The influence of pH on the in vitro permeation of platinum through human skin

Abstract

Background: At platinum mines and refineries, and other industries such as the catalytic industry, workers are at risk of being potentially exposed via dermal contact to soluble platinum salts, which are known sensitisers and allergy-eliciting compounds. The availability of information regarding the permeability of soluble platinum salts through intact human skin and its health effects specifically on the skin is limited. The permeation of platinum was confirmed only at a pH of 6.5 but the influence of a lower pH on platinum permeation has not yet been investigated. The in vitro permeation of metals was investigated in previous studies and showed that a lower pH could lead to an increase in permeation. This could be due to the metals oxidising at a lower pH leading to the formation of permeable ions. Therefore, an acidic environment could potentially increase the permeation of a metal. Aim: The aim of this study was to determine and compare the permeation of a soluble platinum salt, potassium tetrachloroplatinate (K2PtCl4), at a pH of 4.5 and 6.5. Method: Full thickness abdominal skin from two female Caucasian donors, aged 37 and 47, were obtained as biological waste after surgery. The Franz diffusion cell method was used in which the synthetic sweat in the donor compartment of the experimental cells contained 0.3 mg/ml of K2PtCl4. The physiological receptor solution was removed at intervals of 1, 2, 6, 12, 18 and 24 hours for analysis. After 24 hours the receptor and donor solution were removed for analysis and the skin chemically digested before analysis. The mass of platinum in the receptor solution was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The platinum mass in the donor and digested skin solutions were determined by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Results: Platinum permeated through intact human skin, at both pH levels of 4.5 and 6.5. The mass of platinum that permeated through the skin was 58.09% higher at a pH of 4.5 (34.18 ± 7.79.ng/cm2) than at a pH of 6.5 (21.62 ± 4.4.ng/cm2) after 24 hours. The retention of platinum in the skin was statistically significantly higher at a pH of 4.5 (2118.9 ± 62.6.ng/cm2) than at a pH of 6.5 (1771.3 ± 131.9.ng/cm2) (p = 0.02). The mass of platinum that was retained in the skin was statistically significantly higher than the mass that diffused through the skin (p ≤ 0.001) at both pH levels. The lag time at a pH of 4.5 (2.47 ± 0.34 h) was 37.25% shorter than at a pH of 6.5 (3.39 ± 0.28 h) and leaned towards being statistically significant (p = 0.054). Conclusion: A decrease in pH resulted in increased mass of platinum retained inside the skin, which prolongs the exposure time and results in more platinum potentially permeating through the skin. Therefore, an acidic environment, such as a precious metal refinery, poses a greater risk for the permeation of platinum through the skin and the significantly higher risk for retention of platinum inside the skin