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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The results of the key study show that the test substance is highly toxic to algae. The most sensitive NOEC is < 0.017 mg/L based on biomass. The corresponding EC50 is 0.029 mg/L. NOEC and EC50 values based on growth rate are 0.053 and 0.141 mg/L. Values are calculated based on average measured exposure concentrations.

Key value for chemical safety assessment

EC50/LC50 for freshwater algae:
0.029 mg/L

Additional information

Analytical work of the key study showed the test substance disappeared from the test solutions during 3 days of incubation. The disappearance rate was dose-dependent. Disappearance was complete on day 3, at average exposure concentrations0.1 to 0.67 mg/L (nominal), whereas10.1 and 15.1 % of the test substance were still present at 1.07 mg/L and 1.7 mg/L (nominal). Presence or absence of algae did not significantly influence the rate of disappearance.

A supporting study which was conducted with the purpose to explain the analytical findings of the key study showed that the test substance was de-chlorinated with time:As the concentration of the test substance decreases, the concentration of de-chlorinated test substance, i.e. Benzenesulfonamide (CAS 98-10-2), increases. De-chlorination was dose dependent. Within one dose group, comparable de-chlorination rates were found in deionised water, algae medium and algae medium stocked with algae.

This indicates, that rather the testing conditions, than the presence of algal medium and algae cells, e.g. permanent agitation of the solution in semi-open vessels at rather high temperatures and light intensities, caused the de-chlorination of CAS 127-52-6. Based on the results of a valid hydrolysis study, the substance is stable at pH 7 and 9 in deionised water, i.e., no de-chlorination takes place. Abiotic degradation is analyzed in closed vessels in the dark, without agitation and air exchange. Hence, the results obtained are considered artifacts of the specific test design used for algae growth inhibition test.