Remediation Research Of Lobular Mustard On Simulated Sewage-irrigated Soil Polluted By Cadmium

Because of long-term irrigated by swage, sewage-irrigated farmland was polluted by heavy metals seriously, of which cadmium is one of the most serious heavy metal pollution. Heavy metals entered into farmland not only poisoned the soil ecosystem, caused crop pollution and a decrease in production, but also a serious threat to human health, so remediation researches of heavy metal pollution in sewage irrigated farmland is important. Phytoremediation as a cheap and efficient in-situ remediation technologies, received extensive attention of many scholars in recent years, however the low water solubility and bioavail-ability of heavy metals limited its uptake and accumulation by plants. The application of chelating agents not only can activate soil heavy metals, but also can promote the uptake and transport of heavy metals by plants, improved the efficiency of phytoremediation, it is the most widely used measures to streng-then phytoremediation currently.In this study, in view of farmland heavy metal pollution problems caused by sewage irrigation, with Lobular mustard as the remediation plants, self-made simulated sewage irrigated soil heavily polluted by cadmium as research object, using pot experiment, studied the effects and mechanism of three different chelators(EDTA、EDDS and oxalic acid) to strengthen phytoremediation. And use four soil enzyme activities and available phosphorus contents to indicate the effects of chelators on soil quality. In order to provide scientific basis and feasible measures for rational application of chelators to enhance phytoremedia-tion of heavy metal contaminated sewage irrigated farmland. The main conclusions are as follows:(1) The application of chelators influence the biomass of plants, and the effects on aboveground and underground biomass have no significant difference. Lobular mustard biomass decreased after applying EDTA, and the higher the concentration was, the more significant the decrease was. However the applica-tion of EDDS had no significant effect on Lobular mustard biomass. Low concentrations of oxalic acid can promote the growth of Lobular mustard, but a slight inhibition occurred at higher concentrations.(2) The ability of Lobular mustard to uptake and enrich cadmium induced by EDTA was obviously higher than induced by EDDS and oxalic acid. Cd contents of Lobular mustard aboveground and underground part and EDTA, oxalic acid concentration was significantly positively correlated. While induced by EDDS, Cd contents increased firstly and then decreased. The transport coefficients of Lobular mustard induced by EDTA were greater than1, while treated by EDDS or oxalic acid the transfer coefficient decreases with the increase of use concentration, respectively since2mmol/kg and4mmol/kg it was less than1. With the increase of chelators concentration, the total accumula-tion of Cd in plants increased gradually firstly and then stabilized or decreased, total Cd content in rhizosphere soil decreased firstly and then increased. When treated by3mmol/kg EDTA the removal rate of soil total Cd reached76.49%.(3) The application of EDTA significantly changed the distribution of Cd in soil, effectively promoted soil Cd transformed from relatively stable forms to biological effective form. The complex formed with EDTA and Cd was easy to be absorbed by plants. Contents of exchangeable, carbonate bound and Fe-Mn oxides bound Cd in soil were significantly reduced. While induced by EDDS or oxalic acid, contents of all forms of Cd have no obviously change. Three chelators with different concentrations all had no significantly effects on contents of organic bound and residual Cd in soil.(4) Catalase activity was slightly inhibited treated by three different chelators, however the change was not obvious. With the increase of EDTA concentration, invertase activity increased rapidly firstly and then stabilized, while urease activity increased firstly and then decreased. Low concentration of EDDS and oxalic acid can improved invertase activity obviously, however the activity dropped to comparable level of control at higher concentration. Urease activity had no significant change when induced by EDDS and oxalic acid. Phosphatase activity all exhibited increase firstly and then decrease with the increase of chelators concentration.(5) Soil phosphatase activity and total Cd content were significant or highly significant negative correlation induced by three different chelators. Phosphatase activity can be used to evaluate soil Cd pollution levels in chelate-enhanced phytoremediation. Soil invertase activity and total Cd contents was also signify-cant negative correlation when induced by EDTA. The correlation between catalase, urease activity and soil Cd content were not significant in all treatment. Chelators not only indirectly affects soil enzymes activities trough influencing soil Cd content, but itself also has a certain influence on various enzymes activities.(6) Soil available phosphorus content increased obviously after application of EDTA, while the application of EDDS had no significant effect on it. Low concentration of oxalic acid can increase available phosphorus content obvious-ly, but when the concentration reached5mmol/kg, the content dropped to com-parable level of control. The soil pollution of Cd obviously affects the effective-ness of phosphorus, available phosphorus content was significantly negatively correlated with soil total Cd content induced by three different chelators.