Evaluation of Physicochemical Characteristics and Bioavailability of Selected metals in Paddy soil by Sequential Extraction method

Abstract

The modified Community Bureau of Reference (mBCR) sequential extraction procedure was used in order to evaluate the mobility, bioavailability and persistence of selected metals in the paddy soil samples collected from district Sargodha, Pakistan. The operationally defined fractions isolated using BCR procedures were; exchangeable, reducible, oxidiseable and residual. Water soluble fraction of the soil was separated using single extraction method. The concentrations of selected metals in the soil samples were determined by flame atomic absorption spectrophotometer (FAAS), and the metal data were subjected to descriptive statistical and correlation study in order to evaluate the interrelationships among the metals in each fraction of soil. A number of significant correlations among selected metals in the soil samples were found. Multivariate cluster analysis was used to identify the plausible pollution sources and to find out the multiple relationships among the selected metals in all fractions of the soil. Significant anthropogenic intrusions of the metals were noted in the soil. Individual metal contents in different fractions of the soils were also compared. Of the selected metals Ca, Sr and Mn were more bioavailable. Enrichment of the selected metals by anthropogenic activities in the collected soil samples was also calculated, which revealed extremely severe enrichment of Cd whereas Ni, Zn, Ca, Co and Pb exhibited moderate to significant enrichment while Cr, Sr, Cu, Mg and Mn revealed minimal to moderate enrichment in the soil. Study regarding soil texture revealed predominantly silty loam texture of the area. Most of the soil samples showed slightly alkaline nature while organic matter was 8.37%, on the average. Piper diagram showed major contribution of Na and K with chloride and sulphate ions and minor contribution of Ca and Mg with carbonate and bicarbonate ions in the soil.