Study On Characteristics Of Heavy Metal Absorption And Accumulation In The Different Maize Varieties

With rapid development of industry and agriculture, a huge area of farmland in China has been contaminated by heavy metal. Soil is the direct carrier of agricultural products. Soils polluted by heavy metal not only decrease crops yield, but also increase content of heavy metals in edible parts of crops, and threaten to human health via food chain. Maize is one of the most important grain crops at home and abroad. Lots of researches showed that there were significant absorption and accumulation differences of heavy metals among different varieties of maize. So, that screening and cultivating maize varieties with a characteristic of low accumulation of toxic heavy metals is propitious to reducing the accumulation of heavy metals in food chain, and it is a economic and effective way of sustained and safe production in soils slightly and moderately contaminated by heavy metals. In the study, some maize varieties popularized in Suining City, Sichuan Province were chosen as tested materials, absorption and accumulation characteristics of heavy metals (Cr, Cd, Hg, Pb, Cu, As, Zn, Ni) in different varieties of maize and distribution of heavy metals in maize tissues were studied, the interactions between environment and variety for capacity of accumulating heavy metals of maize grain were analyzed, and some maize varieties with low accumulation of heavy metals and good environmental adaptability were screened out. The main results are listed as follows:1. The relationship between contents of heavy metals in maize grains and soilAmong 106 maize grain samples, heavy metals contents of a part of samples exceeded standards, the exceeding standard rate of Hg was 14.15%, Cr was 0.94% and Ni 23.58%, contents of other heavy metals in samples all measured up to maximum values in "Limits of eight elements in cereals, legume, tubes and its products (NY 861-2004)". There were not significant relationships between content of heavy metals in maize grains and soils, very significant positive relationships between content of heavy metals in maize grains and content of DTPA-extracted heavy metals in soils. Except Zn, the correlation coefficients of Pb, Cu, Ni and Cr were 0.098**,0.147**,0.068** and 0.170**, respectively. According to "Limits of eight elements in cereals, legume, tubes and its products (NY 861-2004)", Among the 6 maize varieties popularized in maize Demonstration Zone, Xinhua village, Shehong county, the maxmium contents of DTPA-extractable heavy metals in soil for safely producing edible maize were figured out.2. Screening maize varieties with low heavy metal accumulation in grains(1) Screening maize varieties with low accumulation of heavy metal according to heavy metal concentration in grainsContents of heavy metals (As,Hg,Cu,Zn,Cd,Cr,Pb,Ni) in maize grains of 21 maize varieties in field experiments all measured up to "Limits of eight elements in cereals, legume, tubes and its products (NY 861-2004)". In order to obtain maize varieties fit for planting in soils contaminated by unknown heavy metals, cluster analysis of heavy metals in 21 maize varieties was carried out, some maize varieties with low heavy metals accumulation characters were obtained, and degrees of combined pollution were evaluated by the improved AHP comprehensive index model. Lowest index of combined pollution was Jinyu308, Chuandan15, Yayu10, et al.(2) Stability and adaptation analysis on maize varieties with low heavy metal accumulation characteristicThe interactions between environment and variety obviously affected the accumulating ability of heavy metal in maize grains. Varietal effect of Cu had a dominant role, occupying 77.6% of the total variation; as for As,Hg,Pb,Zn and Cr, the varietal and environmental effect had a dominant role, occupying 63.4%,74.3%,50.3%,69.2% and 57.5%, respectively. By AMMI plot, stability sequences of accumulating heavy metals in different maize varieties were acquired based on different heavy metals, stability of accumulating As was Chendan30> Chuandan428> Zhenghong311> Longdan8> Chuandan418, Hg was Chuandan418> Chuandan428> Chendan30> Zhenghong311> Longdan8, Cu was Chuandan418> Zhenghong311> Longdan8> Chendan30> Chuandan428; and Pb was Chendan30> Chuandan418> Longdan8> Chuandan428> Zhenghong311.3. Absorption and transfer characteristics of heavy metals in different tissues among maize varietiesThere were significant differences of capacity of accumulating and transferring heavy metals in tissues among 21 maize varieties. Except Pb and Zn, the bioaccumulation factor of heavy metal in underground was generally greater than that in aboveground. The distribution law of heavy metals in maize was root> leaf> stem> seed, but some variety was leaf> root> stem> seed. While the contents of Pb and Zn in leaves among 21 varieties were all higher than that in root. Generally speaking, the transfer factors of heavy metals transferred to grains were all low, and there were differences among different heavy metals. The transfer factor of Zn in grains was as 5-10 times as others. The sequence of the average bioaccumulation factors of Cu, Zn, Cr, Ni, Pb, Hg, As and Cd in maize plants was Cu> Zn> Cd> Hg> Cr> As> Ni> Pb, while in grains was Zn> Cu> Hg> Cd> Ni> Cr>As>Pb.