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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 CAS 67786-25-8 to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to OECD 201. The aim of the study was to assess the effects on growth rate and yield production over a period of 72 hours. The study was conducted under static conditions; based on a preliminary range finding test a limit concentration of 100 mg test item/l was tested. The determination of the test item was carried out via HPLC-DAD: the measured concentration at the start of the exposure was 116 % and at the end of the exposure was 10.5 % of the nominal one. No inhibition on the growth of the freshwater green alga Pseudokirchneriella subcapitata was found after 72 hours of exposure to the test item. The NOEC for both inhibition of growth rate and yield, after 72 hours, was 34.9 mg test item/l and the Er/yC50 were both stated as greater than 34.9 mg/l (meas. geom. mean).

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 350 nm. Furthermore, considering the fact that substance is very soluble, not abiotically rapidly degraded and that in the study report no abnormalities of the test solution were observed, it is expected that the low concentration levels recorded at 72 hours are attributable to the method of analysis, rather than to the substance disappearance.

The substance under registration is part of the Stilbene Fluorescent Whitening Agents category, group 4. The studies here reported were performed on members belonging to the category, which differ from the substance under registration (CAS 16470-24-9) in the fact that the substitution on the triazino moiety is dihydroxyethylamino derivative, with different sulphonation degrees: acid form (CAS 4404-43-7), disulphonated sodium salt (CAS 4193-55-9), disulphonated sodium/potassium form (CAS 70942-01-7) and tetrasulphonated (CAS 16470-24-9).

The influence of CAS 16470-24-9 on the growth of the green alga Scenedesmus subspicatus chodat was investigated in a study performed according to the OECD Guideline 201. Based on the growth inhibition curve, the NOEC and the LOEC values were found to be 500 mg/l and 1000 mg/l, respectively. Thus, the EC50 value after 72 hours was greater than 1000 mg/l (RCC Umweltchemie AG., 1990).

Furthermore, the second study on the same substance acute toxicity for Green algae was evaluated in the 72 hours screening test and no growth inhibition for both biomass and growth rate, was observed at the tested concentration of 1000 mg/l (nominal) (Solvias AG., 1999).

 

The studies conducted on CAS 4193-55-9 and CAS 70942-01-7 reported an EC50 at 72 hours greater than 100 mg/l in both cases (Novartis Services AG., 1997 and Solvias AG., 1999).

In conclusion, no aquatic algae toxicity is expected for the substance under registration and an EC50 greater than100 mg/l has been selected as a representative value.