Study On Phytoremediation Of Contaminated Agricultural Soil With Heavy Metals

The soil is not only a major component of the environment, but also a material basis of food and renewable resources for human. In recent years, large areas of land have been contaminated by heavy metals in our country, and thus caused enormous losses of ecological and economic, which have adverse effects on the health of human. Therefore, the remediation of heavy metal contamination in soil is a worldwide urgent issue. The soil contaminated by heavy metal is characterized by Because of the soil contaminated by heavy metal have four characteristics:potentiality, hysteresis, irreversibility and long-term, so it is difficulty to treat the contaminated soil. The traditional physicochemical techniques include turning and deep plowing of soil, the addition of fresh soil, ridging precipitation, sorption, leaching, and washing. However, there are several shortcomings in these remediation methods, such as great engineering quantity, low efficiency, high cost, management difficulty, easy of secondary pollution and large environment disturbance. As an environmental friendly and an insitu environmental remediation technique for heavy metal contaminated soils, phytoremediation is being a new method in soil remediation research. The emerging phytoremediation techniques, with their nature of lower cost and environmental friendly, have received increasing attention in the last decades. Zea mays. L, Helianthus annuus. L and Brassica campestris. L were selected as experimental plants in this study, which can accumulate heavy metals. The main objective of this study was to estimate the remediation efficiency of the plant for the farmland soil contaminated by the heavy metals, and to achieve ecologically sustainable development of economy, society and environment.The results indicate as follows:(Ⅰ) A field experiment was carried out to evaluate the phyremediation abilities of three crops, including Zea mays. L, Helianthus annuus. L and Brassica campestris. L. These experimental fields were contaminated with Pb, Cd and As. The results indicated that the level of Pb, Cd and As were 242.328mg/kg,2.215mg/kg, and 58.240 mg/kg (dry weight) in shoots of Zea mays. L, Brassica campestris. L and Helianthus annuus. L, respectively. Bio-Concentration Factors (BCF) of the three plants were 0.607,0.831 and 0.518, respectively. All of BCFs did not exceed the value of 1. Thus, The three plants were not have basic characteristics of heavy metal hyperaccumulator plant, but the strong bio-concentration ability to objective heavy metal was found.BCF of Pb in Zea mays. L is 2.09 and 3.03 times compared with that of in Helianthus annuus. L and Brassica campestris. L. The phytoextraction rates (PER) of Zea mays. L, Helianthus annuus. L and Brassica campestris. L were 0.668%,0.488% and 0.239% for Pb, Cd and As, respectively. The PER of Zea mays. L for Pb was 5.50 and 12.71 times compared with that of Helianthus annuus. L for Cd and Brassica campestris. L for As. The three tested plants were proved to have the potential value in remediation for the contaminated field soil.(Ⅱ) After treatments of EDTA, NTA, calcium superphosphate, CA and different planting density, the remediation influence for seven configurations were also discussed. The results described as follow:After EDTA treatment for 20d, the level of heavy metals in restoration plants were significantly increased. The chelated effects on the heavy metal of EDTA from high to low was Pb>Cd>As. After treatment of EDTA, the highest value of Pb, Cd and As in restoration plants' shoot were 475.658mg/kg for Zea mays. L,3.006mg/kg for Helianthus annuus. L and 65.187mg/kg for Brassica campestris. L, respectively. After NTA treatment for 20d, the level of heavy metals in restoration plants were significantly increased. The chelated effects on the heavy metal of NTA from high to low was As>Pb>Cd. After treatment of NTA, the highest value of Pb, Cd and As in restoration plants'shoot were 289.836mg/kg for Zea mays. L, 2.427mg/kg for Helianthus annuus. L and 122.218mg/kg for Brassica campestris. L, respectively. After calcium superphosphate treatment for 60d, the level variation of heavy metals in restoration plants was fluctuant, the level of Pb in restoration plants were decreased, and the As level in restoration plants were increased. After treatment of calcium superphosphate, the highest value of Pb, Cd and As in restoration plants' shoot were 209.976mg/kg for Zea mays. L,2.176mg/kg for Helianthus annuus. L and 69.768mg/kg for Brassica campestris. L, respectively. After CA treatment for 60d, the level of heavy metals in restoration plants were significantly increased. The chelated effects on the heavy metal of CA from high to low was Pb>Cd>As. The highest value of Pb, Cd and As in restoration plants' shoot were 379.724mg/kg for Zea mays. L, 3.057mg/kg for Helianthus annuus. L and 20.995mg/kg for Brassica campestris. L, respectively.(Ⅲ) The effects of plants on phytoremediation rates under seven configurations and different treatments were systematically investigated. The results were as follows. The phytoremediation rates of CK in every groups were the lowest in all configurations. Under the same configuration, the phytoremediation rates of Pb, Cd and As by every treatments from high to low were T2>T6>T5>T1>T3>T4>T6>T5>T2>T3>T1>T4 and T3> T6> T2> T1> T5> T4, respectively.(Ⅳ) The results, achieved from the comprehensive assessment by improved model of AHP, indicated that the best configuration to remediate this contaminated soil was the individual planting of Helianthus annuus. L under the treatment of increase planting density, along the three chelating agents, NTA was the best configuration chelating agent, follow then was CA.