The influence of pH on the in vitro skin permeation of rhodium
Jansen van Rensburg, Susanna Jacoba
MetadataShow full item record
In occupational settings where rhodium is produced or used, such as the mining industry, refineries and catalytic industries, workers are at risk of being dermally exposed to this metal in either the metallic form or its salt compounds. A considerable amount of contradictory literature has been published with regard to the sensitising abilities of rhodium and no published information is available on the occupational dermal exposure of rhodium as well as its ability to permeate through the skin. Previous studies conducted on the in vitro permeation of metals, such as nickel, cobalt and chromium, have indicated that certain metals undergo oxidation in the presence of sweat and form ions which are able to permeate through skin. For some metals, this ionisation takes place more rapidly in an acidic environment and a decrease in the environmental pH would cause an increase in the release of ions from those metals. Aim: The aim of this study was to determine whether rhodium in the form of rhodium trichloride (RhCl3) would be able to permeate through the skin in vitro, as well as to determine whether any differences exist between the in vitro permeation of rhodium at a pH of 4.5 and a pH of 6.5. Methods: Full thickness abdominal skin was obtained as biological waste after surgery from Caucasian females ranging between 39 and 42 years of age. The Franz diffusion cell method was used in which the experimental cells contained synthetic sweat with RhCl3 and the blanks did not contain any RhCl3 in the donor compartment. All of the cells contained a physiological receptor solution in the receptor compartment. At intervals of 8, 12 and 24 hours, 2 ml of the receptor solution were removed for analysis. The receptor compartment was rinsed with 2 ml receptor solution which was also removed for analysis and 2 ml of fresh receptor solution was added to the compartment. After 24 hours, the receptor and donor solution was removed respectively for analysis and the skin was removed for digestion, prior to analysis. The mass of rhodium in the receptor solutions were determined using Inductively Coupled Plasma Mass Spectrometry. The donor solutions and digested skin solutions were analysed using Inductively Coupled Plasma Optical Emission Spectrometry. Results: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin with a cumulative increase in permeation over prolonged exposure time. After 8, 12 and 24 hours, the amount of rhodium that permeated through the skin was higher at pH 4.5 than for pH 6.5. After 12 hours, the permeation of rhodium was statistically significantly higher for pH 4.5 than for pH 6.5 (p = 0.02). At both pH values, the percentage of rhodium that accumulated in the skin was higher than the percentage of rhodium that diffused through the skin and the lag time was less than six hours. Conclusion: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin. A decrease in the pH of synthetic sweat led to an increase in the permeation of rhodium and it is recommended that future in vitro permeation studies be conducted at a pH of 4.5, as the skin surface pH of workers are generally considered to be below 5. A higher percentage of rhodium was retained in the skin than the percentage that diffused through, indicating the ability of rhodium to accumulate in the skin, from where it may exert health effects, such as sensitisation.
- Health Sciences