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

Biodegradation in water and sediment: simulation tests

Description of key information

 

Freshwater

Simulation test for freshwater degradation are not available. In the following exposure calculations, degradation half-lives of 15 days for freshwater and 50 days for seawater according to the REACH Guidance R16. (2016) are used. The rates determined in the Closed-Bottle Test with river-, ditch- or seawater are not accepted as simulation tests because the test substance concentrations (1.9 – 10 mg/L) are far above the levels expected in the environment.

 

Sewage treatment plant (STP)

Two CAS tests were conducted with coco alkyl amine (Akzo Nobel, 2002). A CAS unit was fed with primary settled sewage collected from a municipal treatment plant and spiked with coco alkyl amine (57 mg/l), secondary activated sludge from the same plant was used as inoculum. Parallel to this experiment a further test was conducted using activated sludge and wastewater from an industrial treatment plant spiked with the same test substance concentration. The test conditions were largely identical: hydraulic retention time 6 hours, sludge concentration 1-3 g dw/L, sludge retention time 10 days, incubation temperature 20-22°C. The test units were pre-conditioned for one week after which sludge wasting was started. After introduction of the test substance at day 0, removal was measured as non purgeable organic carbon (NPOC). 14 measurements from day 3-23 resulted in mean removal percentages of 97±1% for the test with domestic wastewater and 98±2% for the test with industrial wastewater. During the last week, 5 GC/MS measurements of the components were conducted, the detection limit was 1 µg/L for the saturated C12, C14, C16, and C18 amine resp. 3 µg/L for the unsaturated oleylamine. Based on the measurements, removal percentages for coco amine of >99.98% (municipal) resp. 99.83% (industrial) were calculated.

Removal determined in CAS tests is equal to the sum of degradation and adsorption onto sludge. The results reveal that removal of the test substances is more effective than removal of their organic carbon. The algal toxicity determined in the effluent from tallow amine treatment (Akzo Nobel, 1998) reveals that the water soluble metabolites being formed during the process are much less toxic than the parent compounds. Considering the degradation mechanism this result is expected, as primary degradation leads to a fission of the amino group which means the loss of the surfactant properties and thus to the loss of toxicity. Therefore, the environmental exposure assessment can be based on primary degradation, i.e. removal of the test substances.

A control calculation with the SIMPLETREAT model results in the following distribution: 72.9% degradation, 15.6% adsorption onto primary sludge, 0.7% adsorption onto surplus sludge, 10.8% are directed to water and 0% to air. For the calculation the following parameters were used: for primary settlement Kp_{raw sewage} and sludge Kp_sludge-water= 680 L/kg, and the TGD default value for ready biodegradability (k = 1 h^-1; EC, 2003). Comparison with the results of the CAS tests shows that removal of the test substance is strongly underestimated by the model calculation, indicating that the rate of primary degradation is far above the TDG default value.

According to the TGD (EC, 2003), results of simulation tests should only be used when the concentrations used in the tests are in the same order of magnitude as expected in reality. At sites with the highest release, the influent concentration is lower compared to the CAS tests, so the demand is only approximately fulfilled. However, according to a recent publication of Geerts et al. (2015) on the biodegradaton of cationic surfractants in activated sludge reactors (OECD TG 303A), removal percentages for cationic alkylamine sufactants are largely constant even if influent concentrations vary by a factor of more than 500. For octadecylamine, three influent concentrations had been tested in CAS units, namely 50 mg/L, 5 mg/L, and 0.5 mg/L. Observed effluent concentrations corresponded with 99.8%, 99.1% and >98.8% removal, respectively, while removal via adsorption to sludge was calculated to be 1.8%, 4.8% and 4.1%, respectively. This is equivalent to a primary biodegradation between 98.2% and 95.2% over a variation of influent concentration by a factor of 100. The authors conclude that biodegradation in activated sludge of cationic sufactants most likely follows apparent first order kinetics (Geerts et al., 2015). As such, even at sites with considerably lower influent concentrations compared to the ones applied in the CAS tests above biodegradation extent will be comparable.

Nonetheless, for the exposure assessment the lowest value from the results outlined above, i.e. the removal percentage from the test with industrial sewage (99.83%) is used. The test was run with a hydraulic retention time of 6 hours which is lower than in most industrial treatment plants, so this approach appears to be a realistic worst case.

Biodegradation in sediments

No studies about degradation of primary alkyl amines in sediments are available. For aerobic sediments, based on the result of the study on aerobic transformation in soil) and in line with the REACH Guidance R16. (2016) A.16 -3.2.2, a DT50 freshwater sediment (aerobic) of 16.9 d at 12 deg. C is assigned (value equal to half-life in soil). Correspondingly, the value for bulk sediment is set at 169 d.

Additional Literature

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

• Geerts, R.; van Ginkel, C.G.; Plugge, C.M. (2015): Accurate assessment of the biodegradation of cationic surfactants in activated sludge reactors (OECD TG 303A). Ecotoxicology and Environmental Safety, 118, 83-89

Key value for chemical safety assessment

Half-life in freshwater:

15 d

at the temperature of:

12 °C

Half-life in freshwater sediment:

16.9 d

at the temperature of:

12 °C