Agricultural workers are encouraged to use sunscreen to decrease the risk of UV related skin cancer. Our previous studies have shown certain commercial sunscreens to be penetration enhancers. The focus of this project is to determine whether active ingredients in sunscreen formulations (i.e. the UV absorbing components and/or insecticides for the sunscreen/bug repellant combinations) also act as dermal penetration enhancers for herbicides.

Freshly excised female hairless mouse skin was placed in an in vitro Bronaugh style flow through diffusion chamber with Hank's Balanced Saline Solution, supplemented with 4 % bovine serum albumin, used as the receptor fluid. The epidermal side of the skin was pretreated for 30 minutes with one of 7 active sunscreen ingredients (octyl methoxycinnimate, octocrylene, oxybenzone, homosalate, octyl salicylate, padimate, or DEET). A 100-microliter aliquot of 2,4-D amine spiked with radiolabeled 2,4-D was then placed on the epidermal side of each skin for 24 hours. As the 2,4-D diffused through the skin into the receptor compartment, fractions were collected at 90-minute intervals and later counted via liquid scintillation. The flux of 2,4-D through the skin for each treatment was calculated to determine the cumulative percent of 2,4-D across the skin, and these values compared by ANOVA followed by a Dunnett's Multiple Comparison Test. Values are reported as mean ± s.e.m.

The total percentage of 2,4-D penetrating through the skin in 24 hours ranged from 54.4 ± 5.2 for no sunscreen control to 83.3 ± 2.4 for DEET. Of the 7 active ingredients, all but octocrylene led to a significant increase in total 2,4-D penetration as compared to the control (p < .05). Thus, the active ingredients of sunscreen formulations enhance dermal penetration of the moderately lipophilic herbicide 2,4-D.

Further studies are currently investigating whether combinations of active ingredients present in commercial sunscreen formulations exhibit synergistic or antagonistic penetration effects, with an ultimate goal being to find a combination that minimizes dermal penetration of agrochemicals.