Assessment of Biotransformation Rates, Biomagnification, and Bioconcentration Factors of Difficult-to-Test Substances Using In Vitro Rainbow Trout Liver Subcellular Fractions

In vitro hepatic biotransformation assays have been proposed as methods for expediting and improving bioaccumulation assessment for substances that are difficult to test in conventional in vivo bioaccumulation assays and to reduce animal testing. However, to date, there has been no convincing evidence to demonstrate the ability and limitations of in vitro assays to estimate in vivo biotransformation rates and corresponding bioconcentration and biomagnification factors of difficult-to-test substances in fish. The present study presents the first measurements of in vitro biotransformation rates of superhydrophobic and highly volatile linear and cyclic siloxanes in rainbow trout liver S9 subcellular fractions and the extrapolation of in vitro rates to whole body in vivo biotransformation rates, bioconcentration factors (BCFs), and biomagnification factors (BMFs). In vitro results are tested against measured in vivo biotransformation rates, BCFs, and BMFs in rainbow trout. The study shows the degree of agreement between in vitro and in vivo derived biotransformation rates, BCFs, and BMFs; points to the importance of dosing concentrations on biotransformation rates and corresponding bioaccumulation metrics; highlights the role of nonhepatic biotransformation; and contributes an in-depth analysis of the performance of in vitro hepatic biotransformation assays and in vitro to in vivo extrapolation (IVIVE) methods. The study aims to advance and expedite bioaccumulation assessment and meet the objectives of the UN Stockholm Convention on Persistent Organic Pollutants to reduce risks in indigenous communities from the biomagnification of pollutants in traditional foods.