Toxicity testing in the 21st Century is shifting towards more in vitro based experiments to obtain empirical data for different decision-making contexts, e.g., ToxCast, Tox21, Safety Evaluation Ultimately Replacing Animal Testing (SEURAT). Generally speaking, in vitro toxicity and bioactivity dose-response curves are reported using (initial) nominal concentrations in the test medium, i.e., the amount of chemical added divided by the volume of medium. However, the use of nominal concentrations can be problematic for the interpretation and use of in vitro data for hazard and risk evaluations because nominal concentrations do not account for the behaviour of the chemical in the test system.
To address these concerns, the In Vitro Mass Balance Model (IV-MBM) was designed to simulate the distribution of neutral organic chemicals in the in vitro test systems based on i) the partitioning properties of the chemical and ii) the properties (e.g., volume fraction of serum albumin in the test medium) and dimensions of the in vitro test system. IV-MBM is being used by regulatory agencies (EPA, NTP) in the United States (e.g., Casey et al., Environ Health Persp 2018). Full details of the model are available in the following publication:
– Armitage, J. M.; Wania, F.; Arnot, J. A. 2014. Application of mass balance models and the chemical activity concept to facilitate the use of in vitro toxicity data for risk assessment. Environ. Sci. Technol. 48, (16), 9770-9779. DOI: 10.1021/es501955g