Erionite in New Zealand: A Risk Assessment for Central Interceptor

Erionite is a naturally occurring asbestiform zeolite mineral. The main geological occurrences of zeolites are in tuff, tephra and volcaniclastic rocks deposited in deep ocean basins subject to low temperature hydrothermal alteration or burial diagenesis. An emerging body of research in Europe and North America has established erionite as carcinogenic to humans. Inhalation exposure to erionite fibres may result in increased risk of malignant mesothelioma. In Auckland, the presence of erionite in tuffaceous and volcaniclastic layers of Waitemata Group sedimentary rocks has been known since the late 1970s, however, neither an occupational exposure limit nor an approved code of practice for handling and disposing of erionite containing materials have been developed in New Zealand or internationally. Watercare’s Central Interceptor project is one of several large infrastructure projects in Auckland that handles and disposes of large volumes of Waitemata Group rocks. In the absence of approved guidance, Watercare commissioned Jacobs New Zealand to establish the risks erionite posed to the project. Borehole logs and photographs from the Central Interceptor were reviewed to identify samples with the highest probability of containing erionite for laboratory testing. The accuracy of laboratory tests available in New Zealand and internationally were assessed against the soil guideline values for friable asbestos. Quantitative X-Ray Diffraction testing was considered suitable to screen samples for the presence of erionite. Quantitative X-Ray Diffraction identified one possible occurrence of erionite from thirty-seven samples tested. Consequently, the Central Interceptor project implemented a series of recommendations to limit inhalation exposure of erionite fibres to site workers during construction. Fluidized Bed Asbestos Segregator (FBAS) sample preparation techniques, developed in the United States, used with Transmission Electron Microscopy (TEM) offer detection of erionite in concentrations comparable to soil guideline values established for asbestos. FBAS with TEM may prove fundamental in assessing presence of erionite in the future, once an occupational exposure limit and an approved code of practice for handling and disposing of erionite containing materials have been developed.