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Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

From January 17, 2007 to May 16, 2007

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

KL2 due to RA

Justification for type of information:

Refer to the Quaternary ammonium salts (QAS) category or section 13 of IUCLID for details on the category justification. The study with the read across substance is considered sufficient to fulfil the information requirements as further explained in the provided endpoint summary.

Qualifier:

according to guideline

Guideline:

OECD Guideline 303 A (Simulation Test - Aerobic Sewage Treatment. A: Activated Sludge Units)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Duration of test (contact time):

58 d

Initial conc.:

49 mg/L

Based on:

test mat.

Details on study design:

- A solution of 7.2 g/L in deionized water was directly added to the test unit using a syringe pump. The flow rate of the syringe pump was ~9.6 mL/d giving a calculated concentration of the test substance in the influent of the unit of ~49 mg/L. The domestic sewage supply was supplied at a rate of approximately 1.4 L/d to give a hydraulic retention time of 6h. A volume of 35 mL of sludge was daily removed from the aeration tank to maintain a sludge retention time of 10d. The CAS units were operated between 2 and 3 g/L dry weight as recommended. 

- Samples were withdrawn from the settler at least 2 times a week for the first 8 weeks of the test. After this period at least 5 samples were taken. All samples were analysed for NPOC. Samples of the last week were analysed for the parent compound. The parent compound was also analysed in the influent and activated sludge.

Test performance:

The performance of the control unit was checked (Day 14 and the last d of the test) by measuring the COD removal (Day 14 and the last d of the test) and the concentrations of ammonium and nitrite in the effluent (Day 14). At Day 14 the COD in the influent and effluent were 517 and 55 mg/L, respectively. At the last day the COD in the influent and effluent were 548 and 47 mg/L, respectively. The COD removal percentages were 89 and 91. The ammonium and nitrite concentrations in the effluent at Day 14 were <2.5 and <2.0 mg/L. These results demonstrate that the test is valid.

Key result

% Degr.:

> 99.98

Parameter:

DOC removal

Sampling time:

40 d

Remarks on result:

other: mean removal during Day 40-58

Key result

% Degr.:

0.016

Parameter:

other: via sorption

Sampling time:

57 d

Key result

% Degr.:

0.023

Parameter:

other: via soprtion

Sampling time:

58 d

Transformation products:

not measured

Evaporation of parent compound:

no

Volatile metabolites:

no

Details on results:

- From Day 40 to 58 samples were taken to assess a mean of the removal percentage with organic carbon concentrations. According to the Dixon test, there were no outliers during this period. Subsequently, all data were used in a t-statistic. The mean difference between the NPOC in the influent and effluent was 0.06 ± 1.18 mg/L (95 per cent confidence interval). The mean removal percentage calculated with this mean difference was 99.8 ± 3.5 (95 per cent confidence). This carbon removal is statistically not significant because the t-statistic (n = 15) did not exceed the critical value. The results therefore demonstrate that the continuous activated sludge system treating domestic waste water spiked with test substance removes the organic carbon of test substance (almost) completely from waste water. The high carbon removal percentages also demonstrate that recalcitrant water-soluble substances are not formed during the biodegradation process.
- During the last week of the test the parent compound in the effluent of the test unit was <10 µg/L corresponding to >99.98% removal. Analysis of the test substance present in the activated sludge demonstrated that ~99.98% of the test substance was removed by biodegradation. 
- The performance of the control unit was checked (Day 14 and the last d of the test) by measuring the COD removal (Day 14 and the last d of the test) and the concentrations of ammonium and nitrite in the effluent (Day 14). At Day 14 the COD in the influent and effluent were 517 and 55 mg/L, respectively. At the last day the COD in the influent and effluent were 548 and 47 mg/L, respectively. The COD removal percentages were 89 and 91. The ammonium and nitrite concentrations in the effluent at Day 14 were <2.5 and <2.0 mg/L. These results demonstrate that the test is valid.

Validity criteria fulfilled:

yes

Conclusions:

Based on the results of the read across study, the test substance was removed from waste water at a very high percentage (approximately 99.998%) in the continuous activated sludge test. Removal of the test substance from the influent through adsorption onto sludge was only 0.016 to 0.023% at two sampling times, demonstrating that the test substance was removed almost completely and biodegraded. This suggests that the test substance biodegrades almost completely in conventional biological waste water treatment plants.

Executive summary:

A study was conducted to determine the biodegradation of the read across substance, C12-16 ADBAC, in waste water according to OECD Guideline 303A (continuous activated sludge test (CAS)), in compliance with GLP. The microorganisms were exposed to a nominal concentration of 49 mg/L (36 mg/L carbon) of the test substance for a period of 58 d. A control fed only with domestic wastewater was included in the study. A strong increase in the concentration of non-purgeable organic carbon (NPOC) was noted on Day 2 in the test units. This was probably caused by toxicity of the test substance. The activated sludge acclimatised to the test substance within a few days, resulting in a decrease of the NPOC concentrations. After 3 weeks, very high carbon removal percentages were achieved. The mean removal percentage in the test unit assessed with a HLPC-MS/MS method was 99.998%, indicating ultimate biodegradation. Removal of the test substance from the influent through adsorption onto sludge was only 0.023% on Day 58, showing that the main mechanism of elimination was biodegradation.Based on the results of the read across study, the test substance was removed from waste water at a very high percentage (approximately 99.998%) in the continuous activated sludge test. Removal of the test substance from the influent  through adsorption onto sludge was only 0.016 to 0.023% at two sampling times, demonstrating that the test substance was removed almost completely and biodegraded. This suggests that the test substance biodegrades almost completely in conventional biological waste water treatment plants (van Ginkel, 2007). Based on the results of the read across study, C12-14 TMAC is also considered to biodegrade almost completely in conventional biological waste water treatment plants.

Description of key information

Based on the results of the read across study, C12-14 TMAC is also considered to biodegrade almost completely in conventional biological waste water treatment plants. 

Additional information

A study was conducted to determine the biodegradation of the read across substance, C12-16 ADBAC, in waste water according to OECD Guideline 303A (continuous activated sludge test (CAS)), in compliance with GLP. The microorganisms were exposed to a nominal concentration of 49 mg/L (36 mg/L carbon) of the test substance for a period of 58 d. A control fed only with domestic wastewater was included in the study. A strong increase in the concentration of non-purgeable organic carbon (NPOC) was noted on Day 2 in the test units. This was probably caused by toxicity of the test substance. The activated sludge acclimatised to the test substance within a few days, resulting in a decrease of the NPOC concentrations. After 3 weeks, very high carbon removal percentages were achieved. The mean removal percentage in the test unit assessed with a HLPC-MS/MS method was 99.998%, indicating ultimate biodegradation. Removal of the test substance from the influent through adsorption onto sludge was only 0.023% on Day 58, showing that the main mechanism of elimination was biodegradation.Based on the results of the read across study, the test substance was removed from waste water at a very high percentage (approximately 99.998%) in the continuous activated sludge test. Removal of the test substance from the influent  through adsorption onto sludge was only 0.016 to 0.023% at two sampling times, demonstrating that the test substance was removed almost completely and biodegraded. This suggests that the test substance biodegrades almost completely in conventional biological waste water treatment plants (van Ginkel, 2007). Based on the results of the read across study, C12-14 TMAC is also considered to biodegrade almost completely in conventional biological waste water treatment plants.