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Biodegradation in water and sediment: simulation tests

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Description of key information

In a Continuous activated sludge (CAS) test performed using C12-14 AO, removal of parent amine oxide was > 99.8 % in both units. In a monitoring study performed in the Netherlands, the influent and effluent concentrations of C12 and C14 amine oxide was measured in six municipal sewage treatment plants. The BOD removal was 96-98 %. On the basis of these studies, a removal rate in STP of 98 % is proposed for modelling. In a river water die away study the half-life of amine oxide was determined to be 3.2 days. In a biodegradation test performed using anaerobic digester sludge the rate constant for mineralization of the amine oxide was 1.32/day. The results of these studies are read across to C12-18 AO.

Key value for chemical safety assessment

Half-life in freshwater:
3.2 d
at the temperature of:
20 °C

Additional information

No specific test data are available for C12 -18 AO, however a number of studies have been performed with C12 -14 AO. The findings in these studies are read across to C12 -18 AO. The biodegradation of C12/C14 amine oxide (AO) was evaluated in a continuous activated sludge (CAS) test [Lisec (1995)]. The sludge and sewage were from a municipal sewage treatment plant receiving predominantly domestic waste. The CAS units were dosed with 14C-dodecyl amine oxide. After the CAS units stabilized, radioactivity in the effluent, evolved as CO2, and sorbed to solids was measured. Parent AO and metabolites were measured in effluent and mixed liquor suspended solids (MLSS). Effluent from the CAS units was also used in a subsequent river water die away test.

The inoculum was acclimated to the test substance for 3 weeks prior to testing. Separate CAS units were operated at concentrations of 110 µg/L and 394 µg/L (as active ingredient AO). A radiolabelled 14C tracer was used to monitor mineralization and removal.

In principle, the study followed the OECD 303A guideline, and it was GLP. However, the influent sewage was fed intermittently, not continuously as is typical in a CAS test. More importantly, the effluent was not adequately preserved when sampled, permitting additional biodegradation after exiting the CAS unit. The results from this study, specifically on removal of parent and formation of metabolites, are unreliable, due to the methodological limitations.

Samples from the CAS test (effluent, etc.) were analyzed at the laboratory where the test was conducted and also at the laboratories of the sponsor company. The test laboratory and the sponsor both measured total radioactivity (results summarised below). Based on total radioactivity in the effluent, minus the dissolved 14CO2 in the effluent, the removal of AO was 87 -93% (unit 1), and 79 -86% (unit 2). The mineralization of the test substance was 75% (unit 1) and 70% (unit 2). The sorption to MLSS was 16% (unit 1) and 12% (unit 2). Mass balance was 100% (unit 1) and 98% (unit 2). The sponsor also measured parent and metabolites by TLC-RAD. Based on parent and metabolites in the effluent, the removal of parent AO was >99.9% (unit 1), and 99.8% (unit 2).

The removal of C12/14 amine oxide from wastewater by sewage treatment was determined in a monitoring study in The Netherlands between May and July, 1996 [Debaere G (1996c)]. Six municipal activated sludge treatment plants in The Netherlands were included. The concentration of C12/14 amine oxide was determined in influent and effluent samples. Samples (raw and treated sewage) were collected from the six municipal activated sludge sewage treatment plants (STP) over three consecutive days. The samples were analysed by FI/MS/MS for both C12 and C14 Amine oxide. The removal of amine oxide during activated sludge sewage treatment was >95 to >99% at the six plants. The level of Amine oxide in effluent was below detection in all effluent samples (<0.43 µg/L). The amount of Amine oxide in influent ranged between 9-130 µg/L. The BOD removal at the six plants was 96 to >98%.

Based on the results of the CAS test (removal of parent AO >99.8 % in both units) and the removal of AO from wastewater by sewage treatment seen in the Netherlands monitoring study (BOD 96 to > 98 %) it is considered to be justified to use a removal rate of 98 % when evaluating exposure to the aquatic compartment from release of AO to the environment via STP.

The biodegradation of dodecyl amine oxide (C12 AO) was evaluated in a River-Water Die Away study according to the OECD 314D guidelines [Debaere G (1996)]. The test system consisted of river water, effluent from 2 CAS units, and a small amount of activated sludge from a treatment plant handling primarily domestic sewage. The test period was 14 days, and 14CO2 production and radiochemistry were measured. The river water die away (RDA) test was performed in duplicate: RDA test 1 used effluent from CAS unit 1, and RDA test 2 used effluent from CAS unit 2. RDA test 1 was dosed with 2 µg/L test substance (from the effluent from CAS unit 1). RDA test 2 was dosed with 1 µg/L test substance, and 2.9 µg/L metabolites of parent (from the effluent from CAS unit 2).

After 14 days, the total 14CO2 production in the river die away study was 43% for RDA test 1, and 63% for test unit 2. The half-life of mineralization was 4.3 days in RDA 1, and 2.1 days in RDA 2. After 14 days, loss of parent was 61% in RDA test 1. The % loss of parent in unit 2 was unreliable (7%), because of the presence of significant metabolites at the start in RDA test 2. After 14 days, the amount of parent compound was 0.78 µg/L in RDA test 1, and 0.92 µg/L in RDA test 2. Intermediates were mineralized to below detection limits of the TLC-RAD method (<0.33 µg/L).

The radiochemical mass balances averaged 87 and 99% for RDA tests 1 and 2 respectively. After 14 days in RDA test 1, 43% of the radioactivity was CO2, 39% was parent, and 9% was associated with the solids (total=91%). After 14 days in RDA test 2, 63% of the radioactivity was CO2, 24% was parent, and 24% was associated with the solids (total=111%). Based on the results of the two tests, the half-life in surface water is 3.2 days (the average of 4.3 and 2.1).

A simulation of the mineralization of C12 alkyl amine oxide in anaerobic digester sludge was conducted in accordance with OECD 314C guideline [Edwards DE (1996a)]. A solution of radiolabeled and non-radiolabeled amine oxide was tested at 1 mg/L. The radiolabel (14C) was on the methylene groups (CH2) of the alkyl side-chain.The inoculum was acclimated anaerobic digester sludge harvested from a bench scale anaerobic acclimation reactor. The test treatments were measured in duplicate. The evolution of both 14C-CO2 and 14C-methane was measured. The mean cumulative percent of theoretical % 14C-gas produced was 75.5.The rate constant for mineralization of amine oxide in anaerobic digester sludge was 0.055/hour (equivalent to 1.32/day).

According to Annex IX Section sediment simulation testing is required for substances with a high potential for adsorption to sediment. However column 2 of section states that the study need not be conducted if the substance is readily biodegradable, or if direct and indirect exposure of sediment is unlikely. The substance is readily biodegradable and hence the study is scientifically unjustified.