Each skin disc was treated with a pyrethroid in 15 μl acetone. At the
end of the experiment (24–48 h post-dosing), the peristaltic pumpwas
stopped. The epidermal surface (with the cell top in place) waswashed
six times with 0.5 ml of a mixture of soap:water (1:1) to remove
unabsorbed chemical. A Pipetman® was
used to apply and remove each skin wash twenty times. The skin wash
fractions were pooled into two vials and mixed with scintillation fluid.
The cell top and cell body were individually washed three times with
0.5 ml ethanol. The cell top was placed in a small weigh boat and a
Pipetman® was used to apply and remove each ethanol wash twenty
times. Each ethanolwash of the interior of the cell bodywas applied and
removed twenty times. The cell top and body washes and weigh boat
were kept in separate vials. Skin washes, cell top and body washes,
weigh boats and receptor fluid were mixed with scintillation fluid and
analyzed for radioactivity in the liquid scintillation analyzer. An
experiment was done to determine the wash efficiency using a
100 nmol dose of each of the three pyrethroids. Pyrethroid was applied
to the skin and after allowing the acetone to evaporate (ca. 5 min), the
skin was washed as described above. This wash procedure removed
72.8±11.1% (mean±SD, N=5) of the dose for bifenthrin, 70.4±8.0%
for deltamethrin and 79.5±3.0% for permethrin.