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

Ultraviolet-visible, Fourier transform infrared, and electron spin res onance spectroscopy were applied to samples of representative soil hum ic acids reacted with atrazine for: 4 days at 25 degrees C under envir onmentally relevant conditions (concentration, 140 mu mol L(-1); pH 2- 6.5). The spectra obtained by the three methods indicated that a charg e-transfer mechanism was not operative in the atrazine-humic acid inte raction. The FTIR spectra gave evidence instead for a hydrogen-bonding dr proton-transfer mechanism, especially at pH < 4. The UV-visible sp ectra showed in addition that at pH < 5 humic acid enhanced the rate o f hydroxyatrazine formation, especially for pH < 3. This relatively we ak interaction mechanism with soil humic acid and the very low pH requ ired for significant abiotic degradation of atrazine to its hydroxy de rivative are consistent with recent field studies, suggesting a signif icant potential hazard to groundwater supplies from this widely applie d herbicide.