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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:
26.10.2017-30.11.2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
OECD Guideline for Testing of Chemicals No. 301 F: "Ready Biodegradability: Manometric Respirometry Test", adopted July 17, 1992
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
Commission Regulation 440/2008/EC, Method C.4-D of May 30, 2008: Manometric Respirometry Test (EEC Publication No. L 142/496, May 2008)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
No further details specified in the study report.
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Source of inoculum/activated slude: Aerobic activated sludge, microorganisms from a domestic waste water treatment plance supplied by the sewage treament plant, Rossdorf, Germany.

Conditioning:
- The coarse particles were removed from the aerobic activated sludge by settling for 30 minutes.
-Afterwards the sludge was washed by centrifugation and the supernatant liquid decanted.
-The solid material was re-suspended in test water and centrifuged again. This process was repeated 3 times.
-An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight calculated.
-Calculated alquots of the washed sludge suspension corresponding to 3.5g dry material per L were mixed with test water and aerated overnight. This suspension was used for the experiment.
Duration of test (contact time):
28 d
Initial conc.:
101.6 mg/L
Based on:
test mat.
Remarks:
corresponding to an oxygen demand of about 285.0 mg/L (ThODNH4) and 326.4 mg/L (ThODNO3)
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS:
- Test Temperature: 22 ± 1°C
- Light conditions: darkness
- pH value of test solutions: 7.2 - 7.7 (measured at start of test and pH adjusted to 7.5).
7.2-7.6 (measured at end of test)

TEST WATER:
Analytical grade salts were added to pure water to prepare the following stock solutions:
a) 8.5 g KH2PO4, 21.75 g K2HPO4, 33.4 g Na2HPO4 x 2 H2O, 0.5 g NH4Cl filled up with pure water to 1000 mL volume; The pH-value was 7.4.
b) 11.25 g MgSO4 x 7 H2O filled up with pure water to 500 mL volume
c) 18.2 g CaCl2 x 2 H2O filled up with pure water to 500 mL volume
d) 0.125 g FeCl3 x 6 H2O filled up with pure water to 500 mL volume (with one drop of concentrated HCl per litre to avoid precipitation)
50 mL of stock solution a) and 5 mL of the stock solutions b) to d) were combined and filled up to a final volume of 5000 mL with pure water.

TEST ITEM PREPARATION:
The amounts of test items and reference items were weighed directly into test flasks. No emulsifiers or solvents were used. Each flask was made up to a final volume of 244mL with the prepared test water. The list of samples is as follows, with 2 flasks of each:
Solvent Red 19T (Test substance + inoculum)
CONTROLS:
Inoculum control: (inoculum only)
Procedure control: (sodium benzoate reference item + inoculum)
Abiotic control: Test substance + poisoned with CuS04 solution 1g/L
Toxicity Control: Test substance + Reference item + inoculum
The exact preparations are given in Table 1.

MEASUREMENTS:
The closed test flaks were incubated in a climatised chamber with continous stirring. Evolved Carbon Dioxide was absorbed in an aqueous solution of potassium hydroxide. Measurements were taken daily for 28 days. The change of pressure in the test flasks was measured by means of a manometric method. The amount of oxygen consumed by the activated sludge was calculated from the pressure decrease.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
ca. 0
Sampling time:
28 d
Details on results:
The criterion for ready biodegradability under the conditions of a manometric respirometry test is the degradation of the test item of at least 60%, reached within a 10-day window; the 10-day window starts when the degradation of the test item reaches at least 10% degradation.
Solvent Red 19T never reached a biodegradation of 10% or higher during the incubation time of 28 days. The mean biodegradation at test end after 28 days was 0% (ThODNH4, ThODNO3).

The reference item sodium benzoate was sufficiently degraded to 69% after 14 days and to 67% after 28 days of incubation, thus confirming the suitability of
the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 29% biodegradation was noted within 14 days and after 28 days of incubation (based on ThODNH4, 27% based on ThONO3). According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The degradation rate of Solvent Red 19T was <10% after a test duration of 28 days.
Therefore, Solvent Red 19T is considered to be not readily biodegradable based on ThODNH4/ThODNO3.

The reference item sodium benzoate was sufficiently degraded to 69% after 14 days and to 67% after 28 days of incubation, thus confirming the suitability of
the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 29% biodegradation was noted within 14 days and after 28 days of incubation (based on ThODNH4, 27% based on ThONO3). According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.

Executive summary:

The criterion for ready biodegradability under the conditions of a manometric respirometry test is the degradation of the test item of at least 60%, reached within a 10-day window; the 10-day window starts when the degradation of the test item reaches at least 10% degradation.

Solvent Red 19T never reached a biodegradation of 10% or higher during the incubation time of 28 days. The mean biodegradation at test end after 28 days was 0% (ThODNH4,ThODNO3).

Therefore, Solvent Red 19T is considered to be not readily biodegradable based on ThODNH4/ThODNO3.

The reference item sodium benzoate was sufficiently degraded to 69% after 14 days and to 67% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

In the toxicity control containing both, the test item and the reference item sodium benzoate, 29% biodegradation was noted within 14 days and after 28 days of incubation (based on ThODNH4, 27% based on ThONO3). According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.

Description of key information

The degradation rate of Solvent Red 19T was <10% after a test duration of 28 days.

Therefore, Solvent Red 19T is considered to be not readily biodegradable based on ThODNH4/ThODNO3.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information