Bioavailability of Soil-Bound TCDD: Oral Bioavailability in the Rat

Bioavailability of Soil-Bound TCDD: Oral Bioavailability inthe Rat. SHU, H., PAUSTENBACH, D., MURRAY, F. J., MARPLE, L.,BRUNCK, B., DEI ROSSI, D., TEITELBAUM, P. (1988). Fundam ApplToxicol. 10, 648–654. The implications to the public healthof trace amounts of 2,3,7,8-TCDD in the environment are underevaluation by regulatory agencies in the United States and WesternEurope. One major consideration in such evaluations is the contributionto human exposure via ingestion of TCDD-contaminated soil. An80% figure is under consideration by some regulators for estimatedhuman exposure. A contractor for one agency has, in fact, useda value of 1007% bioavailability for estimating human bioavailability.Several studies have investigated the oral bioavailability ofTCDD from contaminated soil in animals. Most have reported estimatesof 25–50%, although one has reported <0.5 and 85%,depending on the source of the contaminated soil. This paperreports an oral bioavailability of approximately 43% in therat dosed with three environmentally contaminated soil samplesfrom Times Beach, Missouri. This figure did not change significantlyover a 500-fold dose range of 2 to 1450 ng TCDD/kg of body weightfor soil contaminated with approximately 2, 30, or 600 ppb ofTCDD. The relevance of animal oral bioavailability data forthe human remains to be evaluated. However, since regulatoryagencies use animal data for extrapolating to humans, the 43%or 25–50% figure would be more accurate than the 80 or100% estimates.