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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017-10-05 to 2017-11-03
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Principles of method if other than guideline:
N/A
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Identity: TMEDA, termed ATMEDAHP in the report
Purity: 99.9%
Lot number: 17F-1069978
C content: 62.01% (calculated)
Appearance: Clear to slightly hazy, pale yellow liquid
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
The test inoculum was provided by a sample of activated sludge obtained from AZV Staufener Bucht, a municipal STP (140,000 population equivalent) that receives predominantly domestic wastewater. The sample was obtained on the day before the start of the study and washed in tap water and test medium prior to use. Activated sludge was applied at a concentration of 30 mg dry solids/L in each of the test vessels.
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
The test design comprised the following treatments:
3 x test vessels containing TMEDA (20 mg TOC-equiv/L);
3 x reference vessels containing Na benzoate (20 mg TOC-equiv/L);
1 x toxicity control vessel containing TMEDA + Na benzoate (each at 20 mg TOC-equiv/L)
3 x blank control vessels (inoculated test medium, no other addition).
Reference substance:
benzoic acid, sodium salt
Preliminary study:
Not required.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
< 60
Sampling time:
28 d
Remarks on result:
other: not readily biodegradable based on test result
Parameter:
% degradation (CO2 evolution)
Value:
0
Sampling time:
28 d
Remarks on result:
other: No degradation in 2 of 3 replicates throughout the test.
Parameter:
% degradation (CO2 evolution)
Value:
36.5
Sampling time:
28 d
Remarks on result:
other: Significant late-onset degradation in replicate 3 began between D21 and D28
Details on results:
Disparate degradation of TMEDA was observed in the triplicate vessels containing the test substance. No degradation (negative degradation, implying CO2 yield below the background recorded in the blanks) was observed in two of the vessels throughout the entire incubation. The third replicate showed a similar lack of CO2 production up to and including Day 21, but abruptly reached 32.9% ThCO2 yield on Day 28 and 36.5% ThCO2 after terminal acidification, indicating late-onset biodegradation during the final week of the test. Since measured CO2 yield did not reach 60% ThCO2 within 28 days, it may be concluded that TMEDA is not readily biodegradable.

Given the timing of the onset of CO2 production in the third replicate, it is not possible to determine whether biodegradation had reached a plateau by the end of the incubation, or whether it was still in progress at the time when biological activity was stopped by acidification. However, the indication of significant biodegradation in the third replicate does suggest that more extensive and consistent degradation might occur under extended incubation conditions. TMEDA may be considered to be inherently biodegradable, not fulfilling specific criteria.
Results with reference substance:
Mean CO2 production in the triplicate reference vessels containing sodium benzoate exceeded 60% within 4 days.

Table 5.2.1 -1: Biodegradation of TMEDA under ready biodegradability (OECD 301B; CO2 Evolution) test conditions

Day

Biodegradation: blank-corrected CO2 yield as % of theoretical

TMEDA

Na benzoate reference

Toxicity control

0

0

0

0

0

0

0

0

4

‑3.4

‑1.2

‑2.4

60.8

72.7

67.4

33.5

7

‑4.7

‑1.0

‑3.8

74.7

81.9

81.4

37.7

11

‑7.7

‑2.0

‑6.6

80.4

82.2

83.9

38.6

14

‑8.8

‑2.3

‑8.4

81.6

88.1

86.1

38.8

21

‑17.0

‑2.7

‑16.1

79.4

91.3

85.9

35.2

28

‑2.0

‑4.7

32.9

81.8

92.0

92.0

31.0

(29)a

‑21.4

‑2.6

36.5

79.8

92.0

90.4

33.1

a  Includes final purge of CO2following acidification of test media and cessation of biological activity on D 28.

 

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable, not fulfilling specific criteria
Conclusions:
The ready biodegradability of TMEDA was determined according to OECD 301B (CO2 Evolution Test), in compliance with GLP. Mean measured CO2 production after 28 days was below 60% of the theoretical yield and TMEDA is therefore not classifiable as readily biodegradable. However, the indication of significant biodegradation in the third replicate does suggest that more extensive and consistent degradation might occur under extended incubation conditions. TMEDA may be considered to be inherently biodegradable, not fulfilling specific criteria.
Executive summary:

The ready biodegradability of TMEDA was determined in a GLP-compliant test performed according to OECD 301B (CO2 Evolution Test). The test substance was dissolved at a concentration equivalent to 20 mg organic carbon/L in a mineral salts medium inoculated with activated sludge from a STP treating domestic wastewaters, applied at a concentration of 30 mg suspended dry solids/L. Three test vessels were assigned to the test substance. A further three vessels were used for the readily biodegradable reference substance (Na benzoate, also applied at 20 mg organic C-equiv/L) and three more vessels were used for the blank control containing only inoculated test medium. A further single vessel contained TMEDA combined with Na benzoate (each applied at 20 mg organic C-equiv/L) and served as a toxicity control to check for potential inhibition of microbial activity caused by the test substance. All vessels were sealed and continually purged throughout the 28 -d incubation with a flow of CO2 -free air, with the exhaust from each vessel passing through a dedicated absorber wash bottle containing NaOH solution to trap evolved CO2. Samples of the absorber solution were taken at intervals during the incubation and analysed to determine inorganic carbon concentrations and hence the quantity of CO2 evolved from each vessel. Vessels were acidified on day 28 and the air-purge continued for a further 24 h to release any residual CO2 held in the test media. CO2 yields, corrected by subtracting contemporary mean background CO2 production in the blank vessels, were expressed as % theoretical CO2 (ThCO2) yield to indicate the extent of biodegradation.

Disparate degradation of TMEDA was observed in the triplicate vessels containing the test substance. No degradation (negative degradation, implying CO2 yield below the background recorded in the blanks) was observed in two of the vessels throughout the entire incubation. The third replicate showed a similar lack of CO2 production up to and including Day 21, but abruptly reached 32.9% ThCO2 yield on Day 28 and 36.5% ThCO2 after terminal acidification, indicating late-onset biodegradation during the final week of the test. Since measured CO2 yield did not reach 60% ThCO2 within 28 days, it may be concluded that TMEDA is not readily biodegradable. Given the timing of the onset of CO2 production in the third replicate, it is not possible to determine whether biodegradation had reached a plateau by the end of the incubation, or whether it was still in progress at the time when biological activity was stopped by acidification. However, the indication of significant biodegradation in the third replicate does suggest that more extensive and consistent degradation might occur under extended incubation conditions. TMEDA may therefore be considered to be inherently biodegradable, not fulfilling specific criteria.

The reference substance Na benzoate achieved the criteria for classification as readily biodegradable within 4 days, which confirms the activity of the inoculum. CO2 production in the toxicity control exceeded 25% of total ThCO2 within 14 days, which may be taken to signify that TMEDA dosed at 20 mg organic C-equiv caused no inhibition of microbial activity that might account for the limited degree of biodegradtion observed under the conditions of the test.

Description of key information

The ready biodegradability of TMEDA was determined in a GLP-compliant test performed according to OECD 301B (CO2 Evolution Test).

Disparate degradation of TMEDA was observed in the triplicate vessels containing the test substance. No degradation (negative degradation, implying CO2 yield below the background recorded in the blanks) was observed in two of the vessels throughout the entire incubation. The third replicate showed a similar lack of CO2 production up to and including Day 21, but abruptly reached 32.9% ThCO2 yield on Day 28 and 36.5% ThCO2 after terminal acidification, indicating late-onset biodegradation during the final week of the test. Since measured CO2 yield did not reach 60% ThCO2 within 28 days, it may be concluded that TMEDA is not readily biodegradable.

Given the timing of the onset of CO2 production in the third replicate, it is not possible to determine whether biodegradation had reached a plateau by the end of the incubation, or whether it was still in progress at the time when biological activity was stopped by acidification.  However, the indication of significant biodegradation in the third replicate does suggest that more extensive and consistent degradation might occur under extended incubation conditions. TMEDA may be considered to be inherently biodegradable, not fulfilling specific criteria.  

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria
Type of water:
freshwater

Additional information