1.13. Are there still unresolved scientific questions regarding (respirable) crystalline silica and its health effects?
Yes, there are a few.
In his summary hazard assessment, Dr Morfeld points out that the mechanistic causal role of silicosis in the development of lung cancer remains to be clarified.
IARC stated that not all quartzes are carcinogenic, so the main unresolved scientific questions relate to the identification of the factors that affect the variation in the quartz hazard. Which particles’ size? Which quartz species? In which matrices?
A second important question relates to the secondary mechanism of the carcinogenicity, as the weight of evidence suggests that the relative risk of lung cancer is only increased in persons with silicosis.
Are silicosis and cancer mechanistically related? The role of confounders such as smoking habits in the studies’ findings should also be analysed and clarified.
In August 2004, EUROSIL invited a group of 50 experts to an international workshop on Epidemiological Perspectives on Silica and Health organised in New York, proceedings available here. The Workshop gathered together epidemiologists involved in the key epidemiological studies conducted on workers exposed to crystalline silica together with experts in the field of crystalline silica toxicology and exposure determination. The objectives were to review epidemiological research to date, particularly aspects of exposure and health outcome assessment, confounding factors and statistical methodology, and to identify knowledge gaps. According to the group of experts, two main questions remain to be answered regarding crystalline silica toxicity: “Under which industrial conditions, if any, is crystalline silica a human carcinogen”? and: “What is the dose-response relationship between silica and lung cancer/silicosis (thresholds)”?
Further research in this respect is required and is being called for by the industry.
Currently an epidemiological study of fine silica dust exposure, particularly in the low exposure range, is being carried out on the basis of a cohort of approximately 20,000 employees in the porcelain industry in Germany. See posters on the study at the following link.
The many unanswered questions call for further endeavours to rapidly achieve an adequate scientific basis for a reply. This is why industry has supported many research projects and has recently launched an updated heath hazard assessment of crystalline silica and respirable crystalline silica, with a detailed analysis of the literature from the last ten years, since the IARC Monograph, by a team of experts in quartz toxicology and epidemiology.