Branched hexatriacontane

Bioaccumulation: aquatic / sediment

Description of key information

In accordance with Column 2 Adaptation as stated in REACH Regulation (EC) No. 1907/2006 (section 9.3.2, Annex IX) the bioaccumulation study does not need to be conducted if the substance has a low potential to cross bioolgical membranes. 
The optimal range for diffusive uptake is log Kow -1 to 4 according to ECHA guidance chapter R.7c , see toxicokinetic assessment). Moderate log P values (between -1 and 4) are favourable for absorption by passive diffusion. Any lipophilic compound may be taken up by micellular solubilisation but this mechanism may be of particular importance for highly lipophilic compounds (log P >4), particularly those that are poorly soluble in water (1 mg/l or less) that would otherwise be poorly absorbed. 
The submission substance has a log Kow >10 and is therefore not expected to bioaccumulate.
Infact, for reasons mentioned above, members of this category are not expetced to bioaccumulate.

Additional information

Experimental data on Kow are available for several members of this category. For the alkane with CAS No. 68649-11-6 log Kow is measured as >6.5 (Walker and Mullee, 2006) and > 4.82 (Hogg and Bartlett, 1995). For CAS No. 68649-12-7, experimental data measures log Kow as > 5 (Howard, 1982), > 7.6 (Seary, 2000) and > 3.87 (Hogg and Bartlett, 1995). For CAS No. 68037-01-4 an experimental value of >6.5 (Walker and Mullee, 2006) is given. As the majority of the experimental log Kow for substances in this category are greater than 4.5 this indicates that an estimate of the bioaccumulation potential is required.

Non-polar substances have been shown to have a linear relationship between log Kow and BCF in the log Kow range 1 -6. However, at log Kow >6 a decreasing relationship is observed. ECHA’s Guidance on information requirements and chemical safety assessment - Part C: PBT Assessment (2008) states that the aquatic BCF of a substance is probably lower than 2000 L/kg if the calculated log Kow is higher than 10. All of the experimental log Kow values for substances in this category are unbounded due to limitations of the experimental method, so do not allow us to conclude if the log Kow is greater than 10. Calculated partition coefficients have been obtained from EPIWEB 4.0 (USEPA, 2008) and SPARC (Karickhoff et al, 2009) for dec-1-ene dimer, hydrogenated (CAS 68649-11-6) and dec-1-ene trimer, hydrogenated (CAS 157707-86-3) as these are the only two members of this category being registered as substances with predominantly a single carbon number. The calculated log Kow for CAS No. 68649-11-6 is 10.09 and 11.71 and for CAS No. 157707-86-3 is 14.93 and 17.21 (USEPA, 2008 and Karickhoff et al, 2009 respectively). All of the calculated log Kow values are greater than 10.

There is a clear trend of increasing log Kow with increasing carbon number in the alkanes and olefins. Dec-1-ene dimer hydrogenated (CAS 68649 -11 -6) is the category member with the lowest carbon number, and therefore will be the category member with the lowest partition coefficient. This therefore indicates that the calculated log Kow of all category members would be >10. As QSAR models do not have experimental data in this Kow range the reliability of modelled Kow values > 10 is not known. However, as two models indicate a log Kow >10 for the category member with the lowest carbon number we can conclude that members of this category are unlikely to be bioaccumulative and therefore that conducting a study to determine an experimental BCF is not scientifically justified.

 

In addition, the expert paper (Girling 2007) on structural analogue Alkane 4 concluded that the BCF of Alkane 4 will be below 10 and that it will not therefore meet the criterion of BCF >5000 for being considered very bioaccumulative (vB) or the lesser criterion of BCF >2000 for being considered bioaccumulative (B). This expert paper further supports that Alkane 6 is not expected to bioaccumulate.