Skin absorption of metals following exposure to road dust powder

Human skin forms a unique interface between the body and the external environment. Its main role is to protect the internal organs from external factors. Notably, the outermost skin layer, stratum corneum, forms a remarkable barrier for permeation of xenobiotics in general, but unfortunately it may become an entry route of hazardous substances. Metals can penetrate and permeate the skin inducing local effects such as skin sensitization with allergic contact dermatitis and potential metals diffusion into the bloodstream with systemic intoxication[1] [2]. Metals in nano dimensions penetrate and permeate the skin in higher amount[3] [4] compared to bulk materials due to their smaller dimensions[5].Therefore, if the stratum corneum is damaged to various factors such as inflammation, desquamation, defects in lipid distribution or epidermal thickening, the transcutaneous passage of a molecule is expected to be drastically enhanced[6] [7]. In this study, we investigate the percutaneous penetration of metals from the road dust powder in intact as well damaged skin to mimic the effect of skin lesions. In addition, porcine and human skin were compared as skin models. The certified reference material BCR®-723 provided by the European Institute for Reference Materials and Measurements was used as road dust formulation. To evaluate the extent of ionization of metals from BCR®-723, the dissolution of powder in synthetic sweat solutions at two different pH (pH 4.5, 6.5) was carried out. Periodic quantification of metals concentration was monitored and analyzed via inductively coupled plasma - optical emission spectroscopy (ICP-OES). The choice of synthetic sweat solution at pH 4.5 was dictated to reproduce the workplace conditions. Dermal absorption from donor compartment containing metals was monitored for 24 hours. The amounts of metals retained in skin were quantified post-exposure by inductively coupled plasma - mass spectrometer (ICP-MS). Percutaneous absorption of lead (Pb) was higher in both intact skin models (549 ng/cm2 in porcine skin vs 68.80 ng/cm2 in human model). Moreover, cobalt (Co) accumulation was higher in porcine skin reaching a value of 518 ng/cm2 than those found in human skin (1.85 ng/cm2). In contrast with the observations reported in human skin model, chromium (Cr) achieved the lowest skin absorption in porcine model (183 ng/cm2). As expected, metals permeation on damaged skin was enhanced due to the removal of the barrier function. These consequence differences may be due to the skin tissues, but pig skin appeared as the most suitable replacement for human skin.