To examine a simplified and rapid determination method for mercury in sediment, three digestion procedures (included official testing method for sediment and two open system methods) were investigated. The recommended procedure was as follows : A 1Og of air-dried sediment is digested with HNO₃/H₂SO₄/KMnO₄/K₂S₂O₈ in Erlenmeyer flask at 100°C for 2h, then the mercury is determined by cold vapour AAS.
Recovery of mercury, added as Hg²⁺, methyl-and ethyl-mercury chloride and phenylmercury acetate to a river sediment, ranged from 100104%. Analytical results of Pond Sediment (NIES certified reference material) and 13 sediments were well agreed with reference value or results of official method (digestion with HNO₃/KMnO₄ in flask with reflex condenser).
The coefficient of variation was 1.0% for the reference material and ground river sediment. In the case of digestion with HNO₃/NaCl in Kjeldhal flask at 100°C for 2h, recovery of mercury was 100% for the various mercury compounds added to a sediment except methylmercury chloride whose recovery was 80%. This procedure was interfered from residual volatile organics in digested solution.

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Allowable concentration of soluble silicate (S. SiO₂) in treated waste water containing water glass in rainbow trouts (Salmo gairdneri) rearing was examined with acute toxicity tests and histopathological examinations. The polymerization rate of soluble silicate or water glass at pH 7.27.8 in a rearing water and the time course change of electric charge of colloidal silica were measured. These measurements make clear the states of silicate, the mechanism of acute toxicity occurrence and the histopathological phenomena.
The results of this research are summerized as follows.
(1) LC₅₀ (48h) value of rainbow trout (four to five month old) was estimated to be 302±27 mg E l^-1 with initial S. SiO₂ concentration.
(2) Samples which have heigher concentration than 300 mg·l^-1 decreased to 160 mg ± l^-1 through polymerization at pH 7.27.8.
(3) At heigher S. SiO₂ concentration as 350 mg·l^-1, the negative charge of colloidal silica increased with aging time at neutral zone.
(4) The death of rainbow trout were considered to be caused by necrosis of the gill filaments with the colloidal silica.
(5) The allowable S. SiO₂ concentration of a treated waste water containing water glass would be 150 mg·l^-1 in order to avoid sol formation. Thence, 100 mg·l^-1 of S. SiO₂ concentration could practically be set as an allowable concentration of the treated effluent.

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It is impossible to evaluate the water quality in Yodo River, without considering the transverse diffusion and mixing of three rivers (Uji River, Kizu River and Katsura River). Therefore we made up a mathematical model to simulate the behavior of pollutants in Yodo River.
In our diffusion model we introduced the water flow rate as a variable in stead of the river width. As a result the specific diffusion coefficient (α) is expressed an K_yuh₂ (K_y : diffusion coefficient, u : velocity, h : depth). Using the hydraulic data of Takahama point in Yodo River, K_y is about 0.1.
The large scale “Kizugawa Sagan regional sewerage”, which covers six municipalities, is being constructed and its treatment waste water is discharged into the left bank of Uji River. The calculation about the distribution of the effluent from the sewage treatment plant indicated that the raw water quality of Kuzuha waterwoks, located at the most upper Yodo River, would be worse. When the planning is achieved and the water flow rate in Yodo River is low, the increase of TOX formation potential (TOXFP) 524% and that of NH₄-N 1572% at Kuzuha, compared with the present concentration. In the case of which there is no sewerage planning, that of TOXFP is 27% and NH₄-N 4%. Alternative plan, the small scale one, were simulated as well and its result suggested that the water quality would be less influenced.

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A method for the determination of LAS in environmental water and domestic waste water was developed. This method was not interfered by coexisting substances.
Sample water was passed through SEP-PAK C18 cartridge. The cartridge was washed with methanol/0.1M NaCl (3 : 2) 4ml and distilled water, then LAS was eluted with methanol 4ml.This eluent was determined by high performance liquid chromatography with UV and fluorescence detectors.
When the interfereing peaks were on the chromatogram yet, distilled water was added to the eluent. It was passed throgh SEP-PAK ACCELL QMA anion exchange cartridge again. The cartridge was washed with methanol/0.0025M sodium citrate (1 : 1, pH 5.5) 8ml. LAS was eluted with acetonitorile/0.5M NaCl (1 : 1) 5ml. Then, the eluent was determined with HPLC.
The detection limit of total LAS concentration by the proposed method was 0.1μg·l^-1 when sample volume was 1 liter.
This method was applied to the determinations of LAS concentration in influent and effluent from a domestic waste water treatment plant, river and sea water of Osaka Prefecture. The concentration of LAS in river and sea water ranged from 19 to 1, 400μg·l^-1, and from no detection to 7.2μg·l^-1, respectively.

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