ISO 20666:2008

Overview

ISO 20666:2008 defines a standardized 48-hour chronic toxicity test using the freshwater rotifer Brachionus calyciflorus. The method measures population growth inhibition (counting total females - mothers plus offspring) after 48 h exposure to quantify chronic toxic effects. Results are expressed as ECx values (e.g., EC10, EC20, EC50) derived by regression. The standard applies to soluble chemicals, stable suspensions, industrial or sewage effluents (after appropriate pre‑treatment), fresh waters and aqueous extracts, but excludes estuarine/marine samples and unstable chemicals unless exposure concentrations are measured.

Key Topics and Requirements

• Test duration and endpoint: 48 h exposure with population growth inhibition as the chronic endpoint.
• Test organisms: Female Brachionus calyciflorus less than 2 h old at test start; cultures may be from laboratory stocks or hatched cysts.
• Test conditions: Dark environment, thermostatically controlled at 25 ± 1 °C; atmosphere free from toxic dusts/vapours.
• Replicates and controls: Control and test batches typically consist of eight replicates each; control solution is test medium plus food without sample.
• Media and food: Synthetic test medium of moderate hardness; algal food usually Chlorella vulgaris (alternatively Pseudokirchneriella subcapitata), with specified cell concentrations.
• Apparatus: Disposable inert microplates or closed containers, pipettes sized to transfer rotifers, magnifier or image analysis for counting, and devices for algal concentration measurement.
• Sample handling: Sampling and storage guidance follows ISO 5667-16; recommended testing as soon as possible (ideally within 12 h), refrigerated short‑term or frozen under specified conditions when necessary.
• Data analysis: Calculate percent inhibition vs control and derive ECx by regression; validity criteria and reporting requirements are specified.

Applications and Users

ISO 20666:2008 is used in:

• Ecotoxicology laboratories conducting rotifer assays and chronic toxicity screening.
• Environmental monitoring of wastewater effluents, industrial discharges and freshwater quality.
• Chemical registration and environmental risk assessment to determine chronic hazards to planktonic zooplankton.
• Regulatory agencies, wastewater treatment operators, environmental consultants and chemical manufacturers seeking reproducible, comparable data on water quality and ecotoxicity.

Related Standards

• ISO 5667-16 (water sampling for biotesting)
• ISO 5814 (dissolved oxygen measurement)
• ISO 10523 (pH determination)
• ISO 20665 (related biological batch/test terminology)

Keywords: ISO 20666, water quality, chronic toxicity, Brachionus calyciflorus, rotifer assay, 48 h test, population growth inhibition, EC50, ecotoxicology, effluent testing.