An Investigation of the Absorption of Lead (Pb) through Skin with Hair using Synchrotron X-ray Techniques

Abstract

The acknowledged pathways of lead entry to the body include ingestion and inhalation, with absorption rarely cited as a large contributor to body lead burden. This thesis investigates the absorption of lead into skin with hair using both traditional passive diffusion experiments and synchrotron x-ray imaging techniques. Pig skin with hair was used as the test membrane in a Franz diffusion cell set-up. A solution of lead (II) acetate dissolved in deionized water was applied to the skin surface and allowed to passively diffuse through the skin layers into a deionized water receptor solution. Diffusion times of 24, 48 and 72 hours were used to determine total lead content passing through the epidermis and dermis through inductively coupled plasma mass spectroscopy (ICP-MS) for the traditional diffusion analysis. Additional diffusion times of 0.25, 0.5, 1, 2, or 24 hours were studied by synchrotron-based micro x-ray fluorescence (µXRF) and x-ray absorption spectroscopy (XAS) measurements. To our knowledge, this thesis presents the first µXRF images of the elemental distribution of lead in hairy skin following cutaneous application. ICP-MS results show that the diffusion of lead through hairy skin is impeded by the accessory skin structures, resulting in lower lead content in the receptor solution following diffusion through hairy skin compared to hairless skin. µXRF results show the progression of lead diffusion through the skin over time, accumulation of lead in epidermal cells, and significant differences in the depth and intensity of lead diffusion through the skin with respect to the position of the hair underlying the skin surface (p < 0.0125). XAS results show that the Pb2+ ion from the applied lead (II) acetate interacts with subcutaneous components and structures to form different compounds, often PbCO3 and PbCl2, however more physiologically relevant reference compounds should be used for XAS studies in the future to more accurately identify lead compounds formed in skin.