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Amidoamines/imidazolines are poorly soluble in water and also have a strong tendency to adsorb to negatively charged surfaces such as suspended matter, algae and test vessels or organic material (including dissolved organic matter such as humic acids). Many cationic substances in general but long chain amidoamines/imidazolines in particular rank among the most difficult substances to test in environmental toxicology. Standard guideline studies are inappropriate to test substances with such properties and the current REACH Guidance Documents do not provide sufficient guidance concerning bioavailability and exposure assessment for cationic surface-active substances like the amidoamines/imidazolines as these were written with normal hydrophobic chemicals in mind, failing to take into account the lack of bioavailability that occurs in the environment with these substances.

The long-term aquatic ecotoxicity tests with amidoamines/imidazolines were therefore performed in river water to allow a PECaquatic,bulk/PNECaquatic,bulk approach and is considered to be conservative but more environmentally realistic than the standard method. This approach is based on PEC estimations representing ‘total aquatic concentrations’. To characterize the risk to the aquatic compartment the PECaquatic,bulk is compared with the PNECaquatic,bulk derived from river water ecotoxicity studies (ECETOC, 2001).

 

In order to class standard laboratory toxicity study 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 if compared to PECbulk clearly provide a more appropriate assessment of risks for the environment. All effect values given are therefore based on the nominal test item concentrations.

The PNECaquatic bulk should calculated using the assessment factor proposed by the TGD. As long-term NOECs from species representing two trophic levels are available (algae and daphnia) an assessment factor of 50 may be used. However based on the observed lower/comparable toxicity to fish not only for the amidoamines/imidazolines but also for primary fatty amines and mono and dialkyl quats it is considered unlikely that fish toxicity will be critical for this category of substances. A very low acute to chronic ratio is observed in the long-term daphnia test. This observation is consistent with the known effects of cationic surfactants on aquatic organisms, where toxicity is associated with physical binding to respiratory membranes. This explains the steep concentration curves seen and the lack of intermediate chronic effects on reproduction. Hence any additional toxicity testing with fish will not add scientific value to the ecotoxicity profile of the amidoamines/imidazolines other than for obtaining a lower assessment factor. It is therefore concluded that for scientific reasons and in accordance to REACH legislation further testing on fish has to be avoided for reasons of animal welfare and that based on the weight of evidence available on ecotoxicity data for several cationic surfactants a safety factor of 10 may be applied for the derivation of the PNECaquatic,bulk.