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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The key study by Flach (2014) reported ready biodegradability of 2-tetradecyloctadecan-1-ol, a Long Chain Alcohol (C32) Category constituent used in read-across to the Category substance Alcohols, C20-30 (even numbered). Biodegradation of 90.0% was achieved within 28 days after acidification. The  10-day window was fulfilled, since a mean degradation of ≥ 60% was already reached on day 7. Therefore the test item reached the pass level for ready biodegradability (60% ThCO2 and 10-day window).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Alcohols, C20-30 (even numbered), is a UVCB substance that comprises several linear long chain alcohols, predominantly tetracosan-1-ol (C24), hexacosan-1-ol (C26) and octacosan-1-ol (C28). Together, these constituents make up approximately 70% of the composition of Alcohols, C20 -30 (even numbered). Other constituents include, to a much lesser extent, secondary long chain alcohols and complex mixtures of long chain carboxylate esters. On this basis, study data, where available, for each of the long chain alcohol constituents has been evaluated and considered together; this is consistent with the Category approach applied for Long Chain Alcohols (LCA) under REACH. Long chain alcohols are already classified as a category comprising straight and branched alcohols with predominant carbon numbers in the range of C6 to C22. As defined in the ‘Read Across Justification Document’ section 13, data provided for this Category is representative of Alcohols, C20-30 (even numbered) and has been extended to include longer carbon chain length alcohols suitable for assessment purposes.

The OECD SIDS Initial Assessment Report for SIAM 22 (April, 2006) on Long Chain Alcohols presents a category approach for a family of 30 primary aliphatic alcohols within a carbon chain length of C6-22, including linear and branched structures. The SIDS report states that the Category chemicals share the same structural features, similar metabolic pathways, common mode of ecotoxicological action and common levels and model of human health related effects. The report concluded that LCAs can be considered readily biodegradable. In addition, the publication by Federle (2009) concluded that the longer chain LCAs degrade more rapidly than the intermediate chain ones with docosan-1-ol reaching a mineralisation level of 88% at the end of the 28 day study period and 83% within the 10-day window.

Experimental data for the LCA Category has also been evaluated and trends in the environmental fate of long chain alcohols was used to assess Alcohols, C20-30 (even numbered) for the biodegradation endpoint. A conservative approach was taken to read across within the Category where constituents with longer carbon chain lengths (up to C32) are the focus.

Reliable experimental studies (Klimisch scores 1 and 2) were performed in accordance with OECD Guidelines on eicosan-1-ol (C20), docosan-1-ol (C22), 2-decyltetradecanol (C24) and tetradecyloctadecan-1-ol (C32) that are constituents of and analogous to primary constituents of Alcohols, C20-30 (even numbered) and the LCA Category. A modelled prediction was also available for eicosan-1-ol.

The key study by Flach (2014) reported 90% biodegradation of tetradecyloctadecan-1-ol in an OECD 301B CO2-evolution test over 28 days. More than 60% of tetradecyloctadecan-1-ol had degraded within the 10-day study window. The key study demonstrates that tetradecyloctadecan-1-ol, a C32 long chain alcohol, is readily biodegradable. In a study by Flach (2012b), 2-decyltetradecanol degraded by 84% in a 28-day test and achieved the 10-day window confirming the ready biodegradability of this long chain alcohol (C24) that is an analogue to constituents of Alcohols, C20-30 (even numbered). Similarly, three studies examined the biodegradability of Isofol 24, 28, and 32 in an OECD 301F Electrolytic(Manometric) Respirometry Method test. Isofol 24 and 32 demonstrated ready biodegradability by reaching >60% ThOD within a 10 day window. However, Isofol 28 is considered inherently biodegradable achieving >60% ThOD in a 28 day period.

Two studies showed the constituent docosan-1-ol (C22) to be readily biodegradable with 87.9% and 87.5% degradation in 28 days corresponding to studies by Federle (2009) and Flach (2012a), respectively. The constituent eicosan-1-ol (C20) was also reported to be readily biodegradable with 88.4% degradation in the 28-day study by Federle (2009). A study by Mead (2000) reported slow degradation of docosan-1-ol (37%) after 28 days. It is not known why this study is inconsistent when the rate of biodegradation is approximately half the rate of all the other experimental studies. The OECD (2005) predicted eicosan-1-ol to be “inherently biodegradable” when modelled using QSAR. The study by Mead (2000) and the QSAR prediction are attributed with lower weighting than the other experimental studies.

All of the experimental studies and evidence from the published literature demonstrate that constituents and analogues of Alcohols, C20-30 (even numbered) will degrade in the aquatic environment. It is concluded that given the very close similarity between LCA Category alcohols, 2-decyltetradecanol and tetradecyloctadecan-1-ol, as well as similar physico-chemical properties and structure, it is fully expected that Alcohols, C20-30 (even numbered) will rapidly and readily biodegrade in the environment. The weight of evidence (5 of 6 experimental studies) is ready biodegradation of these long chain alcohols, in particular those with longer carbon chain lengths (C24 and C32) corresponding to and extending beyond Alcohols, C20-30 (even numbered).