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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Endpoint:
bioaccumulation in aquatic species: fish
Remarks:
Biotransformation in vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
1. HYPOTHESIS FOR THE CATEGORY APPROACH
The hypothesis is that the category members have similar structures and properties (low bioaccumulation potential, with metabolism and bio-transformation in vivo), which are consistent across the category (Scenario 6 in the RAAF). The consistency of this property across the category is discussed in the endpoint summary.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Please refer to the test material identity information within each endpoint study record and to the endpoint summary. The source chemicals and the target chemical are linear aliphatic alcohols which are members of the long chain linear aliphatic alcohol Category.

The long chain linear aliphatic alcohol Category has at its centre an homologous series of increasing carbon chain length alcohols. The category members are structurally very similar. They are all primary aliphatic alcohols with no other functional groups. The category members are linear or contain a single short-chain side-branch at the 2-position in the alkyl chain, which does not significantly affect the properties (‘essentially linear’). The category members have saturated alkyl chains or contain a small proportion of naturally-occurring unsaturation(s) which does not significantly affect the properties. The branched and unsaturated structures are considered to have such similar properties that their inclusion in the category is well justified.
Impurities: Linear and/or ‘essentially linear’ long chain aliphatic alcohols of other chain lengths may be present. These are not expected to contribute significantly to the properties in respect of this endpoint due to consistent properties (see point 3).
There are no impurities present at or above 1% which are not category members or which would affect the properties of the substance.

3. CATEGORY JUSTIFICATION
The category members are structurally very similar (see point 2) and are biochemically very similar. The metabolic synthesis and degradation pathways are well established. This Category is associated with a consistency and predictability in the physicochemical, environmental, and toxicological property data across its members.

The consistency of observations in this property across the range of chain lengths covered by this Category is described in the Endpoint Summary and in the Category Report attached in Section 13.

In this registration, information on metabolism in vivo in fish is available based on read-across from a member of the category with longer chain length, providing evidence that even a relatively lipophilic category member substance is very rapidly biotransformed.

4. DATA MATRIX
A data matrix for the C6-24 alcohols Category is attached in Section 13.
Reason / purpose:
read-across source
Type:
other: Fate of fatty alcohol over 72 hours following oral exposure
Basis:
other: Expected distribution of residues in a range of tissue types
Remarks on result:
other: Overall, approx 3% expected to remain as free fatty alcohol 72 hours after oral exposure to alcohol (remainder expected to be converted to metabolites).
Endpoint:
bioaccumulation in aquatic species: fish
Data waiving:
study technically not feasible
Justification for data waiving:
other:
Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Remarks:
The result was obtained by the valid application of a well-established predictive method.
Justification for type of information:
QSAR prediction: refer to attached Environmental Fate Category Report and Bioconcentration Position Paper.
Principles of method if other than guideline:
The result was obtained using SRC BCFBAF v3.01 program.
Type:
BCF
Value:
1 400 L/kg
Remarks on result:
other: Using log Kow based methodology
Type:
BCF
Value:
>= 170 - <= 260 L/kg
Remarks on result:
other: Using method with adjustment for metabolism in vivo
Conclusions:
A BCF value of 56-70 l/kg wwt (log BCF 1.75-1.85) was obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

Bioconcentration factor in fish: low (BCF = 9.3 L/kg), estimated using QSAR. The bioconcentration factor (adjusted for bioavailability limitations, rapidin vivometabolism and transformation, and excretion processes) was estimated by CATALOGIC BCF base-line model (version 03.10). Based on this, the substance is non-bioaccumulative.

Key value for chemical safety assessment

BCF (aquatic species):
9.3 L/kg ww

Additional information

No reliable guideline-standard measured bioconcentration studies are available for docosan-1-ol. Reliable and validated QSAR predictions of bioconcentration in fish (adjusted for the mitigating effects of bioavailability limitations, rapidin vivometabolism and transformation, and excretion processes), are available for this substance and its structural analogues in the Alcohols Category, suggesting low values and consistent trends. The predicted values are reliable and are suitable as Key data for the REACH registrations of these substances.

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 severe technical difficulties. Firstly, it is anticipated that maintenance of the test substance in solution would be very difficult, As was demonstrated in the long-term aquatic ecotoxicity studies with several alcohols (see Sections 6.1.2 and 6.1.4), severe difficulties were encountered due to biodegradation and metabolism of the tested alcohols in the test system. Degradation in the invertebrate tests was almost complete within the 24 h test media renewal period and similarly, the long-term ecotoxicity study in fish with decan-1-ol required substantial method development work to overcome severe difficulties. Secondly the CATALOGIC method indicates that as a consequence of the rapid rate ofin vivobiotransformation and metabolism of substance once taken up by the test organism, a study would take a very long time to reach steady-state conditions. These factors also indicate that the relative uncertainty in any measured BCF value would probably be high.

Regardless of the value of bioconcentration factor, there would anyway be no requirement in REACH to conduct chemical safety assessment for predators via secondary poisoning, in view of the consistent lack of systemic toxic effects of the alcohols across this category in mammals via the oral route.

A BCF value of 1400 has been calculated by SRC BCFBAF v3.01 (2012). This model uses a log Kow-based equation with modified algorithms for specific structural features. This version of the software also incorporates a modification for biotransformationin vivo. This is taken as supporting data (based on an understanding that the training and validation underlying the CATALOGIC approach are more robust).

These considerations suggest that it is highly unlikely that this substance would bioaccumulate in biota. Validated quantitative QSAR predictions of BCF are available, which are sufficient for the needs of the REACH chemical safety assessment. The registrants do not propose to attempt a bioconcentration study following OECD Guideline 305.

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

The bioconcentration predictions of alcohols in the range C6-24 (linear, essentially-linear, and unsaturated structural types) were based on their lipophilicity and have been adjusted for the effect of metabolism and the molecular size as mitigating factors. The substances are not ionisable (i.e. no effect of ionisation is expected) and the effect of water solubility is negligible. Of the predicted first level metabolic reactions for linear, essentially linear and unsaturated alcohol structures relevant to this Category, those which reduce the maximum bioaccumulation potential (i.e. BCFMAX) significantly are: oxidation of alcohol group to aldehyde; O-glucuronidation; ω-oxidation and epoxidation. Based on these reactions the starting alcohols are practically eliminated after the first level metabolism. The predicted second and third level metabolic reactions are oxidation of alcohol group to aldehyde; oxidation of aldehyde group to carboxylic acid; β-oxidation and O-glucuronidation (OASIS-LMC, 2019). The CATALOGIC BCF base-line model takes into account the simulated first level metabolism.

This is consistent with previous evaluations which concluded that more simplistic log Kow-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 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).

The expectation of rapid metabolism and biotransformationin vivois also consistent with the rapid biodegradation of the substance, evidence of rapid metabolism in fish, mammals and micro-organisms (Mankura et al. 1987), and see Sections 7.1 and 6.1.4).

BCF values estimated by the CATALOGIC model for 2-methyl and 2-ethyl branched isomeric alcohols are very close to the estimated values for the linear structures of the same carbon number. The presence of branched constituents as impurities is therefore not expected to significantly affect the predicted values. Alcohol isomers with multiple alkyl side-branches 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.

The BCF value estimated by the CATALOGIC model for the unsaturated alcohol (z)-octadec-9-enol is close to the estimated value for the linear saturated structure of the same carbon number.

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 et al. 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. All linear alcohols in this chain length range are readily biodegradable in reliable standard studies.

It is therefore concluded that all of 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 performance of such a test.

References:

Oasis-LMC. Bioaccumulation assessment for linear, unsaturated and branched alcohols (unpublished study). 26 July 2019

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.