Cadmium sorption in sewage-irrigated soils varying in texture and organic matter

Concentration of heavy metals in soil solution and their bioavailability are controlled by sorption reactions in soils which in turn are governed by the soil properties. A study was, therefore, undertaken to determine cadmium (Cd) adsorption isotherms of soils collected from 4 different sewage-irrigated localities (Typic Haplustepts from Kurukshetra, Gurgaon and Typic Ustipsamments from Narnol and Sirsa) in Haryana; these varied in texture, organic matter content and other characterisitcs. The isotherms were well described by a binary Langmuir equation (R² = 0.78–0.95**) that considers two groups of sorption sites, which differ in their Cd bonding energies. Grouping the soils according to the total Cd adsorption capacity followed the order: Gurgaon (952–1489) > Kurukshetra (590–812) > Sirsa (393–530) > Narnoul (322–424 mg kg⁻¹). Clay content in soils (r = 0.94***), CEC (r = 0.93***), pH, (r = 0.88***) and organic matter (r = 0.70***) were the major determinants of strength of Cd adsorption. High adsorption vis-à-vis locking capacity of soils for Cd, which got further enhanced with organic matter accumulation in sewage-irrigated soils, is likely the cause of limited mobility and thus the maximum accumulation of Cd in surface soils only.