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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Based on the available studies on biodegradation, diquat C16-18 is degraded quickly into a metabolite which has a lower sorption potential than the parent. Due to the accumulation of the metabolite as observed in a SCAS test (van Ginkel et al, 2010) diquat C16-18 can not be considered as readily biodegradable. It is very unlikely that a quick further degradation of the metabolite will occur in soil or sediment. Further testing in soil or sediment is therefor not expected to deliver more information.  For sediment therefore a half life value of 30000 days is used until better soil/sediment biodegradation data become available.
The removal of N,N,N’,N’,N’’-pentamethyl-N-C16-18 (even numbered) C18 unsat.-alkyl-1,3-propanediammonium chloride (oxidation of the alkyl chain) in biological wastewater systems through read-across is assumed to be 99.99% removal from the wastewater and 99.98% removal by biodegradation.

Key value for chemical safety assessment

Additional information

Sediment

Based on the available studies on biodegradation, diquat C16-18 is degraded quickly into a metabolite which has a lower sorption potential than the parent. Due to the formation of the metabolite as observed in a SCAS test (van Ginkel et al, 2010) diquat C16 -18 can not be considered as readily biodegradable. It is very unlikely that a quick further degradation of the metabolite will occur in soil or sediment. Further testing in soil or sediment is thereful not expected to deliver more information. For sediment therefore a half life value of 30000 days is used for the sediment until better soil/sediment data become available.

The half-life of the bioavailable fraction of N,N,N’,N’,N’’-pentamethyl-N-C16-18 (even numbered) C18 unsat.-alkyl-1,3-propanediammonium chloride

in the water phase of soils 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

Chemically N,N,N’,N’,N’’-pentamethyl-N-C16 -18 (even numbered) C18 unsat.-alkyl-1,3 -propanediammonium chloride has an alkyl chain linked directly to a nitrogen atom of methylated 1,3-diaminopropane. Other water soluble fatty amine deravatives are also characterized by an alkyl group linked directly to a nitrogen of the hydrophilic moiety (diethanolamine and dimethylbenzylamine). These surfactants are in contrast to N,N,N’,N’,N’’-pentamethyl-N-C16-18 (even numbered) C18 unsat.-alkyl-1,3-propanediammonium chloride completely degraded because the hydrophilic moieties are biodegradable. However, the biodegradation of all surfactants is initiated by an attack on the alkyl chain serving as carbon and energy source for the micro-organisms. The fatty acids are degraded through the b-oxidation cycle. In each cycle, the alkyl chain is progressively shortened by two carbons yielding one molecule of acetyl-CoA. The acetyl-CoA generated in b-oxidation enters the TCA cycle, where it is further oxidised to carbon dioxide and water.

The oxidation of the alkyl chain (primary degradation) is the key to justification of the use of read-across of the results obtained continuously-fed activated sludge (CAS) unit fed with domestic wastewater spiked with fatty amines. The results of structurally related substances are given below. 

 

The removal percentages of the parent compounds of Oleyl bis(2-hydroxyethyl)amine (CAS 25307-17-9)

degraded through oxidation of the alkyl chain from the influent and removal by biodegradation in CAS unit is given below (Akzo Nobel 2010).

 

Surfactant

Removal from wastewater (%)

Removal by biodegradation (%)

Oleyl bis(2-hydroxyethyl)amine (CAS 25307-17-9)

99.999

99.84

For C12 -16 -BKC (CAS 68424 -85 -1) identically high removal and biodegradation percentages in the continuous activated sludge test (CAS test; OECD 303A) were observed (draft CAR BKC (published 07 -09 -2011, Circa.europe.eu)). These data show that for readily biodegradable cationic surfactants in general very high removal percentages will be observed in continuous activated sludge tests. When operated properly, the fraction removed by biodegradation is only influenced by the fraction sorbed in the CAS test (long alkyl chain cationic surfactants are non-volatile).

For the removal of N,N,N’,N’,N’’-pentamethyl-N-C16-18 (even numbered) C18 unsat.-alkyl-1,3-propanediammonium chloride (oxidation of the alkyl chain) in biological wastewater systems therefore also very high removal percentages are anticipated (for the parent). Based on read-across from CAS test results from other cationic surfactants like C12 -16 -BKC and Oleyl bis(2-hydroxyethyl)amine

>99.99% removal from the wastewater and >99.8% removal by biodegradation in the treatment system are considered to be realistic worst-case removal percentages for N,N,N’,N’,N’’-pentamethyl-N-C16 -18 (even numbered) C18 unsat.-alkyl-1,3 -propanediammonium chloride in conventional waste water treatment plants.