Permeability of three herbicides across the isolated frog and pig skins

Aim: Although it is generally accepted that the animal skin represents a barrier to the permeation of pesticides in the living organism, experimental evidences are lacking. For this reason we measured the transcutaneous permeability of three heavily used herbicides (atrazine, paraquat, glyphosate) across the skin of frog and pig. Methods: The ventral skin, from Rana esculenta, and the ear skin, from pig, were isolated and mounted in a specially constructed perfusion apparatus preventing the edge damage interference. Skin was perfused on both sides with a Ringer solution. 1 mCi of the 14C- labelled chemical under investigation was added to one compartment. From the opposite compartment, 4 ml were collected after 6 or 24 h, for frog or pig, respectively. Radioactivity was measured with a scintillation counter. Results: Permeability values of frog skin were higher than those measured in pig skin. For example, in the case of atrazine, values were 57,68 10-3 cm h-1 and 0,92 10-3 cm h-1, respectively. In both cases the rank order of permeability was: atrazine > paraquat > glyphosate. Conclusion: The low permeability of herbicides across the pig skin confirms that the skin is not an important site of permeation of xenobiotics in mammals. On the other hand, the high permeability value of atrazine across the frog skin accounts for its toxic effect on the whole organism and justifies its banning by several countries in Europe.