Sorption and desorption behaviours of 2,4-D and glyphosate in calcareous soil from Antalya, Turkey

2,4-Dichlorophenoxyl acetic acid (2,4-D) and glyphosate are used extensively as a herbicide in vicinity of Antalya, Turkey. Laboratory batch experiments were conducted to investigate the sorption isotherm and sorption-desorption characteristics of 2,4-D and glyphosate. Results indicated that degree of sorption of glyphosate was approximately 50 times higher than 2,4-D (K-d= 34.43 vs. 0.66 L/Kg). The sorption of 2,4-D and glyphosate was described by linear and rate-limited processes for soil. Organic carbon content was most likely responsible for sorption behaviour of 2,4-D and glyphosate. The rapid desorption can be attributed to soft carbon fraction (humic/fluvic acid and lipids) whereas slower desorption can be responsible by hard carbon fraction (black carbon, kerogen) of soils that led to chemically nonideal behaviour (hysteresis). Sorption of 2,4-D was low due to most likely deactivation of organic carbon surfaces by excess carbonate fraction, whereas strong binding of glyphosate onto organic carbon causing high sorption behaviour.