Method for identification of low soluble, biopersistent dusts (GBS) at workplaces

Fine fractions of dusts occurring in occupational settings are of high relevance for the safety at workplaces and therefore are strictly regulated by authorities. Appropriate threshold values should guarantee that lung diseases are not induced in workers exposed up to long periods. Respirable biopersistent granular dusts (GBS) are defined as respirable fine dusts with a negligible solubility in physiological lung fluid that do not exhibit a specific chemistry-related toxicity at volumetric non-overload conditions. In 2012, the MAK Commission derived a new threshold value of 0.3 mg/m3 for GBS, recognizing that in concentrations exceeding the physiological lung clearance capacity GBS can cause chronic inflammation and increase the lung cancer risk in animal experiments. - The objectives were to investigate, whether a general value for the term 'low soluble' can be derived (e.g. a solubility in lung fluid of approx. 1 mg/l). In addition, measuring the inflammatory response in lung lavage fluid, it was investigated whether nanoscaled dusts could possibly fulfill the criteria to be included in the GBS class. - Six micro- and nanoscaled dusts (some of them of commercial relevance) were compared analysing the solubility in the lung fluid (day 3, 28 and 90) and the lung toxicity after intratracheal instillation in rats (day 3 and 28): TiO2 (rutile, micro), TiO2 (anatase, nano), Eu2O3 (micro-nano mixed), BaSO4 (micro), ZrO2 (micro) and amorphous SiO2 (nano). Two doses of 0.5 and 1.5 <mü>l per rat were administered to Wistar rats; these volume doses resulted in a non-overload and moderate overload of lungs, resp. - The differential cell count showed only slight inflammatory cell levels after treatment with TiO2 (rutile) and BaSO4 (PMN < 5% after 3 days in the low dose group; < 15% in the high dose group). In contrast, the TiO2 (anatase) showed a stronger response (PMN > 30% after 3 days). The rare earth Eu2O3 (micro-nano) dust showed the strongest effect (approx. 40% PMN) including a red-coloured lung lavage fluid (BAL after 28 days and solubility analysis are still underway). - New dusts to be included in the GBS group have to fulfill the criteria of low solubility and a non-significant inflammatory response at doses below the overload range. For the most nanoscaled dusts an individual toxicological characterization seems to be adequate. The project was funded by the Federal Institute for Occupational Safety and Health (BAuA), Dortmund - F 2336.