Alain De Meringo

IN VITRO MEASUREMENT OF FIBER DISSOLUTION RATE RELEVANT TO BIOPERSISTENCE AT NEUTRAL pH: AN INTERLABORATORY ROUND ROBIN

Measurements are presented of the dissolution rates in neutral pH simulated lung (SLF) of several man-made vitreous fibers (MMVF) and crocidolite asbestos that were recently in chronic rodent inhalation studies. The measured dissolution rate depended strongly on the fiber composition. The MMVF tested dissolved from 30 times to nearly 1000 times faster than the crocidolite asbestos. Measurements were made in flow-through equipment in four different laboratories in North America and Europe. The standard deviations of the measured values for each fiber were typically between 30 and 50% of average value. It is believed that in order to be relevant to the dissolution of long fibers the extracellular fluid of the lung, the in vitro measurement must be performed at a rate high enough that corrosion products do not accumulate in sufficient concentration affect the dissolution rate.

A new in vitro cellular system for the analysis of mineral fiber biopersistence.

The toxicity of mineral fibers, whether they are natural or man made (MMMF), is usually evaluated in vivo using biopersistence tests in rodents. Development of an in vitro cellular model would be worthwhile in order to reduce, refine and finally replace animal models. For this purpose, we developed an in vitro assay using human monocytic cell line (U-937) to evaluate a new manufactured rock wool fiber (HDN) biodegradation. Experiments on earlier known mineral fibers asbestos (crocidolite) and glass wool fibers (CM44) were also performed. U-937 responded to HDN and CM44 only if they were activated. Among the different activators we used, Escherichia coli living cells as well as FS were the most efficient as evidenced by alterations of HDN and CM44 surface, detected by scanning electron microscopy, and by the measure of silicon released from the rock wool fibers. Asbestos fibers were not degraded when incubated in the presence of living bacteria. The MMMF modifications were function of the fiber composition, the time of exposure to activated cells and the concentration of activators. The pattern of MMMF degradation by our in vitro system was in accordance with those observed in an in vivo study, thus indicating that the fiber degradation by macrophage cells activated by E. coli living cells as well as FS is a valuable system to assess mineral fibers’ biopersistence.