Solvent Controls

As a member of the International Council on Animal Protection in OECD Programs (ICAPO), the Science Consortium is co-leading an Organisation for Economic Co-operation and Development (OECD) project to reduce the number of fish used in aquatic toxicity tests (project no 2.55 on the OECD Work Plan for the Test Guidelines Programme).

In aquatic toxicity tests, the test chemical is usually added to the tank water. To overcome practical issues associated with testing poorly water-soluble chemicals, a small volume of solvent is sometimes also added. As the solvent can influence the outcome of the study, two controls – one in the presence of and one in the absence of solvent – are currently required, doubling the number of fish used in controls.

When a solvent is used, the scientific justification for using both a water and a solvent control is questionable. If only one control is included when solvents are used, the total number of fish used in OECD test guidelines (TG) can be reduced by 17% to 29%.

The project comprises two parts:

Part 1: Update of OECD Guidance Document 23

The first part of this project aimed to reduce the occasions in which solvents are required for testing and was accomplished in the 2018 revision of OECD Guidance Document (GD) 23 on Aqueous-Phase Aquatic Toxicity Testing of Difficult Test Chemicals. As part of the revision, particular attention was paid to updating methods available for testing poorly water-soluble test chemicals while avoiding the use of solvents. Thus, the need for a second control group is eliminated. The updated GD 23 will help reduce the number of fish used in aquatic toxicity studies on difficult-to-test chemicals. This part of the project was co-led by the Science Consortium (representing ICAPO), the US, and the European Commission Joint Research Centre.

A poster on the update was presented at the SETAC Europe meeting in 2019.

Part 2: Eliminating One of the Controls When Solvents Are Used in Aquatic Toxicity Tests

In collaboration with regulators and experts from industry and academia, this part of the project is co-led by the Science Consortium (representing ICAPO) and the US (and was previously co-led by the European Commission Joint Research Centre). The aim is to use statistical analyses of existing data and statistical simulations to investigate whether it is possible to conduct aquatic toxicity studies using only one control when a solvent is used.

This approach has already been examined for the acute fish toxicity test (OECD TG 203). Currently, statistical analyses and simulations of fish early-life stage test (FELS, OECD TG 210 and US EPA OPPTS 850.1400) data are being conducted to investigate the effects of the choice of control (water only, solvent only, or both combined) on the treatment effect values.

If you can contribute data, please contact Dr Gilly Stoddart at [email protected] for more information and a data template. We are particularly interested in receiving the following data:

  • FELS test full study data using the following:
    • fathead minnow and dimethylformamide (DMF) as the solvent
    • rainbow trout and acetone
    • sheepshead minnow and any solvent
    • any fish species and triethylene glycol (i.e. concentration-response data and respective water-only control and solvent control data)
  • FELS test control data in which the solvent was DMF, acetone, or triethylene glycol (i.e. solvent and water-only control data)
  • FELS test data using other species or solvents

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