The E beam induced decomposition of pesticides in water: A gamma and pulse radiolysis investigation on carbofuran

The reactivity of carbofuran (CF) with OH was measured directly by means of pulse radiolysis matched with kinetic UV-vis absorption spectrometry. The hydroxylation attack of CF proceeds with a rate constant k1 = 6.6 x 109 M1s-1, similar to that of benzene forming hydroxycyclohexadienyl radicals (kbenzene+OH = 7.8 x 109 M1s1). It reacts, instead, 30 times slower with the methyl-carbamic acid methyl ester used to probe the reactivity of the carbamic part of the molecule. These kinetic observations and the spectral features in the region 280.330 nm of the hydroxylation products, which resemble those of a cyclohexadienyl type radical, have led to the conclusion that OH and CF form dienyl type radicals, HO-CF·. In deaerated atmosphere, HO-CF· decays in a millisecond time regime via a second order process. In the presence of oxygen, the peroxidation reaction channel prevails, forming HO-CF-OO· (k ∼ 107 M1s1). As monitored after γ radiolysis, oxygen participation makes the global decomposition six times more efficient than in anaerobic solutions (N2O saturated). (author)