Revisiting elimination half live as an indicator for bioaccumulation in fish and terrestrial mammals

Current bioaccumulation regulation is focused on bioconcentration in fish. An extension to terrestrial mammals, e.g. rat, is urgently needed but will have to use a different metric, most likely the BMF. While both metrics are thermodynamically not equivalent the regulative testing requirements for both might be reduced to the investigation of the respective elimination rate constants k₂ for fish or rat. These k₂ values could be derived from animal tests or from in vitro - in vivo extrapolation and could be combined with estimated uptake rate constants to yield either a BCF or a BMF value. The possibility to use in vitro methods for k₂ has the advantage that animal tests can be avoided and it bears the chance to experimentally cover species differences which are currently ignored in bioaccumulation regulation. Existing data for BCF and the respective k₂ values for fish - either from feeding studies or from BCF studies themselves-indicate that this approach works. For terrestrial bioaccumulation this approach still needs further experimental support.