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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For details on endpoint specific justification please see read-across report in section 13 or find a link in cross-reference “assessment report”.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
assessment report
Test performance:
>= 90% removal of non purgeable organic carbon (NPOC) from the domestic wastewater after preconditioning of control and test units for one week. Therefore, starting of sludge wastage and introduction of cationic test items performed subsequently.
Compartment:
activated sludge
% Recovery:
99
St. dev.:
3
Remarks on result:
other: Reported value: Coefficient of variation = 3%; n= 5
Remarks:
Spiking concentration (0.67 mg/g), LOD 67 µg/g
Compartment:
other: filtered effluent
% Recovery:
0
Remarks on result:
other: effluent spiked at 50 µg/L (suspended solids conc. ca. 30 mg/L), filtered (8 µm cellulose nitrate) before HPLC-MS/MS; n= 5
Remarks:
DODMAC obviously fully adorbed to susp. solids and removed by filtration - less heavily adsorbing compounds (e.g. decylamine) very well recovered (103%)
Key result
% Degr.:
69
St. dev.:
6.05
Parameter:
test mat. analysis
Remarks:
Primary Biodegradation, calculated from measured concentrations in activated sludge and the newly derived formula for evaluation (see methods section)
Sampling time:
50 d
Remarks on result:
other: Sampling performed during 2-weeks period at steady state conditions of CAS units (between day 40 and day 60): n=5
Key result
% Degr.:
96.07
St. dev.:
0.79
Parameter:
test mat. analysis
Remarks:
Elimination from waste-water, calculated from influent concentration as well as measured concentrations in activated sludge and effluent, and considering 8 mg/L suspended solids in effluent
Sampling time:
50 d
Remarks on result:
other: Sampling performed during 2-weeks period at steady state conditions of CAS units (between day 40 and day 60): n=5 for sludge, n=3 for effluent;
Key result
% Degr.:
> 88
Parameter:
DOC removal
Remarks:
Non purgeable organic carbon (NPOC) removal (calculated from the difference between NPOC concentrations in effluent of control and test unit) - as a measure of formation of any recalcitrant water-soluble degradation products
Sampling time:
50 d
Remarks on result:
other: sampled between day 40 and 60 upon introduction of test item (units at steady state during the whole sampling period)
Key result
Compartment:
wastewater
DT50:
0.866 h
St. dev.:
0.124
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Calculated from reported first order rate constant for removal of DODMAC from waste-water in CAS test
Transformation products:
no
Remarks:
Based on the high NPOC removal from wastewater of > 88% (given for all cationic surfactants assessed; no details for DODMAC given), formation of any soluble recalcitrant degradation products released into the effluent of STPs can be excluded.
Details on transformation products:
Transformation products were not formed in any relevant amounts.
Evaporation of parent compound:
no
Remarks:
The permanently positively charged DODMAC is non-volatile
Volatile metabolites:
not measured
Details on results:
Activated sludge dry weight concentration in CAS aeration tank: 2.6 to 3.0 mg/L; result for DODMAC-unit: 3.0 mg/L (calculated from figures given in the publication).
Suspended solids concentration in CAS effluent: ca. 30 mg/L.
Dissolved oxygen concentration: >2 mg/L.
Incubation temperature: 19-22 °C.
pH in CAS effluents: 6.8 - 7.4.
Nitrogen concentration in effluents:
- Ammonium nitrogen: <1 mg/L;
- Nitrite nitrogen: <2 mg/L.
Foaming due to high surfactant influent concentrations: not observed.

For further details, see IUCLID section "Any other information on results incl. tables".
Results with reference substance:
No reference substances assessed. However, the study included 5 different cationic surfactants in total, such that substances other than DODMAC superseded the need for a reference substance.

A continuously-fed activated sludge test equivalent to OECD 303A was performed. The hydraulic and sludge retention time was 6 hours and 10 days, respectively; the sludge solids concentration in the aeration tank was 3.0 g/L. The SCAS units (control unit and test units) were preconditioned for one week, resulting in >= 90% removal of non purgeable organic carbon (NPOC) from the domestic wastewater. Accordingly, sludge wastage as well as addition of test item was started (day zero). DODMAC was dosed at a nominal influent concentration of 10 mg/L as a suspension prepared with Tween 80 (1:1 w/w). All samplings for analytical determinations (NPOC in effluent; DODMAC in effluent and activated sludge) were performed at steady state between days 40 and 60. Quantification of DODMAC was performed by HPLC-MS/MS (accelerated solvent extraction for sludge solids).

Elimination from wastewater:

Considering a suspended solids concentration of 8 mg/L in the STP effluent (Franco et al., 2013 - monitoring data from full-scale activated sludge treatment systems), an elimination from waste-water (biodegradation and adsorption) of 96.07% (+/- 0.79%) was determined for DODMAC. This figure was obtained from retracing the calculation methods given in the publication. The authors arrived at the slightly higher value of 96.7%, without giving calculation details for their figure. In the spirit of prudence, the (slightly lower) figure calculated from the published core data is used for assessment. A corresponding first order rate constant for removal from wastewater (biodegradation and adsorption) of 0.8/h (+/- SD: 0.1) is reported.

Biodegradation (primary):

Following routine assessment according to OECD 303, distinction between removal by adsorption on the one hand and biodegradation on the other usually is impossible. Based on a new calculation method given in the publication, a distinction between those removal mechanisms was accomplished: DODMAC was demonstrated to be biodegraded by 69% (SD: 6.05%).

Organic carbon removal:

Based on the high NPOC removal from wastewater of > 88% (given for all cationic surfactants assessed; no details for DODMAC given), formation of any soluble recalcitrant degradation products released into the effluent of STPs can be excluded.

References:

Franco, A.; Struijs, J.; Gouin, T.; Price, O.R. (2013)

Evolution of the sewage treatment plant model SimpleTreat: use of realistic biodegradability tests in probabilistic model simulations

Integrated Environmental Assessment and Management, 9, 569-579

Validity criteria fulfilled:
yes
Remarks:
All validity criteria according to OECD 303 A (22nd January 2001) were met.
Conclusions:
The reliable and valid study (published; Geerts et al., 2015) performed similar / equivalent to OECD 303 A (January 2001) produced the following results:
Elimination from wastewater:
Considering a suspended solids concentration of 8 mg/L in the STP effluent (Franco et al., 2013 - monitoring data from full-scale activated sludge treatment systems), an elimination from waste-water (biodegradation and adsorption) of 96.07% (+/- 0.79%) was determined for the test item.
Biodegradation (primary):
The test item was demonstrated to be biodegraded by 69% (SD: 6.05%).
Organic carbon removal:
Based on the high NPOC removal from wastewater of > 88% (given for all cationic surfactants assessed; no details given for test item), formation of any soluble recalcitrant degradation products released into the effluent of STPs can be excluded.
Executive summary:

The study used as source investigated the behaviour of the source substance DODMAC in sewage treatment plants (CAS test similar / equivalent to OECD TG 303A). The study results determined for the source compound were considered applicable to the target compound. Justification and applicability of the read-across approach (structural analogue) is outlined in the read-across report in section 13 or find a link in cross reference “assessment report”.

Description of key information

The reliable and valid study (published; Geerts et al., 2015) performed similar / equivalent to OECD 303 A (January 2001) produced the following results:


Elimination from wastewater:


Considering a suspended solids concentration of 8 mg/L in the STP effluent (Franco et al., 2013 - monitoring data from full-scale activated sludge treatment systems), an elimination from waste-water (biodegradation and adsorption) of 96.07% (+/- 0.79%) was determined for the test item.


Biodegradation (primary):


The test item was demonstrated to be biodegraded by 69% (SD: 6.05%).


Organic carbon removal:


Based on the high NPOC removal from wastewater of > 88% (given for all cationic surfactants assessed; no details given for test item), formation of any soluble recalcitrant degradation products released into the effluent of STPs can be excluded.


Biodegradation in water: simulation testing on ultimate degradation in surface water:


Waiving according to REACH Annex IX, section 9.2., column 2: the chemical safety assessment does not indicate the need to investigate further the degradation of the substance and its degradation products. Substantiation:
a) PBT / vPvB properties can safely be excluded because the B-criterion is not fulfilled: based on a valid bioconcentration test on fish performed equivalent to OECD 305, BCF was between 13 and 32 L/kg (whole body ww). Also for sediment organisms, BSAF determined on L. variegatus and Tubifex were very low (0.28 and 0.78, respectively).
b) For all exposure scenarios, compartment specific risk characterization ratios for local fresh water had reliably been demonstrated to be pronouncedly below 1 (highest RCR: 0.152).
Monitoring data from the Austrian Federal Environmental Agency (UBA, 2005) that specifically relate to diC16 and diC18 dialkyl-dimethyl quaternary ammonium compounds are in support of the assumption that RCRs based on estimated PECs are conservative (see Annex 2 of the CSR for a detailed analysis of these data): based on measurements (incl. suspended particles) performed in June and August 2004 at 11 sites (in part downstream of STPs) of the Danube and tributaries around Vienna, the highest measured value (240 ng/L) is a factor of about 4 lower than the highest estimated PEC (941 ng/L), and the arithmetic mean of values measured in June (59 ng/L; higher than in August) is still lower than the lowest estimated PEC (66.3 ng/L).
Full consideration of the available literature on biodegradation of quaternary ammonium compounds including relevant analogues for DTDMAC is given in the read-across report (sections 1.4.2 and 1.4.4) attached in IUCLID section 13. Accordingly, it could be demonstrated that dialkyl-dimethyl quaternary ammonium compounds including DTDMAC can be fully mineralized (prolonged closed bottle test) albeit slow due to high adsorption. Specifically, even at minute dissolved concentrations in the presence of relevant solid adsorption surfaces (e.g. silica gel), long-chain dialkyl-dimethyl-QUATs are metabolized by microorganisms able to use this dissolved fraction as sole energy and carbon source (van Ginkel et al., 2003). Thus, degradation of the bioavailable fraction in river water will occur.


 


Biodegradation in water: sediment simulation testing:


Waiving according to REACH Annex IX, section 9.2., column 2: the chemical safety assessment does not indicate the need to investigate further the degradation of the substance and its degradation products. Substantiation:



  1. a) PBT / vPvB properties can safely be excluded because the B-criterion is not fulfilled: based on a valid bioconcentration test on fish performed equivalent to OECD 305, BCF was between 13 and 32 L/kg (whole body ww). Also for sediment organisms, BSAF determined on L. variegatus and Tubifex were very low (0.28 and 0.78, respectively).

  2. b) For all exposure scenarios, compartment specific risk characterization ratios for local fresh water sediment had reliably been demonstrated to be pronouncedly below 1 (highest RCR: 0.287).


 


Monitoring data from the Austrian Federal Environmental Agency (UBA, 2005) that specifically relate to diC16 and diC18 dialkyl-dimethyl quaternary ammonium compounds are in support of the assumption that RCRs based on estimated PECs are conservative (see Annex 2 of the CSR for a detailed analysis of these data): based on measurements of sediments performed in June and August 2004 at 11 sites (in part downstream of STPs) of the Danube and tributaries around Vienna, the highest measured value (2690 μg/kg sed. dw) is a factor of about 6 lower than the highest estimated PEC (15800 μg/kg sed. dw), and the arithmetic mean of values measured in August (546 μg/kg sed. dw; higher than in June) is still lower than the lowest estimated PEC (1113 μg/kg sed. dw).


Low concentrations modelled (PECs) and measured for / in river sediments do agree with low modelled (PECs) / measured aquatic concentrations and are plausible, considering that based on a valid OECD 303 A study (Geerts et al., 2015), elimination form waste-water in STPs is 96.07%, with a biodegradation extent of 69%.

Key value for chemical safety assessment

Additional information

The study used as source investigated the behaviour of the source substance DODMAC in sewage treatment plants (CAS test similar / equivalent to OECD TG 303A). The study results determined for the source compound were considered applicable to the target compound. Justification and applicability of the read-across approach (structural analogue) is outlined in the read-across report in section 13 or find a link in cross reference “assessment report”.

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