Commentary: Asbestos Penetration of the Gastrointestinal Tract

Abstract

My comments are restricted to studies involving gastrointestinal exposure of humans and animals to asbestos via the diet or intubation. There have been three studies designed to determine whether human ingestion of asbestos in drinking water could result in the detection of asbestos in urine or postmortem tissues (1-3). One study concluded that ingested asbestos could not be found in human urine (1). However, other studies found evidence that ingested asbestos could penetrate the GI tract, migrate, and be recovered in urine and tissues (2,3). These two positive human studies were uncontrolled to the extent that inhaled asbestos may have contributed to the positive findings. Hence, we look to controlled animal studies for confirmation of the human findings, especially with regard to dose. There have been at least 12 animal studies involving rats and baboons (4-15). Five rat studies (4-8) and two baboon studies (8-10) presented evidence of asbestos penetration of the GI tract and/or migration to various tissues. Three rat studies (11-13) and two baboon studies (14, 15) found little or no evidence of penetration and migration. The positive animal findings (4-10) are not completely convincing for various reasons: (a) the number of fibers observed on a grid opening basis was quite small (8, 10); (b) the qualitative presentation of data prevented numerical comparisons of test and control fiber count data (4,6); (c) too few control data were obtained (7); and (d) fiber count data were reported in terms of fibers per milligram or milliliter (5). Unless fiber count data are given in terms of fibers per grid opening, it is not possible to know whether the authors' conclusions are based on the observation of one or hun-