Validation of the Hyalella azteca Bioconcentration Test (HYBIT)
Résumé
Bioconcentration factors (BCF) for regulatory purposes are conventionally determined experimentally by aqueous exposure bioconcentration fish tests according to OECD test guideline (TG) 305. Fish bioconcentration studies are time consuming, expensive, and use vertebrate organisms in the range of 100-200 organisms per study. The availability of alternative methods may help to reduce the use of fish for BCF testing. The Hyalella azteca Bioconcentration Test (HYBIT) provides a non-vertebrate alternative for fish bioconcentration studies. The suitability of H. azteca as an alternative test organism for bioconcentration studies was recently investigated. Eighteen substances of different hydrophobicity (log KOW 0.7 - 7.8) were tested under flow-through or semi-static conditions to determine steady-state and kinetic bioconcentration factors (BCFSS and BCFK). It has been shown that the BCFs obtained from bioconcentration studies with the freshwater amphipod H. azteca correlate significantly (r²=0.69) with fish BCF values described in the literature. Thus, H. azteca BCF values can be assessed in accordance with the standard B criteria, e.g. BCF > 2000 (REACH), and thereby enable the prediction of B or non-B classification in the standard fish test. Generally, technical (smaller-scale test systems) and economic reasons (less time-consuming, more cost-efficient) favour the use of H. azteca over fish in bioconcentration studies. In addition, significantly smaller amounts of test substance are required compared to the flow-through test with fish. A protocol for carrying out bioconcentration tests with the aquatic invertebrate species H. azteca under standardized conditions has been developed as part of the project CEFIC-LRI ECO40. This protocol includes both, the flow-through and semi-static test design. Validation was needed to confirm the transferability of the test protocols and to prove the reproducibility of the results obtained in order to support the development of a new OECD TG. For this purpose, a multi-laboratory ring trial involving the HYBIT was carried out in 2020. The ring test has confirmed the high potential of the Hyalella azteca Bioconcentration Test (HYBIT) to be used as a non-vertebrate alternative for bioconcentration studies. The transferability of the test protocols (semi-static and flow-through approach) as well as the reproducibility of the results obtained was proven supporting the development of a new OECD TG.