Effect of pH variation and temperature on pesticides sorption characteristics in calcareous soil

Abstract

The effect of pH value at three levels (5, 7, and 9) and temperature at two levels (25 and 50ºC) on the sorption properties of chlorantraniliprole-CAP, dinotefuran-DNF, bispyribac-sodium-BPS, and metribuzin-MBZ were studied in calcareous soil. The sorption of CAP at pH 5 (38.2%) was significantly higher than that at pH 7 (32.4%) and 9 (28.4%), whereas the sorption of DNF at pH 5 was lower than that at pH 7. The adsorption of BPS at pH 9 was statistically significantly higher than that at pH 5 and pH 7. Regarding the herbicide MBZ adsorption percentages were 47.0, 61.1 and 57.1 % at pH 5, 7 and 9. The number of tested pesticides adsorbed by the soil was significantly influenced by the temperature. The adsorbed amount of CAP was decreased from 37% to 33% as the temperature was increased from 25˚C to 50 ˚C, while no significant differences of adsorbed DNF. Data showed that the adsorption of BPS and MBZ statistically decreases with temperature. The data from the adsorption behaviour of CAP, DNF, BPS, and MBZ in tested soil at different temperatures correspond well with the Freundlich isotherm. The negative ΔG˚ indicated that the adsorption of CAP, DNF, BPS, and MBZ were spontaneous at different temperatures. There was an increase in the entropy of the pesticide-soil systems as shown by the positive values of ΔS˚.