M11 PM Internal Exposure
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 343-344

(MAT-1117-641017) A Time-Variable Model of PAH Bioaccumulation and Metabolism.

Mathew, R¹, McGrath, J¹, Di Toro, D^{1, 2}, ¹ HydroQual, Inc² University of Delaware

ABSTRACT- Recent NOAA laboratory investigations into the bioaccumulation and toxicity of PAHs have focused on low-level time-variable exposures of crude oil to early life stage fish. Fish embryos were exposed to total PAH concentrations ranging from 1 to 85 ppb at the beginning of the experiments. Exposures ranged from 2 weeks to 6 months. Total PAHs were measured in the water and in the organism over time. Typically, less than 5% of the initial aqueous concentration of total PAHs remained at the end of the exposure. The time-variable water and body burden data were fit using a first-order uptake and depuration model. Lipid-water partition coefficients (K_LW) were then computed by dividing the uptake rate by the loss rate. The resulting K_LW were not linearly correlated with the octanol-water partition coefficient (K_OW), in contrast to numerous studies that have shown K_LW to be correlated with K_OW. These results suggest that PAHs are metabolized. A time-variable model of the bioaccumulation and metabolism of PAHs is developed. The model incorporates first-order kinetics for uptake from the water column, depuration from the tissue estimated from the K_OW of the PAH, and a metabolism rate for the biotransformation of tissue PAH. The fact that PAHs are metabolized in early life stage fish is very important when applying constant body burden models, such as the narcosis target lipid model (NTLM), to estimate the critical body burdens because the parent compound residual body burdens are much lower than would be predicted. The NTLM assumes that the metabolites are toxic as well and contribute to the total body burden. This fact is overlooked in a recent application of the NTLM where the authors incorrectly concluded that the NTLM could not predict the critical body burden. Data from experiments using radio-labeled parent PAHs demonstrate that metabolites contribute to the body burden

Key words: PAH, bioaccumulation, time-variable, metabolism