Accumulation of ingested asbestos fibers in rat tissues over time.

With the use of the transmission electron microscope, asbestos fibers have been assessed in kidney cortex of four groups of rats previously exposed to intermediate-range feeding grade chrysotile asbestos. Newborn rats, from mothers gavaged with asbestos during pregnancy, were gavaged twice a week at the dose level of 50 mg/kg beginning at age day 7 until their natural death or sacrifice. The rats were divided into four groups by age: 0-200, 200-400, 400-600 and 600-800 days. Of the 20 rats comprising the four test groups, 17 were positive, average fiber recovery being 5.34 X 10(3)/mg dry weight. Average fiber level in control tissues was 0.23 X 10(3)/mg dry weight. Fiber recovery in tissues from control animals was shown to be significantly lower (p less than 0.005) than that from test tissues. Test groups showed highly significant differences (p less than 0.005) from each other in the fiber levels. Dose-response relationship was not significant (0.05 less than p less than 0.1). The length distribution and the alterations in morphology of the recovered fibers are described. This study is consistent with the passage of chrysotile asbestos across the gastrointestinal wall.