NMR Investigation of the Behavior of an Organothiophosphate Pesticide, Methyl Parathion, Sorbed on Clays

2006-01-15T00:00:00Z (GMT) by Mark R. Seger Gary E. Maciel
The decomposition of methyl parathion (an organothiophosphate pesticide) sorbed on partially hydrated kaolin and montmorillonite clays (in Ca<sup>2+</sup>, Cu<sup>2+</sup>, Zn<sup>2+</sup>, and Al<sup>3+</sup> forms) at high concentration (typically 1−10 wt %) has been examined by nuclear magnetic resonance (NMR), using solid-state <sup>31</sup>P NMR (based on magic-angle spinning and cross polarization or direct polarization) and liquid-state <sup>31</sup>P NMR of DMSO and acetone extracts. The results indicate that methyl parathion is initially physisorbed, appearing by solid-state <sup>31</sup>P NMR to exhibit substantial molecular-level motion. The signals due to unreacted methyl parathion diminish and are replaced by new <sup>31</sup>P NMR peaks resulting from hydrolysis, isomerization, and oxidation reactions over periods ranging from hours to years. <sup>31</sup>P NMR characteristics indicate that these decomposition products are much more tightly bound to the clay than is methyl parathion. Methyl parathion decomposition is most effectively catalyzed by partially hydrated Cu(II)- and Al-montmorillonites (but with different product distributions); Ca-montmorillonite and kaolin were least effective.