NMR Investigation of the Behavior of an Organothiophosphate Pesticide, Chlorpyrifos, Sorbed on Soil Components

Abstract

Phosphorus-31 nuclear magnetic resonance (31P NMR) was used to follow the decomposition of chlorpyrifos (an organothiophosphate pesticide) adsorbed on soil, humic acid, partially hydrated kaolin clay, and partially hydrated montmorillonite clay at high concentration (typically 2-10 wt %). Solid-state 31P NMR (using magic-angle spinning and cross polarization or direct polarization) and liquid-solution 31P NMR of DMSO and acetone extracts indicate that chlorpyrifos is initially physisorbed, appearing by solid-state 31P NMR to exhibit significant motion on the molecular level, which results in almost liquidlike solid-state spectra. Over periods ranging from hours to years, the signals due to unreacted chlorpyrifos sorbed on the clays diminish and are replaced by new 31P NMR peaks resulting from hydrolysis, isomerization, mineralization, and oxidation reactions. The 31P NMR signal characteristics indicate that these decomposition products are much more tightly bound to the clay than is chlorpyrifos. Solid-state 13C and 27AI NMR spectra were less useful for following the decomposition of chlorpyrifos than those obtained by 31P NMR. Solid-state 31P NMR results indicate that a chlorpyrifos loading level of 10% by weight, used in some of the samples to facilitate 31P NMR detection of less-than-dominant decomposition products, exceeds the adsorption capacity of the soil, humic acid, and kaolinite tested, but not Ca2+ -exchanged montmorillonite. This pattern is consistent with intercalation into the montmorillonite, but only surface adsorption on kaolinite.

Sorption-desorption behavior of pesticides and their degradation products in volcanic and nonvolcanic soils: interpretation of interactions through two-way principal component analysis

“…The distinctive high K OC found for CME soil could be attributed to its high clay content and to the presence of montmorillonite. This compound is sorbed on montmorillonite, kaolinite, and gibbsite (Seger and Maciel 2005;Van Emmerik et al 2007). …”

Sorption of atrazine onto humic acids (HAs) coated nanoparticles

“…Though SiO 2 is often used as a background particle for its lack of toxicity to bacteria [1], the investigation of Adams et al [2] suggested that nano-SiO 2 could inhibit bacterial growth. As a kind of naturally abundant mineral, kaolinite has been widely studied as adsorbent for removal of metal ions and organic pollutants from water [3][4][5][6]. To our knowledge, little investigation has been made on the sorption of organic pollutant by nano-SiO 2 and kaolinite coated with HA.…”

Use of NMR techniques for toxic organophosphorus compound profiling

“…Seger and Maciel have presented a number of studies [127][128][129] about the degradation pathways of OP pesticides sorbed on soil and clay. The interesting aspect in these studies from the point of NMR was the application of solid-state 31 P MAS NMR in the direct analysis of soil and clay samples.…”