2) It was confirmed that the adhesion of the biofilm was brought about on the surface of the heated media, where the raw water at low temperature flew at laminar flow and the microscopic part was kept at higher temperature. (3) The mean thickness of the biofilm was computed using the water temperature in influent and effluent, and the flow rate. The calculated value was found to agree approximately with the result observed using the scanning electron microscope at the end of the experimental period. (4) It was found that there were few differences in the surface temperature of the heated media and the biofilm which thickness was about 35μm. Thus, the temperature in the biofilm was considered to be constant.

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In a tributary stream of the upper Muromi river, located west of Fukuoka city, as the spring water containing CO₂ and about 10ppm (Fe) of dissolved iron flows downstream, a large amount of hydrous iron (III) oxide (Fe(OH)₃) precipitates on the stream bed. Judging from the variation in Fe, DO, HCO₃ and dissolved CO₂ concentrations, it is concluded that the Fe (OH)₃ precipitation results from loss of CO₂ from the stream water due to the sudden decrease in the CO₂ partial pressure, followed by the hydrolysis and oxidation of ferrous ion.
On the other hand, MBPMC (2,6-di-tert-butyl-p-tolyl methyl carbamate; a carbamate herbicide) was detected in the stream water by GC-MS analysis. The MBPMC concentration decreased along the stream from 0.6 to 0.4 ppb, and the amount of the precipitated MBPMC approximately correlated with that of the Fe (OH)₃. The Fe (OH)₃ contains naturally-occurring organic materials, suggesting that MBPMC might be adsorbed on the surface of Fe (OH)₃ which is covered with the naturally-occurring organic materials containing hydrophobic groups.

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As a method for collecting suspended substances and polluted sediment particles in sea water, the effectiveness of dredging a concave on the sea floor has been investigated by researchers. In this study, particulate materials were collected by using a polyvinylchloride cylindrical vessel (50cm in diameter, 70cm in depth) which was set on the sea floor of Osaka Bay area as the mouth of the vessel level out the sea floor and the collection effectiveness of this method was also inventigated.
The PVC vessel collected nine times as much particulate material as those under a natural condition and 5% of the horizontal flux of suspended substances in the bottom layer water. The collected particles consisted of 30% suspended substances and 70% surface sediment particles. If this particle collection system of dredging a concave on the sea floor is used jointly with a system of recovering the collected particles, it can be an effective method of purifying polluted sediment in the sea.

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