Recovery of ingested asbestos fibers from the gastrointestinal lymph in rats

Using the transmission electron microscope, asbestos fibers have been assessed in lymph fluid collected from the thoracic lymph duct in five groups of rats previously exposed to asbestos fibers (by ingestion). Ten rats were gavaged a single dose weighing approximately 20 mg. Five were given pure UICC chrysotile A while another group of five had pure UICC crocidolite. All the rats of the chrysotile group were positive animals with recovery rate values ranging from 6.9 × 10^?7 to 3 × 10^?5 (90% of the fibers being recovered during the first 16 hr following the gavage). The crocidolite group had only three positive animals and lower recovery rate values of 5.7 × 10^?8 to 5.6 × 10^?7. A third group was fed a synthetic diet containing 1%, by weight, chrysotile with a majority of short fibers (90% below 4 μm). Of the 15 rats comprising this group, 13 were positive with maximum daily recovery rates ranging from 2.1 × 10^?7 to 2.1 × 10^?6. A group of eight rats fed the same kind of diet but containing a higher proportion of long fibers, showed only four positive animals, however, they had higher daily recovery rates ranging from 1.9 × 10^?5 to 2.1 × 10^?4. No fibers were encountered in the samples of the two control rats. This study demonstrates the passage of chrysotile and crocidolite fibers across the gastrointestinal wall, with the passage rate being higher for long fibers than short ones.