Natural soil colloids to retard simazine and 2,4-d leaching in soil

Natural or synthetic sorbents for pesticides can be used to reduce contamin ation of soils and natural waters. The sorption of simazine and 2,4-D on mo ntmorillonite minerals has been studied and their potential use to retard p esticide leaching in soil evaluated. Simazine and 2,4-D did not sorb on hig h-layer charge montmorillonite, whereas sorption on the lower layer charge montmorillonite SWy varied depending on the saturating cation. Simazine sor ption increased in the order Ca(2+)SWy much less than K(+)SWy < Fe(3+)SWy. Simazine molecules sorb on hydrophobic microsites of the montmorillonite. O nce protonated, further sorption through cation exchange takes place in the interlamellar space of the montmorillonite, as corroborated by X-ray diffr action and FT-IR studies. 2,4-D does not sorb on K(+)SWy or Ca(2+)SWy, but does sorb on Fe(3+)SWy, because the acidic character of this sorbent allows the molecular form of 2,4-D to sorb by hydrogen bonding and/or by hydropho bic interactions. Leaching experiments in hand-packed soil columns indicate that simazine and 2,4-D application as a complex with FeSWy renders later breakthrough and lower maximum concentration peaks, and the total herbicide leached is lower than when applied as the pure analytical grade compound. These results suggest the possible use of natural soil colloids as sorbents for herbicides such as simazine and 2,4-D to retard pesticide leaching in soil, thus reducing their ground water contamination potential.