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

Toxicity to soil macroorganisms except arthropods

Description of key information

Data directly assessing the short-term earthworm toxicity of the registered substance, the reaction products of 1-decene, 1-dodecene, and 1-octene, hydrogenated, are not available.  However, “analogue” read-across data for a primary component of the registered substance, namely, 1-decene dimer, hydrogenated (CAS No. 68649-11-6) have been reported.  Results from a 14-day earthworm study (OECD 207 study guidelines) show that hydrogenated 1-decene dimer (C20) does not cause toxicity at the highest soil concentrations tested (890 mg/kg) (ExxonMobil Biomedical Sciences Laboratory, 2009).  The 14-day LC50 was greater than 890 mg/kg and the 14-day NOEC was greater than 890 mg/kg with no mortality observed for the hydrogenated 1-decene dimer material.  Based on the available read-across data and the “analogue” justification approach discussed below, the registered substance is not expected to cause toxicity in earthworm as well. 
A long-term earthworm study (OECD 222) was carried out recently with the registered substance and the results of the 56 day study indicated no long-term effect on  reproduction at 100 mg/kg dw soil.  The number of juveniles reproduced in the treated group was not statistically different from that in the control group.  Also no long-term effects on adult worm mortality or growth were observed at Day 28.  No mortality in adults was observed for the control or the test group.  The body weights of the control and treated adult earthworms were not statistically different.  
In summary, the acute and chronic testing results indicate that the registered substance is not expected to cause acute or long-term toxicity in the earthworm (Eisenia fetida). 

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

890 mg/kg soil dw

Long-term EC10, LC10 or NOEC for soil macroorganisms:

100 mg/kg soil dw

Additional information

Using the “analogue” read-across approach as discussed below, the read-across results of the earthworm acute toxicity studies for the 1-decene dimer hydrogenated constituent would support the assessment that the registered substance, the reaction products of` 1-decene, 1-dodecene and 1-octene, hydrogenated, would not be expected to cause acute toxicity in earthworm as well. A 14 day NOEC value > 890 mg/kg soil loading was reported for the C20 PAO read-across substance.   

A chronic earthworm reproduction study (OECD 222) was carried out recently with the registered substance and the results of the 56 day study indicated no long-term effect on reproduction at 100 mg/kg dw soil. (NOEC > 100 mg/kg). The number of juveniles reproduced in the treated group was not statistically different from that in the control group. Also no long-term effects on adult worm mortality or growth were observed at Day 28. No mortaility in adults was observed for the control or the test group. The body weights of the control and treated adult earthworms were not statistcally different. No abnormal behavioral or other adverse effect were reported.

It is of interest to note that significant amounts of naturally-occurring n-alkanes and isoalkanes (including C20-C33) components have been found in earthworms (Nooner, et al. 1973) and earthworms appear to be insensitive to exposure to long-chain saturated alkanes. The n-alkanes and isoalkanes were associated with the soil humus which the earthworms ingest. Overall, these findings and the recent earthworm toxicity study results for 1-decene dimer hydrogenated support the fact that saturated alkane materials like the reaction products of 1-decene, 1-dodecene and 1-octene, hydrogenated, pose little toxicity concern to earthworms. Reference: Nooner DW, Oro J and Cerbulis J., Paraffinic hydrocarbon composition of earthworms. Lipids 8: 489 -492 (1973).

 

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 difference 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 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, hydrogenated (C20) 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 60% C20).