Adsorption-desorption behavior of thiram: effect of soil type, temperature and pH

The present study was conducted in order to investigate the adsorption and desorption behavior of tetramethylthiuram disulfide (thiram) using the batch equilibration technique in two soil namely: Ultisols and Inceptisols. The adsorption-desorption isotherms were expressed by the Freundlich equation. The adsorption isotherms of thiram was classified as L-type under Gile’s classification. The Freundlich’s adsorption coefficient (K_d) value for thiram in the Ultisols and Inceptisols soil were 3.78 and 2.10 mL g^-1, respectively. Results indicated that soil organic matter was the main factor affecting thiram behavior in the studied soils. The calculated total percentage desorption values from the Ultisols and Inceptisols soil after the fourth desorption process were 39.2% and 51.6%, respectively. The negative Gibb’s free energy change (ΔG°) values obtained suggest that thiram adsorption is an exothermic process. The effects of temperature (25, 30, and 35 °C) and soil pH (3, 7, 10) were also studied on adsorption of thiram in the test soils. Results showed that adsorption of thiram was not affected by temperature but clearly affected by soil pH.