The Effect of Organic Materials on the Uptake of Heavy Metals by Maize (Zea mays) in Heavy Metals Polluted Soil.
Jolanta Kwiatkowska and Alina Maciejewska. Warsaw Univ of Technology, Politechniki 1 Sq, Warsaw, 00-661, Poland
In biological aspect, heavy metal is a connotation of toxicity as contaminant in ecosystem. The release of trace metals in biologically available forms, as a result of human activity, may impair or alter both natural and man-made ecosystems. The chemical form (speciation) of trace metals in soil solution is greatly dependent on the metal, pH, presence of organic matter and other ions. To reduce the risks associated with introduction of toxic trace metals in the food-chain, it is very important to know the interaction between trace metal ions, soil organic matter, and plants. It was assumed that the organic matter contained in brown coal, brown coal-derived preparation, peat and farmyard manure would decrease the absorption of heavy metals by plants, by forming complex compounds and making the metals immobile. The formation of chelats will cause an exclusion of heavy metals at the stage of their transfer from soil to plants. The experiments were carried out on Haplic Luvisols formed from loamy sand (WRB) in field pots sank into the ground. To the soil a brown coal preparation, the “Rekulter”, brown coal, peat and farmyard manure in the amount of 180, 140, 390 and 630 g per pot respectively, which is equivalent to 5 tons .of organic carbon per ha. The soil was mixed up with liquid form of salts: cadmium as Cd(NO3)2, lead as Pb(CH3COO)2 and zinc as ZnSO4, after blending soil with salts of heavy metals the content of its was: Zn = 90.0; Pb = 60.4; Cd = 0.80 (mg.kg-1 of soil). In 2000 a maize (Zea mays) was grown which was harvested in green forage. The soil samples were mineralised in 2M HNO3 for determined contents of Cd, Pb and Zn. Available form of heavy metals were determined in EDTA. Plants were mineralised in concentrated acids (HNO3 to HClO4, volumetric ratio of 4:1). Content of Pb, Zn and Cd in the soil and plant samples were determined with ICP-AES. The bio-accumulation index (BI) was calculated as a ratio of a heavy metal content in a plant to its total content in a soil. BI was used to evaluate of the mobility of Cd, Pb and Zn in the soil and their availability to plants. The content of heavy metals (Zn, Pb, Cd) in 2M HNO3 in soil after first year of growing plants on polluted soil not changed significantly in soil with organic amendments. The content of soluble (EDTA) zinc, lead, cadmium in soil depended on the organic amendments and decreased in comparison to the control (without organic amendments). Absorbability of heavy metals by soil increased with addition the organic amendments into soil and is the highest for Rekulter. The bio-accumulation (BI) indexes of Cd, Pb, Zn indicate mobility of Cd, Pb and Zn in soils and their availability to plants. The BI decreased with the addition of organic matter and was the smallest at the object with Rekulter for all plant's parts.