Airborne lead arsenate chloride (mimetite) microcrystals in ambient air as a potential health hazard

Airborne lead arsenate chloride (mimetite) crystals ranging from sub-micrometer to 10 μm in length and attached to Zn-bearing phase and soot were observed in ambient air in Zabrze, Poland. Mimetite was identified by Raman microspectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The airborne mimetite, while apparently related to the historic Zn and Pb ore smelting in the region, was collected in a place not directly affected by the smelting. Mimetite commonly occurs in As- and Pb-contaminated topsoil and waste dumps in the region. Six topsoil samples were collected within the small (0.4 km²) As, Pb, and Zn geochemical anomaly recorded in the past and located 0.7 km west of the air sampling site to inspect, whether it might have been a source of airborne mimetite. X-ray fluorescence spectroscopy of the samples did not show elevated concentrations of As and Pb. The investigated mimetite microcrystals became airborne most probably due to aeolian entrainment of dust particles from the unspecified location. Calculated health hazard indices suggest a high carcinogenic risk due to prolonged exposure to mimetite in resuspended dust. Mimetite may be a common ambient air pollutant in other places worldwide affected by current or historic emissions from Zn and Pb smelters.