Effects Of Accompanying Anions On Eco-toxicological Of Cadmium In Soils

With the rapid development of society economy, the accumulation of industrial waste,sludge disposal, the abuse use of fertilizer and pesticides and other human activities causedthe Cd pollution in soils. Cd can not be broken down by microorganisms and its half-lifelasted for15to1100years, so it was difficult to move out of the soil. Cd not only had thepotential ecological risk on the soil environment, but also had hazards to human healththrough the food chain.As catalyst of various soil biochemical reactions, soil enzyme involved in many soilmetabolic processes can indicate soil quality changes. Many scholars have carried out a largenumber of studies on soil enzyme activities in cadmium polluted soils. However, the researchwas mainly limited in a single cadmium salts on soil enzyme activities. Actually, cadmiumoften existed with accompany anions which affected the bioavailability or toxicity ofcadmium. Therefore, when investigated the ecotoxicological effects of cadmium in soils, weshould consider the accompany anion. Meanwhile, it was necessary to carry out the researchof the relationship between soil enzyme activity and cadmium in China’s main type soils.In this paper, the influences of Cd addition on the soil dehydrogenase, phosphatase, FDAhydrolytic enzyme and nitrification activities in different types of soils were studied bytraditional pot incubation and indoor simulation experiments. And we compared the effects ofCl^-, SO₄^2-, NO₃^-, CH₃COO-anions on cadmium ecotoxicological. The main conclusions wereas follows:（1）Under the soil environmental quality standards for agricultural soils, soil FDAhydrolase and dehydrogenase activities were to be a good indicator of soil Cd pollution andthe relationship between soil enzymes and Cd was influenced by soil organic matter and pH.（2）The soil adsorption amount of Cd increaseed with the the cadmium concentration ofequilibrium liquid. Freundlich model can be used to describe the adsorption isotherm processof Cd2+, and the parameters K_Fand1/n which characterized the cadmium adsorption capacityof soil had a significant positive correlation with soil pH. The K_Fvalue of Cd（OAC）2treatment was higer than Cd（NO3）2, CdSO4, CdCl2treatments in all tested soils, and the soiladsorption amount of Cd（OAC）2was largest. Between the cadmium adsorption anddesorption in soils, there was a very significant power function relationship. The acidic soilhad a significantly higher cadmium desorption rate than other soil samples, suffering a greater ecological risk.（3）Cadmium can significantly inhibit soil dehydrogenase enzyme activity. Log-logisticmodel can be used to characterize the relationship between the soil dehydrogenase activityand Cd content, revealing soil dehydrogenase enzyme activity represented soil cadmiumpollution levels within a certain range. The regression analysis of ED₁₀and soil factorsshowed that the organic matter content is the main factor which effectted the toxicological ofCd on soil dehydrogenase enzyme. The presence of CH₃COO-ion reduced the toxic effects ofcadmium on dehydrogenase.（4）Cadmium can significantly inhibit soil phosphatase activity, and the inhibition rateincreased with Cadmium concentration. Complete inhibition model can characterize therelationship between phosphatase activity and cadmium content. The organic matter contentwas also the main factor which effected the impact of Cd on soil phosphatase enzyme. Withthe same cadmium concentration, the inhibition on soil phosphatase of Cd（NO3）2, CdSO4,CdCl2was more obvious than Cd（OAC）2.（5）Cadmium can significantly inhibit soil dehydrogenase activity, and thedehydrogenase activity showed the trend that first decreased and then increased with time.The FDA hydrolase, nitrification activity also reduced in cadmium contaminated soil, but thechange was not as great as dehydrogenase. The aging process reduceed the toxicity ofcadmium on soil dehydrogenase, FDA hydrolysis enzymes and nitrification activity. Underthe same concentration of cadmium, the soil dehydrogenase, FDA hydrolase and nitrificationactiviy in Cd（OAC）2contaminated soil were higher than Cd（NO3）2, CdSO4, CdCl2treatments.The available cadmium content of the test soil samples increased with the concentrationof soil cadmium.The highest concentration of cadmium were occurred in0d in two soilsamples, and soil available Cd contents decreased with incubation time. Throughout theculture phase, cadmium acetate treatment had the lowest available cadmium content withlower soil biological toxicity.