Effect Of Exogenous Organic Matter On The Forms Of Lead And Cadmium In Freeze-Thaw Cycles

With the seasonal alternating, freeze-thaw cycles occurd in northeast of China influence thecontaminant and internal environment of soil in many aspects. The effect of freeze-thaw onphysical and chemical properties of soil and forms of heavy metals has been investigated by manyother reserachers, and had some achievement. But few analyzation about the relationship betweenforms of heavy metals and exogenous organic matter, degree of pollution and ageing time whichare benefit to management of heavy metals had been reported.The phaeozem and burozem which are typically soils of northeast of China were investigatedby laboratory simulation method. We studied the effect of exogenous organic matter on thespeciation of lead and cadmium in freeze-thaw cycles. Then according the response of soilproperties to freeze-thaw, we analyzed the effect of reason exogenous organic matter on forms ofheavy metals. The results as follows:Most of the exogenous Pb turned into residue form while most of Cd turned intoexchangeable form, and the distribution of heavy metals in unfreeze-thaw cycles was similar tofreeze-thaw cycles. But there was still a little transform among the forms of heavy metals infreeze-thaw cycles, and promoting the stability of heavy metal. At the same time, the content ofexchangeable form and organic-binding form of Pb and Cd increased and the content ofcarbonate-bound was reduced as increasing freeze-thaw cycles and water content and decreasingtemperture. The content of Fe-Mn oxide-binding form increased as increasing frequency offreeze-thaw and reduced as increasing soil moisture content and reducing temperture. Compare tophaeozem, the content of exchangeable form, carbonate-bound form and Fe-Mn oxide-bindingform in burozem were higher, so the activity of heavy metal in burozem were higher.Freeze-thaw can destory macro-aggregates significantly, and reduce the value of pH andcation exchange capacity (CEC), and increase Eh of phaeozem. Freeze-thaw had no effect on totalof organic matter in phaeozem. But Freeze-thaw promoted the content of DOM, and reduced thecontent of microbial biomass carbon, and inhibited the activity of fluorescein diacetate (FDA)hydrolysis enzyme, cellulose enzyme and catalase, and promoted activity of protease. Differentfreeze-thaw condition had different effects on properties of soil. As freeze-thaw cycles and soilmoisture content was increased, the damage to aggregates aggravated, and the value of pH, cationexchange capacity CEC and the content of DOM increased gradually, and the activity of enzymewere promoted, and Eh and the content of microbial biomass carbon reduced. When the freezetemperture decreased, the pH increased while CEC and the activity of enzyme reduced. The reasonthat freeze-thaw affected the forms of heavy metals was because it changed the physical, chemicaland biological properties of soil.Application of sludge and straw solid to soil can reduce the content of exchangeable form andincrease the carbonate-bound form of Pb and Cd of soil, but have different effects on Fe-Mnoxide-binding form, organic-binding form and residue form. Application of sludge can reduce thecontent of Fe-Mn oxide-binding form and increase the content of residure form of Pb. Application of sludge increased the content of Fe-Mn oxide-binding form and organic-binding form, andreduce the content of residure form of Cd in soils. Application of staw can reduce the content ofFe-Mn oxide-binding form, and increase the content of organic-binding form and residure form ofPb while increased the content of Fe-Mn oxide-binding form and organic-binding form of Cd insoils. Compare to phaeozem, application of sludge and staw had stronger effect on the content ofcarbonate-bound form and Fe-Mn oxide-binding form of burozem. Effect of application of DOMof sludge and staw on forms of heavy metals was similar to above results in freeze-thaw cycles.Application of sludge and straw solid can aggravate the change of properties of soil, andincrease the content of total organic matter, DOM and microbial biomass carbon, and pormote theactivity of enzymes. However, sludge and staw had different effect on pH of soil, and applicationof sludge reduced the pH while staw increased the pH. Compare to phaeozem, application ofexogenous organic matter can enhance the damage freeze-thaw cycles to burozem, and increasedthe content of DOM and promoted activity of FDA Hydrolysis enzyme and protease. The froms ofheavy metals were changed by sludge and staw soild, because the physicochemical properties ofsoil were changed by slude and staw solid, and DOM had stronge complexation to Pb and Cd.