CONTRIBUTION TO COMPARABILITY OF IN-VITRO AND IN-VIVO MAN-MADE MINERAL FIBER (MMMF) DURABILITY EXPERIMENTS

Toxicologists discuss three major conditions which must be met in orde r to prevent adverse health effects of dust with regard to three neces sary fibre properties: the fibre has to be thin, long, and durable. Fi rst definitions concerning the geometric properties thin and long were made already in 1972; however, the criterion durability has not yet b een defined. The durability of man-made siliceous fibres has been test ed with experimental animals (in-vivo) as well as with purely chemical methods (in-vitro). A reaction of first order was deduced from in-viv o experiments. On the other hand, in-vitro experiments in different se tups proved all to follow zeroth-order kinetics. From that, it was pos tulated sometimes that in-vitro experiments are unsuited to determine the persistence of man-made siliceous fibres. The present study will s how that correct mathematical treatment of in-vivo data leads to the s ame results as obtained from in-vitro experiments. The lg-normal distr ibution in fine fibrous dust is responsible for the seemingly first-or der pattern for mass and fibre number. If the time intervals are chose n to be rather long - as in published in-vivo studies - it is impossib le to demonstrate the deviation from the dissolution process at the be ginning and at the end. This means the solution of the apparent discre pancy between in-vivo and in-vitro experiments. The mathematical model allows to estimate the lifetime of inhaled fibrous particles from kno wn dissolution velocity and fibre size distribution for the worst case , since the chemical process of dissolution of siliceous fibres is sup erimposed by accelerating effects as fragmentation or clearance. The v alidity of the model is shown by comparison with data from an inhalati on study [1 to 3]. Also, the model allows the calculation of the accum ulated fibre number from dose and duration of exposure.