Original Articles: 2011 Vol: 3 Issue: 5
Sequential Extraction of Common Metals (Na, K, Ca and Mg) From Surface Soil
Soil contamination with metals is now a world wide environmental concern. Bio-accumulation of metals by plants and so into food chains imbalances the ecosystem and causes human health problem. Toxicity of an element in soil depends only on its mobility, transformation and potential bioavailability to plants. Water soluble, exchangeable and mild acid soluble fractions of metals are most mobile and bioavailable form present in soil. Sequential extraction of metals from soil by the use of different extractants provides information not only its bioavailability but also the amount bound to different soil fractions. A study was carried out to investigate the fraction distribution of common metals Na, K, Mg and Ca and the influence of extraction time and volume of different extractants on surface soils collected from tea garden belts of Golaghat district of Assam, India. The modified three step sequential extraction procedure was applied for speciation of these elements. The extractant solutions were deionized water, 1M ammonium acetate solution and 25 g/L acetic acid solution. Extraction was first performed for 5 gm soil samples with 30 ml extractant eluate and the soil extract were collected after 10, 15, 20, 60 and 120 minutes for analysis. Soil extracts were also collected after a fixed extraction time of one hour using 10, 30, 50 and 80 ml of different extracting eluate. The study revealed that extraction time more than one hour have no role in speciation of metals from soil and the soil solution ratio greater than 1:6 had no influence on sequential extraction. The amount of Na, K, Mg and Ca in different soil fraction was found to be highest in exchangeable fraction followed by water soluble and acetic acid soluble. A distinct difference was also seen in the estimated values of metal contents using HNO3:HClO4 digestion method and modified three steps sequential extraction method which can be attributed due to medium organic matter and high bulk density of soil.