The noxious substances which have now various exhaust controls in Japan are classified following three groups.
1 Heavy metal element; Lead, Chrome, Cadmium, Mercury.
2 Non-metal element; Arsenic
3 Compound containing carbon; Cyanic compound, Organic phosphoric compound.
First, the exhaust sources and the present state of these noxious substances are stated and then the individual methods which improve to be harmless are explained. Above all a example of a improvement treatment by clays and the work of Cr (VI) pollution place in Tokyo are indicated with actual data.

View full abstract

Problems on heavy metal pollution of soils, chiefly by Cd, were outlined from the point of view of the behavior of pollutant metals, introducing chiefly the results obtained by investigations of the author and his collaborator. On the reaction of metals with clays, humic substances and hydrated oxides, a brief review including our experiment on a clay was given.
1. For the protection of arable soils from pollution by heavy metals the Japanese Government designated legally the specific harmful substances, namely, Cd, Cu, As and their compounds. The requirement for designation on Cd for agricultural land soil pollution policy is that Cd content in brown rice exceeds 1.0 ppm, which brought forward a subject to lower the content of Cd in normally grown rice plants.
2. Natural abundance of several metals in Japanses soils, excepting Cu are somewhat higher than those in the earth crust. Content of Cd in brown rice, about 0.1 ppm, was considered to give fairly heavy burden for human bodies.
3. Cadmium in irrigation water is sorbed effectively by soils. If the content in irrigation water exceed the natural level of abundance, 0.1 ppb, accumulation in soils would proceed.
4. Heavy metals absorbed by plants generally accumulates in the root, hardly increasing the contents in the grain. Cadmium is almost only metal of which the content in rice grain readily increases through absorption from the soil.
5. Absorption of heavy metals by rice plants increases considerably when the submerged water is removed. This phenomenon is most prominent in Cd. Incubation of soils under flooded condition showed abrupt decrease in solubility of Cd corresponding with the change in oxidation-reduction potential for SO₄^2-=H₂S system which was calculated thermodynamically. Solubility of Zn decreased not sufficiently, presumably indicating stoichiometrical shortage of sulfides. Behavior of Cu and Pb during the incubation was more complicated. Arsenate, on the other hand, is reduced under submerged condition to more toxic and soluble arsenite.
6. Zinc and Cd behaved in exchange adsorption on montmorillonite as similar divalent cation as Ca. Coefficients of the Langmuir's adsorption isotherm for these metals were considered to give the CEC of the clay and exchange equilibrium constant.
7. Nature of specific adsorption both by soil humus and hydrated oxides seems to predict that Cd in soils fixed not so tightly, in fact, the fractionation done in Akita prefectural Agricultural Experiment Station applying the method of McLaren and Crawford⁴⁷⁾ showed that the fraction in which the most Cd was contained was exchangeable, followed by organically sorbed one, indicating high availability of soil Cd accumulated by pollution.

View full abstract

This review is the explanation on the relation between clay minerals and their characters and leogolical characters of the same clays come from soft part (so-called landslide clay) of rocks under the circumstance of landslide area. The technical consideration of the characters and assemblage of clay minerals acts upon the good effects on the civil engineering prevension work for landsliding. It is most important that we trace the relationship between clay minerals and their characters which are studied by mineralogist at the soften weathered part of countray rocks, and leological data from the same clays by technical engineers.

View full abstract