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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:
2020-01-08 to 2020-02-05
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
17 July 1992
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: Testing Methods for New Chemical Substances of Japanese Chemical Substances Control Law
Version / remarks:
Method for Testing the Biodegradability of Chemical Substances by Microorganisms (301F). Latest revision, 1 July 2019, Yakuseihatsu 0701 No. 1; 20190619 Seikyoku No. 2; Kampokihatsu No. 1907011)
Deviations:
no
GLP compliance:
yes
Remarks:
according to OECD Principles of Good Laboratory Practice (26 November 1997) and the "Standard Concerning Testing Facility Relating to New Chemical Substances" of Japanese Chemical Substances Control Law
Specific details on test material used for the study:
- Lot Nr: 910064
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: activated sludge was obtained from an aeration tank of a sewage treatment plant treating predominantly domestic sewage in Kurume-shi, Fukuoka, Japan; sampling date: January 7, 2020.
- Storage conditions: not specified
- Preparation of inoculum for exposure: the activated sludge was aerated at approximately 22ºC until use for the test.
- Concentration of sludge: additive amount of the activated sludge into the test vessel was 3.23 mL on the basis of the concentration of suspended solid in the activated sludge
- Concentration of suspended solid in the activated sludge: 2790 mg/L
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline
- Additional substrate: no
- Solubilising agent: none
- Test temperature: 21.4 - 22.3 °C
- pH: 7.4
- pH adjusted: yes
- Aeration of dilution water: no
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: closed system oxygen consumption measuring apparatus (No. CM-052); temperature controlled bath with measuring unit AI-0001 (Asahi Techneion)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: each test solution was stirred with a stirrer
- Measuring equipment: data sampler OM7000A (Ohkura Electric); total organic carbon analyzer (No. TOC-013) TOC-LCPH (Shimadzu)
- Test performed in closed vessels due to significant volatility of test substance: yes
- Details of trap for CO2 and volatile organics: Soda lime No.1 (FUJIFILM Wako Pure Chemical)

SAMPLING
- Sampling frequency: measured continuously with a closed system oxygen consumption measuring apparatus
- Sampling method: total organic carbon analyzer (No. TOC-013) TOC-LCPH (Shimadzu)
- Sample storage before analysis: no


CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (n=2)
- Procedure control: test solution (sludge + sodium benzoate) (n=1)
- Toxicity control: test solution (sludge + test item + sodium benzoate) (n=1)
Reference substance:
benzoic acid, sodium salt
Preliminary study:
No
Key result
Parameter:
% degradation (O2 consumption)
Remarks:
based on BOD
Value:
2
Sampling time:
28 d
Key result
Parameter:
% degradation (DOC removal)
Value:
3
Sampling time:
28 d
Details on results:
All of the test item was hydrolyzed to 2-((hydroxydimethylsilyl)methylthio)acetic acid (X-88-390- OH) under the test conditions of this study. X-88-390-OH did not undergo biodegradation and remained in the test solution.
Results with reference substance:
87% degaradation in 28 days.

Table 1: Analytical results of the test solutions on Day 28.

Sludge + test item Theoretical amount 
Vessel No. 1 Vessel No. 2
BOD*1 mg 2.2 0.2 53.1
Residual amount and percentage residue of DOC  mgC 10.8 19.8 11.1
% 97 97 -
Residual amount and percentage residue of test item - The determination of the test item could not be perforemd because the test item is rapidly hydrolized in water.
Produced amount and percentage production of X-88-390-OH*2 (by HPLC)  mg 32.9 32.9 33.3
% 0.99 0.99 -

*1 The average value of the test solutions (control blank) was subtracted from the values of the test solutions (sludge + test item).

*2 2-((Hydroxydimethylsilyl)methylthio)acetic acid

Table 2: Percentage biodegradation on Day 28.

    Sludge + test item
Vessel No.1 Vessel No. 2 Average
Percentage biodegradation by BOD % 4 0 2
Percentage biodegradation by DOC % 3 3 3
Percentage biodegradation of test item - The determination of the test item could not be performed because the test item is rapidly hydrolized in water. Therefore, the percentage biodegradation of the test item was not calculated.

Table 3: Validity of test conditions

  Value in this test Value of criterion

Difference between extremes of replicate values of percentage biodegradation in test solutions (sludge + test item) on day 28

BOD 4% <20%
DOC 0%

Percentage biodegdradation by BOD in test solution (sludge + sodium benzoate) on day 14

87% ≥60%

Percentage biodegradation by BOD in test solution (sludge + test item + sodium benzoate) on day 14

45% ≥25%

BOD in test solutions (control blank) on day 28

23 and 21 mg/L* ≤60 mg/L

*Measurement values (7.0 and 6.4 mg) / [test volume (300 mL) / 1000] = 23 and 21 mg/L

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
In a Manometric Respiratory Test according to OECD Guideline 301 F the test item was determined to be not readily biodegradable (2% biodegradation based on BOD after 28 days).
Executive summary:

The ready biodegradability of the test substance was investigated according to OECD Guideline 301 F (Ready Biodegradability - Manometric Respirometry Test) and in compliance with the GLP principles. The biodegradation of the test substance was followed by exposing it to microorganisms from the aeration tank of a sewage treatment plant treating predominantly domestic sewage. As a reference compound (procedure control) Sodium benzoate was tested simultaneously. The test item concentration selected as appropriate was 100 mg/L (nominal). The flasks were incubated for 28 days under aerobic and dark conditions at 21.4–22.3 °C. The biodegradability was derived from BOD within the test period. All validity criteria of the test guideline were fulfilled. Since the test item is rapidly hydrolyzed to the ring-cleavage product (X-88-390-OH) in water, the quantitative analysis of the test item in the test solutions could not be performed. Therefore, X-88-390-OH instead of the test item was determined. As a result, the percentage production of X-88-390-OH was 99% in the test solutions (sludge + test item). In addition, the percentage residue of DOC was 97%. These results showed that the test item was hydrolyzed to X-88-390-OH, and X-88-390-OH did not undergo biodegradation and remained in the test solution under the test conditions of this study (2% and 3% biodegradation after 28 days based on BOD and DOC, respectively). In conclusion, the test item is regarded to be not readily biodegradable.

Description of key information

In a Manometric Respiratory Test according to OECD Guideline 301 F the test item was determined to be not readily biodegradable (2% biodegradation based on BOD after 28 days).

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

The ready biodegradability of the test substance was investigated according to OECD Guideline 301 F (Ready Biodegradability - Manometric Respirometry Test) and in compliance with the GLP principles. The biodegradation of the test substance was followed by exposing it to microorganisms from the aeration tank of a sewage treatment plant treating predominantly domestic sewage. As a reference compound (procedure control) Sodium benzoate was tested simultaneously. The test item concentration selected as appropriate was 100 mg/L (nominal). The flasks were incubated for 28 days under aerobic and dark conditions at 21.4–22.3 °C. The biodegradability was derived from BOD within the test period. All validity criteria of the test guideline were fulfilled. Since the test item is rapidly hydrolyzed to the ring-cleavage product (X-88-390-OH) in water, the quantitative analysis of the test item in the test solutions could not be performed. Therefore, X-88-390-OH instead of the test item was determined. As a result, the percentage production of X-88-390-OH was 99% in the test solutions (sludge + test item). In addition, the percentage residue of DOC was 97%. These results showed that the test item was hydrolyzed to X-88-390-OH, and X-88-390-OH did not undergo biodegradation and remained in the test solution under the test conditions of this study (2% and 3% biodegradation after 28 days based on BOD and DOC, respectively). In conclusion, the test item is regarded to be not readily biodegradable.