Photolysis of pesticides: influence of epicuticular waxes from Persica laevis DC on the photodegradation in the solid phase of aminocarb, methiocarb and fenthion

Abstract

Pesticides with N,N-dimethyl and thiomethyl moieties (aminocarb, methiocarb and fenthion) were irradiated under artificial light (lambda > 290 nm) in an amorphous wax phase from Persica laevis DC. The effect of the presence of the wax on the photolysis rate differed in the three pesticides, increasing it in aminocarb, having little effect in methiocarb and slowing it down in fenthion. The presence of the wax affected the qualitative photodegradation behaviour of all the pesticides. The data obtained were compared with those for pirimicarb, which had been studied earlier.

Reviews of Environmental Contamination and Toxicology

“…2, reaction 6) (Abdel-Wahab et al 1966). Because the same products were detected in photolysis of (66) on glass at >290 nm, the oxidation process was likely to occur in the environment (Pirisi et al 2001). Because the same products were detected in photolysis of (66) on glass at >290 nm, the oxidation process was likely to occur in the environment (Pirisi et al 2001).…”

“…Considering the wax chemistry described in Section III.E, many researchers have conveniently examined photodegradation of a pesticide in simple organic solvents as surrogates of waxes, but their significantly different fluidity and simple structures should be kept in mind together with easier photoaddition of a solvent molecule. Photodegradation of carbamate and organophosphate pesticides was examined in thin film of epicuticular waxes extracted from a variety of citrus fruits (Cabras et al 1997b;Pirisi et al 1998Pirisi et al , 2001. Photolysis of 2,4-D (1) has been reported to be enhanced on Zea mays leaves and thus a more realistic model has been considered (Venkatesch and Harrison 1999).…”

“…Arninocarb (66) or mexacarbate (67) were photodegraded on silica gel at 254 nm to more than 10 photoproducts including the N(CH 3)CHO and NHCHO derivatives (Abdel-Wahab and Casida 1967). Methiocarb (68) underwent photoinduced oxidation of the methylthio group on wax-coated glass to form the corresponding sulfoxide and sulfone, while it was degraded to unknowns on glass (Pirisi et al 2001). This oxidation was also reported for pirirnicarb (78) on glass and cellulose plates, and involvement of OH' was assumed .…”

“…18). In the thin film of fruit wax from orange, nectarine, and olive, (143) gave the sulfoxide under sunlight with a trace amount of the sulfone (Cabras et al 1997b;Pirisi et al 2001). The amounts of these dimers greatly decreased in cyclohexane containing methyl 12-hydroxystearate (ester of a cutin acid) with predominant formation of the oxon.…”

“…For propoxur (65) (Kopf and Schwack 1995). However, this oxidation product disappeared in the presence of wax from nectarine fruits, showing that some wax components may act as scavengers of radicals (Pirisi et al 2001). Although the simple photoinduced cleavage of the O-C(=O) bond was observed for aminocarb (66) in organic solvents (Addison et al 1974;Kumar et al 1974), oxidative N-demthylation via the N-CHO intermediate proceeded on glass.…”