Alcohols, C12-15-branched and linear

Bioaccumulation: aquatic / sediment

Description of key information

Bioconcentration factor in fish: moderate (BCF = 67-340 based on log Kow regression, BCF = 510-1000 based on Arnot-Gobas method including biotransformation rate estimates), range for C12 - C15 based on linear structural isomers, estimated using QSAR.

Key value for chemical safety assessment

BCF (aquatic species):

1 000 L/kg ww

Additional information

No reliable guideline-standard measured bioconcentration studies are available for Alcohols, C12-15-branched and linear. In accordance with Section 2 of REACH Annex XI, the study does not need to be conducted because guideline-standard studies of bioaccumulation in fish would be confounded by the technical difficulties of maintaining the test substance in solution. As was demonstrated in the long-term studies of effects of close structural analogues in invertebrates (see Section 6.1.4), severe difficulties were encountered in conducting the study due to biodegradation (including metabolism) of the test substances in the test system was almost complete within the 24 h test media renewal period. Similarly the long-term study in fish conducted with the structurally analogous alcohol decan-1-ol required substantial method development work to overcome severe difficulties maintaining the test substance in the test system (see Section 6.1.2).

There is no requirement in REACH to conduct any secondary poisoning assessment, in view of the consistent lack of systemic toxic effects of the alcohols across this category to mammals. In addition, the rapid biodegradation of the substance, combined with evidence of rapid metabolism in fish, mammals and micro-organisms (Mankura (1987), and see Sections 7.1, 6.1.4), suggest that it is unlikely that bioaccumulation would be seen in studies.

BCF value of 67 -340 have been calculated using SRC BCFBAF v3.01 (2010) for C12 - C15 based on linear structural isomers. This model uses a log K_ow-based equation with modified algorithms for specific structural features. This version of the software also incorporates for the first time a modification for biotransformation in vivo, producing BCF values ranging between 510 - 1000 for lower, mid and upper trophic levels again across the range of constituents. These considerations suggest that it is unlikely that significant bioaccumulation would be exhibited in nature. 

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

All the reviewed data indicate that log K_ow-based QSARs overestimate BCF because they take no account of biotransformation and metabolism of alcohols by a wide range of biota from bacteria to mammals (Veenstra et al., 2009; Mudge, 2008). These observations have recently been critically assessed using cellular biotransformation assays of ethoxylated alcohols and other aliphatic surfactants which confirm that metabolism of the alkyl chain can lower BCF by orders of magnitude (Dyer et al., 2008; Cowan-Ellsberry et al., 2008). For the more soluble chain lengths, evaluated in non-guideline BCF studies on linear alcohols and guideline studies for branched alcohols, predicted BCFs are overestimated by at least an order of magnitude (Fisk et al., 2012).  

Values predicted for 2-methyl branched alcohols are fairly consistent with the predicted values for the linear structures of the same carbon number based on BCFBAF v3.0 estimates, with small variations only associated with small margins of variation in the log K_ow value. The presence of branched constituents is therefore not expected to significantly affect the predicted values; multiply-branched alcohols have been demonstrated to be metabolised ca. 2.5 times less efficiently by pig liver enzyme homogenate than linear structures of the same carbon number (Menzel et al., 2001, in which different isomeric forms of C12 saturated alcohols were studied as well as C14 linear alcohol), but a single branch is unlikely to have a significant impact.  

For the multi-constituent/UVCB long chain alcohols, a single BCF value is difficult to predict. However the values for the constituents present are relevant.   There is ample experimental in vivo evidence of metabolism in various trophic levels. Rapid biotransformation into tissue lipids has been demonstrated by Mankura (1987) in fish (carp), for oleyl alcohol (C18, unsaturated). Biotransformation of linear structures has been demonstrated to be faster than for multiply-branched structures (Menzel et al., 2001) in accordance with expectations based upon the metabolic pathways. Predicted bioconcentration factors, using methods which take account of the expected metabolism in vivo, estimate low BCF values. Experimental studies using structural analogues show low BCF values. All linear alcohols in this chain length range are readily biodegradable in reliable standard studies.  

BCF can be calculated using SRC BCFBAF v3.01 (2010). This model uses a log K_ow-based equation with modified algorithms for specific structural features. This version of the software also incorporates for the first time a modification for biotransformation in vivo. These considerations suggest that it is unlikely that bioaccumulation would be exhibited in nature for alcohols in the C6-24 linear and essentially-linear alcohols category. 

It is therefore concluded that the long-chain alcohols in this category are non-bioaccumulative. This conclusion is considered to be sufficiently well-supported to justify no need for further testing in fish, since vertebrate testing for the purposes of REACH registration should be avoided where adequate existing evidence exists, and in view of the expected severe technical difficulties in conducting such a test.

Further information can be found in the attached position paper.

References:

Cowan-Ellsberry, C.E., Dyer, S.D., Erhardt, S., Bernhard, M.J., Roe, A.L., Dowty, M.E., Weisbrod, A.V., 2008. Approach for extrapolating in vitro metabolism data to refine bioconcentration factor estimates. Chemosphere 70, 1804–1817.

Dyer, S.D., Bernhard, M.J., Cowan-Ellsberry, C., Perdu-Durand, E., Demmerle, S., Cravedi, J.-P., 2008. In vitro biotransformation of surfactants in fish. Part I: Linear alkylbenzene sulfonate (C12-LAS) and alcohol ethoxylate (C13EO8). Chemosphere 72, 850–862.

Peter Fisk Associates Limited (2012) Position paper: Bioaccumulation of Aliphatic Alcohols in the context of REACH registration. Reference: PFA.197.018.002. Date: 10 August 2012.