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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Half live in sediment determined from TGD default values for  readily degradable substances and with calculated Kpsed.

The continuous activated sludge (CAS) test was performed according to ISO Guidelines, and in compliance with the OECD principles of Good Laboratory Practice. The removal of oleyl tripropylenetetramine in a STP was evaluated in a simulation study according to ISO and OECD guidelines. The test was performed in compliance with GLP. The parent was quantified in effluent and sludge and because there is no removal via evaporation the removal via biodegradation calculated from the mass balance.

Oleyl tripropylenetetramine was exposed to micro-organisms maintained by addition of domestic wastewater in the CAS test. Oleyl tripropylenetetramine was spiked at a nominal influent concentration of 50 mg/L (38.4 mg/L carbon; measured) for a period of approximately 63 days and included a control fed with domestic wastewater only. The immediate high removal percentages can be attributed to adsorption and maybe some biodegradation. The mean removal percentage of oleyl tripropylenetetramine-carbon calculated over 15 measurements obtained from day 44 to 60 of the test was 88 ± 5% (95% confidence interval). The high removal percentage over a period of more than 8 weeks indicates that oleyl tripropylenetetramine is biodegraded ultimately. Formation of water soluble compounds during biological treatment of oleyl tripropylenetetramine can be excluded. The effluent of the test unit was turbid during the 63 day test period. Turbidity of effluent points to toxicity of oleyl tripropylenetetramine to activated sludge. Turbidity is caused by lysis products of microorganisms. Inhibitory effects were not noted on the basis of the removal of organic carbon present in the domestic wastewater. To investigate the possible toxicity of oleyl tripropylenetetramine, the test was prolonged for another 4 weeks. During these weeks oleyl tripropylenetetramine was spiked at a concentration of 12.5 mg/L. The control unit was unfortunately not operating properly during these 4 weeks. The results obtained of this period could therefore not be used. An accurate assessment of the removal of oleyl tripropylenetetramine was therefore established with specific analyses. The method (LC-MS/MS) for the determination of oleyl tripropylenetetramine was satisfactory with regard to the linearity, repeatability of the injections, limit of quantification (LOQ), precision and specificity. The mean removal percentage of oleyl tripropylenetetramine in the test unit was assessed with the LC-MS/MS method from day 56 to day 63. The mean removal was 99.9% and 99.8% using octadecyl dipropylenetriamine and octadecyl tripropylenetetramine as representative components, respectively. These analyses demonstrate that the removal of oleyl tripropylenetetramine is almost complete. Mean oleyl tripropylenetetramine concentrations in the sludge of the reactor sampled on days 59 and 60 were 115 mg/L (octadecyl dipropylenetriamine) and 286 mg/L (octadecyl tripropylenetetramine). Mean removal percentages of oleyl tripropylenetetramine from the influent through adsorption onto sludge assessed in two samples was therefore 5.8 (octadecyl dipropylenetriamine) and 14.3 (octadecyl tripropylenetetramine) demonstrating that oleyl tripropylenetetramine is primarily removed by biodegradation. In conclusion, the CAS test demonstrates that oleyl tripropylenetetramine, almost completely removed from the wastewater in conventional biological wastewater treatment plants. The substance is primarily removed by biodegradation. The fraction removed via biodegradation calculated via the mass balance is 94.1% for the triamine and 85.5% for the tetramine.

Key value for chemical safety assessment

Additional information

Biodegradation in sediment

The Kpsed was determined as 50000 L/kg. The suggested half-life for a readily degradable substance with a Kpsed in the range >10000 - <=100000 L/kg is 30000 days for the sediment layer. This value is considered as extremely conservative but in the absence of measured data will be used in the exposure assessment as a worst-case. The half-life of the bioavailable fraction of alkyl dipropylene triamines in the water phase of sediments is expected to be in the order of a few days, which is based on experiments with dialkyldimethylammonium salts (van Ginkel et al, 2003).

Biological wastewater treatment

The removal oleyl polypropylene polyamine consisting of 36% of dipropylene triamine and 43% of tripropylene tetramine in biological treatment plants was simulated in a continuously-fed activated sludge (CAS) unit fed with domestic wastewater spiked witholeyl polypropylene polyamines(Akzo Nobel, 2009b). A control unit fed with only domestic wastewater was included in the study.The incubation temperature of both CAS units ranged from 19 to 21°C. The pH of the effluent of the CAS units varied from 6.0 to 7.4. The CAS test was started with sludge from a plant treating domestic wastewater and maintained by the daily addition of primary settled sewage. The hydraulic retention time and the sludge retention time were 6 hours and 10 days, respectively. The dry weight in the CAS units ranged from 2.7 to 3.5 g/L. The hydraulic retention time was set at 6 hours.

The immediate high removal percentages observed are attributed to adsorption and may be some biodegradation. The removal remained high throughout the study. The mean removal percentage of oleyl polypropylene polyamines-carbon calculated over 15 measurements obtained from day 44 to 60 of the test was 88±5% (95% confidence interval). The high removal percentage over a period of more than 8 weeks indicates that oleyl polypropylene polyamines includingoleyl dipropylene triamine arebiodegraded ultimately. Formation of water soluble compounds during biological treatment ofoleyl dipropylene triaminecan be excluded.

Removal ofoleyl dipropylene triaminein the test unit was assessed with the LC-MS method from day 56 to day 63. A mean removal of 99.9% was determined with octadecyl dipropylenetriamine as representative component. These analyses demonstrate that the removal from the aqueous phase is almost complete. The meanoleyl dipropylene triamineconcentration in the sludge of the test unit sampled on days 59 and 60 was 115 mg/L also determined with octadecyl dipropylene triamine as representative component. The calculated mean removal percentage of oleyl dipropylene triamine from the influent through adsorption onto sludge was 5.8 demonstrating that oleyl dipropylene triamineis primarily removed by biodegradation.In conclusion, the CAS test demonstrates that oleyl dipropylene triamine will be biodegraded almost completely in a conventional biological wastewater treatment plant.