Tetracosanol

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

1. HYPOTHESIS FOR THE CATEGORY APPROACH
The hypothesis is that the category members have similar structures and properties (very rapid biodegradability), 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.

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, the information requirement is extrapolated based on read-across from docosan-1-ol, a neighbouring member of the category with slightly shorter chain length and equivalent physicochemical properties, providing evidence of consistency in behaviour.

4. DATA MATRIX
A data matrix for the C6-24 alcohols Category is attached in Section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Parameter:

% degradation (CO2 evolution)

Value:

87.5

Sampling time:

28 d

Remarks on result:

other: with consideration of the solvent control

Remarks:

Flach 2012

Parameter:

% degradation (CO2 evolution)

Value:

87.9

St. dev.:

6.4

Sampling time:

28 d

Remarks on result:

other: Federle 2009

Description of key information

Readily biodegradable: 87.5% (CO2) in 28 days (OECD 301B; GLP) supported by 87.9% (CO2) in 28 days (OECD 301B; not GLP) both read-across from docosan-1-ol

This value has been reliably read-across to tetracosan-1-ol. These results are supported by consistent findings for analogous alcohols of comparable chain lengths.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

No data are available for tetracosan-1-ol (CAS 506 -51-4), however study reports are available with the closely related substance docosan-1-ol (CAS 661-19-8). These linear structures are very closely related and differ in carbon chain length number, C22 for docosan-1-ol (CAS 661-19-8) and C24 for tetracosanol (CAS 506-51-4).

Their physicochemical, toxicological and ecotoxicological properties and behaviour do not differ significantly, therefore direct read-across from docosan-1-ol to tetracosan-1-ol is scientifically justified.

A reliable study (Federle, 2009), conducted according to an appropriate test protocol (OECD 301B), but not conducted according to GLP, determined the substance to be readily biodegradable (87.9% CO₂ evolution in 28 days), meeting the ten day window. Trichloromethane was used as a solubilising agent in this study. The solvent was then evaporated under a gentle stream of N₂ gas to deposit the test material as a film on the walls of the vessel.

This study (Federle, 2009), using a methodology with appropriate loading method for the low solubility of the substances, was carried out with a range of linear saturated alcohols from four carbon chain length (C4) to twenty-two carbon chain length (C22).

These results are significant and fit for purpose even though the study was not conducted to GLP. The study gave results of 76.1% (C4), 77.7% (C6), 77.9% (C8), 74.6% (C10), 69.0% (C12), 82.2% (C14), 82.4% (C16), 95.6% (C18), 88.4% (C20) and 87.9% (C22) in 28 days. All were readily biodegradable, meeting the ten-day window.

The result of this study is supported by reliable read-across ready biodegradation data for analogous alcohols of shorter (C18 and C20) chain lengths. C18 alcohol (octadecan-1-ol, CAS 112 -92 -5) in the same study gave results of 95.6% biodegradation in 28 days (Federle, 2009).

A study using the same methodology but with GLP gave results of 87.5% biodegradation in 28 days for docosan-1 -ol (Flach, 2012). As a GLP-compliant test this value is used as Key for the target substance.

Another reliable study (Mead, 2000) conducting to an appropriate test protocols (OECD 301B; EU method C.4; EPA OPPTS 835.3110) found the analogous alcohol (docosan-1 -ol; CAS 661-19-8) to be not readily biodegradable (37% in 28 days CO2 evolution). The result from this study is considered as an unexplained outlier.

It is quite normal to observe some inter-laboratory variation in screening studies, particularly for substances where solubility limits may be a factor in degradation rates under the conditions of the testing. Due to the very diluted nature of the inoculum and its limited size, it may sometime happen that no degradation-competent microorganisms are present in a particular inoculum. This is evidenced by the variable mineralisation levels seen for standard reference substances under the conditions of OECD 301 (e.g. glucose, 55-90%; benzoates 61-95%) in studies collated by AISE/CESIO [AISE/CESIO company data, and the 'Study on the possible problems for the aquatic environment related to surfactants in detergents' (WRc Ref EC4294, May 1997)].

In the case where multiple reliable studies exist showing a range of extent of biodegradation in the course of standard tests, the normal approach is to base the interpretation on the higher degradation results, this is in line with ECHA guidance on information requirements and chemical safety assessment. Furthermore, the very low limit of solubility of the registration substance is an important consideration. The studies in which lower levels of degradation were achieved did not use adapted methodology to avoid overloading the test system. An important piece of additional evidence to consider is the availability of ready biodegradation data from a series of tests conducted at the same laboratory at the same time, to examine degradability throughout the series of linear alcohols from C4-C22. Whilst at the time of the study by Federle (2009), the laboratory was not GLP-certified, the data are reliable and consistent throughout the homologous series. In this study (Federle, 2009) docosan-1 -ol (and all other chain lengths studied) was found to be readily biodegradable.

For these reasons, the Mead (2000) study mentioned above is disregarded.

The conclusion of ready biodegradability is consistent with evidence of rapid metabolism of long-chain fatty alcohols in fish, mammals and microorganisms(see IUCLID Sections 5.3.1, 7.1 and 6.1.4).

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

Many biodegradation assays have been carried out on this family of alcohols. Studies generated on single carbon chain length alcohols for tests that conform most closely to ready test biodegradability methods (OECD 301 series) show that alcohols with chain lengths up to C22 are readily biodegradable. In all cases the inoculum was not acclimated. Older reliable data suggest that chain lengths above C18 are not readily biodegradable, however those studies used loading techniques which, while in general still reliable, did not make allowance for the reduced bioavailability caused by the low water solubility of these longest chain substances. Where the substances are introduced into the test vessels by coating onto the flask, very rapid biodegradation was confirmed at all chain lengths tested.

In the older supporting tests, alcohols with chain lengths up to C18 are readily biodegradable. At carbon chain lengths ≤ 14, most tests showed that pass levels for ready biodegradation were reached within the 10 day window. Chain lengths of C16-18 achieved ready test pass levels, but not within the 10 day window. The one test on a single carbon chain length greater than C18 (using docosanol) showed degradation of 37%.

Tests which allowed adaptation are considered to have significant methodological deficiencies in terms of REACH requirements for the present purpose, and are accordingly considered to be Klimisch reliability 3: Invalid. However these also consistently demonstrate extensive biodegradability. Aliphatic alcohols occur naturally in the environment and environmental organisms will be acclimated.

Reliable studies for decanol and tetradecanol that show low levels of degradation are considered to be unexplained outliers. It is usual in the interpretation of such data to take the highest levels of degradation as the key study.

Federle (2009) conducted ready biodegradation screening tests on even-numbered saturated single chain length alcohols (C6-C22) using an appropriate test method (OECD 301B). Although, the test was not conducted in compliance with GLP, the study was found to be consistent with other available data, reliable and acceptable for environmental assessment. All tests substances were found to behave in a similar way. The substances were found to be readily biodegradable meeting the ten day window after a brief lag period. A separate test using the same methodology has confirmed the ready biodegradability result, meeting the ten-day window, at the upper end of the carbon number range (docosan-1-ol) in a GLP-compliant study (Flach, 2012).

Some variability is seen in the ultimate percentage degradation over the course of the study (see Table below). It is quite normal to observe some inter-laboratory variation in screening studies, particularly for substances where solubility limits may be a factor in degradation rates under the conditions of the testing. As discussed above, due to the very diluted nature of the inoculum and its limited size, it may sometime happen that no degradation-competent microorganisms are present in a particular inoculum. This is evidenced by the variable mineralisation levels seen for standard reference substances under the conditions of OECD 301. In the case where multiple reliable studies exist showing a range of extent of biodegradation in the course of standard tests, the normal approach is to base the interpretation on the higher degradation results, this is in line with ECHA guidance on information requirements and chemical safety assessment, and consistent with the availability of ready biodegradation data from a series of tests conducted at the same laboratory at the same time, to examine degradability throughout the series of linear alcohols from C6-C22. Whilst at the time of the study (Federle, 2009), the laboratory was not GLP-certified, the data are reliable and consistent throughout the homologous series. In this study (Federle, 2009) and all other chain lengths studied were found to be readily biodegradable. Degradation under anaerobic conditions is discussed below.

Biodegradation by algae

Rapid degradation in water is indicated by the difficulties encountered in aquatic toxicity tests (chronic Daphnia reproduction) for long chain aliphatic alcohols (Section 6.1.4). Alcohols in the range C10-C15 were found to be rapidly removed from the test medium. This was attributed to metabolism by algae present as a food source in tests, and in later stages of the 21-day tests to bacterial degradation by microbes adsorbed onto the carapace of the test daphnids, despite daily cleaning of the animals.

Natural occurrence

It is important for context to note the findings from studies in the EU and US which consistently show that anthropogenic alcohols in the environment are minimal compared to the level of natural occurrence. 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, Mudge et al.(2012) 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. 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 (Mudgeet al., 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 fromin-situbacterial 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.

Table: Ready biodegradation data on single constituent alcohols

CAS	Chemical Name	Comment	Method	Result % degradation	Result 10 day window	Reliability	Reference
111-27-3	1-Hexanol		301B	77.7% in 28 days at 17 mg/L	69.8%	2	Federle 2009
111-27-3	1-Hexanol		OECD 301-D	77% in 30 days at 2 mg/L 61% in 30 days at 5 mg/L	>60% in 14 days	2	Richterich, 2002a
111-27-3	1-Hexanol		Non-standard	- half life of 8.7 hours	-	2	Yonezawa and Urushigawa 1979
111-87-5	1-Octanol		301B	77.9% in 28 days at 18.8 mg/L	79.2%	2	Federle 2009
111-87-5	1-Octanol		ISO ring test (CO2 headspace biodegr. test)	92% in 28 days at 20 mg/L	>60%	2	Procter & Gamble, 1996
111-87-5	1-Octanol		OECD 301-B	59 % in 29 days at 10 mgC/L	-	2	Huntingdon Life Sciences Ltd. 1996a
111-87-5	1-Octanol		Non-standard	- half life of 1.9 hours	-	2	Yonezawa and Urushigawa 1979
112-30-1	1-Decanol			74.6% in 28 days at 15.1 mg/L	68.6%	2	Federle 2009
112-30-1	1-Decanol		301-D	88% in 30 days at 2 mg/L	>60%	2	Richterich, 2002c
112-30-1	1-Decanol		301-B	29 % after 29 day(s) at 10 mg/L COD	-	2	Huntingdon Life Sciences Ltd. 1996b
112-53-8	1-Dodecanol		301B	69% in 28 days at 15.4 mg/L	63%	2	Federle 2009
112-53-8	1-Dodecanol	Supporting	301-D	79% in 28 days at 2 mg/L	>60% in 14 days	1	Werner, 1993
112-72-1	1-Tetradecanol		301B	82.2% in 28 days at 15.9 mg/L	77.2%	2	Federle 2009
112-72-1	1-Tetradecanol		BODIS ~ISO 10708	92% in 28 days at 100 mg/L COD	>60%	1	Henkel, 1992d
112-72-1	1-Tetradecanol		301-B	28 % after 28 day(s) at 25.4 mg/L	-	1	Mead 1997b
36653 -82-4	1-Hexadecanol		301B	82.4% in 28 days at 15.3 mg/L	75.2%	2	Federle 2009
36653-82-4	1-Hexadecanol		301B	62% after 28 days at 17.1 mg/L	<60%	1	Mead, 1997c
36653-82-4	1-Hexadecanol		BODIS	76 % after 28 day(s) at 100 mg/L COD	<60% after 14 d	2	Henkel KGaA 1992a
112-92-5	1-Octadecanol		301B	95.6% in 28 days at 14.5 mg/L	90.2%	2	Federle 2009
112-92-5	1-Octadecanol	Supporting	301D	38% in 29 days at 5 mg/L 69% in 29 days at 2 mg/L	<60%	1	Henkel, 1992f
629-96-9	1-Eicosanol		301B	88.4% in 28 days at 15.6 mg/L	83.4%	2	Federle 2009
661-19-8	1-Docosanol		301B	87.5% in 28 days at 20 mg/L	75.6%	1	Flach, 2012
661-19-8	1-Docosanol		301B	87.9% in 28 days at 15.3 mg/L	83%	2	Federle 2009
661-19-8	1-Docosanol		301B	37% after 28 days at 12.4 mg/L	<60%	1	Mead, 2000

 

Biodegradation under anaerobic conditions

The anaerobic biodegradability of a range of chain lengths within the category has been investigated (C8, C16 alcohols (two studies), and C16-18 and C18 unsaturated alcohols). All test substances were anaerobically degradable. Results from available studies are presented in the Table below.

Table: Anaerobic degradation of alcohols

CAS	Chemical name	Comment	Method	Source of sludge	Concentration of test substance	Duration	% degradation at end of test	Reliability	Reference
111-87-5	1-Octanol		Serum bottle, gas production + GC analysis	1^oor 2^odigesters	50µg/ml	8 weeks	>75%	2	Sheltonand Tiedje, 1984
36653-82-4	1-Hexadecanol		Batch test using^14C labelled test material	Municipal digester sludge fortified with activated sludge	1 mg/L	28 days	90%	2	Nuck and Federle, 1996
36653-82-4	1-Hexadecanol		Batch test using^14C labelled test material	Municipal sewage digester	10 mg/L	28 days	97%	2	Steber and Wierich, 1987
68002-94-8	Alcohols, C16-18 and C18 unsaturated	Supporting	ECETOC screening test	Municipal sewage digester	50 mg/L	8 weeks	89%	1	Henkel, 1992e

A study by Rorije et al. (1998) on structural requirements for anaerobic biodegradation of organic chemicals is relevant. The study used a computer-automated structure evaluation program (MCASE) to analyse rates of aquatic anaerobic biodegradation of a set of diverse organic compounds, and developed a predictive model. Primary alcohols were one of the most important fragments linked to biodegradability (biophore). The authors discuss how the presence of a biophore indicates a possible site of attack for microbes to follow a metabolic pathway for anaerobic biodegradation.

Biodegradation in STP-simulation tests

Other recent data on ethoxylated alcohols also suggest that the rate of degradation could be higher than usually assigned to readily-biodegradable substances. In an OECD 303A study of the fate of alcohol ethoxylate homologues in a laboratory continuous activated sludge unit (Wind,et al., 2006) useful data about the properties and environmental exposures of alcohols are presented, although the paper describes mainly the properties of alcohol ethoxylates (AE). The waste water organisms were exposed principally to ethoxylates, but the alcohols would be generated by the degradation of the ethoxylates. The test substance comprised a 2:1 mixture of two commercial alcohol ethoxylate surfactants with chain lengths of C12-C15 (odd and even numbered) and C16-C18 (even numbered), respectively. The test substance was dosed at a concentration of 4 mg/L in the influent.

 

Results are shown in the Table below:

Table. Removal of alcohols during an activated sludge test on alcohol ethoxylates.

Alcohol	Conc in effluent ng/L	Conc in sludge µg/g	%removal
C12	18	0.6	98.6
C13	21	0.7	99.5
C14	5.5	0	99.6
C15	2.9	1.1	99.8
C16	1.6	0.01	99.5
C18	58	0.7	99.1
Total	130	2	99.4

 

This shows that most of the alcohol which does not degrade (itself a small amount) was found in the solids in recovery at the end of the study.This study is important in that it indicates that the extent of removal of alcohols is high, from an exposure route that can realistically be anticipated based on the known life cycle.

References:

EU Commission, DGIII, Study on the possible problems for the aquatic environment related to surfactants in detergents, WRc, EC 4294, February, 1997

Flach, F., 2012. Biodegradability in the CO2-evolution test according to OECD 301b (July 1992). Hydrotox laboratory, report number 737, company study number 8571, Sasol, 2 May 2012.

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. 1209–1222.

Nuck, B.A. and Federle, T.W. 1996. Batch test for assessing the mineralization of 14C-radiolabeled compounds under realistic anaerobic conditions. Environ. Sci.. 30:12, 3597-3603.

Rorije E, Peunenburg WJGM, Klopman G (1998) Structural requirements for anaerobic biodegradation of organic chemicals: A fragment model analysis. Environmental Toxicology and Chemistry, Vol. 17, No. 10, pp. 1943 -1950.

Shelton, D.R. and Tiedje, J.M. 1984. General method for determining anaerobic biodegradation potential. Applied and Environmental Microbiology 850-857.

Steber, J., Herold, C.P. and limia, J.M. 1995. Comparative evaluation of anaerobic biodegradability of hydrocarbons and fatty derivatives currently used as drilling fluids. Chemosphere 31:4, 3105-3118.

Steber, J. and Wierich, P. 1987. The anaerobic degradation of detergent range fatty alcohol ethoxylates. Studies with 14C-labelled model surfactants. Water Research. 21:6, 661-667.

Wind, T., R.J. Stephenson, C.V. Eadsforth, A. Sherren, R. Toy. (2006) Determination of the fate of alcohol ethoxylate homologues in a laboratory continuous activated sludge unit. Ecotox and Environ Safety, 64: 42-60.

Federle (2009). Ready Biodegradability Test, The Procter and Gamble Co., Study number65522, 27^thApril 2009

Richterich, K. 2002a. 1-Hexanol: Ultimate biodegradability in the closed bottle test.Final report R 0200259.

Yonezawa, Y. and Urushigawa, Y. 1979. Chemico-biological interactions in biological purification systems. V. Relation between biodegradation rate constants of aliphatic alcohols by activated sludge and their partition coefficients in a 1-octanol-water system. Chemosphere 3:139-142.

Procter & Gamble. 1996. Final report: ISO ring test CO2 headspace biodegradation test. Study ECM ETS 554/02.

Huntingdon Life Sciences Ltd. (HLS). 1996a. Report No. 96/KAS217/0325.

Richterich, K. 2002c.Final report R 0200257.

Huntingdon Life Sciences Ltd.(HLS).1996b. Report No. 96/KAS223/0327.

Richterich. 1993. 1-Dodecanol: Aerobic biodegradation: Closed bottle test. Biological Research and Product Safety/Ecology: Unpublished results; test substance registration no. SAT 910724, Henkel KGaA; Report No. RE 920247 (With English summary report no. R9901416)

Henkel KGaA.1992d.  Report No. 920026 (test substance registration no. SAT 910723, test run no. 118).5 Marz 1992.

Mead, C. 1997b. Safepharm Laboratories, SPL Project Number 140/598.

Mead, C. 1997c. Safepharm Laboratories, SPL Project Number 140/543.

Henkel KGaA. 1992a.Biological Research and Product Safety/Ecology: Report No. RE 920102; test substance registration No. SAT 910721, test run No. 120.26 Juni 1992.

Henkel KGaA.1992f. Report No.RE920246, 18 December 1992.

Mead, C. 2000. Safepharm Laboratories, SPL Project Number 140/1002.