A reductionist mechanistic model for bioconcentration of neutral and weakly polar organic compounds in fish
The bioconcentration factor (BCF) of neutral and weakly polar organic chemicals in fish is modeled using independently calibrated models of chemical partitioning (φsys, KFW), respiratory exchange (k1, k2 = k1/KFW), and biotransformation (kM) as BCF = φsysKFW/(1 + kM/k2). Existing k1 models tend to overestimate for chemicals with logKOW < 3.5, which constituted 30–50% of the examined chemicals. A revised k1 model covering a wider logKOW range (0–8.5) is presented k1 = (5.46 × 10−6MW + 0.261/KOW)−1, where MW is the molecular weight. The biotransformation rate constant kM is modeled using biota internal partitioning and Abraham parameters as reactivity descriptors. The reductionist model was tested using 3 different BCF data sets (EPI, n = 548; Hertfordshire, n = 210; Arnot‐Gobas, n = 1855) and compared to 3 state‐of‐the‐art models: (i) the EPI Suite BCFBAF module, (ii) CAESAR, and (iii) the EPI/Arnot mechanistic kinetic model. The reductionist model performed comparably with the alternative models (RMSEs = 0.72–0.77) with only 5 fitting parameters and no training against experimental BCFs. Respiratory elimination and biotransformation dominate the total depuration (i.e., (k2 + kM)/kT ≥ 0.8) for approximately 98% of the data entries, thus validating the reductionist approximation. Mechanistic models exhibit greater insights and sensitivity to biological variation. The present study shows that a streamlined mechanistic model of BCF is possible for assessment purposes. Environ Toxicol Chem © 2013 SETAC
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