Diisobutyl hydrogen phosphate

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:

2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

Type : mixed population of aquatic microorganisms

Origin : secondary effluent of a wastewater treatment plant treating predominantly domestic sewage (Wupper area water authority, WWTP Odenthal)

Date of collection : 2020-10-05

Pre-treatment : separation of coarse particles by filtration, aeration of the resulting inoculum for one day

Effluent concentration of reaction mixture : 5 mL/L (5.8 mL/1.16 L)

Duration of test (contact time):

28 d

Initial conc.:

5 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

Pre-treatment of the test item
A stock solution was prepared to give the desired test concentration. 1 g were added to 1 litre of mineral medium and stirred for 24 hours on a magnetic stirrer. 5.8 mL of the stock solution were given to the test flasks, filled with ca. 300 mL of mineral medium. Afterwards the inoculum was added and the flasks volume was made up to 1.16 L with mineral medium and the flasks were closed free from air bubbles with glass stoppers.

Concentration of stock solution : 1 g/L

pH value of the stock solution : 7.5

Initial concentration test item : 5 mg/L (5.8 mg/1.16 L)

Pre-treatment of the reference compound

Reference compound name : sodium benzoate (Acros Organics)

Coding number : Ökotox_7/04

Purity : 99.6 %

Batch-no. : A0412860

Expiry date : 2022-10-31

A stock solution was prepared to give the desired test concentration. 500mg were added to 0.5 litres of deionised water and stirred for one hour on a magnetic stirrer. 3.4 mL of the stock solution were given to the test flasks, filled with ca. 300 mL of mineral medium. Afterwards the inoculum was added and the flasks volume was made up to 1.16 L with mineral medium and the flasks were closed free from air bubbles with glass stoppers.

Concentration of stock solution : 1 g/L

pH value of the stock solution : 7.4

Initial concentration reference compound : 2.9 mg/L (3.4 mg/1.16 L)




Pre-treatment of the toxicity control
Two stock solutions were prepared to give the desired test concentrations. 5.8 mL of the test item stock solution and 3.4 mL of the reference compound stock solution were given to the test flasks, filled with ca. 300 mL of mineral medium. Afterwards the inoculum was added and the flasks volume was made up to 1.16 L with mineral medium and the flasks were closed free from air bubbles with glass stoppers.

Initial concentration test item : 5 mg/L (5.8 mg/1.16 L)

Initial concentration reference compound : 2.9 mg/L (3.4 mg/1.16 L)

Exposure conditions

Test volume : 1.16 L

Incubation time : 28 days

Incubation temperature : 22  2 °C

Reference substance:

benzoic acid, sodium salt

Test performance:

The following flasks were used:

 Test suspension (18 flasks)
A measured volume of mineral medium containing a known concentration of the test item (as the nominal sole source of organic carbon) and inoculum.

 Reference control (10 flasks)
In order to check the procedure, the reference compound sodium benzoate was tested in parallel to the normal test runs.

 Inoculum blank (18 flasks)
A measured volume of mineral medium containing only inoculum.

 Toxicity control (10 flasks)
Toxic effects of the test item were determined in toxicity control flasks containing test item, reference compound and inoculum.

Degradation was followed by analysis of dissolved oxygen over a 28-day period. The amount of oxygen taken up by the microbial population during biodegradation of the test item, corrected for uptake by the blank inoculum run in parallel, was expressed as a percentage of ThOD.

The test lasted for 28 days.

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

7 d

Parameter:

% degradation (DOC removal)

Value:

1

Sampling time:

14 d

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

21 d

Key result

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

28 d

Degradation of the test item

Test concentration : 5 mg/L

Theoretical oxygen demand : 1.827 mg O₂/mg

Test item	DO depletion after n days [mg/L]
	3 d	7 d	10 d	14 d	17 d	21 d	24 d	28 d
No.1: (mt0 - mtx) - (mb0 - mbx)	0.0	0.0	0.0	0.1	0.0	0.0	0.0	0.0
No.2: (mt0 - mtx) - (mb0 - mbx)	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
D1: % degradation	0%	0%	0%	1%	0%	1%	0%	0%
D2: % degradation	0%	0%	0%	0%	0%	0%	0%	1%
% degradation, mean	0%	0%	0%	1%	0%	0%	0%	0%

Comments: Abbreviations according to test guideline

 

Degradation of the reference compound

Test concentration : 2.9 mg/L

Theoretical oxygen demand : 1.665 mg O₂/mg

Reference compound	DO depletion after n days [mg/L]
	3 d	7 d	10 d	14 d	17 d	21 d	24 d	28 d
No.1: (mt0 - mtx) - (mb0 - mbx)		3.7		3.8		3.8		4.0
No.2: (mt0 - mtx) - (mb0 - mbx)		3.7		3.8		3.8		4.1
D1: % degradation		76%		79%		78%		82%
D2: % degradation		76%		79%		78%		84%
% degradation, mean		76%		79%		78%		83%

Comments: none

 

 

Degradation of the toxicity control

Test concentration test item : 5 mg/L

Test concentration reference compound : 2.9 mg/L

Toxicity control	DO depletion after n days [mg/L]
	3 d	7 d	10 d	14 d	17 d	21 d	24 d	28 d
No.1: (mt0 - mtx) - (mb0 - mbx)		3.7		3.9		3.9		4.0
No.2: (mt0 - mtx) - (mb0 - mbx)		3.5		3.8		3.9		4.0
D1: % degradation		26%		28%		28%		28%
D2: % degradation		25%		27%		28%		28%
% degradation, mean		25%		28%		28%		28%

Comments: The used concentration of the test item is not toxic to bacteria.

 

Validity criteria fulfilled:

yes

Remarks:

The reference compound sodium benzoate showed 79 % degradation after 14 days.

Interpretation of results:

not readily biodegradable

Conclusions:

According to OECD 301 D Diisobutyl phosphate is considered to be not readily biodegradable.

Executive summary:

The study was performed to assess the ready biodegradability of Diisobutyl phosphate. The study was conducted in accordance with the Council Regulation (EC) 440/2008 Method C.4-E "Closed Bottle Test" (2008). This test method is in all essential parts identical with OECD Guideline 301 D (adopted July 1992).

The test item Diisobutyl phosphate in a mineral medium was inoculated with secondary effluent to result in completely filled, closed flasks and incubated under aerobic conditions for 28 days. During this period, the biodegradation was followed by analysis of dissolved oxygen. The amount of oxygen taken up by microorganisms which reduced the test chemical, corrected for uptake by the blank inoculum run in parallel, was expressed as a percentage of theoretical oxygen demand (ThOD).

 

Diisobutyl phosphate showed:

0　% degradation after 7 days

1　% degradation after 14 days

0　% degradation after 21 days

0　% degradation after 28 days

The biodegradation of Diisobutyl phosphate was 0 % (ThOD) after 28 days. The test item failed the pass level requested in test method OECD 301 D which is a biodegradation ≥ 70 % DOC or ≥ 60 % ThOD.

According to OECD 301 D the test item is therefore considered to be not readily biodegradable.

 

Description of key information

The biodegradation of Diisobutyl phosphate was 0 % (ThOD) after 28 days. The test item failed the pass level requested in test method OECD 301 D. According to OECD 301 D the test item is considered to be not readily biodegradable.

 

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater