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Short-term toxicity to aquatic invertebrates

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Given that the mechanism of toxicity to Daphnia magna was considered due to the physical properties and characteristics of the test material it can be concluded that the NOEC for mortality observed in this study was 0.134 mg/L. A true 48 hour EC50 value could not be determined but is considered to be > 0.134 mg/L., Daphnia magna, OECD 202 Muddiman 2013b.

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Additional information

The short term toxicity of the test material to Daphnia magna was investigated in a study conducted in accordance with the standardised guideline OECD 202 under GLP conditions.

Daphnia were exposed to the test material at nominal concentrations of the test material at 1.0, 2.5, 6.3, 16, 40 and 100 mg/L for 48 hours under static conditions. A control group was exposed to the M4 medium dilution water under the same conditions.

This was a limit of solubility test as the material was not soluble in water. The nominal solutions were prepared and stirred overnight and allowed to stand for approximately 4 hours. The solution used in the test was transferred using a syphon to avoid the transference of any settled test material.

At 0 hours the measured concentrations ranged from 0.0811 to 2.86 mg/L. At 48 hours the measured concentrations above the limit of detection (LOD), assessed as 0.035 mg/L, were not detected. Given the results from the 48-hour analyses, all results are based on geometric mean measured concentrations.

The geometric mean concentrations achieved were 0.053, 0.087, 0.148, 0.134, 0.203 and 0.316 mg/L for the nominal dose levels of 1.0, 2.5, 6.3, 16, 40 and 100 mg/L, respectively.

Following 48 hours of exposure, immobilisation of 0, 5, 15, 0, 95 and 100 % was observed among daphnids exposed to the 0.053, 0.087, 0.148, 0.134, 0.203 and 0.316 mg/L treatment levels, respectively. All immobilised daphnids were observed to be trapped at the surface. No adverse effects were observed in the surviving daphnia exposed to treatment levels below 0.134 mg/L.

An observation of oily substance on the surface of the top two test concentrations (0.203 and 0.316 mg/L as geometric mean measured concentrations) indicates that the test material was present in an undissolved/undispersed form despite attempts to only transfer dissolved/dispersed test material in media for dosing. In addition, sub-lethal observations noted in those daphnia immobilised at 0.203 and 0.316 mg/L by 48 hours corresponded to a physical effect (trapped in meniscus/ at surface).

Sub-lethal observations of being trapped in the meniscus/surface were noted at lower concentrations (0.134 and 0.148 mg/L as geometric mean measured concentrations). This observation was generally reversible, with a very marked decrease of trapped daphnia observed at these rates at 48 hours. Nevertheless this effect is considered to be due to a physical effect of the test material.

Furthermore, as trapped daphnia observations fell between 24 and 48 hours, a low number of daphnids treated at 0.087 mg/L were noted to have attached debris which further demonstrates the likely physical mechanism of the toxicity of the test material to Daphnia magna.

Given that the mechanism of toxicity to Daphnia magna was considered due to the physical properties and characteristics of the test material it can be concluded that the NOEC for mortality observed in this study was 0.134 mg/L. A true 48 hour EC50 value could not be determined but is considered to be > 0.134 mg/L.

The study was conducted to GLP and a standardised guideline. It was therefore assigned a reliability score of 1 and considered suitable for assessment as an accurate reflection of the test substance.