C16-18-(even numbered, C18-unsaturated)-alkylamines acetates

Biodegradation in water: screening tests

Description of key information

In the key study the ready biodegradability was determined with a non-adapted activated sludge for Tallow amine over a period of 28 days according to OECD Guideline 301B.

The test substance was tested in a concentration of 13 [mg/L] in duplicates, corresponding to a carbon content of 10.4 [mgC/L].

The pass level of 10 [%] (start of the degradation phase) was reached by the test substance at the 4th day. In the 10-day-window the test substance came to a mean degradation rate of 46 [%]. After 28 days a mean degradation rate of 61 [%] was reached.

 

In order to check the activity of the study system sodium acetate was used as a functional control. The functional control was degraded to 72 [%] after 13 days and therefore the quality criteria of "degradation > 60 [%] after 14 days" was fulfilled.

In the toxicity control the degradation came to a rate of 51 [%] after 13 days and reached a maximum of 65 [%] after 28 days.

The criteria of the guideline that the degradation in the toxicity control should be > 25 % after 14 days was fulfilled.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

In the key study on biodegradability the pass level for ready biodegradability (60% CO₂ evolution or O₂ consumption) was reached within the test period (generally 28 days), but not within the 10-days window or the 14-day window applicable to OECD 301 tests. However, while within these biodegradation studies often fulfilment or failure of these time-window requirements are reported, the time-window concept is in principle not applicable to primary alkyl amines and acetates:

The time window concept was introduced in ready biodegradability tests as a simple means to quantify the rate of biodegradation (CEFIC, 2006). It relies on the typical S-shaped biodegradation curve observed as a consequence of growth-supporting biodegradation of a pure compound as sole source of carbon. However, it is well known that mixtures of homologous substances differing in chain length or structural isomerism (double bonds) may result in multiple different biodegradation curves (e.g. from different lag phases; preference of one isomer over the other), superimposing such that the observed degradation curve no longer follows the S-shaped form. The similar holds true for substances degraded by consortia, which applies to primary alkyl amines and acetates (deamination as a pre-requisite for β-oxidation of the alkyl chain by other bacteria). Consequently, the 10- (14-) day window criterion cannot be applied to a mixture of homologous substances like primary alkyl amines and acetates (CEFIC, 2006; UN, 2008). In conclusion, the 10-day window criterion is not applicable to multi-component substances like surfactants and “…multi-component substances exceeding the 60 % (resp. 70 %) pass level within the standard test duration of 28 days are considered as readily (bio)degradable substances.” (UN, 2008). Because of this, based on the results of all tests the primary alkyl amines and acetates are classified as “readily biodegradable”.

 

In many tests of primary fatty amines and acetates a similar degradation curve was obtained: after a lag phase of a few days, a rapid increase of degradation up to 50 or 60% of total mineralisation was observed, followed by a third phase when further degradation increased only slowly. The flattened slope in the 3rd phase can be explained by a reduced bioavailability of the test substances. Primary alkyl amines have a high tendency to adsorb onto glass surfaces, which was demonstrated by analytical measurements in the media of ecotoxicity tests as well as during the test on distribution between water and sediment solids.

 

Considering the problem of bioavailability, degradation was further studied with tallow alkyl amine (Akzo Nobel, 1998). Slightly modified Closed Bottle Tests were conducted using different inocula: secondary activated sludge from a plant treating predominantly domestic wastewater, preadapted activated sludge from a CAS reactor, ditch, river and sea water sampled in the Netherlands. To increase bioavailability the medium was mixed by a stirring rod, and the oxygen consumption was continuously measured by an oxygen electrode. The concentration of tallow amine varied from 1.9 to 3.7 mg/L. For the exponential part of the degradation curve, the average specific growth rate was determined. The results are presented in the Table below, together with similar experiments conducted with 2.5 or 10 mg coco alkyl amine/L (Akzo Nobel, 2002).

 

Table Growth rates for tallow alkyl amine (Akzo Nobel, 1998) and coco alkyl amine (Akzo Nobel, 2002c)

	Tallow alkyl amine		Coco alkyl amine
	growth rate µ [d^-1]	lag period [h]	growth rate µ [d^-1]	Lag period [h]
adapted sludge	5.57	21.5
unadapted sludge	5.49	43.8
river water	8.97	33	8.4	30
sea water	4.63	46	6.0	35
ditch water	3.67	25	6.5	70

 

Additional experiments were carried out with benzoate and LAS, which are often used as reference compounds in biodegradation tests. The specific growth rates were 11.41 d^-1 for benzoate and 2.33 d^-1 for LAS (Akzo Nobel, 1998). The results of the modified Closed Bottle Tests indicate that the degradation rates for the primary alkyl amines are within the range found for readily degradable compounds. Furthermore it is obvious that the degradation rates obtained in tests with different inoculi are comparable. This is a strong indication that primary alkyl amines are degraded by microorganisms ubiquitously distributed in the environment, rather than by “specialists”.

 

The relative biodegradability of alkylamines dependent on the chain length was examined by Yoshimura (1980). In an O₂ consumption test similar to MITI I, dispersions (100 mg/l) of a number of primary alkyl amines (C4, C8, C12, C14, C16 and C18) were examined. All amines except of dodecylamine (C12, the main component of coco alkyl amine) were degraded by more than 60% after 12 days. Dodecylamine showed no oxygen consumption at 100 mg/L, but at 30 mg/L about 65% were degraded. However, the results of this study should be taken with care. Primary alkyl amines are toxic to microorganisms, in respiration tests effects were observed at about 10 mg/L, so the high concentrations tested could possibly lead to non-reproducible results. Considering the similar molecular structures, large differences in degradability are not expected. This is supported by the screening tests where no large differences in the degradation rates of the compounds is observed. The degradation pathway (see below) suggests that comparable rates are expected.

 

Metabolisation pathway

Yoshimura (1980) isolated a bacterium from a sludge degrading dodecylamine (the major component of coco amine), which was identified as Pseudomonas putida. This isolated strain could use dodecylamine as the sole carbon and nitrogen source for its growth. The author suggests that primary alkyl amines are biodegraded through either of 2 pathways: a) oxidative deamination to give the corresponding fatty acid and ammonia, or b) w-oxidation on the terminal methyl group to give amino fatty acid, followed by b-oxidation in either case.

Further studies about metabolisation were carried out with derivatives of primary alkyl amines. A common pathway was found for alkylbis(2-hydroxyethyl)amine, alkyltrimethyl­ammonium salts, alkyldimethylamine, and dialkylamines. In the initial step, the C_alkyl-N bond is attacked through a dehydrogenation reaction, forming alkanal as the breakdown product (van Ginkel, 1996). Ammonia was detected as a degradation product of dodecylamine (van Ginkel et al., 1995). The initial reaction step leads to the loss of the surfactant properties and thus to the loss of toxicity (van Ginkel, 1996). The decanals are further degraded through b-oxidation leading to total mineralisation. Unsaturated alkyl chains are degraded through similar reactions (Ratledge, 1994).

 

Conclusions

Studies about the metabolic pathway reveal that the toxicity of primary alkyl amines is strongly reduced by the initial degradation step. Further degradation of the alkyl chains through b-oxidation leads to total mineralisation. As the molecular structure is similar for all primary fatty amines and acetates, large differences in degradability are not expected. Tests in different environmental media resulted in comparable rates, indicating that degrading microorganisms are ubiquitously distributed in the environment.

Generally, biodegradation of chemical substances is classified on the basis of mineralisation rates. It is known that primary alkyl amines are detoxified by the initial degradation step. The alkyl aldehydes being formed are part of the natural fat metabolism occurring in most organisms, therefore it can be assumed that they are much less toxic than the amines. In this case the rate of primary degradation is decisive for the classification, rather than mineralisation.

In the screening tests on ready biodegradability, because of adsorption onto the glass surface, the test substances are only partially accessible to degradation. Further tests (Akzo Nobel, 1998) demonstrated that the rates during the exponential part of the degradation curve are comparable with readily degradable substances. In screening tests mineralisation is detected, the rates for primary degradation are always higher. Furthermore, in CAS-tests removal percentages were found which are characteristic for readily degradable substances. Considering all experimental results, primary alkyl amines and acetates can be classified as readily biodegradable.

Additional Literature

• CEFIC, Conseil Européen des Fédérations de l'Industrie Chimique (2006): 10-Day Time Window; an Unsuitable Pass/Fail Criterion for Fatty Amine Derivatives

• UN, United Nations (2008): Updating of the Second Revised Edition of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). UN/SCEGHS/16/INF.17; Committee of Experts on the Transport of Dangerous Goods and on the Globally Harmonized System of Classification and Labelling of Chemicals. Sub-Committee of Experts on the Globally Harmonized System of Classification and Labelling of Chemicals. Sixteenth session, Geneva, 10-12(a.m), December 2008.
  https://www.unece.org/fileadmin/DAM/trans/doc/2008/ac10c4/UN-SCEGHS-16-inf17e.pdf

• Akzo Nobel (1998): Biodegradation and Environmental Fate of Tallow Amine. Final Research Report March 4, 1998. Akzo Research Laboratories Arnhem, The Netherlands (F98016)

• Akzo Nobel (2002): Assessment of the Biodegradation Kinetics of Cocoamine in Aqueous Ecosystems using the Closed Bottle Test. Akzo Nobel Memorandum, July 16, 2002. Akzo Research Laboratories Arnhem, The Netherlands

• Yoshimura, K. et al. (1980): J. Am. Oil. Chem. Soc. 57, 238-244

• Van Ginkel, C.G. (1996): Biodegradation 7, 151-164

Van Ginkel, C.G. et al.(1995): Tenside Surf. Det. 32(4), 355-359