The purpose of this study is to clarify the infiltration mechanism of seawater by wave action in sheltered tidal flat and to quantify infiltration volume of seawater into sediments. We examined the infiltration behavior of seawater by wave and/or tidal action, infiltration velocity as a function of breaking wave height and slope of tidal flat and influence of wave and tidal action on infiltration volume of seawater. The results obtained were as follow:
1) The semi-circular type infiltration of seawater by wave into the saturated sediments was a new phenomenon that was not considered in previous studies on infiltraion mechanism as filling wedge mechanism.
2) The infiltration velocity of seawater was increased with increasing of breaking wave height and slope of tidal flat. However, the effect of the slope was bigger than that of breaking wave height on seawater infiltration into tidal flat sediments.
3) The one, man-made tidal flat, it was estimated that the infiltration volume was 0.072-0.111m³ · m^-2 · d^-1 by wave and tidal action and 90-94% of its volume was caused by wave action. The other, natural-like man-made tidal flat, it was 0.006-0.008m³ · m^-2 · d^-1 and 50-63% of its volume was caused by wave action.

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A series of field observation were conducted to investigate the behavior of an oxygen deficit water mass in a reach of Tone River downstream from an estuary barrage. Vertical profiles of salinity, DO and velocity were measured along the deepest line. The data show that the anaerobic condition was frequently developed at the salt wedge front because of the oxygen supply restriction at the density interface and the oxygen consumption in a bottom layer. The data also show that the DO budget in the water mass is highly affected by DO transport due to an estuarine circulation.
Numerical simulation by using a two-dimensional k-ε model reproduces the phenomenon successfully. It also suggests that the DO consumption takes place not at the front part of the salt wedge but through the whole way that sea water is transported by the estuarine circulation from the river mouth to the salt edge front, and then that the residential time of salt water in the estuary is an essential factor for the development of the oxygen deficit water mass.

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An increasing proportion of Environmental pollution with mercury take place in a number of developing countries, in particular, tropical region of South America, Africa and Southeast Asia have experienced tremendous increase in uncontrolled sector gold mining activities using mercury amalgamation technique since late 1970s. In order to resolve the these problems, techniques for the remediation of mercury polluted sites has been demanded in these countries.
In our precious reports, we have studied a remediation technology for mercury contaminated soil/sediment by the low temperature thermal treatment with iron chloride (FeCl₂) as additive. This process is characterized by soil heating method using physico-chemical reaction. However, in this reaction system, toxic hydrogen chloride gas are produced during the heating treatment which might corrode an apparatus and released mercury by heating treatment cannot be recovered as metallic mercury because the mercury reacts with hydrogen chloride gas to produce mercury chloride.
In order to overcome these drawbacks, we have undertaken basic research to develop more suitable remediation technology with another additive. As a results, it was found that mercuric sulfide in soils/sediments was removed more effectively by heating treatment with iron sulfide (FeS) as compared with iron chloride. Released mercury by heating treatment was recovered in the potassium permanganate solution. Moreover, this additive (FeS) is applied not only mercuric sulfide, but also other mercury compounds.
Our preliminary experiments with 2,000mg-Hg · kg^-1 dry weight artificially contaminated soil with mercuric sulfide and heating temperature 300°C showed that around 99% mercury was removed.

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The change of environmental loads of surfactants was estimated by using the simple model developed from the statistical treatments of surfactant productions. The practical application of this model in the cities of Hyogo Prefecture elucidated that the yearly changes of estimated loads of anionic surfactants (anionics) were in good agreement with those of riverine MBAS concentrations, indicator of synthetic anionics.
The analysis for the nationwide loads of surfactants indicated that the load of anionics reduced significantly since 1993 due to the decrease of production amount itself and the diffusion of sewerage, whereas that of nonionic surfactants (nonionics) remained unchanged at the level in 1992. These results suggested that the environmental impact of nonionics was relatively enhanced in Japan. The analysis for the environmental loads of surfactants in seven cities of Hyogo Prefecture also led to the similar results.

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This paper describes applicability of the passive sampler containing chelating resin enclosed by the plankton net to the monitoring of heavy metals in a sea area. It was showed that amounts of heavy metals (i.e., Ni, Co, Cd, Zn, Pb, Fe, and Mn) and Al collected by the passive sampler approached constant values with the progress in installation time of 61 days in the sea water. We compared actual concentrations of Ni, Co and Mn in the sea water with amounts of these heavy metals collected by the passive sampler. There was the positive correlation between values obtained from the passive sampler in various sites and concentrations of dissolved Ni, Co in the sea water.
Some monitoring results obtained from the passive sampler reflected nearly environments of each monitoring site. The correlation of monitoring results between the passive sampler and Pacific oyster on Co, Zn was observed. It was suggested that the passive sampler sampler is applicable to the monitoring for the biological impact assessment of heavy metals in the sea area.

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