Understanding bioaccumulation for regulatory compliance

As regulatory frameworks evolve, understanding how chemicals bioaccumulate, in which organisms, and through which pathways, is becoming increasingly critical for ensuring regulatory compliance and maintaining market access.

Bioaccumulation describes how chemical substances accumulate in organisms during environmental exposure, often resulting in higher concentrations than found in the surrounding environment. Assessing this process is essential to understanding chemical behaviour in ecosystems and evaluating potential environmental and human health risks. Importantly, this challenge is magnified for complex substances, such as Unknown or Variable composition, Complex reaction products, or Biological materials (UVCBs), where diverse components may behave differently in terms of bioaccumulation.

Scientists and regulators rely on a suite of key quantitative metrics such as the bioaccumulation factors (BAF), bioconcentration factors (BCF), biomagnification factors (BMF), and trophic magnification factors (TMF) to assess a substance’s bioaccumulation potential and risk. The extent of bioaccumulation depends on several factors:

• Physicochemical properties – such as hydrophobicity, molecular weight and solubility
• Environmental conditions - such as temperature, pH and organic matter content
• Biological traits of the organism – such as lipid content, metabolic capacity and feeding behaviour

A key consideration is bioavailability, which refers to the fraction of a substance that is available for uptake. Bioavailability is influenced by a substance’s solubility, partitioning behaviour and interactions with organic matter or lipids.

Regulatory context and assessment criteria

Understanding whether a chemical meets the bioaccumulation criterion is essential for environmental and human health risk assessment, and critical in the context of the EU REACH regulation, where bioaccumulation data are required for both new and existing substances (manufactured or imported). This understanding then informs:

• whether a substance meets the “B” (bioaccumulative) or “vB” (very bioaccumulative) criteria under PBT/vPvB (Persistent, Bioaccumulative, Toxic/ very Persistent, very Bioaccumulative) assessment frameworks
• hazard classification, risk management measures and regulatory decision-making
• chemical safety assessments and compliance with EU REACH and other regulatory regimes
• design of appropriate testing strategies and weight-of-evidence approaches.

As regulatory expectations grow more sophisticated and more chemicals with challenging testing properties (such as low solubility, volatility or complex composition) are developed and introduced to the market, so too must the tools and approaches used to assess bioaccumulation.

Testing approaches and tools

Experimental studies are a key component of bioaccumulation assessment, with OECD Test Guideline 305 providing the primary globally accepted method for quantifying bioaccumulation in fish by deriving BCF and BMF values. However, these studies can be resource-intensive and technically challenging, particularly for UVCBs, poorly soluble substances, highly volatile compounds, surface‑active substances, strongly sorbing or hydrophobic compounds, and other materials that do not maintain stable aqueous exposure concentrations or exhibit complex partitioning behaviour. As a result, bioaccumulation assessments increasingly rely on multiple complementary lines of evidence rather than testing alone.

Recent research highlights innovative strategies to improve bioaccumulation assessment, including advanced modelling, alternative test organisms, and refined Weight-of-Evidence approaches:

QSARs

Quantitative Structure–Activity Relationships (QSARs) or in-silico methods are widely used to predict bioaccumulation potential, typically through estimates of BCF or related metrics based on chemical structure and physicochemical properties. QSARs are valuable for screening and prioritization, but their applicability may be limited for complex substances or chemicals outside established model domains.

Weight of Evidence (WoE)

To address these limitations, bioaccumulation assessments are increasingly conducted using a Weight of Evidence (WoE) approach, integrating any available data such as experimental bioaccumulation data, QSAR predictions, biotransformation information, and mechanistic understanding. WoE nevertheless rely on the reliability and relevance of the data behind each line of evidence, so essentiality, poor quality data will result in unreliable or low quality WoE. This approach supports transparent and scientifically robust conclusions on bioaccumulation potential that are suitable for regulatory decision-making. The Bioaccumulation Assessment Tool (BAT) and Ricardo’s Persistence Assessment Tool (PAT) are designed to integrate WoE into regulatory submissions.

Bioaccumulation Assessment Tool (BAT)

To streamline and strengthen bioaccumulation assessments, the Bioaccumulation Assessment Tool (BAT) offers a robust, spreadsheet-based platform for integrating multiple lines of evidence. This tool empowers users to conduct transparent, reproducible, and scientifically defensible bioaccumulation assessments.

Persistence Assessment Tool (PAT)

To complement the PBT framework, Ricardo has developed the Persistence Assessment Tool (PAT), a free, user-friendly resource to support the evaluation of chemical persistence. PAT helps users interpret degradation data and apply regulatory criteria for persistence under REACH and other frameworks. 

Support for your business

To comply with regulatory requirements, registrants must provide an assessment of bioaccumulation as part of their chemical safety assessments. At Ricardo, we support clients navigating the complexities of bioaccumulation testing and interpretation, including strategic support for regulatory submissions. We also support organisations in navigating these choices by advising on the most suitable test strategies, helping optimise study design, timelines, and overall cost efficiency.

Our experts support clients to:

• Calculate and interpret bioaccumulation metrics 
• Apply them effectively for regulatory submissions and environmental risk assessments
• Carry out bioaccumulation assessments using state of the art in silico methods following regulatory guidelines
• Commission and monitor biological studies to assess bioaccumulation
• Navigate discussions with regulatory bodies

Our services include:

• Study design and study monitoring including higher tier testing 
• Data interpretation aligned with common guidelines such as OECD guidelines 
• Worldwide regulatory implementation (e.g. ECHA, EU and UK REACH, Biocidal Products Regulation, Plant Protection Products Regulation, Classification Labelling and Packaging, US EPA)
• Alternative to animal testing such as quantitative modelling WoE
• Strategic support for regulatory submissions

By combining scientific expertise with practical tools, we help clients not only meet regulatory compliance  but also make informed decisions about chemical safety and environmental impact.

 Contact our environmental chemistry and toxicology specialists >