Percutaneous metal absorption from airborne particulate matter: evaluating the role of skin barrier integrity

Human exposure to airborne particulate matter (PM), particularly its metal content, represents a growing public health concern due to its potential toxicological effects. While inhalation is generally considered the main exposure route, dermal absorption remains insufficiently explored. This study examined the in vitro percutaneous penetration of selected metals (As, Cd, Cr, Cu, Mn, Mo, Ni, Pb, V) from certified urban road dust (NIST SRM® 1649b) using human skin under both intact and abraded conditions. The particles were applied as a 1 % w/v suspension in artificial sweat medium (pH 4.5), and Franz diffusion cells were used to evaluate metal permeation over 24 h. Complementary solubility tests in simulated sweat solution buffered topH 4.5 and 6.5 showed negligible pH dependence. Scanning electron microscopy revealed submicron primary particles (mean diameter 1.19 ± 0.78 μm) with a high tendency to form agglomerates, accounting for discrepancies with the hydrodynamic size reported in the SRM certificate. No detectable skin absorption was observed for Cd, Cr, and Cu, while the remaining metals showed enhanced permeation in damaged skin, confirming the role of barrier disruption in facilitating transdermal transport. Ni, Pb, and Mn exhibited the highest permeation levels, raising concern due to their sensitizing and toxic potential. These findings provide novel insights into the dermal bioavailability of PM-associated metals and highlight the importance of including skin exposure as a relevant pathway in environmental health risk assessments, especially for populations with compromised skin integrity or in high-exposure occupational settings.