The SILICOAT project

Respirable crystalline silica (RCS) in the form of quartz or cristobalite has been classified as human lung carcinogen (category 1) by the International Agency for Research on Cancer (1997), however, acknowledging differences in hazardous potential depending on source, as well as chemical, thermal and mechanical history. As quartz-containing raw materials are indispensable for manufacturing processes in traditional ceramics industry (wall tiles, tableware, sanitary ware), many workers are potentially at risk to develop respiratory diseases, e.g. lung inflammation, silicosis, or even lung tumors. The SILICOAT project thus aimed at increasing workers' safety by developing and implementing cost-effective RCS coating technologies based on stable, covalent saturation of reactive surface silanol groups. During technical development, in vitro lactate dehydrogenase (LDH) release and alkaline comet assays with primary rat alveolar macrophages (4 h of incubation; 75 <my>g/cm2; particulate negative control: Al2O3; positive control: quartz DQ12) were used for concomitant efficiency testing of promising organosilane coatings, i.e. propyltrimethoxysilane (PTMO) and SIVO160. The industrial quartz F1 served as model quartz for coating development. To judge for quartz-specificity assays were done ± aluminum lactate (quencher of quartz-specific effects). In the final in vitro assays, F1 clearly increased (~5-fold) mean LDH release and tail intensity, compared to Al2O3. Activity of F1 was markedly quenched when coated with 0.5% PTMO or 0.2% SIVO160 (w/w of quartz), leading to 99% inhibition of LDH release, and 81 and 83% inhibition of DNA damage. For the technically most feasible SIVO160-coating an intratracheal instillation study was performed with Wistar rats (2 x 0.5 mg quartz/rat; 5 rats/group; bronchoalveolar lavage [BAL] after 28 or 90 days; vehicle control: 0.9% NaCl; positive control: DQ12). After 28 days, SIVO160 almost completely quenched the F1-mediated changes in BAL parameters. After 90 days, the SIVO160-coating still clearly reduced the marked lung effects of F1 by 76% (total leukocytes), 68% (polymorphonuclear cells), 87% (lymphocytes), 56% (LDH), and 80% (ß-glucuronidase), indicating a persisting coating effect. In conclusion, covalent organosilane-coating of quartz might represent a promising strategy to increase workers' safety in the ceramics industry.