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

Long-term toxicity to aquatic invertebrates

Description of key information

Data directly evaluating the long-term adverse effects of the reaction products of 1-decene, 1-dodecene, and 1-octene, hydrogenated to the freshwater invertebrate, Daphnia magna, are not available.  However, there are “analogue” read-across data for two structurally similar hydrogenated polyalphaolefin (PAO) materials, Alkane 8, a C32 substance (CAS 177966-51-7) and Alkane 1 (CAS 173994-67-7), a C16 substance for read-across assessment.  
 
Using a read-across “analogue” approach, surrogate chronic invertebrate data for the Alkane 1 and Alkane 8 PAO substances support the assessment that the registered substance would not be expected to cause chronic toxicity to invertebrates at the maximum water solubility limits (if tested under WAF conditions). Mitigating factors contributing to the lack of chronic adverse effects in invertebrates observed include the fact that these C16 to C32 substances are very insoluble in water.  
 
NOEL values of 1000 mg/L and 5000 mg/L (loading rates) have been reported for the 21-day chronic survival and reproduction studies in Daphnia magna for Alkane 1 (C16 substance) and Alkane 8 (C32 substance) , respectively. However, the use of NOELs reported for risk assessment is inappropriate as these values are not true NOECs as discussed in CSR Section 7.1.1.

Additional information

A 21-day static renewal chronic survival and reproduction study was conducted to determine the toxicity of Alkane 8 toDaphnia magna. Alkane 8 is a 4.6 cst viscosity PAO material comprising mainly of 1-hexadecene, dimer hydrogenated or essentially a C32 saturated branched alkane material. Daphnids were exposed to individual water accommodated fractions (WAFs) of the test material based on nominal loadings of 100, 500, 1000, 2000 and 5000 mg/L. WAF solutions were renewed every 48 hrs during the conduct of the study. The hydrogenated PAO material, Alkane 8, did not affect the reproductive capacity inDaphnia magnaat maximal water accomodated fractions at 5000 mg/L loading exposure. No immobilization and no reproductive inhibition were observed when compared with controls at any of the WAF solution exposures. The 21 day LL50 (mortality or survival) and the 21-day EL50 (reproduction) was greater than 5000 mg/L WAF. The 21-day no-observed-effect loading (NOEL) was 5000 mg/L WAF (Springborn Laboratories, 1998). 

 

Another surrogate PAO material, CAS# 173994-67-7 [Alkane 1 or 1-octene dimer, hydrogenated, 2 cst viscosity, a C16 saturated branched alkane material] was also evaluated for long-term toxicity testing in invertebrates. It did not adversely affect the reproductive capacity inDaphnia magnawhen tested as water accommodated fractions (WAF) at loadings up to a maximal of 1000 mg/L. No significant immobilization or reproductive inhibition was observed when compared with controls at the WAF solution exposures. The 21-day LL50 (mortality or survival) and the 21-day EL50 (reproduction) was estimated as greater than 1000 mg/L WAF. The 21-day no-observed effect loading (NOEL) was 1000 mg/L WAF (based on mortality and reproduction) (Covance Laboratories, 2001). 

Based on theread-across “analogue”data for theAlkane 1 and Alkane 8 PAO substances, the registered substance would not be expected to cause chronic toxicity to invertebrates at the maximum water solubility limits (if tested under WAF conditions). Mitigating factors contributing to the lack of chronic adverse effects in invertebrates observed include the fact that these C16 to C32 substances are very insoluble in water. 

 

Read-across Justification (analogue approach):

Several criteria justify the use of the read-across approach to fill data gaps for the registered substance using Alkane 1 (a branched PAO with a total of 16 carbon atoms) and Alkane 8 ( a branched PAO with a total of 32 carbon atoms). These substances are all hydrogenated poly alpha olefins, i.e., branched saturated paraffins or alkanes produced by oligomerization of 1-octene or 1-hexadecene. As explained in the “analog-approach” 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 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 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 (i.e., water solubility and high lipophilicity) of the registered substance may be predicted from the properties of the read-across substance(s) and more specifically, why the data submitted for Alkane 1 (C16 substance) and Alkane 8 (a C32 substance) are appropriate for the purposes of read-across assessment of the registered substance. The C16-C32 range covered by the read-across PAO surrogates demonstrated no chronic adverse effects to daphnids (i.e., NOEL 1000 mg/L and 5000 mg/L , nominal loading rates).The lack of chronic adverse effects is most likely attributable to the very poor water solubility (<0.001 mg/L) and the high log Kow (>10) of the PAO substances as well to the inherent non-reactivity nature of the saturated branched alkane molecular structure for the hydrogenated PAO substances. These surrogate PAOs are very water-insoluble and have high log Kow, properties and are structurally analogous or homologous with the registered substance, Therefore, it is scientifically reasonable that the read-across PAO substances (C16 and C32) should be able to bracket the carbon range in the registered substance (i.e., C18-C24). Therefore, it is reasonable to assume that the chronic daphnia data reported for the C16-C32 PAO surrogates should be predictive of that expected for the registered substance (C18-C24 range).