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The test item: Fatty acids, C18 unsat, reaction products with diethylenetriamine (AAI-DETA; CAS no 1226892-43-8) is a multicomponent mixture (UVCB) of cationic surface-active constituents with different water solubilities. The fate of cationic surfactants in general deviates from standard chemicals. These substances are therefore considered as difficult substances for which the results of standard guideline studies are very difficult to interpret when considering them in a standard way. The reasons are the intrinsic properties like the relatively low water solubility and strong sorption to equipment and organisms. Classical ecotoxicity testing with these substances using reconstituted water often leads to test results which are poorly reproducible and are associated with high uncertainty. In addition, because of the complex sorption mechanisms (van der Waals and Ionic mechanisms) the actual dissolved exposure concentration cannot reliably be estimated.

Long-term daphnia and algae tests where therefore performed following two different approaches.

One which is focused on determining the intrinsic toxicity of AAI-DETA (for C&L purposes), is performed according to the Water Accommodate Fraction (WAF) approach as described in “OECD guidance document on aqueous-phase aquatic toxicity testing of difficult test chemicals” (No. 23 Feb. 2019) with a daily refreshment of the test solutions.

As indicated the test item is a UVCB substance with constituents of different water solubility. This means that only a fraction of the total mass of the UVCB added to the test solution may be dissolved in the WAF. The term "loading rate" instead of "nominal concentration" has therefore been advocated for expressing exposures of UVCBs that neither wholly dissolve nor completely form a stable dispersion or emulsion over the required test range (Girling et al., 1992). The loading rate is the mass to volume ratio of the UVCB to test medium used in the preparation of a WAF. Results should be calculated from the loading rates of the entire UVCB as either a median lethal loading (LL50), median effective loading (EL50) or 10 percentile effective loading (EL10) value. These loading levels from the WAF are used directly in the classification criteria (see also Annex I.4.5 of the CLP guidance document). 


The other which is more suited to derive a realistic risk ratio (RCR) for the aquatic compartment, is performed according to the PECaquatic bulk/PNECaquatic bulk approach as described in ECETOC Technical Report “Environmental Risk Assessment of difficult substances” (TR 88, 2003) with a three times a week refreshment of the test solutions. The so called “Bulk approach” is used in the environmental risk assessment to cope with the earlier mentioned lack of realistic PEC estimation. Instead of using the dissolved PECwater, the Bulk concentration (dissolved + sorbed) in water is used. This bulk approach requires a PNECwater, bulk that means that testing has to use river water which contains dissolved organic carbon and suspended organic and inorganic matter, instead of reconstituted water.

Tests according to the bulk approach were thus performed because the partitioning of cationic surfactants to soil, sediment or suspended matter is rather complex which explains why there is no alternative Equilibrium Partitioning Method (EPM, di Toro, 2008) formula for these substances available yet. The use of the Bulk approach however elegantly bypasses this deficiency as it eliminates the EPM on both the exposure and effect side.