In vivo evaluation of chemical biopersistence of man-made mineral fibers.

Techniques developed at the Harwell Laboratory for the determination of the biopersistence of man-made mineral fibers (MMMF) in vivo are described. Results obtained with samples of glass fiber with a range of compositions, and with a sample of rockwool, are summarized. With glass fibers the rate of dissolution of fibers in vivo depends not only on their chemical composition, but also on their length. Certainly, for all fibers exceeding 10 microns in length, the longer the fiber the more rapidly it dissolves. This effect is attributed to differences in the microenvironments to which long and short fibers are exposed. Although this phenomenon appears to operate with all glass fibers, it may not apply to other types of MMMF that dissolve more readily in environments with low pH. Finally, the article examines the validity of the intratracheal method of administration for studying the biopersistence of MMMF in vivo and the use of the rat for this purpose.