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Toxicity to aquatic algae and cyanobacteria

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Description of key information

EL50 (72h) > 10 mg/L for Pseudokirchneriella subcapitata (OECD 201)
ErC20 (72h) = 0.145 mg/L for Desmodesmus subspicatus (QSAR estimation, used for long-term assessment)
Nevertheless this endpoint is not used for PNEC-calculation as PNEC-values are calculated on the basis of a HC5-approach, except for PNEC aqua (intermittent releases).

Key value for chemical safety assessment

Additional information

As there are no data available for alcohol ethoxylate ((Z)-9-Octadecen-1-ol ethoxylated, < 2.5 EO, CAS 9004-98-2) the toxicity to algae is assessed on the basis of data from a study with a similar alcohol ethoxylate (C16-18, < 2.5 EO, CAS 68439-49-6). The study was performed according to OECD guideline 201 and GLP, with the uni-cellular freshwater green alga Pseudokirchneriella subcapitata as test species. Due to the very low water solubility of the substance, the test media were individually prepared by applying the Water Accommodated Fraction (WAF) approach according to the OECD guidance No. 23. The test design includes eight replicates of the control (test medium only) and four replicates of each of the five test concentration (0.01, 0.10, 0.32, 1.0 and 10.0 mg/L). The concentrations of the test item in the aqueous phase were determined by chemical analyses at the start and at the end of the test using GC-MS. The measured concentrations were below the LOQ in all test media at start and end of the test. Since the substance is a UVCB compound, the nominal loading was used for the test evaluation. There was no inhibition of algal growth up to the highest loading of 10 mg/L and the 72 hour ErL50 (based on specific growth rate) and EyL50 (based on algal yield) were estimated to be > 10 mg test item/L, in terms of the nominal loading (BASF, 2015).

Additionally a category read-across is prepared to a study conducted with the pure homolog C16 alcohol ethoxylated (2EO) (BASF, 1997). The alcohol C16 ethoxylate (2EO) was tested in a limit-test using an eluate of a 100 mg/L stock solution. The test was conducted according to the EU-guideline 92/69/EWG. The resulting EC50 -values for growth and biomass were determined to be > 100 mg/L.

Since only a few data on the long-term aquatic toxicity for the mixtures within the category are available, the assessment on long-term aquatic toxicity is based for all category members on alcohol ethoxylate specific QSARs (Wind & Belanger, 2006; Boeije et al., 2006; Belanger et al, 2006). The QSARs considered all three trophic levels (algae, invertebrates and fish). The effects are described as EC20 values, since the QSARs are more robust for the EC20 values than for NOEC or EC10 values. For the described mixture of for alcohol ethoxylate ((Z)-9-Octadecen-1-ol ethoxylated, < 2.5 EO, CAS 9004-98-2) the QSAR for long-term toxicity on green algae Desmodesmus subspicatus (Wind & Belanger, 2006) result in an EC20-value of 0.054 mg/L based on biomass and 0.145 mg/L based on growth rate, respectively. This result (ErC20 = 0.145 mg/L) is used as key value for the assessment on long-term effects.