01920naa a2200145 a 450000100080000000500110000800800410001910000160006024500470007626000090012352015220013270000200165470000130167477300870168710264241999-12-22       1996    bl ---       0--  u    #d1 aSPOSITO, G.  aAtrazine complexation by soil humic acids.  c1996  aAtrazine complexation pathways with soil humic acid remain a controversial issue, in part because of the absence of direct spectroscopic information. Recent optical and magnetic resonance spectral data indicate that proton-transfer and, to a lesser extent, hydrogen bonding are as important as electron-transfer in the mechanisms of reaction between atrazine and humic acid, whereas other s-triazines appear to react more strongly by electron transfer mechanisms. Two representative temperate-zone humic acids were selected to probe the issue of complexation mechanisms more decisively. They were reacted at pH &lt 7 with 140mmol mE-3 atrazine solution under exclusion of light. Infrared and electron spin resonance spectra of the resulting products gave evidence for proton-transfer and, under certain conditions, electron-transfer reactions. The spectroscopic data were analyzed in terms of the molecular properties of humic acids and s-triazines. The analysis suggested a general guiding principle to characterize the complexation mechanisms of s-triazines with soil humic acids. Proton-transfer is favored (and electron-transfer is disfavored) for humic acids of high acidic functional group content and for s-triazines of low basicity. Electron-transfer mechanisms are favored for humic acids of low acidic functional group content and for s-triazines of high basicity. This principle illustrates the importance of specific molecular structure to understanding reactivity between the s-triazines and humic acids.1 aMARTIN-NETO, L.1 aYANG, A.  tJournal of Environmental Quality, Madisongv.25, n.6, p.1203-1209, Nov./Dec. 1996.