MECHANISM OF ATRAZINE SORPTION BY HUMIC-ACID - A SPECTROSCOPIC STUDY

Ultraviolet-visible, Fourier transform infrared, and electron spin resonance spectroscopy were applied to samples of representative soil humic acids reacted with atrazine for: 4 days at 25 degrees C under environmentally relevant conditions (concentration, 140 mu mol L(-1); pH 2-6.5). The spectra obtained by the three methods indicated that a charge-transfer mechanism was not operative in the atrazine-humic acid interaction. The FTIR spectra gave evidence instead for a hydrogen-bonding dr proton-transfer mechanism, especially at pH < 4. The UV-visible spectra showed in addition that at pH < 5 humic acid enhanced the rate of hydroxyatrazine formation, especially for pH < 3. This relatively weak interaction mechanism with soil humic acid and the very low pH required for significant abiotic degradation of atrazine to its hydroxy derivative are consistent with recent field studies, suggesting a significant potential hazard to groundwater supplies from this widely applied herbicide.