Ethylenediamine-N,N'-di(acetic acid)

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17-01-2017 till 16-02-2017

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

Version / remarks:

OECD, 1992

Deviations:

yes

Remarks:

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)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

Secondary activated sludge (12-01-2017) was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands. This plant is an activated sludge plant treating predominantly domestic wastewater. The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 0.40 g Dry Weight (DW)/L of activated sludge was aerated for one week. The sludge was diluted in the bottles to 2.0 mg/L (van Ginkel and Stroo, 1992). The inoculum was not pre-adapted to the test substance.

Duration of test (contact time):

28 d

Initial conc.:

4 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

The Closed Bottle test (OECD TG 301) was performed according to the study plan. The study plan was developed from ISO Test Guidelines (1994). Use was made of 10 bottles containing mineral salts medium and inoculum, 6 bottles containing mineral salts medium, inoculum and sodium acetate, 10 bottles containing mineral salts medium, inoculum and test substance. The concentrations of the test substance and sodium acetate in the bottles were 4.0 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 completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles 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 Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.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:

acetic acid, sodium salt

Remarks:

CAS reg. No. 127-09-3 Purity >99% Batch/lot number BCBP8197V Appearance white crystals

Key result

Parameter:

% degradation (O2 consumption)

Value:

5

Sampling time:

28 d

Remarks on result:

other: The lack of biodegradation in the Closed Bottle test does not mean that ethylenediaminediacetic acid is recalcitrant in nature because the stringency of the test procedures could account for the recalcitrance in the Closed Bottle test.

Results with reference substance:

Sodium acetate was degraded by 81% of its theoretical oxygen demand after 14 days.

Table I Dissolved 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	8.4	8.4	4.3
	8.4	8.4	4.3
Mean (M)	8.4	8.4	4.3
14	8.3	8.1	3.8
	8.2	8.2	4.0
Mean (M)	8.3	8.2	3.9
21	8.1	7.9
	8.0	7.9
Mean (M)	8.1	7.9
28	7.9	7.8
	8.0	7.8
Mean (M)	8.0	7.8

O_c         Mineral salts medium with inoculum.

O_t         Mineral salts medium, inoculum and test substance (4.0 mg/L).

O_a          Mineral salts medium, inoculum and sodium acetate (6.7 mg/L).

 

Table II Oxygen consumption (mg/L) and the percentages biodegradation of the test substance, Ethylenediaminediacetic acid (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	0.0	4.1	0	76
14	0.1	4.4	3	81
21	0.2		5
28	0.2		5

 

 

Validity criteria fulfilled:

yes

Remarks:

The test is valid as shown by an endogenous respiration of 0.7 mg/L and by the complete degradation of the reference compound, sodium acetate.

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

Ethylenediaminediacetic acid was not biodegraded (5% at day 28) in the Closed Bottle test and should therefore not be classified as readily biodegradable. The lack of biodegradation in the Closed Bottle test does not mean that ethylenediaminediacetic acid is recalcitrant in nature because the stringency of the test procedures could account for the recalcitrance in the Closed Bottle test.

Executive summary:

In order to assess the biotic degradation of ethylenediaminediacetic acid, 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. Ethylenediaminediacetic acid was not biodegraded (5% at day 28) in the Closed Bottle test and should therefore not be classified as readily biodegradable. The lack of biodegradation in the Closed Bottle test does not mean that ethylenediaminediacetic acid is recalcitrant in nature because the stringency of the test procedures could account for the recalcitrance in the Closed Bottle test.

The test is valid as shown by an endogenous respiration of 0.7 mg/L and by the complete degradation of the reference compound, sodium acetate. Sodium acetate was degraded by 81% 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

Ethylenediaminediacetic acid is inherently biodegradable based on the results of a Zahn Wellens test published in literature. Ultimate biodegradability was demonstrated in a prolonged ready test.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

The biodegradability of ethylenediamine based complexing agents and related substances has been studied by Pitter and Sykora (2001) and Sykora et al 2001. They concluded that disubstituted ethylenediamines e.g. ED2A are potentially degradable. They observed >90% degradation of ED2A in an Zahn Wellens inherent biodegradability test within 500 hours using non-adapted sludge as inoculum indicating that ED2A is inherently biodegradable. Adapting the sludge used for the inoculum for 5 days reduces the lag period equivalently. When using 30 day adapted sludge, 100% degradation of ED2A was observed within 100 hours.

Van Ginkel (2017a) tried to show ready biodegradability of ED2A-H2 in a valid closed bottle test using non-adapted activated sludge under GLP conditions but observed only 5% degradation after 28 days. Using the same test setup but river water as inoculum van Ginkel (2017b) was able to show >60% biodegradation in a non-GLP test after prolongation of the closed bottle test till 84 days after inoculation.

Based on these observations it is concluded that Ethylenediaminediacetic acid is not readily biodegradable but ultimately biodegradable. The results from Pitter and Sykory (2001) show that ED2A is inherently biodegradable.