2,3-dichlorobenzoic acid

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

2,3-dichlorobenzoic acid

EC Number:

200-039-5

EC Name:

2,3-dichlorobenzoic acid

Cas Number:

50-45-3

Molecular formula:

C7H4Cl2O2

IUPAC Name:

2,3-dichlorobenzoic acid

Test material form:

solid: crystalline

Study design

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Duration of test (contact time):

28 d

Details on study design:

The amount of oxygen consumed by the microorganisms when metabolising the test item is called Biochemical Oxygen Demand (BOD). The BOD of test item is determined by the manometric respiratory - OxiTop® system. The principle of the determination of BOD by OxiTop® - system is based on the measurement of the consumption of oxygen by a pressure sensor in the top of the tightly closed test vessels. Test vessels with the test item solution and mixed bacterial culture, so called inoculum, are under continuous stirring in an incubator at 21 ± 1 °C for 28 days. The carbon dioxide which is evolved during the biodegradation is absorbed by sodium hydroxide granulates. The reduced amount of oxygen causes definite pressure changes in the test vessels which are measured by the apparatus. The amount of oxygen taken up by microorganisms during biodegradation of the test item is expressed as a percentage of theoretical oxygen demand (ThOD). The percentage of biodegradability of the test item is calculated on the base of quotient of 28-day biochemical oxygen demand (BOD28) and theoretical oxygen demand. The pass level for the biodegradability is 60% of ThOD for Manometric Respirometry method. The pass value has to be reached in 10 days (10-d) window within the 28-day period of the test. The 10-d window begins when the degree of biodegradation has reached 10% ThOD and must end before day 28 of the test. Biodegradability classification of the test item is made according to OECD 301 guideline, which says that chemicals which reach the pass level up to 28-d period are deemed to be readily biodegradable.

Reference substance

Reference substance:

acetic acid, sodium salt

Results and discussion

Test performance:

Preparation of inoculum test culture: Before the test 300 ml stock culture was filtered through a filter with 0.2 mm pore size to remove the bigger insoluble particles and then the dry substance content of the filtrate was determined. The measured value was 10.73 g/L. For preparing the inoculum culture 181 ml mineral medium was added to 19 ml filtered stock culture. The calculated dry mass of inoculum culture was 1 g/L.
Preparation of test vessels: Following test vessels were prepared and analysed for the study:
- Test item (in two replicates)
- Blank control (in two replicates)
- Reference solution (positive control)
- Reference and test item solution (toxicity control)
- Sterilized solution of test item (abiotic control)
Measurement of Biological Oxygen Demand values: The BOD values of the test vessels were collected and stored by measuring heads. The data were read out from the heads by the controller. The controller shows directly the BOD concentrations in mg/L. The daily BOD values were documented.
Measured BOD values of blank control: The maximum measured BOD value of the blank controls was 9.9 mg/L which is less than 60 mg/L so the used inoculum was proper for the test.
Measurement of pH: At the beginning and at the end of the test the pH was measured. The pH of test solutions was not adjusted at the beginning of the test.
The following table shows the measured pH values at the beginning and at the end of the test: A slightly elevated level of pH was observed throughout the incubation period.
Measurement of temperature: The temperature inside the incubator at the test vessels was measured and registered continuously by Extech SD200 thermometer and data logger. Throughout the test the temperature was nearly constant.

% Degradation

Key result

Parameter:

% degradation (O2 consumption)

Value:

1

Remarks on result:

other: mean of two replicates

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

According to OECD guideline the test item should be classified as readily biodegradable if the percentage biodegradation reaches 60% of theoretical oxygen demand within 28 day period in a 10-day window. Based on ready biodegradability testing results the 2,3-Dichlorobenzoic acid is not readily biodegradable.