Development of a bioaccumulation test using Hyalella azteca

A test concept for bioconcentration tests with the freshwater amphipod Hyalella azteca (HYBIT) was recently described. It was shown that the Hyalella bioconcentration factors (BCFs) derived for compounds with different hydrophobic characteristics (log Kow 2.4 – 7.8) show a strong correlation to those from fish tests. This project was carried out to elucidate the suitability of the HYBIT test for testing an extended range of substance classes including difficult to test compounds and, if required, to further enhance the test concept. The bioaccumulation potential of highly lipophilic UV stabilisers and ionic organic ⁠PFAS⁠ as well as silver, titanium dioxide and gold nanomaterials were tested. The two possible set-ups to conduct bioconcentration studies with H. azteca using a semi-static test set-up or a flow-through approach were applied. The solvent-facilitated and solvent-free application of the hydrophobic test compounds were compared. Due to the difficulties regarding the aqueous exposure of nanomaterials, biomagnification studies were also carried out as part of this project. We could show that the HYBIT approach permits the application of difficult to test compounds and enables to derive bioaccumulation endpoints for regulatory assessment. Due to the shorter exposure periods required, and the smaller experimental units used, the HYBIT approach provides several advantages in comparison to the flow-through fish test. As a non-vertebrate test, the Hyalella bioconcentration (or biomagnification) test may help to further reduce the amount of fish required for the regulatory testing of chemicals.