Research and analysis

Lipid normalisation in the OECD 305 dietary test - summary

Published 11 April 2023

Applies to England

1. Chief Scientist’s Group report summary

This project explored the currently accepted calculations in the main test method used to understand how chemicals accumulate in fish. We reviewed the available evidence to understand how the lipid (fat) content of fish and their food used during the test affects the results. The findings provide guidance to help the Environment Agency interpret these tests when we assess the hazards of a substance.

1.1 Background

Bioaccumulation refers to the movement of a substance into an organism from its environment. Determination of bioaccumulation potential is an important part of hazard assessment under chemical legislation such as UK REACH.

The main laboratory method to investigate how substances accumulate in organisms is the Organisation for Economic Co-operation and Development’s Test Guideline 305: Bioaccumulation in Fish – Aqueous and Dietary Exposure (OECD TG 305). One of the options described within OECD TG 305 involves dietary exposure. The substance being investigated is added to the food that the fish eat and the concentration of that substance in the fish is measured over time. The results are used to calculate the biomagnification factor (BMF), which is the concentration of the substance in the fish relative to the concentration in the food. The BMF can be compared with regulatory thresholds to decide if a substance should be designated as bioaccumulative.

Explanatory guidance for OECD TG 305 was produced in 2017 (Guidance Document on Aspects of OECD TG 305 on Fish Bioaccumulation, Series on Testing & Assessment No. 264). It states that the calculation of a BMF value should include adjustments based on the lipid contents of the fish and the food (called lipid normalisation). However, research published in 2018 by the Chemicals Evaluation and Research Institute (CERI) in Japan indicated that the calculation of a BMF value should be adjusted based on the lipid content of the fish only (called lipid standardisation).

1.2 Approach

We reviewed the research by CERI and considered the results in relation to other published evidence.

1.3 Results

The latest evidence suggests that the lipid content of the food used to expose fish to a substance will affect the BMF value when it is calculated according to the current ‘lipid normalisation’ method. That is, a higher BMF value is calculated when the food used in the test has a higher lipid content. This can be explained by differences in the lipid content of the food which affects:

• where a substance will be found in that food, and
• how that food is absorbed during digestion.

The effect of the food lipid content on the calculated BMF value is reduced using the ‘lipid standardisation’ calculation. This means the calculated BMF values from different tests can be compared with more confidence. Nevertheless, the BMF value that is calculated according to the current ‘lipid normalisation’ calculation is still valuable to report, because it shows the true potential for biomagnification of a substance that is mainly found in lipids.

The main conclusion is that both values are important and should be reported.

1.4 Publishing details

This summary relates to information from the following output:

Title: Lipid normalisation in the OECD 305 dietary test

April 2023

Project manager: Steph Jones, Chemicals Assessment Unit, Chief Scientist’s Group

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: [email protected].

© Environment Agency