Pesticide residues in food — 2007: Toxicological ... - ipcs inchem

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demonstrated that the highest tissue concentrations were found in the liver for the triazole label, and in
fat and plasma for the phenyl label. Residues from the triazole-labelled compound were significantly
less than those from the phenyl-labelled compound. Tissue residues in females were slightly less than
in males. Multiple pre-treatment with unlabelled difenoconazole had no effect on tissue distribution.
Dermal absorption
Studies of dermal penetration in rats given difenoconazole as an application to the skin in vivo
and studies with rat and human skin in vitro were conducted using non-radiolabelled difenoconazole
(purity, 99.3%) and [triazole-U- 14 C]difenoconazole.
The absorption, distribution and excretion of radioactivity was studied in male HanBrlWIST
(SPF) rats after a single dermal administration of 14 C-labelled difenoconazole mixed with the nonlabelled
difenoconazole formulated as SCORE 250 EC. At the highest dose, the specific activity was
54 kBq/mg (1.5 µCi/mg).
For the highest dose, difenoconazole was dissolved in blank formulation at a concentration of
250 g/l, representing the undiluted product. For the intermediate and lowest dose, this formulated
material was mixed with water in a ratio of 1 : 200 (w/v) and 1 : 5000 (w/v), respectively. The applied
nominal doses were 0.5, 13 and 2600 μg/cm 2 and these were left in place for 6 h. The determination
of dermal absorption at the highest dose was repeated in a separate experiment, using an application
of 2400 μg/cm 2 . In each experiment, groups of 16 rats were exposed for 6 h, after which the skin was
washed, and four rats per group were killed at 6, 24, 48 and 72 h after dose application. The amount
of radiolabelled difenoconazole remaining in the skin was determined at each sampling time after
washing and skin-stripping to separate the stratum corneum from the epidermis. Urine and faeces
were collected up to 72 h and blood residue concentrations were measured at 72 h.
At the lowest, intermediate and highest doses, respectively, systemic absorption within 6 h was
15.3%, 7.5% and 7.1% and the penetration rates was 0.013, 0.162 and 30.4 μg/cm 2 per h. The ratios
of these penetration rates, i.e. 1 : 12 : 2400 were proportional to the application concentrations, i.e.
1 : 26 : 5100. There was, however, a substantial variation in the data that was attributed to the irritancy
of the formulation vehicle, SCORE 250 EC; this resulted in a broad range of individual values for
dermal absorption of up to 45% of the administered dose. For the study in rats in vivo, in a worst-case
scenario the mean dermal absorption values at the lowest intermediate and highest doses, respectively,
were 37.6%, 14.6% and 10.6%. Nevertheless, concentrations of residues in the blood were generally
very low: the highest concentrations (as difenoconazole equivalents) were 0.01 μg/ml and 0.26 μg/ml
at the intermediate and highest doses, respectively, 6–8 h after appliciation (Hassler, 2003c).
The penetration of non-radiolabelled difenoconazole (purity, 99.3%) and [triazole-U- 14 C]
difenoconazole through isolated rat and human epidermal membrane preparations in vitro after stripping
the stratum corneum from skin was determined after an exposure of 24 h to difenoconazole at a
concentration of 0.05, 1.28 or 250 mg/ml, achieving applications of 0.5, 12 or 2345 μg/cm 2 . Before
dose application, the integrity of the epidermal membranes and their suitability for use in the study
was assessed by measuring the penetration of tritiated water applied to the membranes and comparison
of the results with exclusion criteria. Rat skin membranes with permeability coefficients (Kp)
of > 3.5 × 10 −3 cm·h −1 and human skin membranes with Kp > 2.5 × 10 −3 cm·h −1 were excluded from
the subsequent experiment. After this membrane integrity check and before dose application, the
receptor chamber was refilled with ethanol : water (1 : 1 v/v).
Within 24 h, the proportions of radiolabel penetrating the membranes at the lowest, intermediate
and highest concentrations, respectively, were 71%, 64% and 23% for the preparations of rat skin
and 7.6%, 7.0% and 0.7% for the preparations of human skin. Although the studies with human skin
in vitro indicated that dermal absorption was approximately 8% (7.6%) for the lowest concentration,
if the amount retained in skin is considered as potentially absorbable it increases to 15%. However,
the main objective of the comparative studies of rat and human skin in vitro was to evaluate the
DIFENOCONAZOLE 201–272 JMPR 2007