Kinetic studies of the AOP radical-based oxidative and reductive destruction of pesticides and model compounds in water.
Chemosphere
; 197: 193-199, 2018 Apr.
Article
em En
| MEDLINE
| ID: mdl-29351878
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 = (3.89⯱â¯0.28) x 109, (2.20⯱â¯0.15) x 109, (2.02⯱â¯0.15) x 109 and (2.93⯱â¯0.10) x 109â¯M-1â¯s-1, respectively, at 20⯱â¯2⯰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 4.9⯱â¯0.3%. Analogous kinetic measurements for the hydrated electron induced reduction of these pesticides gave specific rate constants of k = (3.38⯱â¯0.14) x 109, (1.38⯱â¯0.10) x 109, (1.19⯱â¯0.12) x 109 and (1.20⯱â¯0.06) x 109â¯M-1â¯s-1, 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.
Palavras-chave
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Compostos Organofosforados
/
Compostos Organotiofosforados
/
Paration
/
Praguicidas
/
Fention
/
Malation
Idioma:
En
Ano de publicação:
2018
Tipo de documento:
Article