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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Refer to the analogue approach justification document provided in IUCLID section 13.
Reason / purpose:
read-across source
Related information:
Composition 1
Test material information:
Composition 1
Parameter:
% degradation (O2 consumption)
Value:
39
Sampling time:
28 d
Remarks on result:
other: ThODNH4
Remarks:
Source: CAS 10023-48-0, Hammesfahr, 2017
Parameter:
% degradation (O2 consumption)
Value:
25
Sampling time:
28 d
Remarks on result:
other: ThODNO3
Remarks:
Source: CAS 10023-48-0, Hammesfahr, 2017
Interpretation of results:
not readily biodegradable
Conclusions:
The target substance is not readily biodegradable according to OECD criteria, based on experimental findings from a structurally closely related source substance (degradation < 60% after 10-d window and after 28 d, OECD 301 F, CAS 10023-48-0); read-across
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
30 Nov - 28 Dec 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
17 Jul 1992
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
May 2008
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Hess. Ministerium für Umwelt, Energie, Landwirtschaft und Verbraucherschutz, Wiesbaden, Germany (24 Sep 2013)
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: Activated sludge from the aeration tank of aomestic wastewater treatment plant, Rossdorf, Germany
- Storage conditions: aerobic
- Storage length: overnight
- Preparation of inoculum for exposure: The activated sludge used for this study was settled for 30 min before it was washed by centrifugation and the supernatant liquid phase decanted. The solid material was re-suspended in test water and centrifuged again. This procedure was performed three times. The sediment of the last washing was resuspended in test water and aerated overnight until use. An aliquot of this final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material per L (± 10%) were mixed with test water and then aerated until use. This suspension was used for the experiment.
- Concentration of sludge: 3.5 g/L on dry matter base
- Initial cell/biomass concentration: 28.7 mg sludge/L
Duration of test (contact time):
28 d
Initial conc.:
102.5 mg/L
Based on:
test mat.
Initial conc.:
135 mg/L
Based on:
other: ThODNH4
Initial conc.:
210.8 mg/L
Based on:
other: ThODNO3
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Reconstituted Test Water, prepared from analytical grade salts.
- Solubilising agent: No emulsifiers or solvents were used.
- Test temperature: 22 ± 1 °C
- pH: 7.3 - 7.6 (at the start of the test), 6.9 - 8.3 (at the end of the test)
- Suspended solids concentration: 28.7 mg sludge/L
- Continuous darkness: Yes.

TEST SYSTEM
- Culturing apparatus: BSB/BOD-Sensor-System, Aqualytic, Dortmund, Germany
- Number of culture flasks/concentration: 2
- Measuring equipment: BSB/BOD-Sensor-System, Aqualytic, Dortmund, Germany
- Test performed in closed vessels due to significant volatility of test substance:
- Test performed in open system: The test flasks were closed gas-tight by a measuring head.
- Details of trap for CO2 and volatile organics if used: A potassium hydroxide solution (45%) was used for trapping the produced carbon dioxide.

SAMPLING
- Sampling frequency: The change of pressure in the test flasks was measured by means of a manometric method each day. The temperature was recorded by means of the automated software AMR Wincontrol. pH values were measured in the procedure control, a separately prepared test flask with test item (to prevent loss of test item in the test flasks) and a separately prepared test flask without test item (control) at test start and in all flasks at the end of the test, except in the abiotic and toxicity control, using a pH-electrold WTW pH 340i.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 replicates: activated sludge in test water.
- Abiotic sterile control: 1 replicate: test item and CuSO4 in test water.
- Toxicity control: 1 replicate: test item, reference item and activated sludge in test water.
- Procedure control: 1 replicate: reference item and activated sludge in test water.
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
39
Sampling time:
28 d
Remarks on result:
other: ThODNH4
Remarks:
Source: CAS 10023-48-0, Hammesfahr, 2017
Parameter:
% degradation (O2 consumption)
Value:
25
Sampling time:
28 d
Remarks on result:
other: ThODNO3
Remarks:
Source: CAS 10023-48-0, Hammesfahr, 2017

READY BIODEGRADABILITY OF THE TEST ITEM

The degradation rate of the test item did not reach 60% within the 10 -day window or after 28 d. Therefore, the test item is not considered readily biodegradable.

BIODEGRADATION OF THE REFERENCE ITEM

The reference item (sodium benzoate) was sufficiently degraded to 81% after 14 d and to 84% after 28 d of incubation. The percentage biodegradation of the reference item confirms the suitability of the used aerobic activated sludge inoculum.

BIODEGRADATION IN THE TOXICITY CONTROL

In the toxicity control containing both the test item and the reference item (sodium benzoate), 55% (ThODNH4) biodegradation was recorded within 14 d and 76% (ThODNH4) biodegradation after 28 d of incubation (44% and 61% based on ThODNO3). According to the test guidelines, the test item is not considered inhibitory to aerobic activated sludge microorganisms because degradation was > 25% within 14 d.

ABIOTIC CONTROL

The oxygen demand in the abiotic control was 0 mg/L throughout the test duration.

VALIDITY CRITERIA

The test fulfilled the validity criteria of the guideline (Table 1).

Table 1. Validity criteria of OECD guideline 301F.

Criterion from the guideline

Study results

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

The difference of duplicate values at days 26 and 28 differed by 3% and 0% (THODNO3) and by 4% and 0%

(THODNH4,).

Yes

Percentage degradation of the reference compound has reached the pass levels by day 14.

The reference item sodium benzoate was degraded to more than 60% after 4 days of incubation.

Yes

The oxygen uptake of the inoculum blank is normally 20-30 mg O2/L and should not be greater than 60 mg/L in 28 days.

The oxygen demand of the inoculum control (medium

and inoculum) was 27.5 mg O2/L.

Yes

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The degradation rate of the test item did not reach 60% within the 10-day window or after 28 d (OECD test 301 F). Therefore, the substance is not considered readily biodegradable, according to the OECD criteria. The procedure control with the reference item confirmed the suitability of the activated sludge. In the toxicity control, degradation was > 25% after 14 d, indicating that the test item is not inhibitory to activated sludge microorganisms.

Description of key information

Not readily biodegradable (39% ThODNH4/25% ThODNO3 in 28 d, OECD 301 F); read-across

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There is no study available, in which the ready biodegradability of the target substance 2-[3-[(4-Amino-2-methylpyrimidin-5-yl)methyl]-4-methyl-1,3-thiazoniol-5-yl]ethyl dihydrogen diphosphate (CAS 136-09-4) was investigated. Therefore, read-across to the structurally and physico-chemically related source substance 2-{3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-4-methyl-1,3-thiazol-3-ium-5-yl}ethyl hydrogen phosphate (CAS 10023-48-0) was conducted in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. Based on the physico-chemical similarity, the source substance is considered a suitable proxy for the assessment of the ready biodegradability of the target substance. A detailed analogue approach justification is provided in IUCLID section 13 of the technical dossier.

 

In the available study, the ready biodegradability of the source substance (CAS 10023-48-0) was investigated according to OECD guideline 301 F and GLP. Since the test item contains nitrogen, the evaluation of biodegradation was based on ThODNH4 and ThODNO3. In the manometric respirometry test, 102.5 mg/L test item, corresponding to a theoretical oxygen demand of about 135.0 mg/L ThODNH4 and 210.8 mg/L ThODNO3, was inoculated with 28.7 mg sludge/L for 28 d. The consumption of oxygen was determined by measuring the change of pressure in the flasks. Evolved carbon dioxide was absorbed in an aqueous solution (45%) of potassium hydroxide. A procedure, toxicity and abiotic control were run in parallel.

After 28 d, the mean biodegradation was 39% (ThODNH4) and 25% (ThODNO3). The degradation rate of the test item did not reach 60% within the 10-day window or after 28 d. Therefore, the test item is not readily biodegradable, according to the OECD criteria. The procedure control confirmed the suitability of the activated sludge. The toxicity control reached a degradation of 76% (ThODNH4) and 61% (ThODNO3) after 28 d, indicating that the test item is not inhibitory to activated sludge microorganisms according to the guideline criteria.

Based on the high degree of structural and chemical similarity of the target and source substance, the target substance is expected to exhibit a similar environmental fate as the source substance. Therefore, it can be concluded that the target substance 2-[3-[(4-Amino-2-methylpyrimidin-5-yl)methyl]-4-methyl-1,3-thiazoniol-5-yl]ethyl dihydrogen diphosphate (CAS 136-09-4) is not readily biodegradable according to OECD guideline criteria.

[Type of water: freshwater]