Adsorption-desorption of cypermethrin and chlorfenapyr on Jordanian soils

Abstract

In this study, adsorption kinetic experiments were conducted on agricultural soil samples from Southern Jordan to investigate the adsorption behavior of the heavily used insecticide cypermethrin and the pesticide chlorfenapyr. Soil samples classified as sand and loamy sand with 1.77–2.02% organic matter content were collected from two locations within 0–30 cm depths in Tafilah, Jordan, and tested as adsorbents, and it was found that the adsorption of the two substances followed pseudo-second-order kinetics which implies that the adsorption process is chemisorption. The second-order rate constants were 1.01–2.03 g/mg h for cypermethrin and 11.38–13.03 g/mg h for chlorfenapyr. Adsorption isotherm experiments were also carried out at a constant temperature and variable initial adsorbate concentrations and it was found that the Langmuir model provided a slightly better fit to the adsorption data in comparison with the Freundlich model. The Langmuir maximum adsorption capacities were 8.88–9.08 mg/g for cypermethrin and 36.23–45.25 mg/g for chlorfenapyr while the Langmuir constants were 0.0123–0.0157 L/mg for cypermethrin and 0.003–0.0037 L/mg for chlorfenapyr. Higher adsorption rates were observed in the loamy sand soil due to the higher organic matter, clay, and silt contents. Nonetheless, it was concluded that the leaching potential of these substances to groundwater is low due to the physical nature of these chemicals as well as the adsorption behavior of the soil.