Characterization and potential toxicity of asbestiform erionite from Gawler Downs, New Zealand

Abstract

Abstract Erionite is the name for a zeolite mineral series originating from diagenesis or hydrothermal alteration of volcanic rocks. The particular erionite “species” is based on the dominant extra-framework cation, erionite-Ca, erionite-K, or erionite Na. Irrespective of the species, erionite can display a fibrous/asbestiform morphology and has been linked with cases of malignant mesothelioma, a disease typically associated with asbestos exposure. Characterization of new discoveries of erionite is therefore important to assess any potential exposure hazards. This study describes a new asbestiform erionite from vesicles within the Upper Cretaceous Mt. Somers Volcanics Group (MSVG), Canterbury, New Zealand. The erionite is within the Hinds River Dacite, the youngest unit within the MSVG at Gawler Downs, ~100 km west of Christchurch, in the foothills of the Southern Alps. A multi-analytical approach was taken to analyze the sample which included micro-Raman spectroscopy, thermogravimetric analysis, electron microscopy, electron microprobe analysis, and X-ray powder diffraction with the Rietveld method. Results confirmed the mineral as fibrous erionite-K. The chemical composition of the mineral is unique due to the presence of higher levels of Mg. While Fe was also identified, this was due to smectite flakes occurring on the surface of the erionite fibers. According to the World Health Organization (WHO) respirable mineral fiber definition, where length ≥5 μm, width ≤3 μm, and aspect ratio (L/w) ≥3:1, the Gawler Downs erionite fibers are respirable, while the fibers themselves exceed respirable thickness. In addition to morphology, a value for the potential toxicity model was computed to be 2.28 for the Gawler Downs erionite. This is similar to those of other carcinogenic erionites from Karain, Turkey (2.33), and Nevada, U.S.A. (2.28). Taken together, results indicate Gawler Downs erionite represents an environmental hazard. Nevertheless, further investigation is required to determine potential environmental exposure pathways by which erionite may become airborne and assess the actual environmental risk in the Gawler Downs area.