ATRAZINE COMPLEXATION BY SOIL HUMIC ACIDS

Atrazine hyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] complexati on pathways with soil humic acid remain a controversial issue, in part because of the absence of direct spectroscopic information. Recent op tical and magnetic resonance spectral data indicate that proton-transf er and, to a lesser extent, hydrogen bonding are as important as elect ron-transfer in the mechanisms of reaction between atrazine and humic acid, whereas other s-triazines appear to react more strongly by elect ron transfer mechanisms. Two representative temperate-zone humic acids were selected to probe the issue of complexation mechanisms more deci sively. They were reacted at pH < 7 with 140 mmol m(-3) atrazine solut ion under exclusion of light. Infrared and electron spin resonance spe ctra of the resulting products gave evidence for proton-transfer and, under certain conditions, electron-transfer reactions. The spectroscop ic data, and those from other published studies, were analyzed In term s of the molecular properties of humic acids and s-triazines. The anal ysis suggested a general guiding principle to characterize the complex ation mechanisms of s-triazines with soil humic acids. Proton-transfer is favored (and electron-transfer is disfavored) for humic acids of h igh acidic functional group content and for s-triazines of low basicit y. Electron-transfer mechanisms are favored for humic acids of low aci dic functional group content and for s-triazines of high basicity. Thi s principle illustrates the importance of specific molecular structure , as opposed to class structure, to understanding reactivity between t he s-triazines and humic acids.