Study On The Heavy Metal Pollution Of Farmland Soil Under Sewage Irrigation From The Wuhu Smeltery And The Remediation By Weeds

With the development of modern industry,the release of heavy metals into the environment has been accelerating annually.Heavy metal contamination poses a threat to human health and life quality.So it has become a serious problem in environment and society.This problem may be partially soved by the phytoremediation which offers a cost-effective "green"method for soil remediation.There are now three subsets of this technology applicable to soil remediation:(1)phytoextraction,using hyperaccumulator plants or high biomass metal accumulating plants to remove toxic metals from soil; (2) phytovolatilization, using plants to stimulate volatilization of metals from soil or plant surface;and (3) phytostabilization, using plants to transform soil metals from toxic forms to less toxic forms.Hyperaccumulators are the plants which have been selected by the heavy metals-contaminated environment.It is the tolerance and concentration of heavy metals that demonstrate hyperaccumulators have the ability to remediate soils contaminated by heavy metals.Hyperaccumulators are able to accumulate over 1000mg·kg^-1Cu (Pb, Ni etc) or over 100mg·kg^-1Cd etc(Dry-Weight).This paper studied the heavy metal pollution of farmland soil under sewage irrigation from the Wuhu smeltery and the feasibility of the remediation by weeds.At the same time,effects of the combinative pollution of Cu and Zn on Ludwigia prostrate Roxb and preliminary studies of its mechanism were studied. The pollution of heavy metal in farmland soil of the sewage irrigation area was discussed.The contents of copper, zinc, lead, nickel and manganese in soil samples were measured.The results were showed that the contents of copper, zinc, lead, nickel and manganese were 182.45³2.8mg·kg^-1,98.43⁴0.90mg·kg^-1,35.75³0.98mg·kg^-1,44.65³6.30mg·kg^-1 and 98.95⁷7.55mg·kg^-1, respectively. The total and extractable Cu in the soil of 100m were 182.45mg·kg^-1 and 81.91mg·kg^-1 respectively which were 9.3 and 34 times higher than the contrast.At the same time,the pollution index was calculated based on both the heavy metal-background values standard of Anhui Province and the state standard values of soil-environmental quality in China.The result indicated that the soils were contaminated compoundly in great universality based on the heavy metal-background values of Anhui Province.As for contaminated degree,copper was the most severe.Based on the state standard values of soil-environmental quality in China,the average integrated pollution index of the city was 2.75 which was the result of soils having been contaminated by copper. The differences of activities of three soil enzymes (urease, sucrase, catalase) in the smeltery polluted and control(CK) farmland soil were studied.Among the three test enzymes,soil urease was the most sensitive one to Cu.Soil urease activities of 100m,200m,400m and 800m were lowered 77.4%,54.2%,52.4% and 33.9% respectively compared with CK,and its activities had significant correlation with soil Cu contents.Therefore,it is feasible to use soil urease activity as an indicator index of soil Cu pollution in sewage irrigation area near the smeltery. The contents of four heavy metal elements including Cu,Pb,Zn and Ni in 30 weed species and six sites collected from the sewage area near the smeltery were determined and numerically analyz.The results showed that the organs followed an order as roots>leaves>stems based on their average concentrations of four elements.The elements ranked as Cu>Zn>Ni>Pb according to their concentrations in weeds,the accumulation coefficients were in the order of Zn>Cu>Pb>Ni in weeds.The accumulation coefficients of Cu in roots of Alopecurus aequalis Sobol.,Zizania latifolia Turcz.,Bidens pilosa L.,Ludwigia prostrate Roxb,Paspalum distichum L. and Phragmites australis (Cav.) Trin. were 2.54,2.69,4.82,10.74,7.33 and 4.60, respectively.The roots of these weeds had high enriching abilities of Cu.Cu concentrations in some weeds were as follow(Dry-Weight):roots of Alopecurus aequalis Sobol 813.4mg·kg^-1, roots of...