1-Dodecene, mixed with 1-decene and 1-octene, dimers, hydrogenated

Toxicity to aquatic algae and cyanobacteria

Description of key information

Data directly assessing the short-term toxicity of the registered substance “reaction products of 1-decene, 1-dodecene and 1-octene, hydrogenated” in algae and aquatic plants are not available.  However, read-across data for one main component, 1-decene dimer with dodecene, hydrogenated (CAS 151006-58-5) have been reported, which showed no acute toxicity at the maximum water solubility limit (96 hr NOEL > 1000 mg/L nominal loading)..  Using an “analogue” justification approach, this read-across data support the assessment that the registered substance is also expected to cause no acute toxicity to algae at its water solubility limit under the WSF test conditions, owing to their molecular structural and physico-chemical similarities.  The use of NOELs for risk assessment is inappropriate as these values are not true NOECs as discussed in CSR Section 7.1.1

Additional information

Algae toxicity data for the major primary component, 1-decene dimer with dodecene (CAS 151006-58-5) have been reported and can be used for read-across assessment of the registered substance.  The acute toxicity of 1-decene dimer with dodecene hydrogenated (C20-22) as measured by biomass and growth rate to the green alga (Selenastrum capricornutum) was evaluated in freshwater. Water soluble fractions solutions (WSF) of this substance did not produce any acute toxicity to algae up to loadings of 1000 mg/L WSF relative to controls under the conditions of this study. No significant inhibition of algal growth (biomass or growth rate) was observed for this test substance at its maximal water solubility level in the WSF under the conditions of this test (ABC Laboratories, 1990). 1-Decene dimer with dodecene hydrogenated did not affect the growth (rate or biomass) of the freshwater alga,Selenastrum capricornutum, in the presence of up to 1000 mg/L loading WSF over a 96 hr period. The 72-hr and 96-hr ErL50, EbL50 values were determined to be >1000 mg/L WSF. The 96 hr NOEL was estimated to be greater than 1000 mg/L loadings. The results from the 96 hour alga toxicity study show that 1-decene dimer with dodecene, hydrogenated does not cause acute toxicity to algae at its water solubility limits under the WSF test conditions. Based on the available read-across data and the “analogue” justification approach discussed below, the registered substance (“reaction products of 1-decene, 1-dodecene and 1-octene, hydrogenated”) would be expected not to cause acute toxicity to algae at its maximum water solubility limits.

 

Read-across Justification (Analogue Approach):

 

Several criteria justify the use of the read-across approach to fill data gaps for the registered substance using the 1-decene dimer with dodecene, hydrogenated constituent substance. These substances are all hydrogenated poly alpha olefins, i.e., branched saturated paraffins or alkanes produced by oligomerization of 1-octene, 1-decene, and/or 1-dodecene. As described in the read-across justification appended to the CSR, these substances (being branched saturated alkanes) are similar in molecular structure, physicochemical properties, use, and manufacturing processes. Especially relevant to aquatic toxicity are the comparable water solubilities (i.e., very poorly water soluble, < 0.001 mg/L or < 1 ppb) and partition coefficients (log Kow >10). Based on these unifying considerations, the slight difference in carbon number among these analogues is not expected to impact aquatic toxicity. Therefore, it is scientifically reasonable to predict the ecotoxicological properties for the registered substance from the properties determined for the read-across analogue(s). These substances are related branched alkanes having analogous or homologous molecular structure and very similar inherent physico-chemical properties and are thus expected to exhibit similar toxicological effects.

The nature of the read-across approach utilized here is aligned with the “analogue approach” as described in section R.6.2.3 of the ECHA document ‘Guidance on Information requirements and chemical safety assessment Chapter R.6: QSARs and grouping of chemicals’ (ECHA, 2008e). The “analog” similarity among molecular structure and molecular weight which provides the basis for the read-across justification is scientifically founded and therefore adequately clarifies why the properties of the registered substance may be predicted from the properties of the read-across substance(s) and more specifically, why the data submitted for 1-decene dimer with dodecene, hydrogenated (includes C20-C22) are appropriate for the purposes of read-across assessment of the registered substance which contains similar molecules with carbon numbers in the ranges of 18-24 carbon atoms.