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Long-term toxicity to aquatic invertebrates

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Description of key information

In a long-term Daphnia reproduction test (21 days) it can be concluded that up to the water solubility of DOT(EHMA) there is no toxicity. The NOEC was determined to be 0.286 mg/L.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.286 mg/L

Additional information

In a semi-static design, ten daphnids per concentration were individually exposed to dilutions containing 1, 5, 10, 50 and 100% of the WAF prepared at 100 mg/L, and twenty daphnids were individually exposed to untreated test medium (blank control). Test solutions were renewed three times a week. The total test period was 21 days. Samples for analysis were taken from all test solutions at the start and the end of the first, third, sixth and eighth renewal interval. Additionally, samples were taken from the freshly prepared highest test solution at the start of the fifth, seventh and ninth interval.

Analytical results were consistent within the groups and remained stable during the periods between media changes. Reported exposure concentrations for each group were calculated by taking the mean of analytical results of whole intervals for the group. Thus, average exposure concentrations were as follows:

As WAF: 1, 5, 10, 50 and 100%

As Sn: 5.2, 21, 46, 229 and 508 µg/L

As DOT(EHMA): 33, 134, 286, 1448 and 3213 µg/L

Sn was not detected in control samples, except for one occasion, when a 4.1 µg/L concentration was measured.

None of the twenty parental daphnids died during the test period in the control. Incidental mortalities occurred at all but the lowest treatment level, with 1, 1, 2 and 2 dead parents at 134, 286, 1448 and 3213 µg/L, respectively. Hence, parental mortality was not related to concentration.

The average cumulative number of young per reproducing female in the control after 21 days was 134.6 ± 14.2. The reproduction curves recorded at all the treatment levels closely followed the curve of control. However, at the two highest test concentrations, 1448 and 3213 µg/L, offspring included considerable numbers of immobile young. The number of mobile offspring at the two highest treatment levels was statistically significantly reduced. Based on total offspring produced, only the highest treatment level showed a statistically significant reduction.

Mean body length was significantly reduced at 1448 and 3213 µg/L.

No unhatched eggs were observed in any of the concentrations tested. No small or pale parental daphnids were observed in the control or the test concentrations throughout the test period.

Considering the extremely low solubility of the test substance, super-saturated solutions were prepared. In this context tested concentrations expressed as WAF are far above the water solubility of the test substance. Therefore the effects noticed cannot necessarily be attributed to the parent compound.

In the frame of this long-term Daphnia reproduction test, it can just be concluded that up to the water solubility of DOT(EHMA) there is no toxicity.

Furthermore The study was conducted with a test item containing ca. 3 -4 % of Ethylhexylthioglycolate (EHTG, CAS: 7659 -86 -1, EC: 231 -626 -4) as impurity EHTG is better soluable in water as DOTE and shows the following ecotoxicity: EC50 (48 h) Daphnia = 0.38 mg/L EC50 Algae = 0.41 mg/L and is thus classified as Aquatic Acute 1 H400 and Aquatic Chroinic H410 Is likely that the observed effects in the study are caused or exacerbated by the impurity EHTG