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Ecotoxicity testing with cationic surfactants is complicated as these substances tend to sorb to negatively charged surfaces like glassware and test organisms. The reproducibility of these tests is in general poor. When cationic surfactants enter the environment they will be immediately sorbed to the suspended matter and DOC present in the environment. The toxicity will due to this sorption be mitigated. The degree of this mitigation is however poorly predicted with the currently available exposure models (e.g. EUSES) as they only predict sorption based on interaction with organic matter where the main sorption of these substances will be due to ionic interaction. To increase the reproducibility of the ecotoxicity testing and to compensate for the deficiency of the bioavailability modeling tests have been performed with river water. To ensure the representativeness of the test results, realistic worst-case river water (DOC close to 3 mg/L and suspended matter close to 15 mg/L) has been used. These river water studies should therefore be considered as higher tier studies. This approach is also applied in EU risk assessments of DODMAC and primary fatty amines and is known as the Bulk-approach (ECETOC TR88 2003).

In order to classify a standard laboratory toxicity study as valid, it is of particular importance that - besides information on test substance, test method / conditions and test organism used - suitable precautions are taken to prevent the loss of test substance by adsorption and that exposure concentrations are based upon measured levels.

For ecotoxicity tests performed using the bulk-approach, however, adsorption to suspended matter and DOC is acceptable and only adsorption to glassware should be accounted for. For a valid bulk approach test the concentration-effect relationship should be based on the sum of adsorbed and dissolved substance in the volume of the medium tested. One of the advantages of the bulk approach tests with these difficult substances is that in the presence of suspended matter, humic acids and/or algae, the residual sorption to glassware will be negligible. The results of these bulk approach tests are therefore much easier to interpret, more environmental realistic, and when compared to PECbulkclearly provide a more appropriate assessment of risks for the environment. All effect values given are therefore based on the nominal test item concentrations.