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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Half life in water and sediment determined from TGD default values for not biodegradable substances and using the Kpsed.

Results from the OECD 302a (Inherent Biodegradability: Modified SCAS) test show that Tetramine di-C16-18 can be removed completely from waste water in an STP mainly via sorption but also via biodegradation. No water soluble degradation products are formed due to this biodegradation indicating that Tetramine di-C16-18 is ultimately biodegradable.

Key value for chemical safety assessment

Half-life in freshwater:
1 000 000 d
at the temperature of:
12 °C
Half-life in freshwater sediment:
10 000 000 d
at the temperature of:
12 °C

Additional information

Biodegradation in sediment

Although Tetramine di-C16 -18 is biodegradable, a classification as not persistent according to the REACH guidance is for the time being not possible. This means that a half-life in soil of 1000000 days and 10000000 days for bulk sediment as suggested by EUSES for a not biodegrable substance are assumed for risk assessment purposes.

It should be noted however that based on the Kpsoil which is in the range of 10000 to 100000 L/kg already for a readily biodegradable substance a half-life in soil of 30000 days is assumed. This means that there is only a marginal difference in the PECsoil for a readily biodegradable substance or a substance which is considered not biodegradable (4.3% after 30 days and 9% after 180 days). Thus for a strongly sorbing substance the PEC in sediment will be similar to soil, almost independent from the fact whether the substance is readily biodegradable or not.

 

Biological wastewater treatment

Tetramine di-C16 -18 can be removed completely from waste water in biological wastewater treatment plants as demonstrated in a semi-continuously operated activated sludge unit (SCAS). In this unit Tetramine di-C16 -18 is removed by both biodegradation and adsorption. Analysis of the parent compound adsorbed onto the activated sludge shows that approximately 40 to 50% of the Tetramine di-C16 -18 is removed by biodegradation. The complete removal of Tetramine di-C16 -18 assessed by measuring organic carbon removal demonstrates that water soluble substances are not formed during the biodegradation of Tetramine di-C16 -18. The alkyl chains and the hydrophilic moiety, N,Nā€™-bis(3-aminopropyl)-1,3-propanediamine of Tetramine di-C16 -18 are both readily biodegradable (AkzoNobel unpublished results). The fraction of Tetramine di-C16 -18 degraded biologically in the SCAS unit is therefore most likely mineralized (ultimately biodegradable).