PARENT SESSION

1J - Bioaccumulation
Poster Hall
8:30 AM - Wednesday, 30 April 2003
Chair: Tarazona, J.¹, ¹
Co-chair: Gobas, F.², ²

(WEP/61) Predicting biomagnification potential of chemicals accounting for their metabolism.

Mekenyan, Ovanes¹, Dimitrov, Sabcho¹, Pavlov, Todor¹, Kotov, Stefan¹, Comber, Mike², Parkerton, Tom², Phillips, Richard², ¹ Laboratory of Mathematical Chemistry, University “Prof. As. Zlatarov”, Bourgas, Bulgaria, Bulgaria² ExxonMobil Biomedical Sciences, 1545 Route 22 East, P.O. Box 971, Annandale, NJ 08801-0971, USA

ABSTRACT- Accumulation of hydrophobic chemicals in biota is not always related to their octanol/water partition coefficients. A lot of very persistent lipophilic chemicals are successfully detoxified in fish and other organisms. The rapid elimination of these xenobiotics is probably due to their metabolic transformation into more hydrophilic products. Although skin, gills, lungs and other organs may exert low metabolic activity, the liver is accepted to be the most important organ for biotransformation. This study is an attempt to evaluate the biomagnification of chemicals with account for their vulnerability to be metabolized. Applications of simulators for microbial metabolism (by employing CATABOL software) on chemicals with published biomagnification in fish showed that all ready biodegradable chemicals are not biomagnified. However, not ready degradable chemicals were found to have broad range of biomagnification. A two-step metabolism was anticipated to explain this variation. The first one is associated with nutritional process observed in organisms associated with building of proteins, lipids and carbohydrates. The second metabolic step is typical for higher organisms that are trying to excrete chemicals, which cannot be used for nutrition by applying the liver metabolism. The later simulates the non-synthetic (phase I) biotransformations that undergo xenobiotics during their "first pass" in the liver. The phase I includes oxidative, hydrolytic, redox and reductive reactions. These transformations are followed by synthetic enzymatic reactions (phase II), such as glucuronidation and sulfate binding, which transformed metabolites into easily excretal product from the organism. The interplay between nutritional and liver metabolic machineries mimicked by a battery of metabolic simulators was found to be decisive for the ultimate fate of chemicals in organisms.

Key words: bioaccumulation, biomagnification, nutritional metabolism, liver metabolism