Model surface water prepared by extracting a leaf mold and the river water pretreated by coagulation sedimentation were treated by the fixed bed columns packed with 5 kinds of GAC. The adsorption abilities for precourcers of organohalogen were examined after 2030 days when the adsorption effect attained to pseudo-steady state and the biological decomposition effect was unremarkable. The smaller substances in molecular weight could be adsorbed at the shorter contact time. It was found that the maximum adsorbable molecular weight (M_max), which was determined from gel chromatogram, could be estimated by the contact time (θ, min) for each GAC irrespective of the water samples, and the following equation was obtained in the range of θ from 1 to 12 min.
M_max=kθ+80
Furthermore, it was found that the values of k increased with increase of the pore volume of GAC from 2 to 10 nm in diameter.

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The latent toxicity of pesticides to aquatic organisms was assessed using a freshwater shrimp, Paratya compressa improvisa, in water samples collected from several rivers in the Tsukuba district or Takahamairi bay, lake Kasumigaura, from April 1989 to March 1990. The 4-day mortality of the shrimp increased frequently to high levels in the riverwaters, reaching 100% at maximum, from May to August, in the season pesticides were discharged into the aquatic environment. The 7-day mortality of the shrimp also increased to 5060% at maximum in June or August in areas of lake water 500 m distant from the mouths of the three rivers investigated, although it was much lower than that of the river water itself.
The high mortality of the shrimp in the river waters was considered mostly atributable to the effects of pesticides in the rivers, such as fenthion, fenitrothion and BPMC. The quality of the river or lake waters was found to have changed, making the habitat very undesirable for pesticide-sensitive aquatic organisms such as the shrimp during the season of maximum pestichde discharged into environment.

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The quantitative analysis of self-purification process related to phytoplankton and zooplankton in eutrophicated water is investigated. From microcosm experiments, following results are obtained :
(1) The first reaction of organic decomposition in eutrophicated water is the endogenous respiration by phytoplankton, and then the bacterial decomposition gradually occurs. Zooplankton promotes bacterial activity.
(2) The degradation process of particulate materials is expressed with first order reaction, and the rate constants range from 0.02 to 0.07 d^-1. Following this reaction, nutrients are released into water, but the release of phosphorus is sometimes delayed, especially at a low temperature, such as 10°C.
(3) The oxygen consumption rate can be approximately expressed with the sum of the respiration rates of three organism groups : bacteria, phytoplankton and zooplankton. Phytoplankton's respiration rate Rp (mgO₂·l^-1·hr^-1) can be estimated with the photosynthesis rate Pr (mgO₂·l^-1·hr^-1) by the equation R_p=k * Pr, where k is ranging from 0.05 to 0.3, depending on algal species.
(4) Water temperature has an influence on reaction rate of each process with the thermal effect coefficients of 1.051.10 on COD, 1.091.14 on N and 1.091.26 on P.

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Biodegradation of tetrachloroethylene (PCE) was studied in order to explicate the source of cis-1, 2-dichloroethylene (cis-1, 2-DCE) in groundwater.
Depletion of PCE was observed by incubation with microoganisms, which lived in the soil sample from a drainage of the laundry. A bacterium which degraded PCE was isolated from this soil sample.
This bacterium (strain T) found to be an obligatory anaerobic gramnegative rod, and grew in the liquid medium containing mineral salts, yeast extract and L-cysteine monohydrochloride. The organism did not form a colony on any plate media under an anaerobic condition.
The growth of strain T and PCE degradation were observed between 15°C and 35°C, and between pH6.0 and p19.5.
PCE was transformed to TCE and then to cis-1, 2-DCE by strain T under an anaerobic condition. It was suggested that this pathway was conducted by reductive dehalogenation. Strain T could degrade more than 90% of 30mg·l^-1 PCE in 60hours.

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