PARENT SESSION
PW13 - Trophic Transfer
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P868) Intestinal absorption, toxicokinetics and biomagnification of POPs: new developments and hypotheses.
Kelly, Barry*,1, Gobas, Frank1, 1 Simon Fraser University, Burnaby, British Columbia, Canada
ABSTRACT- Gastro-intestinal uptake and elimination are crucial components affecting the extent of biomagnification of POPs in fish, wildlife and humans. A mechanistic understanding of this process is therefore important for accurate model development and to better assess the bioaccumulation and relative risk potential of various chemicals of commerce. We review the current state of knowledge and recent findings describing mechanisms and models for intestinal absorption and biomagnification of organic chemicals. Biomagnification factors (BMFs) of non-metabolizable PCBs tend to increase with trophic position in the food-chain. BMFs of PCB 153 range from 3 for fish to 50-100 for piscivorous birds, wolves, marine mammals and humans. The two competing hypotheses for describing the biomagnification phenomenon are (1) a molecular diffusion model and (2) a micelle-facilitated or lipid co-assimilation model. Both models can predict the extensive biomagnification observed in higher trophic organisms. The molecular diffusion model suggests high trophic organisms with efficient digestive systems exhibit extensive gastrointestinal magnification causing a high chemical fugacity in the gastrointestinal tract (GIT). In this model, the organism's tissues' at steady state attain a fugacity equal to the high fugacity in the GIT. The co-assimilation model suggests chemical absorption is greatly facilitated by advective transport via mixed micelles from the GIT into the organism, which increases with higher feeding rates. This second model predicts that at steady state the chemical fugacity in the organism's tissues' are elevated above the fugacity in the GIT (i.e., internal disequilibria). We postulate that micelle facilitated uptake will undoubtedly affect the time to achieve steady state (i.e., net absorption = 0), but may only influence the steady state BMF if the organism's digesta transit time is rapid, thereby forcing a chemical disequilibria between the organism and its GIT. We suggest several approaches for conducting laboratory and field studies investigating the mechanism of biomagnification under steady state conditions.
Key words: intestinal absorption, POPs, biomagnification, models