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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

In a 72 hour toxicity study, the cultures of the diatom (Skeletonema costatumCCAP 1077/5) were exposed to Cardolite NC-603 (Technical Grade) at nominal concentrations of 0, 62.5, 125, 250, 500 and 1000 mg/l nominal Water Accommodated Fraction (WAF) loading rates. The test was conducted under static in accordance with the guideline ISO 10253 (Water quality - Marine Algal Growth Inhibition Test with Skeletonema costatum and Phaeodactylum tricornutum).

The EL50 based on the biomass endpoint was evidently 250 mg/l and the EL50 based on growth rate was estimated to be 1300 mg/l. There were no substance related phytotoxic effects. However, there is uncertainty associated with the measurements of cell density measured at the two highest loading rates since there was a disparity in the colour and character of those test solutions after 72 hours compared to those of the controls and 62.5, 125 and 250 mg/l WAFs. It is, therefore, possible that the changes observed were due to a physical rather than a toxicological effect.

The study is classified as Klimisch Code 2 (reliable with restriction) as it was performed to an internationally recognised method (ISO 10253) and was conducted to Good Laboratory Practice.

It is recognised that because of the low water solubility of Technical Grade (and the two other grades) the loading rate data may not reflect the lower actual concentration of the substance to which organisms were exposed in the algal toxicity study and which were not characterised during the test. On this basis, it is only possible to conclude that there is evidently no toxicity of Technical Grade to algae (in terms of growth inhibition) at the water solubility limit.

The available data for the three grades indicates that they all show low measured water solubility in the range 0.2 to 0.3 mg/l. All three substances also show high measured octanol-water partition coefficients (log Kow >6.2 in all cases). This data indicates that the measured data for the key physico-chemical properties that underpin the likely short term aquatic toxicity of the three grades are consistent. On this basis it would be expected that the three grades would show similar responses in the short-term aquatic toxicity tests. This hypothesis is currently supported by the results of the long-term OECD TG218 ecotoxicity test that was conducted on both Distilled and Distillation Residue Grades following an interpolation approach. Therefore, it is considered appropriate to read-across from the data for Technical Grade to Distilled Grade with the result that it has been estimated that there will also be no adverse effects of Distilled Grade on short-term fish lethality at the substances water solubility limit.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
0.3 mg/L
EC10 or NOEC for marine water algae:
0.3 mg/L

Additional information