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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Slight toxic effects were observed in a test using water accomodated fractions.

Key value for chemical safety assessment

EC50 for freshwater algae:
103.9 mg/L
EC10 or NOEC for freshwater algae:
7.8 mg/L

Additional information

Due to the low water solubility and the impurity profile of the substance a GLP study according to EEC guideline 92/69 (1992) using water accomodated fractions was performed. Algae were exposed to water accommodated fractions at 100, 30, 10, 3, 1, 0.3 mg/l loading after separation of undissolved substance by centrifugation. Due to the high adsorption tendency test vessels were silanised before testing. The EC50 for inhibition of growth corresponds to 100 mg/l loading, the EC50 for biomass reduction corresponds to 16 mg/l loading. The NOEC is at 10 mg/l (loading). Statistical re-evaluation of the data (2017) retrieved following effect values: ErC10 72h 7.8mg/L (loading, WAF), ErC50 72h 103.9 mg/L (loading, WAF).

Since the impurities might have a higher solubility level than the main component, the composition of the test product in the water phase could differ markedly from the original composition of the test product when solutions were prepared at levels above the solubility limit. The concentrations of the impurities in the test solutions were not analysed in the test solutions. Given the observed effects and the number of impurities, the WAF approach was appropriate for this algae study and effects concentrations could be based the loading rates.

Furthermore, concentrations measured in the WAFs prepared at 30 and 100 mg/l exceeded the expected solubility level of 2 mg/l, indicates the presence of an undissolved fraction, in spite the fact that the procedure for preparation of test solutions included centrifuging at a relative high rate to remove any undissolved test substance. This undissolved fraction may have significantly contributed to the effects on algal growth by causing possible mechanical damage.

The study fulfills the validity criteria.

Comments on pH increase:

The pH increase observed in the study is normal in algae studies where significant growth of the algal cells is observed. The guideline states that the pH should not increase by more than 1.5 units in the control group. However, this is not a validity criterion. Algal cells need CO2 from the test system. If there is a strong exponential growth of the cells, the CO2 in the test system will be decreased and as a consequence the pH will increase. Especially, as the test media are not heavily buffered. The present study showed exponential algal cell growth which is clearly indicative of a “healthy” test system. The increasing pH does therefore not affect the outcome of the study. From the comparison of pH and reduction in mean growth it can be seen that only in the lowest concentrations showing no significant effects, pH shifts to pH > 9.0 were observed. Therefore, it can be concluded that the pH drift did not affect the results.