Adsorption and Persistence of Ethylenethiourea in Soils

The Freundlich equation provided a good fit (r²> 0.9) for the adsorption data on ETU in all the soils. Freundlich constant K values for ETU in all the soils ranged from 1.860 to 2.306. The values for 1/n (energy of adsorption) were less than unity (1/n < 1) for ETU and indicated non-linear relationship between the ETU concentration and adsorption and therefore can be characterised as L-type of adsorpiion. The sorption coefficients of ETU for organic carbon (K_OC.) ranged from 128 to 581 mg ml⁻¹. The Gibb's free energy (DG°) were always negative indicating that the adsorption was exothermic. The degradation pattern of ETU residues indicated a close correspondence to first order exponential degradation kinetics in soils. Among the factors studied, the soil moisture at field capacity and temperature of 25°C were found to accelerate the degradation. However, the persistence of ETU residues was higher from air-dry moisture, temperature of 15°C and sterile soil conditions.