The dermal bioavailability of radiolabelled benzo[a]pyrene from acetone or from oils of differing viscosity, assessed by DNA and protein binding.

Tritium-labelled benzo[a]pyrene ([3H]BaP) was applied to mouse skin in acetone or mineral oils of differing viscosity. Epidermal DNA and protein were extracted after 24 or 48 h and the degree of adduct formation determined by the radioactivity present. When [3H]BaP was applied in acetone, the degree of DNA and protein binding was around 15-20 times greater than that observed when a low-viscosity oil was used as a vehicle. When applied in oils of differing viscosity, however, only a twofold difference was seen across the whole viscosity range (13.5 cSt* at 40 degrees C to 1665 cSt at 60 degrees C). From measurements made of urine and faecal radioactivity and from small-scale investigations using other routes of administration, it was clear that the grooming activity of the animals had a marked effect on skin absorption and macromolecular binding. It is possible that greater grooming activity with low-viscosity oils may explain why oil viscosity did not have a greater effect on binding levels, but further studies are needed to investigate this. These findings may have important implications in the interpretation of long-term skin painting studies and may assist in the interpretation of analytical data and short-term biological assays.