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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:
February 2018 - March 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
Ammonium chloride was omitted from the medium to prevent nitrification.
Principles of method if other than guideline:
Minor deviations from the guidelines of the Closed Bottle test (OECD TG 301 D) were introduced; a) ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification (omission does not result in nitrogen limitation as shown by the biodegradation of the reference compound), and b) river water instead of an effluent/extract/mixture was used as inoculum.
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Remarks:
river water instead of an effluent/extract/mixture was used as inoculum.
Details on inoculum:
River water was sampled from the Rhine near Heveadorp, The Netherlands (08-02-2018). The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream. The river water was aerated for 7 days before use to reduce the endogenous respiration (van Ginkel and Stroo, 1992). River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.
Duration of test (contact time):
28 d
Initial conc.:
8 mg/L
Based on:
test mat.
Remarks:
76.4% purity
Initial conc.:
6.1 mg/L
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The Closed Bottle test (OECD TG 301 D) was performed according to the study plan. The study plan was develo¬ped from ISO Test Guidelines (1994). Use was made of 10 bottles con-taining only river water, 6 bottles con¬taining river water and sodium acetate, 10 bottles con-taining river water with test substance. The concentrations of the test substance, and sodium ace¬tate in the bottles were 8.0 and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were com¬pletely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bot¬tles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.
Reference substance:
other: Not included in the screening test
Preliminary study:
84% degradation observed after 28 d using activated sludge as inoculum
81% degradation observed after 28d using river water as inoculum
Test performance:
Test conditions
The pH of the media was 8.0 at the start of the test. The pH of the medium at day 28 was 7.9 (test) and 8.0 (control). The temperature ranged from 22.6 to 22.9°C which is within the prescribed temperature range of 22 to 24°C.
Key result
Parameter:
% degradation (O2 consumption)
Value:
81
Sampling time:
28 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
75
Sampling time:
7 d
Details on results:
Theoretical oxygen demand (ThOD)
The calculated theoretical oxygen demand (ThOD) of the active ingredient (iron trigluconic acid, trisodium salt) is 0.75 g/g. The ThOD of the test substance is only 0.57 g/g because the ThOD of NaCl (19.3%) and water (2.7%) is 0.0 g/g. The ThOD of sodium acetate is 0.78 g/g

Toxicity
Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of the test substances to micro¬organisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the ino¬culum by the test substance at day 7 was not detected (Table I). Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Test conditions
The pH of the media was 8.0 at the start of the test. The pH of the medium at day 28 was 7.9 (test) and 8.0 (control). The tem¬perature ranged from 22.6 to 22.9°C which is within the prescribed temperature range of 22 to 24°C.

Validity of the test
The validity of the test is demonstrated by an endogenous respiration of 1.1 mg/L at day 28 (Ta¬ble I). Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 82 (Table II and Figure). Final¬ly, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

The Closed Bottle test results
Iron trigluconic acid, trisodium salt was biodegraded by 81% at day 28 in the Closed Bottle test. Over 60% biodegradation was achieved in a period of approximately 5 days immediately following the attainment of 10% biodegradation after 1 day (Figure), therefore fulfilled the 14-day time window (10-day time window for other OECD 301 tests) criterion for ready biodegradable compounds. The test item should therefore be classified as readily biodegradable.
Results with reference substance:
The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 82

Table IDissolved oxygen concentrations (mg/L) in the closed bottles.

Time (days)

Oxygen concentration (mg/L)

 

Oc

Ot

Oa

0

8.7

8.7

8.7

 

8.7

8.7

8.7

Mean (M)

8.7

8.7

8.7

7

8.2

4.9

8.7

 

8.1

4.7

4.4

Mean (M)

8.2

4.8

4.4

14

7.8

4.4

3.4

 

7.8

4.3

3.6

Mean (M)

7.8

4.4

3.5

21

7.8

4.2

 

 

7.8

4.1

 

Mean (M)

7.8

4.2

 

28

7.5

3.8

 

 

7.6

3.9

 

Mean (M)

7.6

3.9

 

Oc         River water with nutrients.

Ot         River water with nutrients, test substance (8.0 mg/L). 

Oa          River water with nutrients and sodium acetate (6.7 mg/L).

Table II Oxygen consumption (mg/L) and the percentages biodegradation of the test substance (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test.

Time (days)

Oxygen consumption (mg/L)

Biodegradation (%)

 

Test substance

Acetate

Test substance

Acetate

0

0.0

0.0

0

0

7

3.4

3.8

75

73

14

3.4

4.3

75

82

21

3.6

 

79

 

28

3.7

 

81

 

 

 

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Valid test performed according to guideline OECD 301D with minor acceptable deviations applying GLP conditions.
Executive summary:

In order to assess the biotic degradation of iron trigluconic acid, trisodium salt, a ready bio­degradability test was performed which allows the biodegradabi­lity to be measured in an aerobic aqueous medium. The ready biodegra­dability was determined in the Closed Bottle test performed according to slightly modified OECD, EU and ISO Test Guidelines, and in compliance with the OECD prin­ciples of Good Laboratory Practice.

The test itemdid not cause a reduction in the endogenous respiration at day 7. The test substance is therefore con­sidered to be non-inhibitory to the inoculum. The test item was biodegraded by 81% at day 28 in the OECD 301 D Closed Bottle test and should therefore be classified as readily bio­degradable.

The test is valid as shown by an endogenous respiration of 1.1 mg/L and by the total mineraliza­tion of the reference compound, sodium acetate. Sodium acetate was degraded by 82% of its theo­retical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Description of key information

Iron trigluconic acid, trisodium salt (CAS no.: 2101772 -89 -6) was shown to be readily biodegradable using river water as inoculum. More than 70% degradation was already observed after 7 days.

Iron trigluconic acid, trisodium salt is like sodium glucoheptonate (CAS no.: 31138 -65 -5) readily biodegradable. 79.5% degradation after 28 days was observed for sodium glucoheptonate. For both Iron trigluconic acid, trisodium salt and sodium glucoheptonate the criteria for the 10 -day window were fulfilled.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Iron trigluconic acid, trisodium salt (CAS no.: 2101772 -89 -6) was shown to be readily biodegradable using river water as inoculum. The study performed by van Ginkel (2018) is performed according to OECD 301D using slightly adapted procedures. The biodegradation was measured by following the course of the oxygen decrease in the bottles using a special funnel and because it was a preliminary test without using a positive control. 6.1 mg a.i./L of Iron trigluconic acid, trisodium salt was shown to be extremely rapidly degraded. More than 70% degradation was already observed after 7 days.

For Sodium heptogluconate (CAS no.: 31138 -65 -5), the substance which is for this dossier used as source chemical (analogue) for read across, similar results were observed in the ready biodegradability study available for this substance.

The study by Bessems was performed according to OECD 301B and 79.5% biodegradation of a mixture of α- and ß-sodium glucoheptonate (CAS no 31138-65-5) was observed at day 28 of the study and should therefore be classified as readily biodegradable.

Although the test is not performed under GLP and quality criteria are missing the result together with the biodegradation result from α-na-hepto-gluconate and ß-na-hepto-gluconate can be used as supporting evidence.