Overview
EN ISO 23196:2023 (ISO 23196:2022) - adopted by CEN - defines a standardized method to calculate biological equivalence (BEQ) concentrations from results of in vitro bioassays used in water quality assessment. BEQ expresses the biological activity of an environmental sample (or a defined mixture/pure chemical) as the concentration of a reference compound that produces an equivalent effect on a measured biological process (e.g., enzyme induction, cellular growth). The standard is applicable to environmental water samples, extracts (including tap water) and solutions of chemicals or mixtures.
Key topics and requirements
- Scope and definitions: clear definitions for BEQ, reference compound (RC), concentration-effect relationship, concentration factor (CF), ECx (x %-effect concentration), LOQ, negative control material.
- RC-approach: recommended robust method for deriving BEQ by modelling the concentration-effect relationship of a reference compound and normalizing assay responses so negative control = 0% and RC maximum effect = 100%.
- Procedure highlights (Section 5.2):
- Assessment of experimental data suitability for BEQ calculation.
- Fitting concentration–effect data for the reference compound.
- Calculation of fit quality measures and validity criteria.
- Normalization of reference and sample data to percentage effect.
- Determination of the RCx (concentration producing x% effect, e.g., RC10, RC50).
- Interpolation to calculate the sample concentration factor at the chosen ECx and computing the BEQ concentration.
- Validity and reporting: specified validity criteria and test-report requirements ensure reproducibility, comparability and traceability of BEQ results.
- Recognizes applicability to different bioassays after demonstration of assay suitability; aligns with literature and guidance (e.g., OECD 455) on BEQ derivation.
Applications and users
Practical uses of EN ISO 23196:2023 include:
- Environmental monitoring laboratories calculating BEQs for surface waters, wastewater effluents and drinking water surveillance.
- Regulatory agencies and water managers using BEQ data to inform risk assessment, trend analysis and potential effect‑based trigger (EBT) implementation in regulation.
- Research groups developing or validating in vitro bioassays and reference compounds.
- Water utilities and consultants performing mixture-effect screening and prioritizing chemicals for targeted chemical analysis.
Related standards
- ISO standards on water quality biological methods (ISO/TC 147) and related assay guidance (e.g., OECD 455) are relevant for method selection, validation and interpretation.
- EN ISO 23196:2023 complements chemical analytical standards by providing an effect-based, comparative metric (BEQ) to interpret bioassay responses.
Keywords: EN ISO 23196:2023, BEQ, biological equivalence, water quality, in vitro bioassays, reference compound, concentration-effect relationship, RC approach, ECx, effect-based trigger (EBT).