Study On The Immobilization Remediation Of Heavy Metal Pollution In The Farmland Soil Of Bijie City,Guizhou Province

Long-term mining,dressing and smelting of lead/zinc mines in Bijie City of Guizhou Province have already caused serious heavy metal pollution of local farmland soil,endangering the health of local residents together with residents in the lower reaches of the Yangtze River and the Pearl River.This thesis aims to analyze the pollution status of heavy metals in Bijie's farmland and to remediate the polluted soil using phosphate containing materials and phosphate solubilizing bacteria(PSBs).(1)The pollution characteristics of 11 heavy metals,namely Pb,Zn,Cu,Ni,Co,Mn,Cr,V,Hg,As and Cd,in 177 farmland soil from Bijie City,were analyzed systematically and results showed that the contents of Pb,Cd and Zn exceeded the farmland soil standard largely;the accumulation of Pb and Zn in the farmland soils in Bijie resulted mainly from metal smelting,while other human activities,such as fertilization,mining and combustion of coal might affected the accumulation of Cd;polluted sites with very high potential ecological risk located mostly in Weining County and Hezhang County,in the west of Bijie City.(2)Soil micorbial community characteristics analysis showed that,in the long-term heavy metal polluted farmland soils,the most polluted soil had the highest microbial activity and the abundance of genus Sphingomonas and Thiobacillus was significantly higher in more polluted soil;soil components,like organic matter and available phosphorus,might mitigate the toxic effects of heavy metal pollution on soil microbial community by reducing the availability of heavy metals and providing nutrients for microbial communities.(3)The addition of potassium dihydrogen phosphate and dipotassium hydrogen phosphate could significantly reduce the availability of Pb and Cd,and the effect on the availability of Zn was not significant;the addition of phospate could partly enhance the soil microbial activities by decreasing the availability of heavy metals and providing nutrients for microbial community;the increase of pH by high dosage addition of phosphate might have a negative impact on soil microbial community;potassium dihydrogen phosphate was more suitable for the remediation of local polluted soil than dipotassium hydrogen phosphate.(4)One consortium of PSBs was isolated from heavy metal polluted soils,which had high phosphate releasing capability and high resistance to heavy metals;the consortium was mainly comprised of Enterobacter spp.,Bacillus spp.and Lactococcus spp.;the consortium could facilitate the release of phosphate ion in calcium phosphate,and significantly increase the content of available phosphorus in soil,therefore immobilizing more available heavy metals;under the effects of PSB consortium,the increased contents of available phosphorus and the decreased heavy metal availability indirectly enhanced the soil microbial activity.In summary,this study enriches the technology and theory of heavy metal pollution control in farmland soil;meanwhile,can further contribute to the development of the remediation of heavy metal contaminated soil in Bijie City and the protection of local residents' health as well as the water security of the Yangtze River and the Pearl River.