Theoretical and Physical Chemical Considerations of Chemical Fate and Bioaccumulation Models: Implications for Global Regulatory Assessment
Chemical fate models can provide insights into processes influencing environmental fate and bioaccumulation of chemicals. Currently, experimental data are generally obtained for regulatory assessment of organic chemicals; however, it is believed that concentration- or fugacity-based fate models can be very useful for making estimations prior to testing or for assisting in the interpretation of results. This thesis aims to take a modelling perspective on regulatory aspects of chemical assessment by addressing the three main criteria used internationally for regulation including Persistence, Bioaccumulation, and Toxicity (PBT) of chemicals. Regulations usually use ‘bright-line’ or ‘pass/fail’ criteria, which may not take all relevant considerations into account, especially when assessing chemicals with new or unusual physical chemical properties. Four studies are presented each of which address relevant issues observed in assessing chemical fate including i) kinetic delays seen in highly hydrophobic substances, which may obscure persistence assessments, ii) assessment of lipid-normalization for calculating bioaccumulation metrics, iii) presentation of the Chemical Exposure Toxicity Space (CETS) tool for estimating successful toxicity test conditions, and iv) application of the CETS tool to two non-fish aquatic organisms. It is demonstrated that simple uptake models can be used to successfully address these problems and the benefit of estimating results before conducting experiments is discussed. It is demonstrated that using simple chemical fate or bioaccumulation models can be very useful by providing insight into unexpected results as well as to help prevent wasted tests by predicting results beforehand.