Influence of Water and Temperature on Adsorption of Parathion by Soils

Abstract

Temperature and water effect on the adsorption of parathion (O, O‐diethyl O‐p‐nitrophenyl phosphorothioate) by soils was studied using 14C‐tagged parathion. The parathion was applied in aqueous solutions and in hexane over a concentration range of 1–10µg/ml. It was found that the parathion is adsorbed by soils from aqueous solution without any appreciable thermic effect. In a dry soil‐hexane‐parathion system the slightly polar parathion molecules efficiently compete with the apolar hexane molecules for adsorption sites. In hydrated soil‐hexane‐parathion systems there was no parathion adsorption. Generally as the soil water content increases, parathion adsorption decreases. The water‐temperature composite effect in a soil‐hexane‐parathion system was also studied. The rise of temperature in the soilhydrated parathion‐hexane system favors the endothermic process of water desorption, resulting in greater free adsorption sites, and consequently, in increasing parathion adsorption.

Sorption of organophosphorus and carbamate insecticides by soil

“…Temperature and the purity of water and solute can also influence solubility measurements. Bowman and Sans (1977) reported a water solubility for parathion of 12.9 ppm at 20°C, and Yaron and Saltzman (1972) found a value of 4.3 ppm at 10°C. The commonly quoted literature value Is 24 ppm at 25°C (Gunther et al 1968).…”

“…Kahn (1977) reported that Freundlich k values for the adsorption of fonofos on cation saturated humic acid decreased as temperature increased. This observation indicated that adsorption was exothermic; however, Yaron and Saltzman (1972) found no appreciable thermic effects in parathion adsorption if a correction was made for the increased water solubility at higher temperatures.…”

Fate and transport processes controlling the migration of hazardous and radioactive materials from the Area 5 Radioactive Waste Management Site (RWMS)

“…At low water content, sorption sites of the inorganic surfaces can effectively sorb organic compounds, however, at high water content, sorption of organic compounds is controlled by soil organic matter. Adsorption of a number of organic and volatile organic compounds (VOCs) has been found to be greater as soil moisture decreases (Hance, 1977;Bailey and White, 1964;Yaron and Saltzman, 1977;Estrella et al, 1993;Steinberg and Kreamer, 1993). Studies have shown that soil water content drastically inhibits vapor-phase sorption given that the solubility of the tested gas in water is low.…”

“…Water substantially reduces the surface activity of the inorganic surfaces by occupying the high-energy sorption sites. The polar water molecules have a greater affinity for available sorption sites on soils than the nonpolar organics (Yaron and Saltzman, 1977;Hance, 1965). The polar water molecules tend to reduce organic compound sorption, although, organics will sorb, even under saturated condition, because of their hydrophobic behavior (their tendency to avoid the polar water molecules in solution).…”

“…Adsorption processes are typically exothermic and desorption processes are typically endothermic, thus, an increase in temperature would normally be expected to reduce adsorption and favor the desorption process. Increasing soil temperature results in a weakening of the attractive forces between the solute and the solid surfaces and a corresponding increase in solubility of the solute in the solution phase (Yaron et al, 1985;Bailey and White, 1970;Mills and Biggar, 1969;Yaron and Saltzman, 1977).…”