Evidence of airborne dispersion of respirable-sized carcinogenic erionite fibres of volcanic origin

Erionite is a naturally occurring fibrous zeolite classified as a Group 1 carcinogen. Although the aerosolization and characteristics of erionite fibres found within sedimentary rock formations have been extensively studied, the potential forerionite fibres, particularly the woolly type found in vugs and vesicles within volcanic rocks to become airborne, and their resulting characteristics remains poorly understood. This study investigates the occurrence and characteristics of volcanic woolly erionite fibres in surface dust collected from shrub twigs near an erionite-bearing outcrop in Gawler Downs, New Zealand. Samples were analysed using scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) to determine the morphological and elemental characteristics of fibres, and transmission electron microscopy (TEM)-selected area electron diffraction (SAED) with continuous data collection (MicroED) analysis was performed to determine the crystallographic unit-cell parameters and confirm the fibres as erionite. Despite the large crystal sizes and confinement of erionite within consolidated rocks, respirable-sized woolly erionite fibres were detected in the surface dust at 50 % of the sampling stations, with higher abundance observed at sites located closer to the erionite-containing outcrop. Among the detected fibres, 88 % were within the respirable size range, and 47 % met the WHO criteria for hazardous fibres. The TEM-SAED analysis coupled with MicroED confirmed that 79 % of the tested fibres were indexed as erionite. No offretite was detected. These findings provide the first clear evidence that respirable-sized erionite fibres can become airborne and be locally dispersed when volcanic erionite-bearing outcrops are disturbed by environmental or mechanical processes, highlighting a previously underestimated inhalation risk associated with roadside exposure near such outcrops.