Differences Of Mercury Uptake Ability Among8Wheat Varieties And Effects Of Chelating Agents Application On Hg-contaminated Soil And Wheat Growth

Mercury (Hg) is highly toxic and poses a serious threat to the environment and humanhealth. Hg contamination in ecological environment has been recognized as a serious globalproblem, threatening the health of millions of people. An effective way to reduce thecirculation of heavy metal is to select a wheat species with ability to accumulate less heavymetal. Also, heavy metals cannot be decomposed, but they can form more toxicmetallorganics under the action of microorganisms. Hg contaminated soil is particularlychallenging to restore. In this paper,8most popular wheat varieties (Xumai30, Shanmai979,Xiaoyan22, Jimai22, Wanmai52, Zhengmai9023, Shixin618, Hengmai5229) in Chinawere selected. Pot experiments with laboratorial analytical methods were carried out to studythe differences of Hg uptake, accumulation and distribution. Based on that, differentconcentrations of4chelating agents (including EDTA, EDDS, NTA and CA) applied into twosoil types to investigate the effects of chelating agents on wheat seedlings growth, Hgabsorption, accumulation and translocation. The objective is to provide a theory basis forphytoremediation of Hg contaminated soil. The main results were as follows:1. After adding with2mg·kg-1Hg to the Loessial soil, the biomass and grain yield ofShanmai979decreased by1.95%and0.61%compared with control, while which increasedfor other seven wheat varieties. In addation, Hg concentrations in shoots, leaves, glumes andgrains of8wheat varieties were increased significantly for Hg treatment. Different parts ofwheat have different Hg uptake ability. Highest Hg accumulation in shoots, leaves, glumesand grain was found in Xiaoyan22, Shixin618, Hengmai5229, and Xumai30respectively.Jimai22had the lowest Hg concentration in leaves, and Xiaoyan accumulated least Hg inglumes and grain. The distribution portion of Hg in shoots was significantly higher in treatedsamples, but lower in leaves and grains. Considering the yield and food safety, Xiaoyan22was the best choice for Hg resistance in Loess soil.2. After adding with0.3mg·kg-1Hg to the Red soil, the biomass and yield of all7wheatvarieties were decreased except Hengmai5229. The highest Hg concentration was observed in shoots, followed by leaves, glume and grain. Hg distribution rates were all increased for Hgtreament, which may be related to dry weight.Highest Hg concentration in shoots, leaves,glumes, and grains occurred in Hengmai5229, Wanmai52, Shixin618, and Xiaoyan22andWanmai52, respectively. Hengmai5229accumulated least Hg in the grains. Considering theyield and food safety, Hegnmai5229was the best choice species for the agriculture.3. In Loess soil, wheat seedlings growth affected by both the types and concentrations ofchelating agents. Compared with the control treatment, low concentrations of chelating agentshad less effects on wheat growth than high concentrations. However, adding1mmol·L-1CAin soil could significantly increase root length, while amended8mmol·L-1EDTA could mostsignificantly decrease shoot length of wheat seedling. Shoot biomass decreased significantlywith the chelating agent concentration rising, but no significant effect was found on rootbiomass (5mmol·L-1and8mmol·L-1treatments). Contents of Hg in shoots and rootssignificantly increased under all chelating agent treatments. More Hg had been translatedfrom roots to shoots for EDTA treatment. The translocation coefficient reached the peak valuewhen1mmol·L-1EDTA was added. Because of larger biomass and higher Hg translocationcapacity, EDTA was the most suitable species among four tested chelating agents to eliminatesoil Hg contamination.4. In Loess soil, chelating agents can decrease pH value of soil and8mmol·L-1NTA hadthe most significant effect. EC value of soil was increased with chelating agents raise andmost significant effect occurred under8mmol·L-1EDTA treatment.8mmol·L-1EDTA causedhighest uptake of Hg, while1mmol·L-1NTA caused lowest. Appearance of chelating agentsincreased the concentration of active state trace element in soil. The peak value happened on7th day, and starting decrease at14days. Chelating agents with higher concentration hadhigher ability to uptake trace element. EDTA has highest dissolution effect on Fe and Mn,while EDDS for Cu, and NTA for Zn.5. Wheat growth was affected by types and concentrations of chelating agents in Red soil.All the chelating agents enhanced the root elongation and EDDS had the most significanteffects. However, the enhancement decreased as the chelating agents concentration increase,which also reduced the height and biomass of the wheat. Adding cheatling agents can increasethe Hg uptake in wheat and EDDS had the most significant effects. Hg accumulation washigher in the roots than the shoots, but chelating agents can enhance the transport of Hg fromroots to shoots, and the highest transport rate occurred under8mmol·L-1EDDS treatment,which is the best choice for Hg remedation.6. In Red soil, chelating agents affected pH and EC value in soil. At low concentration (1mmol·L-1), EDTA decrease pH value most significantly, but at high concentration (1mmol·L-1) EDDS did. Chelating agents increased EC value and EDTA had the most significant effect.Uptake of Hg was increased as the thelating agents concentration increasing.8mmol·L-1EDDS caused highest Hg accumulation and1mmol·L-1CA caused the lowest uptake. All ofchelating agents caused the highest uptake of Hg in8mmol·L-1. With the concentration ofEDTA、EDDS and NTA increasing, the uptake value of Hg increased. The results of chelatingagents uptake trace element showed that EDTA has highest dissolution effect on Fe Mn andZn, while EDDS for Cu.