Phosphorothioic acid, O,O-bis(2-methylpropyl) ester, sodium salt (1:1)

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

11 April, 2012 - 6 June, 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Also according to GLP principles.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

ISO DIS 9439 (Ultimate Aerobic Biodegradability - Method by Analysis of Released Carbon Dioxide)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Sodium O,O-diisobutyl phosphorothioate

EC Number:

610-992-2

Cas Number:

53378-52-2

Molecular formula:

C8 H18 O3 P S . Na

IUPAC Name:

Sodium O,O-diisobutyl phosphorothioate

Test material form:

other: grease-like solid

Specific details on test material used for the study:

- Name of test material (as cited in study report): S10783
- Name: Sodium diisobutyl monothiophoshate
- CAS: 53378-52-2
- Molecular formula: C8H18O3PS.Na
- Molecular weight: 248.26
- Storage condition of test material: not indicated in the study report
- Purity: 70%

Study design

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

The source of test organisms was activated sludge freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage. The freshly obtained sludge was kept under continuous aeration until further treatment. The concentration of suspended solids was 3.1 g/L in the concentrated sludge (information obtained from the municipal sewage treatment plant). Before use, the sludge was allowed to settle (45 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.

Duration of test (contact time):

28 d

Initial test substance concentration

Initial test substance concentration 1

Initial conc.:

39 mg/L

Based on:

test mat.

Initial test substance concentration 2

Initial conc.:

12 mg/L

Based on:

other: Total Organic Carbon (TOC)

Parameter followed for biodegradation estimation

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: 1 litre mineral medium contains: 10 ml of solution (A), 1 ml of solutions (B) to (D) and Milli-RO water
Stock solutions of mineral components
A) 8.50 g KH2PO4; 21.75 g K2HPO4; 67.20 g Na2HPO4.12H2O; 0.50 g NH4Cl; dissolved in Milli-Q water and made up to 1 litre, pH 7.4 ± 0.2
B) 22.50 g MgSO4.7H2O dissolved in Milli-Q water and made up to 1 litre.
C) 36.40 g CaCl2.2H2O dissolved in Milli-Q water and made up to 1 litre.
D) 0.25 g FeCl3.6H2O dissolved in Milli-Q water and made up to 1 litre.

- Test temperature: between 21.8 and 22.3 °C.
- pH:
At t=0 d: 7.4 - 7.6
At t=28 d: 7.5 – 7.9
- pH adjusted: only before the start of the test. pH was 7.7 to 7.8 and adjusted to 7.4 - 7.6.
- Aeration of dilution water: Not before the test, the test is aerated continously
- Suspended solids concentration: The concentration of suspended solids was 3.1 g/L in the concentrated sludge (information obtained from the municipal sewage treatment plant). Before use, the sludge was allowed to settle (45 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.

- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 2 litre all-glass brown coloured bottles
- Number of culture flasks/concentration:
Test suspension: containing test substance and inoculum (2 bottles).
Inoculum blank: containing only inoculum (2 bottles)
Positive control: containing reference substance and inoculum (1 bottle).
Toxicity control: containing test substance, reference substance and inoculum (1 bottle).
- Method used to create aerobic conditions:
Synthetic air (a mixture of oxygen (ca. 20%) and nitrogen (ca. 80%)) was sparged through the solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 ml/min).
- Test performed in open system: yes
- Details of trap for CO2 and volatile organics if used:
CO2 was trapped in barium hydroxide solution. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl (1:20 dilution from 1 M HCl (Titrisol® ampul). Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day, for the inoculum blank and test suspension. Titrations for the positive and toxicity control were made at least 14 days.


SAMPLING
- Sampling frequency: Titration were made on day: 3, 6, 8, 10, 14, 17, 22, 27 and 29
- Sampling method: Titration of the whole volume of CO2-absorber

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes

Reference substance

Reference substance:

acetic acid, sodium salt

Results and discussion

% Degradation

% Degradation 1

Parameter:

% degradation (CO2 evolution)

Value:

4

Sampling time:

29 d

Remarks on result:

other: HCl added on the 28th day (last CO2-measurement on the 29th day)

% Degradation 2

Parameter:

% degradation (CO2 evolution)

Value:

6

Sampling time:

29 d

Remarks on result:

other: HCl added on the 28th day (last CO2-measurement on the 29th day)

Details on results:

The relative biodegradation values calculated from the measurements performed during the test period revealed no significant biodegradation.

In the toxicity control more than 25% biodegradation occurred within 14 days (29%, based on ThCO2). Therefore, the test substance was assumed not to inhibit microbial activity.

BOD5 / COD results

Results with reference substance:

The positive control substance was biodegraded by at least 60% (81%) within 14 days.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test substance was not readily biodegradable under the conditions of the modified Sturm test protocol performed in this study.

Executive summary:

The ready biodegradation of the substance under the conditions of the carbon dioxide (CO2) evolution test (modified Sturm test) was investigated according to OECD guideline 301 B and GLP principles. A test concentration of 12 mg/L (as TOC) was tested in duplicate during 28 days. The relative biodegradation values calculated from the measurements performed during the test period revealed 4 and 6% biodegradation of the substance, for replicate A and B, respectively (based on ThCO2). In the toxicity control, the substance was found not to inhibit microbial activity. The study is considered to be reliable without restrictions.

In conclusion, the substance was determined to be not readily biodegradable under the conditions of the modified Sturm test.