Study On Bio-enzyme Under Chemical Regulation For Cadmium Pollution In Soil

Generating the phytoavailability of cadmium(Cd) in the soil with chemical method is a lowcost and convenient way to remediate contaminated soil. Calcium carbonate and humic acid have the potential to be the generator because of their chemical properties. In the study, the efficiency of calcium carbonate and humic acid for Cd phytoavailability generation was studied, as well as the associated changes of enzymes in the soil and plants(pakchoi) grown in the soil.Both calcium carbonate and humic acid could lower the Cd phytoavailability in soil significantly. When there was exogenetic Cd in soil, with calcium carbonate quantity increasing, Cd concentration in the pakchois decresed firstly and then rised in quadratic form. When calcium carbonate concentration in soil was in the range of 5.9-6.8g·kg-1, Cd concentration in the plant was the lowest, as well as the accumulation ability of Cd. Convertly, Cd phytoavailability and the concentration in the pakchois kept decreasing with humic acid concentration rising.When there was exogenetic Cd in soil, soil urease, alkaline phosphatase and catalase activities rised firstly and then decreased in quadratic form with calcium carbonate concentration in soils increasing. When calcium carbonate concentration was in the range of 4.1-8.4g·kg-1, the activities of the three enzymes reached the highest point in general, and the improvement effect was well. However, the soil enzyme activities increased with humic acid concentration in the soil. Through the vertical comparison, the activities of three enzymes increased with the planting time, which reached the highest point at the 40 th planting day.When there was exogenetic Cd in soil, the biomasses of shoot and root of pakchoi changed in quadratic form with calcium carbonate concentration in soil, and the highest point occurred when the concentration ranged from 5.0 to 7.9g·kg-1. Superoxide dismutase and malate dehydrogenase activities in the plants increased firstly and then declined with calcium carbonate concentration rising, and the lowest point exist when the concontration was in the range of 5.5-7.3g·kg-1 and 5.9-7.2g·kg-1, respectively. The variation tendancy of nitrate reductase was similar to that of plant biomass, and when calcium carbonate concentration was in the range of 5.9-7.5g·kg-1, the activity reached the highest point. Convertly, with humic acid concentration in soil increasing, both plant biomass and nitrate reductase activity kept increasing, while the activities of superoxide dismutase and malate dehydrogenase activities kept falling down.In conclusion, both calcium carbonate and humic acid can generate the Cd phytoavailabiliy in soil, as well as improve the soil enzyme activities. They can also improve the physiological metabolism of the pakchoi grown in the soil. As for calcium carbonate, in order to achieve the best comprehensive efficiency, the quantity should be kept in the range of 5.9-6.8g·kg-1.