Effect of humic substance on diffusion and toxicity of environmental polutants and application of it as clean up reagent

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To evaluate the effects of humic substances on the diffusion and toxicity of environmental pollutants, the interaction between humic substances and some pollutants were investigated and the following new information was obtained. Furthermore, the possibility of humic substances as cleanup reagent for environment was confirmed.1. The humic substances were extracted from peat soil sampled at some points in Hokkaido and purified to humic acied and fulvic acid. It was found that the chemical properties of these humic substances differed from one another.2. The humic acid formed a complex with chromium (III), and the equilibrium condition of the complex formation was achieved after 30 hours. The equilibrium constants and rate of the complexing reaction were obtained.3. The effects of humic substances on the redox reaction of chromium were investigated as well as some organic acids. The low molecular compounds such as tannic acid, gallic acid and wood vinegar reduced Cr (VI) to Cr (III) quickly, while the reduction rate of Cr (VI) with humic substances was slow significantly. On the other hand, Cr (III) was oxidized to Cr (VI) with manganese in the presence of oxygen. However, the presence of humic acid showed the suppression effects on the oxidation of Cr (III) to Cr (VI). Tannic acid, gaelic acid and wood vinegar did not show such effect. These results suggested that the complexing ability of humic acid with Cr (III) playd an important role to the suppression of the oxidation reaction.4. Humic substances binded with poly-aromatic hydrocarbon (PAH) compounds and enhanced the solubility in water. The enhancement of the solubility of PAH in water was found in three phases system containing solid particle, water and humic substances. In this case, the solubility of PAH was controlled by the distribution to humic phase in water and humic phase on the surface of solid particle.