T. Kromer et al., Photodegradation and volatilization of parathion-methyl on glass and soil dust under laboratory conditions, HUMAN AND ENVIRONMENTAL EXPOSURE TO XENOBIOTICS, 1999, pp. 363-374
A new device ("photovolatility chamber") was designed to simultaneously exa
mine the direct and indirect photolysis of C-14-labelled pesticides on surf
aces and their volatilization behaviour, excluding photolysis in air. Both
continuous air sampling, which quantities volatile organic compounds and (C
O2)-C-14 separately, and the detection of surface-located residues guarante
e a complete radioactivity and mass balance. In model experiments using a B
orofloat glass surface and soil dust, the volatilization and photodegradati
on of [phenyl-UL-C-14]parathion-methyl were measured under constant climati
c conditions lair temperature and humidity) determining the influence of si
mulated sunlight and O-3.
Depending on the experimental conditions, parathion-methyl was converted to
paraoxon-methyl 4-nitrophenol, unknown polar products and (CO2)-C-14. With
respect to the direct photolysis of parathion-methyl (experiments without
O-3), polar compounds and (CO2)-C-14 were the major metabolites, due to the
rapid photochemical mineralization of 4-nitrophenol to (CO2)-C-14, which w
as confirmed in separate experiments with [C-14]4-nitrophenol. Paraoxon-met
hyl and 4-nitrophenol formation was mainly mediated by the combination of O
-3 and light, suggesting an indirect photochemical reaction with OH radical
s, since neither light alone nor O-3 alone showed comparable effects.
Due to photochemical product formation, which is an antagonistic process, t
he volatilization of unaltered parathion-methyl from both surfaces generall
y decreased in the presence of light, particularly in combination with incr
easing O-3 concentrations.