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Title: Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons

Abstract

Man-made organophosphorus compounds have been widely distributed throughout our environment as pesticides since their development during and after WWII. Many important studies have documented their relative persistence and toxicity. Development and use of some organophosphorus compounds as nerve agents gave rise to a separate but parallel effort to understand environmental persistence. In this latter case, the experiments have focused mainly on evaporation rates and first-order reaction kinetics. However, because organophosphorus compounds are easily polarized, the ionic content of a surrounding media directly factors into these reaction rates, but limited work in this regard has been done under environmentally relevant conditions. Furthermore, limited experiments investigating persistence of these agents on soil has resulted in widely varying degradation rates. Not surprisingly, no studies have investigated affinities of organophosphorus nerve agents to mineral or organic matter typically found in soil. As a result, we initiated laboratory experiments on dilute concentrations of nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) to quantify persistence in simulated environmental aqueous conditions. A quantitative analytical method was developed for VX and its degradation products using High Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (HPLC-ESI-MS). VX hydrolysis rate is known to have a pH-dependency, however, the type of buffer and the relative proportionmore » of different nucleophiles in solution significantly affect the overall rate and mechanism of degradation. For example, dissolved carbonate, a weak nucleophile dominating natural water, yielded pseudo-first order rate constants of {approx} 8 x 10{sup -3}/hr at pH 5 and 2 x 10{sup -2}/hr at pH 11. This small pH-dependent variation departs significantly from widely accepted rates at this pH range (4 x 10{sup -4}/hr to 8 x 10{sup -2}/hr) that were based on chloride and hydroxyl (strong nucleophile) dominated experimental solutions. Because of its overwhelming abundance in solution relative to hydroxyl ion, bicarbonate likely effectively competes in nucleophilic attack on phosphorus. The addition of natural dissolved organic matter at 100 mg/L in pH 7 bicarbonate buffered solution slowed VX hydrolysis rates {approx}2 times relative to controls, suggesting hydrophobic interaction. Adsorption experiments derived isotherms from batch aqueous experiments on montmorillonite clay, iron-oxyhydroxide goethite, and on amorphous silica. VX had moderate affinity for montmorillonite and amorphous silica, and very low affinity toward goethite. The addition of dissolved organic matter into solution enhanced VX adsorption to goethite, consistent with its high affinity for hydrophobic organic matter (log K{sub oc} = 2.52). Diisopropylaminoethylthiol (DESH), a hydrolysis product of VX showed equivalent adsorption to montmorillonite, and poor affinity to goethite and silica. However, hydrolysis products O-Ethylmethylphosphonic acid (EMPA) and methylphosphonic acid (MPA) strongly adsorbed on goethite, but not on montmorillonite or silica, suggesting a ligand-exchange mechanism. VX degraded rapidly when completely dried onto goethite followed by rehydration, consistent with an irreversible chemical adsorption mechanism.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab., Livermore, CA (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15015167
Report Number(s):
UCRL-TR-209748
TRN: US200509%%359
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 8 Feb 2005
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; ACID CARBONATES; ANIONS; CHLORIDES; GOETHITE; HYDROLYSIS; HYDROXIDES; ION EXCHANGE; MONTMORILLONITE; ORGANIC MATTER; PHOSPHORUS; REACTION KINETICS; SILICA; SPECTROSCOPY; WEAPONS

Citation Formats

Davisson, M L, Love, A H, Vance, A, and Reynolds, J G. Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons. United States: N. p., 2005. Web. doi:10.2172/15015167.
Davisson, M L, Love, A H, Vance, A, & Reynolds, J G. Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons. United States. https://doi.org/10.2172/15015167
Davisson, M L, Love, A H, Vance, A, and Reynolds, J G. Tue . "Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons". United States. https://doi.org/10.2172/15015167. https://www.osti.gov/servlets/purl/15015167.
@article{osti_15015167,
title = {Environmental Fate of Organophosphorus Compounds Related to Chemical Weapons},
author = {Davisson, M L and Love, A H and Vance, A and Reynolds, J G},
abstractNote = {Man-made organophosphorus compounds have been widely distributed throughout our environment as pesticides since their development during and after WWII. Many important studies have documented their relative persistence and toxicity. Development and use of some organophosphorus compounds as nerve agents gave rise to a separate but parallel effort to understand environmental persistence. In this latter case, the experiments have focused mainly on evaporation rates and first-order reaction kinetics. However, because organophosphorus compounds are easily polarized, the ionic content of a surrounding media directly factors into these reaction rates, but limited work in this regard has been done under environmentally relevant conditions. Furthermore, limited experiments investigating persistence of these agents on soil has resulted in widely varying degradation rates. Not surprisingly, no studies have investigated affinities of organophosphorus nerve agents to mineral or organic matter typically found in soil. As a result, we initiated laboratory experiments on dilute concentrations of nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) to quantify persistence in simulated environmental aqueous conditions. A quantitative analytical method was developed for VX and its degradation products using High Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (HPLC-ESI-MS). VX hydrolysis rate is known to have a pH-dependency, however, the type of buffer and the relative proportion of different nucleophiles in solution significantly affect the overall rate and mechanism of degradation. For example, dissolved carbonate, a weak nucleophile dominating natural water, yielded pseudo-first order rate constants of {approx} 8 x 10{sup -3}/hr at pH 5 and 2 x 10{sup -2}/hr at pH 11. This small pH-dependent variation departs significantly from widely accepted rates at this pH range (4 x 10{sup -4}/hr to 8 x 10{sup -2}/hr) that were based on chloride and hydroxyl (strong nucleophile) dominated experimental solutions. Because of its overwhelming abundance in solution relative to hydroxyl ion, bicarbonate likely effectively competes in nucleophilic attack on phosphorus. The addition of natural dissolved organic matter at 100 mg/L in pH 7 bicarbonate buffered solution slowed VX hydrolysis rates {approx}2 times relative to controls, suggesting hydrophobic interaction. Adsorption experiments derived isotherms from batch aqueous experiments on montmorillonite clay, iron-oxyhydroxide goethite, and on amorphous silica. VX had moderate affinity for montmorillonite and amorphous silica, and very low affinity toward goethite. The addition of dissolved organic matter into solution enhanced VX adsorption to goethite, consistent with its high affinity for hydrophobic organic matter (log K{sub oc} = 2.52). Diisopropylaminoethylthiol (DESH), a hydrolysis product of VX showed equivalent adsorption to montmorillonite, and poor affinity to goethite and silica. However, hydrolysis products O-Ethylmethylphosphonic acid (EMPA) and methylphosphonic acid (MPA) strongly adsorbed on goethite, but not on montmorillonite or silica, suggesting a ligand-exchange mechanism. VX degraded rapidly when completely dried onto goethite followed by rehydration, consistent with an irreversible chemical adsorption mechanism.},
doi = {10.2172/15015167},
url = {https://www.osti.gov/biblio/15015167}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2005},
month = {2}
}