In Vitro Exposure Assessment Improves Hazard Ranking of Bisphenol A Alternatives

Abstract

In vitro toxicity data can be used for comparative hazard assessment of the problematic plastic chemical bisphenol A (BPA) and its replacement chemicals. Hazard assessment is exclusively based on nominal effect concentrations of the BPA alternatives, but due to their diversity of physicochemical properties and stability, this may lead to inaccurate hazard ranking. In the present study, chemical stability as well as freely dissolved concentrations (Cfree) were determined for BPA and 24 of its alternatives. BPA and 22 alternatives were found to be stable in bioassay medium for up to 48 h. The diglycidyl ether of BPA (BADGE) was completely degraded in medium. For BPPH, a loss of up to 37% was observed. A mass balance model was used to derive Cfree of the stable chemicals in the bioassay medium. For model validation, Cfree in bioassay medium, as well as binding to proteins and membrane lipids, was measured for BPA and 15 of the alternatives. Experimentally determined Cfree agreed with model predictions within a factor of 10. Relative effect potencies (REPs) of the BPA alternatives compared to BPA were calculated based on nominal (REPnom) and freely dissolved effect concentrations (REPfree) for two representative end points (activation of estrogen receptor α and inhibition of mitochondrial membrane potential). For hydrophilic and moderately hydrophobic BPA alternatives, REPnom and REPfree agreed well. REPfree was up to 147× higher compared to REPnom for hydrophobic and highly protein-bound alternatives like TCBPA or BPAF. BP-MIBK had the highest estrogenic potential based on REPnom, but the highly protein-bound BPAF was identified as most potent based on REPfree. TCBPA has a lower estrogenic potential than BPA based on REPnom (0.11), but based on REPfree (12.8), it is more potent than BPA. The results of the present study highlight the need to correct for different in vitro exposure conditions to allow accurate hazard ranking.