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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Desmodesmus subspicatus was exposed under static conditions for 72h to a saturated solution of the substance (initial concentration 100 mg/L). No toxic effect was observed (Scheerbaum, 2002b).

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
100 mg/L

Additional information

No effect was observed up to 100 mg/L (saturated solution); and hence EC50 is > 100 mg/L.

The substance is characterised by a poor water solubility and, based on the presence of isocyanate structures, only a transient existence in water. Isocyanates are known to rapidly hydrolyse under the formation of the corresponding amines and inert, insoluble polyurea compounds. The amount of amine and polyurea formed strongly depends on the method used to dissolve the substance in the test media. A low stirring velocity promotes the formation of polyurea compounds, whereas at high dispersion methods the formation of the environmental relevant amine is preferred. To prepare the test solutions for the present study, solutions were stirred for 24 h on a magnetic stirrer as high dispersion solution techniques do not reflect situations which might occur in the environment.

Biological assays are designed to assess effects of the dissolved (bioavailable) fraction rather than physical hazards caused by particles present in the test medium. Thus, test solutions were filtrated prior to test begin to remove undissolved particles preferably consisting of polyurea compounds. However, the insoluble inert polyurea are not assumed to cause environmental hazards due to a reduced uptake of high molecular mass compounds. The test item concentrations in the test medium were quantified by the means of DOC analysis to get a rough impression of exposure conditions over time. The test was conducted as a limit test investigating a nominal concentration of 100 mg/L. An achievement of that concentration is not feasible due to the following facts: (i) the test item is characterised by a poor water solubility and (ii) removal of undissolved particles, consisting of inert, insoluble polyurea compounds, through filtration prior to test begin and (iii) it is expected that the amount found by DOC analysis refers to the dissolved organic solvent as a result of the sample composition.

Nevertheless, the chosen test design well addresses situations which might occur in the environment (no high dispersion stirring, formation of transformation products and the assessment of ecotoxicological effects therof) enabling a proper description of the environmental behaviour of the substance.