Overview
EN ISO 20079:2006 (identical to ISO 20079:2005) defines a standardized duckweed growth inhibition test using Lemna minor to assess the toxic effect of water constituents, treated municipal wastewater and industrial effluents. The method quantifies inhibition of vegetative growth over a fixed exposure period (seven days) by comparing growth in test solutions with controls and reporting effective concentrations (EC(r) values). This standard is widely used for routine water quality and ecotoxicity testing of dissolved substances and mixtures.
Key topics and technical requirements
- Test organism: Lemna minor (duckweed) maintained in axenic stock cultures, with pre-cultures used to prepare inoculum.
- Observation parameters: frond number, frond area, chlorophyll content and dry weight - at least two observation parameters are recommended.
- Test duration and principle: plants exposed for 7 days; growth inhibition is determined from average specific growth-rates and expressed as EC(r) (e.g., EC(r) based on frond number).
- Test media and dilution: combination of test sample, dilution water and nutrient medium; dilution series or fixed dilution steps are used to establish concentration–response relationships.
- Interferences to consider: poorly soluble, volatile, or photo-/bio‑degradable substances, and reactions with dilution water or nutrients that may alter test integrity.
- Validity and precision: the standard includes criteria for test validity, methods of calculation, and precision assessment (see clauses on validity criteria, calculation parameters and precision).
- Documentation: detailed reporting of procedures, conditions, and results (test report requirements included).
Applications and users
- Environmental testing laboratories conducting ecotoxicity screening of chemicals, effluents and treated wastewater.
- Wastewater treatment facilities and industrial effluent managers assessing compliance and treatment performance.
- Regulatory agencies and risk assessors evaluating environmental effects of plant protection products, industrial discharges and chemical substances.
- Ecotoxicologists and researchers using Lemna minor as a model for higher aquatic plants and primary producers.
Practical benefits include a rapid, sensitive assay for plant-level toxicity, useful for routine monitoring, effluent characterization and comparative hazard assessment.
Related standards
- ISO 5667-16 - guidance on biotesting of samples (sampling practices).
- ISO 10260 - spectrometric determination of chlorophyll‑a (relevant for chlorophyll observation parameter).
- Prepared by ISO/TC 147 (Water quality) and endorsed as EN ISO by CEN for harmonized use across European member bodies.
Keywords: EN ISO 20079:2006, duckweed growth inhibition test, Lemna minor, water quality, toxicity testing, wastewater, EC(r) values, ecotoxicity, effluent testing.
