Erionite and Malignant Mesothelioma

Erionite and Malignant Mesothelioma

Asbestos-induced malignant mesothelioma (MM) remains a global public health concern, including in New Zealand. Construction and building trades workforce has the highest mesothelioma incidence. There is also an increasing concern in non-occupational or environmental asbestos induced MM for both men and women. Studies report that New Zealand is one of a number of high-income countries with elevated incidence of MM (2.6 per 100,000) due to occupational exposure to airborne asbestos fibres. Indeed, recent reports have highlighted devastating outcomes of the asbestos related disease epidemic here. These include cases of how MM was apparently a consequence of exposure to asbestos in home, following transfer of the asbestos fibres from the workplace. This was thought to have occurred on the hair and clothes of occupationally-exposed family members. 

Erionite, a naturally occurring fibrous mineral that belongs to a group of minerals called zeolites.

Erionite is produced in silica-rich volcanic eruptions and is then later dissolved by water and recrystallized as zeolites, often in sedimentary rocks. When aerosolised and inhaled, erionite fibres have been associated with health effects similar to those typically seen with exposure to asbestos, such as malignant mesothelioma (MM). Several studies have reported how erionite was found to be the causative agent for the mesothelioma epidemic in the Cappadocia region of Turkey, where there is an extremely high level of mortality (800 cases/100,000 population) from exposure to erionite in rock used to build houses. 

Most of the affected population had been exposed to erionite by inhalation since childhood, resulting in up to 50% of all deaths in three villages. Many of the affected people later migrated to Germany and Sweden, and cases of MM caused by erionite were also identified in those Turkish immigrants. Genetic susceptibility was also thought to be a possible factor in determining the susceptibility of the population to MM, specifically the pathogenic role of BAP1 mutations resulting in mesothelioma, and in other cancers globally, as well as in Cappadocia specifically.9 The prevalence of the BAP1 gene in the global population and its more recent link to other cancers globally, along with studies linking MM to erionite exposure in countries other than Turkey (including the US and Mexico), suggest that the results from Cappadocia may not be accounted for entirely by local conditions or be atypical at global scales. 

In the US, the carcinogenic properties of erionite have recently sparked interest in erionite as an occupational and public health hazard, particularly in areas where erionite is found in regional bedrock or sediments. However, data concerning health outcomes there are equivocal. A study of North Dakota quarry and road workers reported only a few cases of pleural changes.

Regardless of that study, although the long-term health impacts remain uncertain, there is concern about inhalation of airborne dust and particulates containing erionite fibres from gravel pits, quarries, roads, building, and construction sites. Thus, erionite is now classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen (ie, carcinogenic to humans). Erionite, also appears to be a more potent human carcinogen than asbestos in causing MM However, in contrast to asbestos, erionite mineral fibres do not have established occupational exposure limits (OELs). Despite the establishment of OELs for asbestos, controversy remains as to whether short intense exposure to asbestos is particularly harmful since it is complicated by non-linear dose concentration-duration-risk relationships.

There is also uncertainty as to how asbestos dose-response may relate to erionite dose-response for a number of reasons. Epidemiological data alone typically lack accurate fibre counts (for erionite or asbestos exposure) and are inconclusive about risks at specific concentrations.12 Fibres also vary in toxicity due to morphology and chemical characteristics (composition, surface reactivity, biopersistance etc). There even exists considerable heterogeneity in the responses of cells within the same local volume of tissue,12 and in vitro techniques do not provide accurate estimates of biologically-effective doses (eg, the numbers of fibres accumulated in mesothelial tissue over time). Nevertheless, exposure concentration does appear to part-control the latency interval between first exposure to asbestos or erionite and the development of MM. Indeed, workers in trades with higher levels of exposure (eg, naval personnel removing asbestos from warships; builders; extractive industry workers), may experience shorter latencies compared to those exposed to lower amounts of asbestos.13 Age at first exposure also appears to be important. Indeed, once a sufficient amount of asbestos or erionite has been inhaled, such as by a six-year-old child growing up in a village or suburb contaminated with erionite, they will develop MM, which suggests that additional exposure(s) may not significantly increase the risk. However, the threshold above which asbestos and erionite will cause MM, varies among individuals due to genetics, exposure to co-factors, the exact characteristics of the mineral fibre inhaled, etc


Article Reference: https://www.nzma.org.nz/journal-articles/erionite-in-auckland-bedrock-and-malignant-mesothelioma-an-emerging-public-and-occupational-health-hazard