Diquat dibromide

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:

11 Nov 2020 – 09 Dec 2020

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:

(1992)

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Version / remarks:

(2008)

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Version / remarks:

(1998)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source: Waste water treatment plant treating predominantly domestic wastewater Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany
- date of collection: 11.11.2020 (day of test start)
- Sludge was filtered (2 mm) to remove coarse particles, washed once with tap water and maintained under aerobic conditions until use. The sludge was left for settlement for ca. one hour, the supernatant was discarded, and the concentration was adjusted to 4.7 g/L in tap water based on dry mass measurements.
- Test Concentration: 29.5 mg dry material/litre

Duration of test (contact time):

28 d

Initial conc.:

52.5 mg/L

Based on:

ThOD

Remarks:

considering total lack of nitrification

Initial conc.:

68 mg/L

Based on:

ThOD

Remarks:

considering total nitirification

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

All test assays except for the abiotic controls were filled up to 250 mL with inoculated mineral medium. No emulsifiers or solvents were used.
The reference item sodium benzoate was added from a stock solution (procedural control, toxicity control).
The test material was used without further purification. The test item was added to ensure a final concentration of 100 mg/L as an aqueous stock solution.
A toxicity control containing both test and reference item at the same concentrations as in the individual solutions (test item 100 mg/L, reference item 100 mg/L) was prepared to determine the possible toxicity of the test item against the inoculum.
Inoculum controls containing mineral medium only were prepared.
Abiotic controls were prepared to measure any possible abiotic degradation by sterilizing a solution of the test item at about 100 mg/L by the addition of 10 mL/L NaN3 (100 g/L).

Before the start of the test, the pH values of all solutions were determined and adjusted to pH 7.4 ± 0.2 with H2SO4 (50 g/L). At the end of the test, the pH values of all solutions were determined again.

The percentage biodegradation of test item and of the reference item sodium benzoate was calculated based on their biochemical oxygen demand (BOD) and theoretical oxygen demand (ThOD). Since the test material contains nitrogen, the % biodegradation was calculated based on the ThODNH3 (no nitrification) and ThODNO3 (complete nitrification).
At Day 0 and Day 28 (end of test), the concentration of nitrate and nitrite in the inoculum control and test material flasks was measured spectrophotometrically using commercially available test kit(s) (NANOCOLOR® Nitrat 50 985064 and NANOCOLOR® Nitrit 91867, Macherey-Nagel).

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (O2 consumption)

Value:

-11.8

St. dev.:

7.3

Sampling time:

28 d

Remarks on result:

other: based on ThOD(NO3)

Parameter:

% degradation (O2 consumption)

Value:

-15.2

St. dev.:

9.4

Sampling time:

28 d

Remarks on result:

other: based oht ThOD(NH3)

Results with reference substance:

In the procedure controls, the reference item was degraded by an average of 89% by Day 14, confirming the suitability of the activated sludge. At the end of the test (Day 28), the reference item was degraded by an average of 96%.

Biodegradation in the toxicity control
The percent biodegradation in the toxicity control, which contains both the test item and the reference item, was calculated based on the sum of the ThOD of the test item and the reference item. Within 14 days of incubation, biodegradation of 67% and 62% was observed based on the ThODNH3 and ThODNO3, respectively. Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days.

Biodegradation in the abiotic control
No degradation was observed in the abiotic control.

Nitrification
Nitrite-N and nitrate-N concentrations were measured in the media of inoculum blanks and the test assays at test start and test end and are reported below.

Since the biodegradation rate – even considering the total lack of nitrification – was clearly below the threshold value for ready biodegradability, the effects of nitrification did not need to be considered.

Sample flask	Replicate	Nitrate-N Concentration (mg/L)		Nitrite-N Concentration (mg/L)
		Day 0	Day 28	Day 0	Day 28
Inoculum Control	1	0.68	0.68	<0.03	<0.002
	2	0.45	0.90	<0.03	<0.002
Test Item	1	0.45	0.45	<0.03	<0.002
	2	0.68	0.68	<0.03	<0.002

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test substance was not readily biodegradable under the conditions of the test within 28 days.

Executive summary:

The ready biodegradability of the test substance was determined by observing the biochemical oxygen demand (BOD) using manometric methods over 28 days. Aerobic activated sludge was used as the inoculum. As a procedural control, the reference item sodium benzoate
was tested. The toxicity control contained both test item and the reference item sodium benzoate.
The test item was not readily biodegradable under the conditions of the test within 28 days.

Description of key information

The substance is not readily biodegradable in water.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater