Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8851912 | Chemosphere | 2018 | 29 Pages |
Abstract
Absolute second-order rate constants for hydroxyl radical (HO) reaction with four organophosphorus pesticides, malathion, parathion, fenthion and ethion, and a suite of model compounds of structure (EtO)2P(S)-X (where Xâ¯=â¯Cl, F, SH, SEt, OCH2CF3, OEt, NH2, and CH3) were measured using electron pulse radiolysis and transient absorption techniques. Specific values were determined for these four pesticides as k = (3.89â¯Â±â¯0.28) x 109, (2.20â¯Â±â¯0.15) x 109, (2.02â¯Â±â¯0.15) x 109 and (2.93â¯Â±â¯0.10) x 109â¯Mâ1â¯sâ1, respectively, at 20â¯Â±â¯2â¯Â°C. The corresponding Brönsted plot for all these compounds demonstrated that the HO oxidation reaction mechanism for the pesticides was consistent with the model compounds, attributed to initial HO-adduct formation at the P(S) moiety. For malathion, steady-state 60Co radiolysis and 31P NMR analyses showed that hydroxyl radical-induced oxidation produces the far more potent isomalathion, but only with an efficiency of 4.9â¯Â±â¯0.3%. Analogous kinetic measurements for the hydrated electron induced reduction of these pesticides gave specific rate constants of k = (3.38â¯Â±â¯0.14) x 109, (1.38â¯Â±â¯0.10) x 109, (1.19â¯Â±â¯0.12) x 109 and (1.20â¯Â±â¯0.06) x 109â¯Mâ1â¯sâ1, respectively, for malathion, parathion, fenthion and ethion. Model compound measurements again supported a single reduction reaction mechanism, proposed to be electron addition at the PS bond to form the radical anion. These results demonstrate, for the first time, that the radical-based treatment of organophosphorus contaminated waters may present a potential toxicological risk if advanced oxidative processes are used.
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Authors
Kristin K. Clark, Stephen P. Mezyk, Amberashley Abbott, James J. Kiddle,