Cutaneous toxicity of the benzidine dye direct red 28 applied as mechanistically-defined chemical mixtures (MDCM) in perfused porcine skin.

Complex chemical mixtures at hazardous waste sites can potentially consist of a marker chemical and several other chemicals, each of which can have different modulating actions on the dermatotoxicity of the marker chemical and/or other components in the mixture. A total of 16 mixtures, consisting of a marker chemical direct red 28 (DR28), a solvent (80% acetone or DMSO in water), a surfactant (0 or 10% sodium lauryl sulfate, SLS), a vasodilator (0 or 180 microg methyl nicotinate, MN) and a reducing agent (0 or 2% stannous chloride, SnCl2) were selected. Isolated perfused porcine skin flaps (IPPSFs), which have been proven to be an in vitro model for assessing absorption and toxicity, were utilized. These mixtures did not cause severe dermatotoxicity. However, light microscopic observations depicted minor alterations (intracellular and intercellular epidermal edema) with DMSO mixtures than with acetone mixtures. The presence of SLS caused an alteration in the stratum corneum. Enzyme histochemical staining for alkaline phosphatase (ALP) and nonspecific esterase (NSE) revealed no significant treatment effects, but increased staining for acid phosphatase (ACP) in the stratum basale was significant when associated with SLS or SLS + MN in DMSO mixtures. At 8 h post-dose, only DMSO mixtures containing SL + MN, SL + SnCl2, or SLS + MN + SnCl2 significantly increased transepidermal water loss. In conclusion, this study demonstrated that various mixtures, especially those containing SLS alter the epidermal barrier differently with complex interactions occurring simultaneously.