Tweet
ShareOne of the most frequently used aquatic toxicity tests is the acute fish toxicity test – Organisation for Economic Co-operation and Development (OECD) Test Guideline (TG) 203 – which uses lethality as an endpoint. Replacement, reduction, and refinement approaches are available that can instead be used to protect environmental health. The available replacement methods are described below.
Rainbow Trout Gill Cell Line Cytotoxicity Assay
An in vitro assay for cytotoxicity using the rainbow trout gill cell line, RTgill-W1 (OECD TG 249), was adopted by the OECD in 2021 and has the potential to play an essential role in replacing the acute fish toxicity test. The assay predicts fish acute toxicity for a broad range of substances in many areas, including product development, screening, and as an element of testing strategies. In contrast to the acute fish toxicity test, this method provides mechanistic information by quantifying cell viability using fluorescent measurements for metabolic activity and integrity of cell and lysosomal membranes. Moreover, with a shorter exposure time compared to the acute fish toxicity test, the cell line assay allows for higher throughput.
The Science Consortium is collaborating with the Swiss Federal Institute of Aquatic Research and Technology (Eawag) to develop the Fish Cell Acute Toxicity (FACT) database, a comprehensive collection of fish cell viability data related to chemicals aligning with OECD TG 249. The aim of the database is to strengthen confidence in the assay.
In Silico Models
Quantitative Structure–Activity Relationship (QSAR) models help predict toxicity based on analogue substances and chemical categories. Available QSAR models for acute fish toxicity include literature models (see here and here), free data repositories for pre-calculated QSAR predictions (e.g. the Danish (Q)SAR database and an element of the OECD QSAR Toolbox), free computerised models (e.g. US Environmental Protection Agency (EPA) ECOSAR), commercial computerised models (e.g. KREATiS iSafeRat and MultiCASE EcoTox Models). QSAR models can be used in a weight-of-evidence approach to predict the potential environmental effects of chemicals.
Integrated Approaches to Testing and Assessment for Acute Fish Toxicity
As a member of the International Council on Animal Protection in OECD Programmes (ICAPO), the Science Consortium is co-leading an OECD project together with Austria (project no 2.54 on the OECD Work Plan for the Test Guidelines Programme), to replace, reduce, and refine the use of adult fish in acute fish toxicity testing by developing an integrated approach to testing and assessment (IATA) for acute fish toxicity. The IATA under development includes a broad range of information, such as the physicochemical properties of the test chemical and data generated using QSARs, in vitro methods such as the RTgill-W1 cytotoxicity test, and/or the fish embryo acute toxicity test. The IATA aims to estimate whether algae, aquatic invertebrates, or fish are the most sensitive species as surrogates for all aquatic organisms, according to the EU Regulation 1272/2008 on classification, labelling and packaging. The IATA is supported by the finding that the acute fish toxicity data requirement can be addressed by alternative bioassays, including fish cell line testing, and available daphnid acute toxicity data. It has also been demonstrated that the application of environmental extrapolation models combined with data from alternative methods, including mechanistic indicators of toxicity, may provide at least the same level of environmental protection as the acute fish toxicity test. A presentation on the development of the IATA was given at the EUSAAT Congress in 2024, at the World Congress in 2023, and a poster on a draft IATA was presented at the SETAC Europe meeting in 2019.
Another activity in the area of reducing fish testing is a retrospective analysis of acute fish toxicity tests, which has been conducted by the US EPA Office of Pesticide Programs to investigate the relative sensitivity among species to help determine whether there is a basis for reducing the number of species used in acute fish toxicity testing. A recording of a presentation about this subject is available in the Science Consortium and EPA webinar series on the use of new approach methodologies (NAMs) in risk assessment.
Click here to return to the main Aquatic Toxicity page.