Document Detail

Reduction of the pesticides oxamyl and methomyl by FeII: effect of pH and inorganic ligands.
MedLine Citation:
PMID:  11878379     Owner:  NLM     Status:  MEDLINE    
This work examines the effect that pH and selected inorganic ligands have on the kinetics of reactions between FeII and two structurally related oxime carbamate pesticides, oxamyl and methomyl. In anoxic solutions containing FeII, these compounds degrade by parallel elimination and reduction pathways. Rates of FeII-independent carbamate elimination (EIcb mechanism) are proportional to [OH-], increasing 10-fold for each unit increase in pH. In homogeneous solution, rates of carbamate reduction by 0.5 mM FeII are relatively constant at pH <7, but increase dramatically between pH 7 and pH 8.3. At pH >8.3, Fe(OH)2(s) precipitation occurs, and carbamates react with both solution-phase and solid-phase FeII. Carbamate reduction by FeII is not significantly affected by the presence of chloride, bromide, nitrate, perchlorate, and sulfate. In contrast, increased rates of carbamate reduction are observed in solutions containing fluoride, carbonate, and phosphate. Kinetic measurements are interpreted in terms of changing FeII speciation according to the expression kred = [FeII]sigmaikialphai, where k(red) is the pseudo-first-order rate constant for carbamate reduction, [FeII] is the total FeII concentration, and ki and alphai are the second-order rate constant and fractional concentration of each FeII species, respectively. It follows that the overall kinetics of carbamate reduction is a function of the identity and concentration of individual FeII species present in solution as well as the inherent reactivity of each species with carbamates. The magnitude of ki is related to the standard one-electron reduction potential (E(H) degrees) of the corresponding FeIII/FeII redox couple.
Timothy J Strathmann; Alan T Stone
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Environmental science & technology     Volume:  36     ISSN:  0013-936X     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2002 Feb 
Date Detail:
Created Date:  2002-03-06     Completed Date:  2002-08-20     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  653-61     Citation Subset:  IM    
Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
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MeSH Terms
Carbamates / chemistry*
Hydrogen-Ion Concentration
Insecticides / chemistry*
Iron / chemistry*
Methomyl / chemistry*
Reg. No./Substance:
0/Carbamates; 0/Insecticides; 0/Ligands; 16752-77-5/Methomyl; 23135-22-0/oxamyl; 7439-89-6/Iron

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