Influence of Epicuticular Waxes on the Photolysis of Pirimicarb in the Solid Phase.

The influence of epicuticular waxes extracted from different fruits on the photodegradation of pirimicarb (I) in the solid phase was studied. Waxes were extracted with CHCl3 and CHCl3/CH3OH from nectarines (N), oranges (OR), and mandarin oranges (M). All of the waxes affect the qualitative behavior of the photodegradation of I:  the formation of photoproducts N-formylpirimicarb (II) and demethylpirimicarb (III) was hindered. This influence was found to be independent of the light sources (sunlight or lamp > 290 nm) and of the solvents employed in the extraction of the waxes. The photodegradation rate (Kobs) of I was reduced to a different extent by the presence of waxes, from N and O, and was increased from M (irrespective of the extraction solvent). The photodegradation rates of II and III were both reduced by all waxes, M included. The waxes extracted with CHCl3/CH3OH show a higher inhibition effect on Kobs than those with CHCl3. The scales of rate reduction were similar under sunlight and artificial li...