Docosan-1-ol

Endpoint summary

Description of key information

The environmental fate of docosan-1-ol is summarised as follows.

Stability and degradation (water, soil and sediment)	Readily biodegradable. Very short environmental half-life; biodegradable by a range of organism types.
Stability and degradation (atmosphere)	Half-life of 11.9 h for photochemical degradation by hydroxyl radicals.
Bioaccumulation	BCF 9.3 l/kg ww in fish (estimated); extensive metabolism in vivo is to be expected.
Transport and distribution	Modelling predicts predominant compartment to be soil (or sediment, where local release is to water). Volatility: low, based on Henry’s law constant of 0.40 Pa.m³/mol at 12°C. Adsorption: very high, based on Koc of 1310000 l/kg.
Reported natural levels	In general fatty alcohols are detected at low concentrations in WWTP effluents. Only a very small proportion is attributable to anthropogenic alcohols.

Additional information

Overview of the trends in environmental fate properties across the Category

The alcohols in this category are susceptible to very rapid biodegradation. Depending on test methodology, this may appear to show a trend with decreasing rate as carbon number increases, though this is largely related to the trend of decreasing limit of solubility in water, which can artificially limit the biodegradation rate unless care is taken with substance loading technique.

The alcohols have also been shown to be rapidly biodegraded in sewage treatment plant simulation tests; under anaerobic conditions; in soil; in activated sludges from sewage treatment plants; in fresh water die-away tests; and also in ecotoxicological aqueous test media. The numbers of category members with available data are limited, though the available data is sufficient to demonstrate consistency in this property.

The alcohols in this category undergo atmospheric photodegradation with half-lives in the range ca. 10-30 hours under typical European conditions associated with reaction with hydroxyl radicals based on measured and predicted results.

Long chain alcohols have no hydrolysable structural features and would not be expected to be degraded by oxidation under normal environmental conditions.

Adsorption to organic carbon obeys a predictable relationship with log Kow, as expected based on structure. Interaction with inorganic components of soil and sediment substrates would not be expected to be significant.

There is evidence for very low bioaccumulation levels, below the threshold of the B criterion, but there are few reliable BCF values in view of technical difficulties in performing such a test. Significant biotransformation is to be expected, as discussed below.

Biochemistry (environmental species):

- Metabolic Synthesis

Bacteria and plants are known to synthesise fatty alcohols within the chain length range C6-24, relevant to this Category of alcohols. Synthesis begins with formation of fatty acids, formed by Type II synthesis in bacteria and plants. Type II synthesis is series of reactions similar to Type I but independent of one another, which yield fatty acids with between 8 and 16 (18) Carbon atoms. Double bonds can be formed at a variety of positions. Bacteria form branched chain and odd chain length fatty acids and alcohols. Fatty acids can be shortened or elongated in cells. Fatty alcohols are formed from fatty acids through the two step fatty acid reductase (FAR) process (Mudge, 2008).

In other environmental species, long chain aliphatic alcohols are formed as part of fatty acid breakdown in aquatic invertebrates and vertebrates.

- Metabolic degradation

Long chain aliphatic alcohols are metabolised by a pathway that also acts on alkanes and fatty acids (Mudge, 2008). Alkanes may be oxidised to alcohols and alcohols converted via short-lived aldehydes to fatty acids (which are exempt from REACH). The fatty acids produced by the action of alcohol dehydrogenase followed by aldehyde dehydrogenation enter the β-oxidation cycle producing acetyl-CoA products (and a propionyl-CoA from odd chain-length molecules) and ATP. The products enter into the metabolic processes of the cells. Long chain alcohols are also intermediates in the microbial breakdown of alkanes and waxes.

Long chain aliphatic alcohols are metabolised by algae, to the extent that it is difficult to maintain concentrations in aquatic studies in which Daphnia are fed on algae (Schäfers, 2005a-d). Alcohol dehydrogenases are found in all plants and animals. There are many publications in the public domain which describe the cellular metabolism of alcohols and the ubiquity of the enzymes involved (Höög, J-O et. al., 2003; Duester, G et. al., 1999).

Natural occurrence in the environment

Long chain aliphatic alcohols occur naturally in the environment. Studies in the EU and USA consistently show that anthropogenic alcohols in the environment are minimal compared to the level of natural occurrence.

Concentrations of C16 and C22-24 long chain alcohols have been summarised (Mudge, 2008). The concentrations have been found to be very similar in different parts of the world. The highest concentrations are found in suspended sediments.

Using stable isotope signatures of fatty alcohols in a wide variety of household products and in environmental matrices sampled from river catchments in the United States and United Kingdom, it has been estimated that 1% or less of fatty alcohols in rivers are from waste water treatment plant (WWTP) effluents, 15% is from in situ production (by algae and bacteria), and 84% is of terrestrial origin (Mudge et al., 2012). Further, the fatty alcohols discharged from the WWTP are not the original fatty alcohols found in the influent. While the compounds might have the same chain lengths, they have different stable isotopic signatures (Mudge, 2012).

In conclusion, the environmental impact of these studies is that it has confirmed that the fatty alcohols entering a sewage treatment plant (as influent) are partly derived from detergents, but these are not the same alcohols as those in the effluent which arise from in-situ bacterial synthesis. In turn, the fatty alcohols found in the sediments near the outfall of the WWTP are derived from natural synthesis and are not the same alcohols as those in the effluent; they are found in waters where there is no anthropogenic source (Mudge, 2012).

References:

Duester, G et al., (1999). Recommended nomenclature for the vertebrate alcohol dehydrogenase gene family. Biochemical Pharmacology, Volume 58, Issue 3, 1 August 1999, Pages 389–395.Höög, J-O, Strömberg, P., Hedberg, J. J. & Griffiths, W. J. (2003). The mammalian alcohol dehydrogenases interact in several metabolic pathways. Chemico-Biological Interactions, 143-144, 175-181.

Mudge, S. M., Belanger, S. E., Nielsen, A. M., (2008). Fatty Alcohols — Anthropogenic and Natural Occurrence in the Environment. Royal Society of Chemistry, London, UK. ISBN 978-0-85404-152-7.

Mudge, S.M, Deleo, P.C., Dyer, S.D. (2012). Quantifying the anthropogenic fraction of fatty alcohols in a terrestrial environment. Environmental Toxicology and Chemistry, Vol. 31, No. 6, pp. 1209–1222Schäfers, C. (2005a). Daphnia magna, reproduction test in closed vessels following OECD 211. C10 fatty alcohol. GLP code: SDA-005/4-21. Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) 57377 Schmallenberg, Germany.

Schäfers, C. (2005b). Daphnia magna, reproduction test in closed vessels following OECD 211. C12 fatty alcohol. GLP code: SDA-001/4-21. Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) 57377 Schmallenberg, Germany.

Schäfers, C. (2005c). Daphnia magna, reproduction test in closed vessels following OECD 211. C14 fatty alcohol. GLP code: SDA-006/4-21. Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) 57377 Schmallenberg, Germany.

Schäfers, C. (2005d). Daphnia magna, reproduction test in closed vessels following OECD 211. C15 fatty alcohol. GLP code: SDA-002/4-21. Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) 57377 Schmallenberg, Germany.