METAL CONTAMINATION DUE TO MINING AND MILLING ACTIVITIES AT THE ZAWARZINC MINE, RAJASTHAN, INDIA .2. DISPERSION IN FLOODPLAIN SOILS OF STREAM

The Tiri river carrying mine discharges and milling effluents frequent ly inundates its floodplains. Fresh deposition of metal-contaminated s ediments is mixed with the top soils by ploughing and biological activ ity, and has caused a considerable increase in the heavy-metal concent ration of top soil. Samples collected from the top soils on the floodp lain have been analysed for Pb, Zn, Cu, Cd, Fe and Mn to recognize the extent of contamination and geochemical process of dispersion. With t he help of simple statistics and curvilinear regression analysis a dis tance-decline pattern in levels of heavy metals on the floodplain soil s is recognised. Correlation matrix and R-mode factor analyses of norm alised soil metal data have been used to study the relationship among the different geochemical pools taking up metals in the soil. The R I factor indicates contribution from gross lithology of the terrain and association of Cu with this factor advocates it to be autochthonous. P b-Zn-Cd with minor contribution from Fe-Mn-Cu in the R II factor are c onsidered to be input from mine discharges. Atmospheric dust fallout a nd flash flooding of the river bank are the two factors contributing m etals to the top soil. ''Easily exchangeable'', ''carbonate-bound'', ' 'reducible'' (bound to multiple hydroxides of Fe and Mn), ''oxidisable '' (organically bound and sulphidic) and ''lithogenic phase'' are the five operationally defined geochemical pools into which the heavy meta ls are positioned in the soil. Scavenging capacities (SC's) of these g eochemical pools have been estimated for each heavy metal and competit ion ratios (CR's) are computed to examine the relative affinity of the metals for the above-mentioned pools. The reducible phase for Pb, and organics for Zn and Cu, and carbonates for Cd are found to be the dom inant sinks in the floodplain soils.