Erionite in New Zealand: initial assessment and characterization

Erionite is a naturally occurring zeolite mineral originating from diagenesis or hydrothermal alteration of volcanic rocks. Typically, the two main types of rock in which erionite occurs are tuff and basalt. Erionite generally displays a fibrous morphology, and as with asbestos fiber exposure, when it is aerosolized and inhaled, fibrous erionite has been linked to cases of malignant mesothelioma, a fatal and aggressive tumor. Importantly, fibrous erionite appears to be similar or even more carcinogenic than the six regulated asbestos minerals. The first health issues regarding erionite exposure and mesothelioma were noted in Cappadocia (Turkey), and more recently, occupational exposure issues have emerged in the USA. The International Agency for Research on Cancer (IARC) has classified erionite as a Group 1 carcinogen. Nevertheless, when erionite fibers remain undisturbed in rock and/or, they are not thought to pose a risk to human health. In New Zealand, erionite has been found in surface rock exposures at numerous locations throughout both the North and South Islands, including (from north to south) Kaipara, Auckland, Taupo Volcanic Zone, Banks Peninsula, and the Moeraki coast. New Zealand is one of a number of high-income countries with elevated incidence of malignant mesothelioma (2.6 per 100,000), thought to result from occupational exposure to airborne asbestos fibers. However, recently people with no known asbestos exposure history have presented with mesothelioma. Thus, understanding the distribution and character of erionite in New Zealand may be important, as residential land development is occurring in some areas where erionite is known to be present. As an example case study, during an investigation at Auckland on the North Island, Miocene tuffaceous rocks from the Waitemata Group were studied using a range of analytical techniques, including SEM, TEM, Raman Spectroscopy, XRPD and FT-IR Spectroscopy. The preliminary investigation revealed that erionite-K was present within surface rock exposures, and exhibited a fibrous morphology. Dimensional analysis indicated just under half of the fibrous minerals satisfied the requirements for a respirable airborne fiber (length, L ≥5μm, a diameter, w ≤3μm, and L/w value ≥3:1). Research is ongoing in New Zealand into: (1) improved delineation of erionite geological occurrence, (2) mineralogical and chemical characterization, and, (3) transport pathways in rock and soil, all of which will contribute to future risk assessment.