JRC scientists have contributed to two new OECD Test Guidelines that describe how to measure in vitro fish hepatic clearance. This information is key for making more reliable predictions of bioconcentration of chemicals in fish when combined with mathematical models.
Intrinsic clearance relates to the rate at which the liver can break down a chemical which has been taken up by a fish from its surroundings.
The two new OECD Test Guidelines (319A and 319B) do not require the use of any live fish for the measurements since they are based on cryopreserved rainbow trout hepatocytes or rainbow trout liver fractions.
The project at the OECD was co-led by the European Union (represented by the JRC) and the USA (represented by Health and Environmental Sciences Institute, HESI) and ran from 2014 to 2018. It included a laboratory ring-trial involving six laboratories to assess the transferability and reproducibility of the two methods which was coordinated by HESI. The new Test Guidelines are accompanied by OECD Guidance Document 280 (PDF) that provides information on how to best perform the two in vitro methods.
Moreover, it describes how the in vitro intrinsic clearance data can be used as input to mathematical models to predict a fish bioconcentration factors (BCF), which is a measure for bioaccumulation.
Information on accumulation in aquatic organisms is important for understanding the behaviour of a chemical in the environment. This information is used for hazard classification and assessment of Persistence, Bioaccumulation and Toxicity (PBT). In general, the BCF is estimated using a variety of predictive approaches including mathematical models based on physio-chemical properties and structure-activity relationships (QSAR) or, if deemed necessary, derived from experimental data from studies on aquatic species, usually fish.
However, most of the conventional prediction models neglect metabolism and thus may overestimate bioaccumulation and trigger unnecessary animal tests.
Depending on the regulatory framework, predicted BCFs based on in vitro data may be used to:
- screen chemicals for their bioaccumulative properties;
- assess the bioaccumulation potential as part of a weight of evidence approach or read-across;
- or to decide whether a full in vivo fish study is warranted.
Predicted BCFs based on in vitro data may not fully replace in vivo fish bioaccumulation tests. However, they provide an alternative if in vivo testing is technically not feasible or if the corresponding regulatory framework does not allow vertebrate testing.
Moreover, EURL ECVAM supported this project by making available a fish in vitro biotransformation database covering intrinsic clearance data determined with in vitro methods (hepatocytes, S9, microsomes). The database is publicly available from the JRC Data Catalogue and may help users of the new OECD TG 319a and 319b to determine whether their test chemicals fall within the applicability domain of the methods.
Read more in:
- OECD (2018), Test No. 319A: Determination of in vitro intrinsic clearance using cryopreserved rainbow trout hepatocytes (RT-HEP), OECD Guidelines for the Testing of Chemicals, Section 3, OECD Publishing, Paris, doi: 10.1787/9789264303218-en
- OECD (2018), Test No. 319B: Determination of in vitro intrinsic clearance using rainbow trout liver S9 sub-cellular fraction (RT-S9), OECD Guidelines for the Testing of Chemicals, Section 3, OECD Publishing, Paris, doi: 10.1787/9789264303232-en