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Short-term toxicity to aquatic invertebrates

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Description of key information

At the water accommodated fraction (WAF) with a nominal loading of 100 mg/L of the test item  no effects were observed on Daphnia magna. 
The REACH substance has a high molecular weight (98.98% > 1000 Dalton). Under environmental conditions the substance will be oxidized to very big polymeric structures with a very high molecular weight. The bioavailability of the substance is negligible (low potential to cross biological membranes). This will be supported by all toxicological studies. Based on the high molecular weight the substances should not be bioavailable.

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Additional information

Two acute immobilisation tests with daphnia magna (STRAUS) according OECD Guideline for Testing of Chemicals, No 202 (2004) are available.Due to the low water solubility of the test item, a dispersion of the test item with the loading rate of 100 mg/L was ultrasonic treated for 15 minutes in the first test and continuously stirred at room temperature in the dark over 96 hours. Then, the dispersion was filtered. The undiluted filtrate with the loading rate of 100 mg/L and dilutions 1:2, 1:4, 1:8 and 1:16 of the undiluted filtrate with the loading rate of 100 mg/L were used as test media. This corresponds to theoretical concentrations of 100, 50, 25, 12.5 and 6.3 mg/L. Additionally, a control was tested in parallel.

 

In the second test the preparation of aqueous media was different. In view of the difficulties associated with the evaluation of aquatic toxicity of poorly water soluble test items, a modification of the standard method for the preparation of aqueous media was performed. An approach endorsed by several important regulatory authorities in the EU and elsewhere (ECETOC 1996 and OECD 2000), is to expose the organisms to a Water Accommodated Fraction (WAF) of the test item in cases where the test item is a complex mixture and is poorly soluble in water and in the permitted solvents.

Using this approach, the aqueous medium was prepared by shaking the test item with dilution water at 20 rpm for 24 hours at room temperature to ensure equilibration between the test item and the water phase.100 mg/L of the test item were weighed out and transferred into a brown glass flask with an appropriate amount of dilution water. After the completion of shaking and following a 1-h settlement period, the test item phase was separated by siphon and the test organisms exposed to the clear aqueous phase, the WAF. Twenty daphnids were exposed to the WAF and the control.

 

In the first test an EC50 of 48 mg/L is reported, in the second test no effects were observed on Daphnia magna at the WAF with nominal loading of 100 mg/L of the test item. The effect shown in the first report probably based on the different method of preparing the Water Accommodated Fraction (WAF). The method used in the second test is more reliable and therefore these test is used as the KEY study.