Testing the ability of in-vitro depletion rates to assess the biotransformation rate and bioconcentration factor of hydrophobic chemicals in rainbow trout (Oncorhynchus mykiss)

The objective of this study was to test the ability of in-vitro biotransformation rates to predict in-vivo biotransformation rates and BCFs to ultimately improve chemical bioaccumulation assessment. In-vitro biotransformation rates of hydrophobic chemicals pyrene, methoxychlor, cyclohexyl salicylate, and 2,6 dimethyldecane were determined using a rainbow trout liver S9 preparation and then input into two in-vitro-in-vivo extrapolation (IVIVE) models to estimate in-vivo biotransformation rates (kMET) and modelled BCFs. Comparisons of in-vitro derived kMET values using both IVIVE models were in reasonable agreement when compared to in-vivo derived kMET values for pyrene and methoxychlor. Estimated BCFs from this study for pyrene, methoxychlor, and cyclohexyl salicylate were also in good agreement with estimated BCFs from previous studies using in-vitro biotransformation rates as inputs to IVIVE models, but were significantly higher compared to empirical BCFs. This indicates the potential usefulness of in-vitro biotransformation assays and IVIVE models for estimating kMET and BCFs, however kMET values from IVIVE models and BCF estimates should only be considered a conservative estimate at this time due to the uncertainty (i.e. extrahepatic metabolism) associated with these models and the further work required to fine-tune these models.