Contaminated soil and groundwater are becoming a major problem in developing countries such as India. One of the big polluting sources is agriculture when irrigation with a poor treated sewage water and other contaminated water and/or when fertilisation with sewage sludge is used to a large extent. Dumping of garbage and industrial wastes in watercourses and wetlands during the dry seasons is also a contribution to the pollution problem. The main concern is the plant availability to absorb these elements and when a toxic level to livestock and humans is reached.
In the industrial city of Coimbatore in the central part of Tamil Nadu, South India, extensive studies of different pollutants have been carried out during the last decades, but only a few on heavy metal contamination. This study, made in the urban areas of Coimbatore in Mars to June 2001, is one of the first attempts to analyse copper and zinc contents in the soil, surface- and groundwater, and to estimate the ratios between the total content and the different adsorption fractions. The major fractions are water soluble, exchangeable, organically complexed or bonded to oxides/hydroxides.
The analyses of the total Cu and Zn contents in the soil samples showed concentrations within normal ranges, though higher values for Zn than for Cu. Contamination of these elements in the soil of Coimbatore Urban Area is thus not yet a fact. Cu is mainly bonded to organic matter and oxide particles and thus less bio available than Zn, which mainly is in water-soluble and exchangeable form, the most potential fractions for plant uptake. Column studies showed that both of the elements are quickly adsorbed. The column was pumped through with prepared water solution containing Cu and Zn of known concentrations for 6 days. A soil mixture was prepared for the soil samples collected in field when they separately was not enough for one column. The removal efficiency was high for both of the elements but initially faster for Zn. A Batch experiment was carried out on the soil mixture. Six different concentrations of each Cu and Zn was shaken for 24 hours and then analysed on the soil solution concentration. Isotherm curves of copper and zinc, with the soil solution concentration against the mass adsorbed per unit mass of dry solids, showed a fast initial adsorption. At higher sorbate concentrations, a smaller and smaller fraction of Cu and Zn is adsorbed.
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