Influence Of Organic Matter And Attapulgite On Speciation Of Cd In Soil

With the rapid development of the industry,agriculture,transportat ion and people's living standard,and the accelerated process of urbanization in C hina,the pollution of heavy metals in the soil has become increasingly prominent in C hina.People's awareness of environmental protection continue to strengthen,this proble m has become the hot issue with the common concern.The toxicity and harm of the heavy metals is greater than other kinds of pollutants because of its continuous accumulation.The heavy metal can inhibit the growth of animals and plants.The heavy metal Cd can continuously enriched through food chain and caused severe lesions of human bones,liver,kidneys and other organs.The total amount of heavy metals in soil can not reflect the biological toxicity and bioavailability accurately because total evaluation has some limitations.A large number of experimental studies show that the bioavailability and mobility are quite different of the different forms of heavy metals,as well different inhibitory effect of plant growth.Therefore,the research on the conte nts and its variation of different forms of heavy metals in soil has important significance in the treatment and remediation of heavy metal pollution.Adding passivating agent is the effective technical means and methods of treating heavy metal pollution in soil.This study took organic fertilizer from Gansu Shuangtai Aotu Technology Co.,Ltd.and Attapulgite from Linze County in Gansu Province as passivating agent.Two groups experiments of adding organic fertilizer and attapulgite were set.For each treatment group six different concentration were set up as inactivation experiment.In the paper the content of Cd and the form distribution in the BCR sequential extraction method were determinated in different time points(the 3,6,12,24,48 days).The difference of the Cd content in various forms and the correlation between growth indexes of corn and forms of heavy metal were analyzed to study the changes of the contents of Cd in soil and the effects on bio availability of different concentrations of heavy metals.(1)After 48 days,the acid soluble state and reduced state of Cd in the samples almost showed a decreased trend(Removal of acid soluble state of concentrations of Cd 4 mg / kg of CK and organic matter addition 40g/kg;Cd concentration 8mg/kg of organic matter added weight 10,20,40 g / kg;Removal of the reduced state of Cd concentration is 2mg / kg of organic matter addition amount is 40g/kg,the concentration of Cd 6mg / kg of CK,Cd concentration 8 mg / kg of organic matter addition to 80 g/kg,the Cd concentration was 12 mg / kg in the outside).In addition the oxidation state of 12 mg/kg,the content of Cd in oxidation state decreased,and the content of residual showed the decreasing trend.After 48 days of adding attapulgite,the Cd of acid soluble state content in treatment of 2 mg/kg showed an increasing trend and acid solution State content in the rest treatments was significantly decreased.The Cd content in treatment of 12 mg / kg in reduced state increased,and reduced state content in the rest treatments was significantly decreased.The oxidation state of Cd content increased in every treatment.The residue state content of heavy metal Cd in each treatment decreased,except the treatment of 16 mg/kg.(2)After 48 days of adding organic fertilizer and attapulgite,the content of heavy metal Cd in acid soluble,reduced and residual content showed a decreasing trend,and the Cd content in oxidation state of adding attapulgite showed an increasing trend while the Cd content in oxidation state of adding organic fertilizer decreased.Accoring to the changes of Cd in acid soluble state,reduced state,the oxidation state and residual state,it showed that the content in non-steady state and steady state decreased.And the actual reduction va lues of Cd in acid soluble and reducible were significantly higher than the changes of residual state and oxidation state.The results showed that the content of effective Cd was reduced,as well the biological toxicity and environmental risk of heavy metal Cd.(3)The difference of Cd content in four forms were analysed,the results showed that: in the addition of organic fertilizer and attapulgite,the Cd content of acid soluble and reducible increased with the increasing of Cd concentration,the content also showed a certain difference.but the oxidation state and residual state did not have the same trend.It is suggested that the exogenous Cd concentration and the Cd in soil will significantly affect the unsteady state of acid soluble and original state.And the change of Cd content with the different addition proportion of organic fertilizer and attapulgite was not a certain trend,but the various forms of Cd content in each treatment also showed a certain difference.(4)The correlation between content of Cd in four forms and growth indices of the corn was analyzed,the results showed that: The Cd content in acid soluble and reducible showed negative correlation with growth indices(emergence rate and plant height).The Cd had inhibition effect on p lant growth,it reflected a certain biological toxicity and environmental risk.The residual state belongs to the "steady state",its content had no effect on corn growth and showed positive correlation with growth indices.And the Cd in oxidation state did not have obvious biological toxicity on plant growth because its small proportion.