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

Toxicity to microorganisms

Description of key information

Data directly assessing the short-term toxicity of the registered substance to aqueous microorganisms are not available.  However, “analogue” read-across data for two main constituents (CAS 68649-11-6 and CAS 151006-58-5) and another analogue, Alkane 4 (CAS 151006-62-1) have been reported.  Read-across results from two studies with activated sludge sewage inocula indicate that C20-C36 PAO substances did not cause toxicity to mixed microorganisms.  Using specific strains in other tests, it was shown that 1-decene dimer hydrogenated (C20) was not inhibitory to Pseudomonas putida or Photobacterium phophoreum.  Based on the available read-across data and the “analogue” justification approach discussed above, the registered substance (i.e., "reaction products of 1-decene, 1-dodecene, and 1-octene, hydrogenated”) also would not expected to be inhibitory or harmful to activated sewage sludge microorganisms or to other aqueous microbes.  The use of NOELs reported in the table above for risk assessment is inappropriate as these values are not true NOECs as discussed in Section 7.1.1.

Additional information

Activated Sludge Microorganism Toxicity Data

Data directly assessing the short-term effects or toxicity potential to activated sludge / sewage treatment micro-organisms of the registered substance are not available. However, data for one major constituent, 1-decene dimer with 1-dodecene, hydrogenated (CAS 151006-58-5) and for a structurally related PAO analog, Alkane 4 (1-dodecene trimer hydrogenated, CAS 151006-62-1, a C36 substance) have been reported and can be used for read-across assessment (see table in the CSR). SafePharm Laboratories (1995) have reported that 1-decene dimer with 1-dodecene hydrogenated (CAS 151006-58-5) (C20-C24) did not inhibit activated sludge microorganisms in a ready biodegradability screening test. The C20-C24 substance was found to be not inhibitory to microorganisms in the activated sludge inoculum and did not affect the biodegradation of the reference material, sodium benzoate in the toxicity controls in the study. In addition, an analogue PAO substance, Alkane 4 (CAS 151006-62-1), a C36 substance did not affect the respiration rate of activated sewage sludge microorganisms and gave a 3 hr EL50 value of greater than 1000 mg/L and a NOEL value of 1000 mg/L nominal loading (SafePharm Lab. 2000). Based on the available read-across data and the “analogue” justification approach discussed below, the registered substance(i.e., "reaction products of 1-decene, 1-dodecene, and 1-octene, hydrogenated”) is not expected to be inhibitory or harmful to activated sewage sludge microorganisms.

Aquatic Microorganism (Pseudomonas putidaandPhotobacterium phosphoreum) Toxicity Data

Studies with the registered substance to directly evaluate the short-term toxicity effects to aquatic micro-organisms are not available. However, read-across data have been reported for 1-decene dimer hydrogenated substance (CAS 68649-11-6) in two microbial strains. Lebertz (1997) evaluated the toxicity of 1- decene dimer hydrogenated to Pseudomonas putida in a DIN 38412 test and reported no inhibitory effects at exposure levels of 0.1, 1 and 10 gm/L loadings (16-hr NOEL >10 gm/L). In addition, Carpenter (1995) has reported Microtox assay data for polyalphaolefin (PAO) substances including the 2 cst viscosity PAO substance, 1-decene dimer hydrogenated substance (C20) (CAS 68649-11-6). The assay measures photo-luminescence response of the marine bacteriumPhotobacterium phophoreum. Adverse effects are indicated by a decrease in photoluminescence. The 2 cst PAO substance (i.e., 1-decene dimer hydrogenated, CAS 68649-11-6) was evaluated as a WSF solution using a 5 minute exposure interval. The WSF test solution of the 2 cst PAO substance (C20 substance) did not demonstrate any inhibition to photoluminescence at loadings up to 49,500 mg/L (nominal loading). The WSF solutions were expected to exceed the water solubility limits of the test material. Based on the available read-across data and the “analogue” justification approach discussed below, the registered substanceis not expected to be inhibitory or harmful to aquatic microorganisms likePseudomonas putidaorPhotobacterium phosphoreum.

 

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, hydrogenated constituent substance. These substances are all hydrogenated poly alpha olefins, i.e., branched saturated paraffins or alkanes produced by oligomerization of the corresponding 1-alkene (e.g., 1-octene, 1-decene, 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 variation in carbon number among these analogues is not expected to significantly impact their ecotoxicity. Therefore, it is scientifically reasonable to predict the ecotoxicological properties for the registered substance from the properties determined for the read-across analogues. These substances are related branched alkanes having analogous or homologous molecular structure and 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 “analogue” similarity among molecular structure and molecular size 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 hydrogenated (C20), 1-decene dimer with 1-dodecene, hydrogenated (C20-C24) and Alkane 4 (C36) 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 (containing at least 85% or more C20-C24). All these PAO substances including the C36 Alkane 4 substance are very water insoluble (<0.001 mg/L) and very lipophilic (high log Kow >10) which contributes to their non-bioavailability or non-partitioning in the water phase which makes it unlikely for these unreactive substances to cause adverse effects or toxicity to microorganisms in the aqueous environment. They are all branched alkane substances and that the data reported for the range of C20-C36 substances clearly indicate the lack of adverse effects that they have on aquatic bacteria or activated sludge microbes. The aqueous insolubility, high log Kow and non-bioavailability characteristics of these analogous PAO substances (C20-C36) as well as their inherent non-reactivity are most likely responsible for their observed lack of toxicity.

By the criteria discussed above, Alkane 4, although as a trimerized C-12 olefin reaction product is nevertheless a “branched alkane” except a higher homolog with C36 total carbon atoms and it is chemical “analogue” of the branched alkane related to the registered substance (C18-C24). These substances are hydrogenated oligmerized alpha-olefin products that are analogous or homologous branched alkane substances. By the chemical analogue approach, Alkane 4 is molecularly similar and have characteristically related physico-chemical properties of being very water insoluble unreactive branched alkane (water solubility: 1.02 E-13 mg/L calculated) and having a high log Kow ( log Kow = 17.9 calculated) (using US EPA EPI-Suite model). Alkane 4 like the registered substance have characteristic very low water solubility (<0.001 mg/L or lower) and very high log Kow (>10) which make them non-partitioning in the water phase, which mechanistically contribute to their non-toxicity in aquatic organisms. For these reasons and the several criteria discussed previously, it is scientifically reasonable to predict the ecotoxicological properties of the registered substance from Alkane 4 from their commonality in molecular structures (as analoguous branched alkane) which are inherently inert and unreactive in nature) and their very low water solubility and high log Kow physico-chemical properties.