Adsorption of oxamyl and phosphamidon (Dimecron) was determined from dilute solutions of montmorillonite saturated with different cations, e.g., Li+, Na+, K+, Cs+, Fe3+, and Al3+. Adsorption of oxamyl was found to be greater than adsorption of Dimecron. The shapes of the isotherms depended on the exchangeable cations. The adsorption varied directly with the polarizing power of the exchangeable cation and inversely with changes in temperature, organic matter, and ionic strength up to 0.6, after which it became constant. The enthalpy changes (ΔH°) calculated from the temperature coefficient of the equilibrium constant showed that the process is exothermic. The adsorption of pesticides on montmorillonite gives rise to an entropy loss that is higher for trivalent cations. Various studies, e.g., infrared (IR) and x‐ray, as well as thermodynamic parameters and Freundlich adsorption isotherms, revealed the existence of protonation or coordination (or both) between exchangeable cations of clay and oxygen of > C=0 group of the pesticides. However, desorption studies showed the presence of physical adsorption.

The kinetics of interaction with soil of three carbamate pesticides (I, II, III) used as nematicides and herbicides was studied at four different temperatures from solutions of six soil samples of Aligarh district. The values obtained for rate constants for adsorption and desorption were in good agreement with those obtained from the Lindstrom model, which proved useful in the simultaneous evaluation of adsorption (k1) and desorption (k2) rate constants. The rate constants for pesticides were in the order III > I > II on all the six soil samples. The data for rate constants, activation energies, heats of activation, entropy of activation and thermodynamic parameters indicated a partly physical and partly chemical adsorption of pesticide on the soil surfaces. Adsorption occurred via coordination and/or protonation of the exchangeable cations with the amidic carbonyl group, and hydrogen bonding and dipole association at the crystal edge and basal surfaces. The adsorptivity of the soils may be attributed to the organic matter content and percentage clay content.

ABSTRACT:The effects of various organic manure [farm yield manure (FYM), sewage sludge and poultry manure] application on adsorption-desorption of three carbamate pesticides [oxamyl(I);S-Ethyl-Nmethylcarbamoyl)oxy]thioacetimidate (II) and N-Phenyl (ethyl carbamoyl) propyl carbamate (III) on six soil samples of Aligarh district was studied. Addition of organic manure increased soil organic carbon content and electrical conductance while pH decreased. The results of the study denoted that adsorption isotherms were 'L' type and adsorption-desorption data conformed to Freundlich adsorption isotherm equation. The adsorption increased with the increase in organic manure and followed the order sewage sludge > FYM > poultry manure. The adsorptivity of soils was in order soil No. 1 > 2 > 3 > 4 > 5 > 6. The adsorption capacity was significantly positively correlated with soil organic carbon and CEC and negatively correlated with soil pH. Desorption was more in unamended soil than manure amended soil and decreased with the increase in amount of organic manure. Desorption showed hystersis, indicate by the higher adsorption slope (1/n ads) compared with desorption slope (1/n des). @JASEM Pesticides adsorption and desorption are the key processes determining whether pesticide used will have any impact on environmental quality. For most of the pesticides soil organic matter and clay contents are the most important properties which affect the sorption and transformation (Durovic et al., 2009; Osborn et al., 2009; Villavarde et al., 2008). The use of composts derived from source-separated municipal solid waste/animal manure/FYM is now a common agronomic practice throughout the world. Such amendments improve the physico-chemical properties of the soil. Application of such composts affect the fate and mobility of applied pesticides in soil as addition of compost increases besides nutrients the soil organic matter content (Paustin et al., 1992). Carbamate pesticides are widely used as insecticides, nematicides and herbicides (Hague, 1979). Investigations on the adsorption of carbamate pesticides by clays have shown that they are adsorbed by co-ordination and/or protonation at the carbonyl oxygen by exchangeable cations of clays (Bansal 2009(Bansal , 1983 Li et al., 2003). The purpose of the present study is to study the effect of different amount of organic manure (FYM, sewage sludge and poultry manure) on the extent of adsorption/desorption of three polar water soluble carbamate pesticides; MATERIAL AND METHODSThe six soils (1-6) selected for this study were taken from different parts of Aligarh district at plough layer (0-30 cm). They were air dried at room temperature and sieved by passing through a 100 mesh sieve. Their physico-chemical properties were determined by the usual soil laboratory methodology and clay mineralogy by an X-ray diffraction procedure on orientated specimen. Physico-chemical properties, clay mineralogy and classification are given in Table 1. Soil amendment : Soils (1-6) were amended with 0, 2.5 and 5 g...

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