02018naa a2200157 a 450000100080000000500110000800800410001910000160006024500540007626000090013030000190013952015170015870000200167570000130169577301520170810270661999-12-22       1996    bl ---       0--  u    #d1 aSPOSITO, G.  aMechanisms of atrazine reactions with humic acid.  c1996  anão paginado.  aAmong the post-emergent herbicides, atrazine (6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine) is the one most applied worldwide. It is also widely detected in water supplies, thus an important indicator of pesticide contamination, with growing public concern over its potential carcinogenic effects. The complexation pathways of atrazine with humic acid remain controversial, in part because of the absence of direct spectroscopic information. The basic question is whether 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. Representative tropical and temperate-zone humic acids were reacted at pH&lt7 with 140 mmol 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. These spectroscopic data and those from other published studies were analyzed in terms of the molecular properties of humic acids and s-triazines, out of which emerged a guiding principle to characterize the complexation mechanisms of s-triazines with humic acid: 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...1 aMARTIN-NETO, L.1 aYANG, A.  tIn: AMERICAN GEOPHYSICAL UNION MEETING, Dec. 1996, San Francisco, CA, Estados Unidos. Abstracts... San Francisco: American Geophysical Union, 1996.