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Long-term toxicity to aquatic invertebrates

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Description of key information

NOEC 21d Daphnia = 6.59 mg/l

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
6.59 mg/L

Additional information

The Reproductive Toxicity Daphnia study on CAS 16090-02-1 presents a number of uncertainties:

- the analytical part is not clear. The recovery rates are quite variable and in general very low (5-20 %). It seems that the test substance precipitates with time, which makes it especially important to perform an in-situ analytics. There is a lack of documentation in the report;

- precipitation of solid particles can cause detrimental effects when the daphnids appendages become trapped inside, obstructing normal feeding and/or propulsion of the daphnids and/or respiration of the daphnids in the water column. Additionally, particle formation or the flocculation of the tested substance in the water column can result in direct obstruction of the setae responsible for transporting food into the food groove, thereby causing additional stress and adverse effects of the test species. As a consequence, the result of the chronic assay is not reliable and should not be used for the risk assessment;

- this study should be conducted in semistatic or flowthrough conditions.

 Aquatic toxicity-testing on CAS 16090-02-1 presents a number of critical issues because of factors like:

- strong influence of pH on solubility;

- strong adsorption to organic fracion;

- influence of cation on solubility under customary test conditions (flocculation can occur);

- increase of toxicity for speciates like calcium.

Based on the dissertation [1]:

- the substance forms strong ion-pairs with calcium ions in water;

- the octanol-water partition coefficients of the ion-pairs are two orders of magnitude higher than the partitioning coefficient of the native substance;

- the strongly decreased hydrophilicity due to ion-pair formation decreases the water solubility;

- the cited experimental results suggest precipitation of ion-pairs/complexes (the medium for the daphnia test contains Ca2++). During a test performed in Bayer facilities (not more available) microscopic pictures of daphnia antennas have been taken that showed crystalline deposits, which have been interpreted as calcium complexes of same brightener. The test was then stopped.

As a conclusion, it can be stated that the study presents a number of failures in supporting the endpoint and will be not considered for Risk Assessment or for the classification purposes.

Nevertheless, a further Daphnia magna reproductive study is available on a similar substance CAS 16470-24-9. The substance is included into the category (as described in the Category Justification Report attached to the section 13 of the dossier), and presents a very high similarity according to Tanimoto distance (> 0.9). It is much more soluble, because of higher sulphonation (650 g/l respect to 1.9 g/l of the CAS 16090-02-1) and it is therefore environmentally more bioavailable. The organic functionality is different, since it is a dihydroxyethyl amino derivative instead than a morpholino derivative, but this functionality makes the analogous substance biologically more active and reactive than the morpholino derivative; therefore CAS 16470-24-9 can be considered as a good representative conservative substance to be tested and to make a Read Across evaluation. 

The impurity profile indicated that the content of inorganic salts in the CAS 16470-24-9 is much lower (10 % versus about 20 %) than in the CAS 16090-02-1); contrariwise, the organic impurities content is higher. This considerations make the analogous substance a conservative representative, since inorganic impurities described in the substance identification have not a potential toxic effect by themselves (if not based on physical interaction) and read across is therefore justified.

The solubility and ionic interaction effects in the laboratory testing of CAS 16090-02-1 are an artefact and do not represent a realistic environmental situation, as the concentrations of CAS 16090-02-1 hardly exceed 2 μg/l. Under environmental conditions it can be expected an almost complete dissociation [2].

The result of the study on the analogous substance was considered to establish the NOEC for the substance.

REFERENCE

[1]“Poiger, T.: Behavior and Fate of Detergent-derived Fluorescent Whitening Agents in SewageTreatment. Swiss Federal Institute of Technology, Zürich,1994. ”

[2]HERA Report 2004: Substance: Fluorescent Brightener FWA-1 (CAS 16090-02-1)