The Hyalella azteca Bioconcentration Test (HYBIT) provides a non-vertebrate test for bioconcentration in aquatic environments. The test consists of two phases: the exposure (uptake) and post-exposure (depuration) phases. During the uptake phase, a group of H. azteca is exposed to the test chemical at one or more chosen concentrations. They are then transferred to a medium free of the test chemical for the depuration phase. The concentration of the test chemical in the analysed H. azteca is followed through both phases of the test. Parameters which characterise the bioaccumulation potential include the uptake rate constant (k1), the depuration rate constant (k2), the steady-state bioconcentration factor (BCFSS) and the kinetic bioconcentration factor (BCFK).