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PT13 Aquatic Ecotoxicology I
(PT176) Incorporation of a biotransformation process into the Damage Assessment Model (DAM).
Lee, J-H1, Landrum, P1, 1 Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, MI, USA
ABSTRACT- Damage Assessment Model (DAM) was developed to describe and predict the time course of toxicity for non-polar organic compounds based on a simple first-order kinetic model in the absence of biotransformation. In this study, DAM was modified by a toxicokinetic model with a first-order elimination and Michaelis-Menten biotransformation routes to assess and predict the toxicity of easily biotransformed compounds. It was assumed that cumulative damage from the parent compound, metabolites, and/or a biotransformation inhibitor are additive and total sum of cumulative damage is the determinant for toxic response. From the above assumptions, two types of toxicity curves (log LC50(t) or MLR50(t) vs log time), based on the exposure concentration or the body residue, can be derived in the absence (LC50(t)p and MLR50(t)p) and in the presence (LC50(t)p,I and MLR50(t)p,I) of a biotransformation inhibitor and compared with the LC50(t)p0 and MLR50(t)p0 without biotransformation. To derive the toxicity curves and estimate the toxicodynamic parameters, the inverse problem of parameter and function estimation was solved by a numerical methods or model structure simplification. For pentachlorobenzene in Hyalella azteca, MLR50(t)p and MLR50(t)p,I were smaller than MLR50p0 over a specific range of exposure times, but had the same intercept (MLR50t=1) and the MLR50 at infinite time. LC50(t)p and LC50(t)p,I were larger than LC50(t)p0, but have the same intercept. The difference between LC50(t)p and LC50(t)p,I was well explained by the differences in the toxicokinetic parameters. So the influence of the inhibitor on toxicity was negligible. Also, the MLR50(t)p and MLR50(t)p,I were similar because body residue for metabolites was negligible.
Key words: biotransformation, damage assessment model, pentachlorobenzene, Hyalella azteca
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