Overview
ISO 20079:2005 - Water quality - Determination of the toxic effect of water constituents and waste water on duckweed (Lemna minor) - Duckweed growth inhibition test - specifies a standardized laboratory method to measure growth inhibition of the duckweed Lemna minor exposed to dissolved substances, treated municipal wastewater and industrial effluents. The test quantifies substance-related effects over a seven-day exposure by comparing growth in test media against controls and reporting effective concentrations as EC(r) values (e.g., EC(r) for frond number).
Key topics and technical requirements
- Test principle: Monocultures of Lemna minor are grown in a concentration series of the test sample for seven days; growth inhibition is calculated from observation parameters and average specific growth-rates.
- Observation parameters: frond number, frond area, chlorophyll content, dry weight. The standard requires evaluation for at least two parameters (based on average specific growth-rate).
- Result metric: EC(r) values (effective concentration causing x% inhibition of growth-rate).
- Apparatus: cylindrical vessels (≥150 ml), uniform covers, temperature- and light-controlled facilities, pH-meter, spectrometer for chlorophyll (665/750 nm), luminometer, image analysis system, autoclave and sterile filtration.
- Reagents & media: use high-purity dilution water (conductivity ≤ 10 µS/cm); pH-stabilized modified STEINBERG medium (final pH 5.5 ± 0.2) is specified; details for stock solutions and preparation are provided.
- Biological material: use defined stock cultures, pre-cultures and inocula of Lemna minor (axenic monocultures recommended).
- Interferences: the method flags limitations for non-soluble/poorly soluble, volatile, bio- or photodegradable substances and substances that accumulate at the water surface.
- Quality control: validity criteria, documentation requirements, and calculation methods (including segmented and average specific growth-rates) are defined to ensure reproducibility.
Applications and users
ISO 20079 is used for:
- Ecotoxicity testing of chemicals, pesticides and industrial discharges
- Assessment of treated municipal wastewater and industrial effluent toxicity
- Environmental monitoring, compliance testing and effluent permitting
- Regulatory submissions, hazard classification and environmental risk assessment
- R&D in ecotoxicology and water treatment performance
Primary users include accredited environmental testing laboratories, regulatory agencies, wastewater treatment operators, chemical and agrochemical manufacturers, and environmental consultants.
Related standards and annexes
- Normative references: ISO 5667-16 (sampling guidance for biotesting) and ISO 10260 (spectrometric chlorophyll-a determination).
- Annexes: preparation of nutrient media (Annex A), simplified lowest ineffective dilution (LID) evaluation for waste water (Annex B), and supplier list for Lemna species (Annex C).
Keywords: ISO 20079, duckweed growth inhibition test, Lemna minor, water quality test, ecotoxicity testing, wastewater toxicity, EC(r), modified STEINBERG medium.
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