ISO 6341:2012

Overview

ISO 6341:2012 specifies an internationally recognized acute toxicity test to assess water quality by measuring the inhibition of mobility (immobilization) of the water flea Daphnia magna Straus. The method determines a 24 h or 48 h EC50 (effective concentration causing immobilization of 50% of test organisms) and is applicable to soluble substances, stable suspensions, industrial and sewage effluents, treated/untreated waste water, aqueous extracts/leachates, fresh waters, sediment eluates and pore waters.

Key topics and technical requirements

• Test organism: Neonate Daphnia magna (<24 h old), from healthy laboratory cultures or hatched ephippia; avoid first-brood progeny.
• Endpoint: Immobilization - inability to swim during 15 s after gentle agitation. Outcome reported as 24 h EC50 or 48 h EC50.
• Test structure: Preliminary range-finding test followed by a definitive test; optional limit test (commonly at 100 mg/L if soluble or stable).
• Environment & conditions: Temperature-controlled room or incubator at (20 ± 2) °C; tests in the dark or under 16 h light / 8 h dark photoperiod; testing atmosphere free from toxic vapours/dusts.
• Media & water quality: Use pure water and appropriate dilution/culturing water (recommendations include pH around 7.8 ± 0.5, hardness ~225 ± 50 mg/L as CaCO3, dissolved oxygen >7 mg/L). Annex A provides preparation of Elendt M4 medium.
• Controls & reference checks: Include control batches and sensitivity checks (reference substance recommended: potassium dichromate). Validity criteria and reporting requirements are specified for reliable interpretation.
• Apparatus & reagents: Standard laboratory glassware, dissolved oxygen meter, sieves, pipettes; reagents of analytical grade.

Applications

ISO 6341:2012 is used for:

• Routine ecotoxicological screening of industrial discharges and municipal effluents.
• Regulatory compliance testing for water quality and wastewater permits.
• Product and chemical safety assessment during development and registration.
• Sediment pore-water and leachate testing for environmental risk assessment.
• Research in aquatic toxicology and environmental monitoring programs.

Who should use this standard

• Environmental and commercial testing laboratories
• Regulatory agencies and water-quality assessors
• Wastewater treatment operators and consultants
• Chemical manufacturers and ecotoxicologists

Related standards

Normative references include:

• ISO 5667-16 (sampling guidance for biotesting)
• ISO 5814 (dissolved oxygen determination)
• ISO 10523 (pH measurement)

ISO 6341:2012 provides a robust, reproducible acute bioassay protocol for assessing aquatic toxicity using Daphnia magna - a key tool in water quality monitoring, effluent control and ecological risk assessment.