Effects Of Soilbuffer Capacity On Heavy Metalbioavailability In Soil

With the development of industry and city, the soil heavy metal pollution isincreasing seriously which threats human survival and health. The soil heavy metalalways exists as water-soluble state, exchangeable state, organic combination state,iron-manganese oxide combination state, carbon bounded form and the residual form.Only the water-soluble state and exchangeable form can be absorbed by crops whichmeans they are plant effectiveness. Soil buffer capacity can affect the heavy metalbioavailability in soil directly as one of the important physical and chemical propertiesof soil in order to affect the efficiency of heavy metal phyto-remediation. The researcheson the factors of soil buffer capacity are much more than the researches on the effects ofsoil buffer capacity on heavy metal bioavailability in soil.The buffer capacity of soil on activity of heavy metals was studied based on theadsorption desorption experiment of soil with different buffer capacity. The Sedumalfredii Hance, S.Sarmentosum, Beta vulgarisvar.cicla.L and Beta vulgarisvar.cicla.G.were used to carry out pot experiment in order to study the effect of different buffercapacity on the ability to absorb and accumulate biomass and heavy metal in plant onthe ground and underground. The effect of buffer capacity on plant effectiveness ofheavy metal was studied to provide fundamental basis for the enhance ofphytroremediation efficiency of heavy metal in soil. The results show that:(1) The changing curve which the adsorption quantity changes with buffer capacityis an S-shaped under different initial concentration. It shows that the adsorption quantityincreases with the reduction of buffer capacity.The desorption amount increases with theincrease of initial concentration and decreases with the reduction of buffer capacity andthey changed with a decreasing trend. The desorption amount decreases with the increase of adsorbing capacity and the activity of heavy metal in soil increases with thereduction of buffer capacity.(2) The soil buffering capacity to Cd increases and the toxicity reduces with thedecrease of buffer capacity. The four plants all show the effect of growth promoting andthe amplification of the biomass of them are different. The hyperaccumulator plantshows stronger heavy metal resistance ability compared with control plant.(3) With the reduction of buffer capacity, the enrichment factor decreases, thetransport coefficient of plants increases, the enrichment ability to heavy metal decreasesand the plant effectiveness of heavy metal decreases.(4) With the reduction of buffer capacity, the species distribution of Cd changes,the exchange state content decreases obviously, the content of iron-manganese oxidecombination state and residual form increase. The transformation to combined stateincreases the fixity of soil on Cd and decreases phyto-availability of Cd.