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Toxicity to aquatic algae and cyanobacteria

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Description of key information

EC50 (72 h) > 100 mg/l (nominal)

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L

Additional information

The toxicity of the test item to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to OECD 201. The study was conducted under static conditions. Based on a preliminary range finding test, six concentration levels were tested in a geometrical series with dilution factor of 2.5 (nominal): 5.12, 128, 32.0, 80.0, 200 and 500 mg/l. The determination of the test item was carried out via HPLC-DAD from the concentration levels and the control at the start of the exposure (0 hours) and the end of the exposure (72 hours). The measured test item concentrations in the freshly prepared media were in the range of 113 to 119 % (0 h), but in the old test media (72 h) the measured test item concentrations were in the range of 6 to 16 %; all test replicates foamed and showed a dose related opalescence (BASF SE, 2015). The test substance concentrations recorded at the end of the study resulted very low respect to the nominal ones. This can be attributed to two different reasons. First of all, part of the substance resulted foamed, thus it is not clear if this can contribute to decrease the substance availability. If (and eventually how much) the foamed and opalescent solution may impact the study outcomes is not described and cannot be determined.

Then, it has to be taken into account that stilbene-type fluorescent whitening agents (FWAs) undergo photoisomerization. Taking into account the available information about the phototransformation in water (Kramer 1996, IUCLID section 5.1.3), equilibrium in distribution between the FWAs' E/Z isomers is expected to be in the range of 300 - 310 nm and lower/higher wavelengths are characterized by the predominance of the Z-isomer specie or vice-versa. Thus, during the test, it is expected that the analyses measured only one of the two isomers present in the tested solutions because the determination of the test item concentration was carried out by HPLC-DAD at the wavelength of 353 nm.

As a consequence, based on the physical form of the test solution that can affect study results and based on the test concentration measurements, the test results cannot be considered reliable and a clear conclusion cannot be reached.

No reliable data about the aquatic algae and cyanobacteria toxicity are available on CAS 13863-31-5, therefore data from the similar substances CAS 4193-55-9, 70942-01-7 and 16470-24-9 are reported.

These analogous are all dihydroxyethylamino derivative disulphonated sodium salt,, disulphonated sodium/potassium salt and tetrasulphonated sodium salt, respectively. In the case of the CAS 70942-01-7 the presence of potassium ion has no relevant toxicological influence for the endpoint. The water solubilities are 48.2, 13.45 and 650 g/l, respectively, which are higher than the substance under registration (0.77 mg/l), thus they are more bioavailable in the water compartment and can be considered as a conservative examples.

Furthermore, the chemical structures are very similar, with Tanimoto similarity higher than 95 %: the substance under registration has a methyl where the analogous has a hydroxyethyl substituent on the nitrogen atom. Based on the OECD Toolbox modelling of the liver metabolisation, both structure share the same monohydroxy derivative as main metabolite. Biological reactivity for the substance under registration is therefore not expected higher that the considered analogues substances.

Acute toxicity for Green algae (Pseudokirchnerella subcapitata) was evaluated in the 72 hours screening test, according to the OECD guideline 201 in CAS 70942-01-7. A single dose was administrated at 100 mg/l, at which the grown inhibition was recorded at 2 % (Solvias AG., 1999).

The result was confirmed with the outcomes on analogous dihydroxyethyl derivatives sodium salt (CAS 4193-55-9) and the tetrasulphonated sodium salt (CAS 16470-24-9); in both cases a value of EC50 greater than 100 mg/l was set.

No aquatic algae toxicity is expected for the substance under registration.