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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 Persistence, Bioaccumulation and Toxicity (PBT) assessment.

Bioconcentration describes the accumulation of a water-borne chemical by an aquatic organism, whereas bioaccumulation covers the uptake from all environmental sources, e.g. water, food and sediment.

The bioconcentration potential of a chemical, expressed as the 'BCF', is either predicted or measured. The BCF describes the ratio of the concentration of a chemical in the whole organism to its concentration in the water, under equilibrium conditions.

Fish is the preferred species for bioconcentration/bioaccumulation testing and derivation of a BCF, although data from tests using invertebrates or reliable BCF prediction models can be used.

Experimental determination of bioconcentration/bioaccumulation may not be necessary if it can be demonstrated that a chemical has a low potential to bioaccumulate, by using physicochemical properties (e.g. log KOW < 3) or other evidence.

Since bioaccumulation is the result of absorption, distribution, metabolism and excretion (ADME) processes, information on ADME processes derived with in vitro methods is used to improve the prediction of BCF models, in particular information on metabolism.

The EURL ECVAM Strategy to replace, reduce and refine the use of fish in aquatic toxicity and bioaccumulation testing (published in 2014) provides an overview of ongoing projects.

Regulatory framework

[collapsed]Bioconcentration/Bioaccumulation testing is stipulated for environmental hazard and risk assessment by the regulatory framework on:

EU/OECD test guidelines
Bioaccumulation in Fish: Aqueous and Dietary Exposure: OECD test guideline 305/ EU test method C.13

OECD guideline development

Development of test guidelines measuring in vitro fish intrinsic clearance rates.

This OECD project (under the lead of USA and the European Commission represented by JRC (EURL ECVAM) aims at standardising two in vitro methods using rainbow trout S9 fraction (Johanning et al., 2012) or cryopreserved rainbow trout hepatocytes (Fay et al., 2015) to determine in vitro fish intrinsic hepatic clearance rates.

The project builds on work carried out within the framework of the ILSI HESI project "Bioaccumulation" (see below). ILSI HESI coordinated a multi-laboratory ring trial to assess the reliability, transferability, and predictive value of the two in vitro methods (2014-2016). Based on the results of the ring trial, two OECD TGs and a guidance document are in preparation and consultation with WNT experts started in April in 2017. Draft documents are available here.

The fish intrinsic hepatic clearance rate derived with the two in vitro methods can be extrapolated to a whole-body metabolism rate constant. Inclusion of measured biotransformation rates enhances the reliability of models to predict the BCF (Nichols et al., 2013; Laue et al., 2014).
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Alternative test methods under validation by EURL ECVAM

[collapsed]Currently there are no test methods under validation.

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Development and optimisation of alternative methods

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Contribution to the ILSI HESI Scientific Committee on Bioaccumulation

The ILSI HESI Scientific Committee on Bioaccumulation (of which EURL ECVAM is a member) has launched several projects on development and standardisation of in vitro methods to be used in bioaccumulation testing (e.g. fish cells and their suitability to determine metabolism and uptake) and improvement of bioaccumulation/bioconcentration.

Several studies* resulted in the optimisation of two in vitro methods using either rainbow trout liver S9 fraction (Johanning et al., 2012) or cryopreserved rainbow trout hepatocytes (Fay et al., 2015). See also above "Development of test guidelines measuring in vitro fish intrinsic clearance rates".

* EURL ECVAM contribution via contract CCR.IHCP.C434207.X0 to standardisation of S9 assay.[/collapse]