Behaviours of 7 organic phosphate esters (OPEs) in several water treatment processes were studied. The results are as follows :
1) TOP, TPP and TCP showed rapid decrease (48 hours after, 40-60%) in activated sludge biodegradation. TBP and CRP were in the intermediate range, and TCPP and TCEP were degraded hardly. Effect of acclimation was appeared for TBP, TCPP, TPP and TCP.
2) The OPEs except for TBP and TCPP showed NaOH hydrolysis. TCEP, CRP, TPP and TCP showed rapid decrease (1 hour after at pH 13, 80-100%), and TOP were degraded more slowly.
3) TOP and TCP were removed by the coagulating sedimentation with Al₂2(SO₄)₃, FeCl₃ and PAC effectively (maximum, 80-95%), and TPP was removed with FeCl₃ and PAC (20-25%). In the coagulating sedimentation with Al₂(SO₄)₃, maximum removal rate was shown in the range between pH 5 and pH 8.
4) All OPEs were adsorbed on activated carbon powder very effectively (at 0.1 g/l, 90-100%), and TPP and TCP were most adsorbent. Freundlich equation was applicable to the adsorption isotherms of OPEs.
5) TPP amd TCP were rapidly destroyed by UV irradiation with low and high pressure mercury lamps (1 hour after, 100%). TBP and TOP were in the intermediate range, and TCPP, TCEP and CRP were destroyed more slowly.
6) TOP, TPP and TCP reacted with chlorine, especially under acidic conditions, even at the low chlorine concentration (3 mg/l).

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Fluctuation of water quality in the brackish Lake Nakanoumi was observed from 1975 to 1984. The water quality of bottom layer at the three stations (St. 3, St. 4 and St. 11) were measured for thirteen items. And nine items (Water Temperature, DO (%), Cl^-, T-P, PO₄-P, T-N, NO₃-N, NH₄-N and SS) were analysed by the Principal Component Analysis method.
The first component (Z₁) indicated the nutrients loading from bottom sediments. The second and third components (Z₂ and Z₃) indicated the nutrients loading from river and the value of suspended matter in the bottom layer, respectively. About 75% of total variance of the original data were contributed to these three components (Z₁, Z₂ and Z₃) by the Principal Component Analysis.
From the analysis of Z₁ score, periodical variation was observed remarkably; low in winter and high in summer. In addition, the characteristic pattern indicating the situation of nutrients loading into bottom layer in Lake Nakanoumi was recognized by analysis of correlation between Z₁ and Z₂ scores.

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Dissolved organic matter in the interstitial water of the bottom sediments (DOMI) collected from Yonago Bay in Lake Nakanoumi was separated to six organic fractions (F-1, F-2, F-3, F-4, F-5 and F-6) by gel chromatography. The effects of these fractions on the yield of phytoplanktons were examined by adding them to algal growth medium and comparing with that of control. The test phytoplanktons were isolated from brackish Lake Nakanoumi and then cultured in an aseptic condition.
The growth and the rate of Asterionella japonica, Coscinodiscus sp., Chaetoceros sp., Prorocentrum minimum and Planktonema lauterbornii were considerably accelerated by addition of DOMI (F-1, F-4, F-5 and F-6), whereas addition of DOMI (F-2 and F-3) did show inhibitory effect on the growth of some phytoplankton species.

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In the presence of sufficient dissolved oxygen, sediment oxygen demand (SOD^t_T) results from various chemical and biochemical reactions. The first objective to clarify the mechanism of SOD^t_T is to differentiate biochemical (SOD^t_o) from chemical sediment oxygen demand (SOD^t_c).
The scope of this paper is to estimate the effectiveness of SOD^t_o inhibition by toxicants (i.e. mercuric chloride, formaldehyde and phenol) from the view point of the kinetic studies.
At lower concentration of organic matter in the BOD bottle, these toxicants show the best inhibiting effect for holding oxygen demand at a nearly constant level after 1 day of incubation, but these toxicants lost their potency with increasing of organic matter concentration.
The mercuric chloride- and formaldehyde- treated sample did not appear to affect the rate-constants of bacterial growth (k_i=1.6 day^-1) and endogenous respiration phase (k_e=0.10 day^-1), but it did appear to suppress the amount of the ultimate oxygen demand of both the phases.
The k_i and k_e values determined from the phenol-treated sample are 0.20 day^-1 and 0.10 day^-1, respectively. And this inhibitor introduced the delay of bacterial growth reaction. Information on ultimate oxygen demand is similar to the result found in mercuric chloride- and formaldehyde- treated SOD^t_T.

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