Transdermal penetration of atrazine, alachlor, and trifluralin: effect of formulation.

Commercial formulations of herbicides contain surfactants and other compounds to increase absorption by targeted plants. These chemicals, however, are also potential penetration enhancers for mammalian skin. The effect of formulation on dermal absorption of the herbicides atrazine, alachlor, and trifluralin and their commercial formulations Aatrex, Lasso, and Treflan was determined. In vitro absorption studies were performed by placing hairless mouse skin in a Bronough flow-through diffusion system. Donor solution was spiked with (14)C-labeled herbicide, and its penetration through the skin was monitored in 90-min fractions. Results demonstrate that dermal penetration of commercially formulated compound was significantly greater (p < 0.05) than that of the pure compound at the same concentration. The physical properties of a herbicide predicted penetration (r(2) = 0.97-0.99) for commercial formulations but were not as effective at predicting absorption for the pure compounds (r(2) = 0.51-0.71). The solvents associated with the hydrophobic herbicide Treflan altered dermal penetration of the more hydrophilic herbicides Lasso and Aatrex. Furthermore, although the most hydrophobic compound had the least penetration, it accumulated in the stratum corneum at the greatest rate. These studies can have important implications on future experiments performed to predict percutaneous penetration of herbicides.