Skin absorption of potential toxic metals following exposure to urban dust

Urban dust is a mixture of particles suspended in the atmosphere. Their sources include factories, home heating, power plants, waste incinerators, combustion engines, construction activities, fires, natural windblown dust, etc. Major components of particulate matter (PM) are metals, organic compounds, materials of biologic origin, ions, and carbon-based particles. Recently, it has been reported that PM is associated with increased risks of skin diseases, especially atopic dermatitis in children. The skin constitutes a protective barrier to external physical and chemical aggression. Although it is generally considered poorly permeable to xenobiotics, it has been demonstrated that skin represent an entry route for metal ions. Metals may penetrate inside the skin inducing more or less local effects such as skin sensitization (Ni, Cr, Co) and potential metals diffusion into the circulatory system. The aim of this study was to investigate the percutaneous penetration of potential toxic metals (Pb, As, Cd, Cr, Ni, etc.) following exposure to urban dust using the Franz diffusion cell method. The urban dust (Standard Reference Material 1649b, NIST) dispersed in synthetic sweat (1%w/v) has been applied to intact as well damaged skin for a 24-hour exposure period. Receiving phases and skin tissues has been collected and analysed by Inductively Coupled Plasma – Mass Spectrometry for the quantification of potential toxic metals. The present study demonstrates that, after the application of urban dust on the skin surface, some metals, and in particular the hazardous Pb, As, Ni and Cd, can penetrate the dermal layers and permeate into the receiving phase. Moreover, absorption through damaged skin is significantly higher than through intact skin, as a result of the weaker cutaneous barrier function. These results confirm those of a previous study that evaluated the skin absorption of metals after exposure to road dust and suggest that dermal absorption of metals could be relevant in environmental exposure scenarios.