MIXED-MODE SORPTION OF HYDROXYLATED ATRAZINE DEGRADATION PRODUCTS TO SOIL - A MECHANISM FOR BOUND RESIDUE

This study tested the hypothesis that sorption of hydroxylated atrazin e degradation products (HADPs: hydroxyatrazine, HA; deethylhydroxyatra zine, DEHA; and deisopropylhydroxyatrazine, DIHA) to soils occurs by m ixed-mode binding resulting from two simultaneous mechanisms: (1) cati on exchange and (2) hydrophobic interaction. The objective was to use liquid chromatography and soil extraction experiments to show that mix ed-mode binding is the mechanism controlling HADP sorption to soils an d is also a mechanism for bound residue. Overall, HADP binding to soli d-phase extraction (SPE) sorbents occurred in the order: cation exchan ge much greater than octadecyl (C-18) much greater than cyanopropyl. B inding to cation exchange SPE and to a high-performance liquid chromat ography octyl (C-8) column showed evidence for mixed-mode binding. Com parison of soil extracted by 0.5 M KH2PO4, pH 7.5, or 25% aqueous CH3C N showed that, for HA and DIHA, cation exchange was a more important b inding mechanism to soils than hydrophobic interaction. Based on diffe rences between several extractants, the extent of HADP mixed-mode bind ing to soil occurred in the following order: HA > DIHA > DEHA. Mixed-m ode extraction recovered 42.8% of bound atrazine residues from aged so il, and 88% of this fraction was identified as HADPs. Thus, a signific ant portion of bound atrazine residues in soils is sorbed by the mixed -mode binding mechanisms.