The quartz hazard revisited: the role of matrix and surface

In this paper we discuss evidence regarding the basis of changes in the qua rtz surface that relate to changes in the ability to cause key biological r esponses such as inflammation and genotoxicity. Different samples of quartz , coal and coal fly ashes were subjected to various acellular and biologica l assays. In vivo endpoints included instillation of samples and measuremen t of PMN numbers in bronchoalveolar lavage (BAL) and incidence of lung tumo urs in rats. In vitro assays included cytotoxicity to epithelial cells, rel ease of pro-inflammatory mediators from various cells and radical (generati ng) activity of the particle surface as measured by electron spin resonance (EPR). We demonstrate that amelioration of the quartz surface activity can occur in workplace samples of quartz, such that they have very little infl ammogenic activity, despite their ability to generate OH-radicals from thei r surface. These effects, also shown in coal mine dusts and coal fly-ashes, are due to minerals and organic compounds which can both decrease or enhan ce biological activity and thus may contribute to toxicity in a complex way that is not easily predicted. A broad programme of further research is nee ded before we have a sound understanding of the mechanisms of quartz toxici ty and can achieve differential standard setting for mixed-dusts containing quartz.