METHOD FOR DETERMINING IN-VITRO DISSOLUTION RATES OF MAN-MADE VITREOUS FIBERS - DISCUSSION

A ''state-of-the-art'' method for determining the in-vitro dissolution rate of man-made vitreous fibres (MMVF) is described. The dissolution rate is determined using an artificial lung fluid, adjusted to pH val ues of 7.5 or of 4.5, reflecting that the dissolution in vivo takes pl ace both in the near-neutral lung fluid and in the acidic environment of the macrophages. The method is based on flow-through equipment and prescribes well-defined conditions using a ratio of the flow rate to s urface area of 0.03 mu m/s. The results obtained with this method corr elate to results from in-vivo tests, and thus the method provides a to ol for a comparative evaluation of the biodurability of different fibr e types. The described method seems suitable to be established as a pr ovisional standard test, until further investigations allow the defini tion of a final standard test. The empirically derived carcinogenicity index (KI) extrapolates the in-vitro results obtained for some fibre types at the neutral pH value to other very different fibre types. The proposed in-vitro method avoids these uncertain generalizations, as i t is based on actually measured dissolution rates at pH values 7.5 and 4.5, respectively.