Study On The Relationes Between Soil Hexavalent Chromium And Soil Biochemically Activity

With the speeding up of industrialization, the waste water was more and more irrigated in farmland, and led to more serious pollution in the soil. The result investigated by Ministry of Agriculture of China showed that the area of land irrigated by the waste water was about 1.4×10⁶ hm² and the area of land polluted by the heavy metal made up 1/5 of total arable land .The soil,the crop and the vegetable were polluted seriously by Chromium that was one of the four primary elements leading to pollute the environment.Soil enzyme was one of the principal components in soil, which took part in mostly biochemistrical reactivities in soil and played an impotant role in nutriment recycling, energy metabolizing, pollutant remediation and monitoring to a certain degree. Many domestic and overseas scientists finished a lot of research on their relationships and acquired some better results,but it was seldom to study Chromium influence on soil enzymicl activity. So it is necessary and important to study deeply on the relationships between Chromium and soil enzyme activity in both theory and practice.By simulative method, we systematically studied not only the relationships between soil dehydrogenase, uresae, alkaline-phosphatase and the heavy metals [Cr(VI)] in three soil types of China, but also the reaction mechanism between enzymes and the metal by means of enzymatic kinetics. The results were as follows:1. Cr(VI) could decreased soil pH remarkably that decreased continuously with the concentration of Cr(VI) increasing,and their relationship reached the significant negative correlation;The changing sequence of the total and the water-soluble Cr(VI) by soil pH was Sandy soil > Red soil > Lou soil.2. In the same ecological zones, with the rise of soil fertility the concentration of water-soluble Cr(VI) decreased remarkably in alkaline-soil of Lou soil and Sandy soil but increased in acidic-soil of Red soil; The concentration of water-soluble Cr(VI) decreased remarkably after Cr(VI) adding in the soil,and the decreasing content was slowed down with culturing time increasing;Their relationship reached remarkable significant positive correlation between water-soluble and total Cr(VI) concentration.3. The activities of dehydrogenase,urease and alkaline-phosphatase that decreased remarkably with the decline of soil fertility could be indicators of the soil fertility in the same ecological zones; Their relationship reached remarkable significant positive correlation respectively between the activities of soil enzymes and the organic matter , total nitrogen and alkaline-nitrogen.4. Cr(VI) remarkably activated soil dehydrogenase activity of Lou soil ,but inhibited soil dehydrogenase activities of Sandy soil and Red soil; The Ecological Dose ED₁₀ and ED₅₀ that were the token of the concentration of Cr(VI) when the soils had been slight and medium polluting station could be calculated by the relationship between soil dehydrogenase activities and the concentration of Cr(VI),and the critical total Cr(VI),water-soluble concentration of Sandy soil and Red soil were 15.60,78.01 mg·kg^-1 , 0.23,1.14 mg·kg^-1; The dehydrogenase activity of Sandy soils decreased continuously with culturing time increasing; Correlation coefficients reached -584^**,-0.635^**,-0.580^**,-0.523^**,-0.497^**,-0.417^** between soil dehydrogenase activity and the water-soluble Cr(VI) concentrations for Sandy and Red soil tested respectively.5. Cr(VI) remarkably inhibited soil urease activities especially when the concentration of Cr(VI) was high (>50mg·kg^-1); The critical total Cr(VI),water-soluble concentration of three soils that got by soil urease activities were 17.07,87.47 mg·kg^-1 , 0.17,0.86 mg·kg^-1; The urease activity of Red soils decreased in the mass with culturing time increasing; Correlation coefficients reached -0.422^**,-0.687^**,-0.450^**,-0.735^**,-0.482^**,-0.672^**,-0.433^** between soil urease activity and the water-soluble Cr(VI) concentrations for the three soil tested respectively.6. Cr(VI) remarkably inhibited soil alkaline-phosphatase activities; The critical total Cr(VI),water-soluble concentration of three soils that got by soil alkaline-phosphatase activities were 21.84,109.22 mg·kg^-1, 0.37,1.85 mg·kg^-1; Correlation coefficients reached -669^**,-0.536^**,-0.740^**,-0.779^**,-789^**,-0.586^**,-0.484^**,-0.403^** between soil alkaline-phosphatase activity and the water-soluble Cr(VI) concentrations for the three soil tested respectively;7. The critical total Cr(VI),water-soluble concentration of soil were 15.60,78.01 mg·kg^-1 , 0.17,0.86 mg·kg^-1 when the soils had been slight and medium polluting station.8. By means of urease and alkaline-phosphatase enzymatic kinetics, it showed that Km changed in the same rank quantitatively ,and V_max increased with the rise of soil fertility; Enzymeatic reaction Km was the same and V_max was reduced with increasing Cr(VI) concentrations, showed there was mechanism of no-competitive inhibition between Cr(VI) and the soil enzyme;The kinetic parameters such as V_max/K_m and k that were reduced with the increase of Cr(VI) concentration could be one of indexes as V_max to monitor soil polluted by Cr(VI) on a certain extent.