Hexadecyldimethylamine

Biodegradation in water and sediment: simulation tests

Description of key information

Biodegradation in Sewage Treatment Plants
One Key studies is available for C12-14 DMA sufficiently reported to demonstrate a elimination of >99.6% in an OECD303A Test. This result is supported by studies form the substances HYEQS and C20/22 ATQ.  A supporting study is also available for Amines, Coco alkyl (C12-18-(even numbered)-alkylamines). These studies conclusively show that DMA category members will be fast and effectively eliminated in STP firstly by adsorption on particulate matter and secondly by immediate and effective biodegradation by more than 90% in the plateau phase.
Biodegradation in Surface water
In a reliable River Water Die Away test with the radio labelled supporting substance HYEQS the first order rate constant for primary biodegradation was 1.13 day-1, and the rate constant for mineralization was 0.09 day-1. Within 21 days 80% evolved as CO2.
Biodegradation in Sediment
No studies in sediment are available but the half-life in soil (see IUCLID section 5.2.3) of 16.9 d at 12 deg C can be used instead.

Key value for chemical safety assessment

Half-life in freshwater:

14.8 d

at the temperature of:

12 °C

Half-life in freshwater sediment:

16.9 d

at the temperature of:

12 °C

Additional information

Biodegradation in Sewage Treatment Plants

For the DMA category member C12-14 DMA elimination in sewage treatment plants was determined with a non-adapted activated sludge mixed with inoculum from garden soil and surface water from River Alz, southern Germany Simulation Test (Coupled Units Test). In deviation from the guideline, no DOC concentrations were determined. The purpose of the measurement was to check the rate of elimination of the test item. Therefore only one model activated sludge plant was used. Test duration was limited to 6 days. Inoculation was made by introducing 3 litre of the composite inoculum with a dry matter content of 2 g/L in the aeration vessel, because of the short duration of the test. Due to these deviations, the study is rated as reliable with restrictions (RL2). The test item was tested in a concentration of 4-28 mg (test material) dissolved in drinking water, corresponding to a oxygen demand (COD) of 45-116 mg O2 /L. The elimination of the test item in the aerobic simulation test was followed by gaschromatographic analyses. The elimination (removal via biodegradation and via sorption) of the test item was between 98.80 and >99.99%. The test item strongly sorbs to sewage sludge. Biodegradation will occur in the dissolved as well as in the sorbed phase.

The first key study (RL 1, according to GLP) was performed according to OECD 303A with the supporting substance HYEQS. HYEQS is of high similarity to C12-14 DMA in that it has essentially the same alkyl chain distribution and – like DMA category members - two methyl substituents at the amino group. The only difference is an additional hydroxyethyl substituent at the amino group rendering it a quaternary amine being permanently positively charged. This is however a minor difference as due to protonation at environmentally relevant pH values also DMA category members are predominantly positively charged at the amino group (for details, see category document, chapter 1). HYEQS was continuously dosed into the activated sludge unit resulting in an influent concentration of 200 µg/L (137 µg/L C12 isomer, 50 µg/L C14 isomer). Influent and effluent concentration of HYEQS were measured daily using LC MS MS (LOQ C12 organic medium = 0.96 µg/L, C14 0.35 µg/L) including the sludge adsorbed fraction. Already one day after the start of the test the elimination of HYEQS was > 99.95% for C12 and 99.89% for C14. After 2d biodegradation of HYEQS was >99% (quantification of free and sludge adsorbed fraction). The biodegradation rate during the plateau phase was >99.9%.

The second key study (RL 1, according to GLP) was performed according to OECD 303A with the supporting substance C20/22 ATQ. C20/22 ATQ may be regarded as worst case for DMA category members due to its longer alkyl chain. A further difference is that it has – in addition to the two methyl substituents at the amino group inherent to all DMA category members - an additional methyl substituent at the amino group, rendering it a quaternary amine being permanently positively charged. This is however a minor difference as due to protonation at environmentally relevant pH values also DMA category members are predominantly positively charged at the amino group (for details, see category document, chapter 1). C20/22 ATQ was continuously dosed into the activated sludge unit resulting in an influent concentration of 300 µg/L (41 µg/L C20 isomer, 243 µg/L C22 isomer). Influent and effluent concentration of C20/22 ATQ were measured daily using LC MS MS (LOQ C20 influent= 4.1 µg/L, C22 24.3 µg/L; LOQ C20 effluent= 2.1 µg/L, C22 12.1 µg/L) including the sludge adsorbed fraction. Already one day after the start of the test the elimination of C20/22 ATQ was > 99% (C20 and C22 fraction). Biodegradation of C20/22 ATQ has started immediately and reached a maximum of 98% during the plateau phase (quantification of free and sludge adsorbed fraction). Biodegradation of the C20 fraction was 94-98% (median 96%) and of the C22 fraction 87-93% (median 91%).

A further Aerobic Sewage Treatment Plants Simulation test (according to OECD 303A, GLP, RL1) was conducted with the supporting substance Amines, Coco alkyl (C12-18-(even numbered)-alkylamines) (Akzo Nobel, 2002a,b). For similarity discussion see chapter 1 of this CSR). In part a of the test, sludge and waste water was from a municipal STP, while in part b these were from an industrial plant. CAS units were fed with primary settled sewage spiked with coco alkyl amine (57 mg/l), secondary activated sludge from the same plants was used as inoculum. 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.

It can be concluded that DMA category members can be eliminated fast and effectively in STP firstly by adsorption on particulate matter and secondly by immediate and effective biodegradation by more than 90% in the plateau phase.This means that adsorption does not impede biodegradation, which is confirmed by the tests on ready biodegradability and the simulation tests on biodegradation in soil. Biodegradation in Surface water A River Water Die Away test with the radio labelled supporting substance HYEQS was conducted equivalent to OECD 314D guideline (Biodegradation in Treated Effluent-Surface Water Mixing Zone; reliability category 1)

HYEQS is of high similarity to C12-14 DMA in that it has essentially the same alkyl chain distribution and – like DMA category members - two methyl substituents at the amino group. The only difference is an additional hydroxyethyl substituent at the amino group rendering it a quaternary amine being permanently positively charged. This is however a minor difference as due to protonation at environmentally relevant pH values also DMA category members are predominantly positively charged at the amino group (for details, see chapter 1 of this CSR).

The rate and extent of both primary (loss of parent) and ultimate (mineralisation to CO₂) biodegradation was determined in river water inoculated with both sewage effluent and activated sludge. A small portion of the activated sludge was adapted to the test material before the test. The test system consisted of: 89% river water, 10% sewage effluent, and 1% combined activated sludge liquor. Biodegradation was determined by Liquid Scintillation Counting of 14C-radiolabelled HYEQS for a test duration of 21 days.

HYEQS degraded rapidly with a half-life of 0.61 days for loss of parent. No parent compound remained by day 5. The half-life of mineralization was 7.7 days (CO₂evolved), and by day 21 80% of the test substance had evolved as CO₂. After 21 days, 0% remained as parent, 11.6% was present as metabolites, 8.4% was present in the solids, and 80% was evolved CO₂. The first order rate constant for primary biodegradation was 1.13 day^-1, and the rate constant for mineralization was 0.09 day^-1.Thus, also for DMA category members rapid and ultimate biodegradation in surface waters is expected Biodegradation in Sediment According Annex IX, Section 9.2.1.4 column 2 of the REACH Regulation 1907/2006/EC a Sediment simulation test needs not to be carried out if the substance is readily biodegradable. Thus, the biodegradation of DMA category members in sediment was not tested. Based on ECHA REACH Guidance on Information Requirements and CSA, R.16 Environmental Exposure Assessment, Section R.16.5.4.5 (May 2010) a soil half-life may also be applied for aerobic sediment if no other data are available. A median (3 soils) half-life of 8.9 d at 20 degree C for soil was derived from an OECD 307 Aerobic Soil transformation study (see IUCLID Section 5.2.3) performed with the supporting substance hexadecanamine which will be used for sediment assessment.