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(70-15) The Environmental Significance of Cadmium and Lead in Contaminated Soils. Saad, Inaam Ali Abdalla*,1,2,3, Yahaya, Abdul Hamid1,3, Arof, Abdul Kariem1,3, 1 Institute of Postgraduate Studies and research, University of Malaya, 50603 Kuala Lumpur, Kuala Lumpur, Kuala Lumpur2 Abdul Hamid Yahaya, Chemistry Department, University of Malaya, 50603 Kuala Lumpur, Kuala Lumpur, Kuala Lumpur3 Abdul Kariem Arof, Physics Department, University of Malaya, 50603 Kuala Lumpur, Kuala Lumpur, Kuala Lumpur ABSTRACT- The increased inputs of heavy metals from the widespread disposal of industrial wastes have created an increased attention to the issue of their fate, bioavailability and environmental significance. This study was carried mainly to study the chemical speciation and plant uptake of cadmium and lead in soils amended with Cd and Pb nitrate salts at rates of 5-40 mmol/kg for incubation time varied between 3-15 month. Soil type had significant effect on the solid - solution equilibrium of the added metals. The speciation of metals in soils is essential in understanding their chemical and biological interactions in the soil environment. The solid phase speciation of Cd and in soils amended with such metals at rate of 5mmol/kg was estimated using ICP-MS after the soils were sequentially extracted with IM NH4OAc to remove the water soluble and the exchangeable metals, with 0.125 M Cu (OAc) 2 to remove complexed metals and with 1M HNO3 to dissolve the occulted precipitated and residual metal The soil solution chemistry of heavy metal is of great importance in assessing their bioavailability and estimates their toxicity. MINTEQA2 version 3.0 used to explore the speciation of the studied metals the solution of the three soils revealed the majority of metals as the free ionic Cd2+ and Pb2+, The speciation of the studied metals was greatly influenced by soil type and residence time. Greenhouse experiments were conducted to study Cd and Pb uptake by plant grown on soils amended with theses metals at levels from 0-20mmol/kgsoils, using Lettuce (Lactuce sativa) as bio-monitor. Significant positive correlations were obtained between the bioconcentration of Cd and Pb by plant and the metal amendments, exchangeable chemical fraction and residence time. The relative bioavailability of Pb is higher than that of Cd. The soil-plant-man exposure pathway is identified as the major exposure pathway to contaminants. The estimated plant- soil bioconcentration factor for Cd and Pb was found to be slightly elevated with the residence time of the contaminant. Thus the study concluded that amount of Cd and Pb contaminants available for human intake is subjected to gradual elevation in response to the metal mass loading and the length of time soil is exposed to the specific contaminant. Key words: Heavy metals, contaminated soils, risk assessment, exposure |
