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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 17 January, 2007 to 16 May, 2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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)
Specific details on test material used for the study:
- Purity: 49.2% of test substance in water.
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 6 h. A volume of 35 mL of sludge was daily removed from the aeration tank to maintain a sludge retention time of 10 d. The continuous  activated sludge test (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  Samples were withdrawn from the settler at least 2 times a week for the first 8 weeks of the test.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 non purgeable organic carbon (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 day of the test) by measuring the COD removal and the concentrations of ammonium and nitrite in the effluent was measured on 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

- 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 was statistically not significant because the t-statistic (n = 15) did not exceed the critical value. The results therefore demonstrated that the continuous activated sludge system treating domestic
waste water spiked with the test substance removed the organic carbon of the test substance (almost) completely from waste water. The high carbon removal percentages also demonstrated 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. 

Validity criteria fulfilled:
yes
Conclusions:
Under the study conditions, the test substance was removed from waste water at a very high percentage (approximately 99.998%) in the continuous activated sludge test which demonstrated that the primary biodegradation of the test substance was practically complete. 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 and almost completely biodegraded. This suggests that the test substance biodegraded almost completely in conventional biological waste water treatment plants (van Ginkel, 2007).
Executive summary:

A study was conducted to determine the biodegradation of the test substance in water and sediment 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%. 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 (van Ginkel, 2007).

Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
May, 2002
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 306 (Biodegradability in Seawater)
Deviations:
yes
Remarks:
modified for longer measurements; details of substance identity is missing
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
other: Seawater (West Kapelle Netherlands)
Duration of test (contact time):
84 d
Details on study design:
- The closed bottle test was performed according to an OECD Test Guideline 306. The test was made with 3 bottles containing only seawater and 3 bottles containing seawater and the test substance. The test substance was added at a concentration of 2 mg/L. The biodegradability was determined by following the course of the oxygen decrease in the bottles using a special funnel. This funnel fits exactly in the bottle and serves as an overflow reservoir permitting multiple measurements in one bottle. The oxygen concentration was measured at Day 0, 7, 14, 21. 28. 42, 56 and 84.
- The test substance is toxic to microorganisms. Therefore it was also tested in the presence of silica gel to reduce the concentration in the water phase. During the test period, the test substance should be released slowly from the silica gel (0.5 g/bottle). Although no additional oxygen consumption was expected, controls with silica gel were carried out as well.
Key result
% Degr.:
34
Parameter:
O2 consumption
Sampling time:
28 d
Remarks on result:
other: without silica gel
Key result
% Degr.:
31
Parameter:
O2 consumption
Sampling time:
28 d
Remarks on result:
other: with silica gel
Key result
% Degr.:
46
Parameter:
O2 consumption
Sampling time:
84 d
Remarks on result:
other: without silica gel
Key result
% Degr.:
61
Parameter:
O2 consumption
Sampling time:
84 d
Remarks on result:
other: with silica gel
Details on results:
This test highlighted the benifits of reducing toxicity by addition of silica gel as a substrate.

Validity criteria fulfilled:
yes
Remarks:
Valid with restrictions as supporting evidence
Conclusions:
Under the study conditions, the test substance was biodegraded at 38 and 31% on Day 28 in the absence and the presence of silica gel, respectively (closed bottle test). Since, in the prolonged closed bottle test with silica gel the test substance was biodegraded at 61% on Day 84 it is expected to be biodegraded in seawater.

Executive summary:

A study was conducted to determine the biodegradation in seawater and sediment according to OECD Guideline 306 (biodegradation in seawater). Three bottles containing only seawater and 3 bottles containing seawater and the test substance were used. The test substance was added at a concentration of 2 mg/L. The biodegradability was determined by following the course of the oxygen decrease in the bottles using a special funnel. The funnel fitted exactly in the bottle and served as an overflow reservoir permitting multiple measurements in one bottle. The oxygen concentration was measured on Days 0, 7, 14, 21. 28. 42, 56 and 84. The test substance was toxic to microorganisms and was therefore studied in the presence of silica gel to reduce the concentration in the water phase. During the test period, the substance should be released slowly from the silica gel (0.5 g/bottle). Although no additional oxygen consumption was expected, controls with silica gel were carried out as well. Under the study conditions, the test substance was biodegraded by 38 and 31% on Day 28 in the absence and the presence of silica gel, respectively. Since the test substance was biodegraded at 61% on Day 84 in the prolonged closed bottle test with silica gel, it is expected to be biodegraded in seawater (van Ginkel, 1994).

Description of key information

The mean removal percentage of the test substance in the continuous activated sludge test was determined to be 99.998% after 40 days.

Key value for chemical safety assessment

Additional information

Study 1. A study was conducted to determine the biodegradation of the test substance in water and sediment 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%. 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 (van Ginkel, 2007).

Study 2. A study was conducted to determine the biodegradation in seawater and sediment according to OECD Guideline 306 (biodegradation in seawater). Three bottles containing only seawater and 3 bottles containing seawater and the test substance were used. The test substance was added at a concentration of 2 mg/L. The biodegradability was determined by following the course of the oxygen decrease in the bottles using a special funnel. The funnel fitted exactly in the bottle and served as an overflow reservoir permitting multiple measurements in one bottle. The oxygen concentration was measured on Days 0, 7, 14, 21. 28. 42, 56 and 84. The test substance was toxic to microorganisms and was therefore studied in the presence of silica gel to reduce the concentration in the water phase. During the test period, the substance should be released slowly from the silica gel (0.5 g/bottle). Although no additional oxygen consumption was expected, controls with silica gel were carried out as well. Under the study conditions, the test substance was biodegraded by 38 and 31% on Day 28 in the absence and the presence of silica gel, respectively. Since the test substance was biodegraded at 61% on Day 84 in the prolonged closed bottle test with silica gel, it is expected to be biodegraded in seawater (van Ginkel, 1994).