Overview
ISO 23196:2022 - Water quality: Calculation of biological equivalence (BEQ) concentrations specifies a standardized method to express the biological activity measured in in vitro bioassays as a biological equivalence (BEQ) concentration. BEQ concentrations translate the effect of an environmental sample, extract, solution or defined mixture into the concentration of a reference compound (RC) that produces an equivalent effect. This enables quantitative interpretation and cross-laboratory comparison of bioassay results for water quality assessment.
Key topics and technical requirements
- Scope: Applicable to in vitro bioassays based on effects on biological processes (e.g., enzyme induction, cellular growth) once assay applicability is proven.
- RC-approach: Model the concentration-effect relationship of a reference compound, normalize response so negative control = 0% and RC maximum = 100%, determine RCx (concentration causing x% effect).
- Calculation principle: Derive sample concentration factor (CFx) at the same x% effect by interpolation, then calculate BEQ as BEQ = RCx / CFx.
- Data quality & fitting:
- Require sufficient data points (e.g., at least two more points than model parameters).
- Sigmoidal concentration-effect curves are typically fitted (five‑parameter logistic often used).
- Assess upper and lower plateaus, goodness-of-fit and validity criteria before deriving BEQ.
- Normalization & ECx: Use x%-effect levels (ECx/RCx) such as EC10, EC25, EC50 depending on assay purpose.
- Documentation: Follow procedure steps and report fit quality, normalization, interpolation and validity checks.
Practical applications and users
- Who uses it:
- Environmental and public-health laboratories performing bioassays on surface, tap or treated water.
- Water utilities and regulators converting bioassay responses into comparable metrics.
- Environmental consultants, researchers and method developers assessing mixtures, extracts or unknown samples.
- Why use ISO 23196:2022:
- Converts biological activity into a comparable concentration metric (BEQ) for trend analysis and monitoring.
- Facilitates inter-laboratory comparability and supports interpretation against effect-based trigger (EBT) values in risk assessment.
- Useful for monitoring complex mixtures where chemical analysis alone cannot capture biological effects.
Related standards
- OECD 455 (reporting of similar bioassay approaches referenced in the document)
- ISO standards cited in definitions and methods: ISO 6107, ISO 15952, ISO 15839, ISO 7405
- Useful keywords: ISO 23196:2022, BEQ, biological equivalence, water quality, in vitro bioassays, concentration-effect relationship, reference compound, ECx, CF, effect-based trigger (EBT)
This standard provides a robust, reproducible framework to quantify biological activity in water quality testing and to communicate results consistently across laboratories and regulatory contexts.