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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

48 hour EC50 (immobilization) to Daphnia magna: 0.40 mg/L (OECD Guideline 202).

Key value for chemical safety assessment

Additional information

The short-term toxicity of the substance, IOA (CAS# 29590-42-9), to Daphnia magna was assessed in two studies. In the key study, which was conducted under static, closed conditions, the 48-hour EC50 was reported as 0.40 mg/L based on mean measured concentrations. The supporting study also utilized static, closed conditions, and the 48-hour EC50 was 1.40 mg/L based on initial measured concentrations. For reasons detailed below, the 48-hr EC50 for Daphnia magna has been determined to be 0.40 mg/L. 


The determination of the acute toxicity to Daphnia magna in the key study was based on OECD Guideline 202 utilized measured concentrations and was GLP-compliant. Daphnid neonates (< 24-hours old) were exposed to nominal concentrations of 0, 0.5, 1.0, 2.0, 4.0 and 8.0 mg/L, corresponding to mean measured concentrations of <0.04, 0.24, 0.53, 1.21, 2.78, and 7.40 mg/L for 48-hours. The 48-hour EC50 was 0.40 mg/L based on mean measured concentrations. This study is classified as acceptable and satisfies the guideline requirements for an OECD Guideline 202, acute toxicity study with freshwater invertebrates. It has been given a reliability score of 2 (reliable with restrictions) because of sharp reduction in measured test substance concentrations (ca. 50%) over the exposure period and low recovery (77%) from the test medium.


The supporting study, while also based on OECD 202, was not GLP compliant. In addition, a final report on the chemical analyses was not available, only summary values. It has been determined that the notified substance is readily biodegradable and volatile, and difficulties have been noted with maintaining a constant concentration in water during ecotoxicological studies such as the aforementioned key study.  There was an approximate loss of 45% of the test substance in the test solutions of the supporting study by 48 hours. The EC50, 1.40 mg/L was calculated based on initial concentrations. Because the analytical report is not available, it is felt it is not warranted to recalculate the EC50 based on mean measured concentrations. The EC50 reduced by 45% is approximately 0.6 mg/L.   Therefore, the results of this study are considered supportive of the key study.