Sulfonic acids, shale-oil, sodium salts

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:

initiated: 2016-08-22, experimental: 2016-11-16 to 2016-12-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

recommended study/method

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

MHRA, date of issue: 28/10/2016

Specific details on test material used for the study:

technical grade: aqueous solution (31% dry matter in water)

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, adapted

Details on inoculum:

A mixed population of sewage treatment micro-organisms was obtained on 16 November 2016 from the final effluent stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

PREPARATION: The sample of effluent was filtered through coarse filter paper (first approximate 200 mL discarded) and the filtrate maintained on continuous aeration in a temperature controlled room at approximately 21 °C prior to use.

MINERAL MEDIUM: The mineral medium used in this study (see Annex 2) was that recommended in the OECD Guidelines.

Duration of test (contact time):

28 d

Initial conc.:

5 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST ITEM PREPARATION: The test item was dissolved directly in mineral medium. A nominal amount of test item (100 mg) was dissolved in mineral medium and the volume adjusted to 100 mL to give a 1000 mg/L stock solution. An aliquot (30 mL) of this stock solution was dispersed in a final volume of 6 liters of inoculated mineral medium to give a test concentration of 5.0 mg/L. The volumetric flask containing the stock solution was inverted several times to ensure homogeneity of the solution. A test concentration of 5.0 mg/L was employed in the study as the Chemical Oxygen Demand (COD) of the test item was determined to be 0.69 mg O2/mg (see Annex 3). Hence, if complete degradation of the test item occurred, the oxygen depletion in the test vessels would be 3.45 mg O2/L and as such de-oxygenation of the test media would not occur.

REFERENCE ITEM PREPARATION: A reference item, sodium benzoate (C6H5COONa), was used to prepare the procedure control vessels. An initial stock solution of 1000 mg/L was prepared by dissolving the reference item directly in mineral medium, and an aliquot (18 mL) dispersed in a final volume of 6 liters of inoculated mineral medium to give a test concentration of 3.0 mg/L. The volumetric flask containing the reference item was inverted several times to ensure homogeneity of the solution.

TOXICITY CONTROL: A toxicity control, containing the test item and sodium benzoate, was prepared in order to assess any toxic effect of the test item on the sewage treatment micro-organisms used in the study. An aliquot (15 mL) of the 1000 mg/L test item stock solution plus an aliquot (4.5 mL) of the sodium benzoate stock solution were dispersed in a final volume of 3 liters of mineral medium to give a final concentration of 5.0 mg test item/L plus 1.5 mg sodium benzoate/L.
The volumetric flasks containing the stock solutions were inverted several times to ensure homogeneity of the solutions.

PREPARATION OF TEST SYSTEM: The following test preparations were prepared and inoculated in 250 mL Biological Oxygen Demand (BOD) bottles (darkened glass) with ground glass stoppers:
a) An inoculum control, consisting of inoculated mineral medium.
b) The procedure control containing the reference item (sodium benzoate), in inoculated mineral medium to give a concentration of 3.0 mg/L.
c) The test item, in inoculated mineral medium to give a concentration of 5.0 mg/L.
d) The test item (5.0 mg/L) plus the reference item (1.5 mg/L), in inoculated mineral medium to act as a toxicity control.
Test media a to d were inoculated with sewage treatment micro-organisms at a rate of 1 drop of inoculum per liter.
The pH of all of the above test preparations was measured using a Hach HQ40d Flexi handheld meter prior to being transferred by siphon to BOD bottles, which were firmly stoppered to exclude all air bubbles. Sufficient bottles were prepared to allow a single oxygen determination per bottle with duplicate bottles for each test medium at each sampling occasion. The BOD bottles were incubated in darkness in a temperature controlled water bath at temperatures of between 20 and 21 °C.

Reference substance:

benzoic acid, sodium salt

Remarks:

> 99.5 %

Test performance:

The oxygen depletion of the inoculated control did not exceed 1.5 mg O2/L after 28 days, the residual oxygen concentration in the test bottles remained at 4.45 mg O2/L or greater in all test vessels and the difference between the extremes of replicate oxygen depletion values at the end of the test was less than 20% in all vessels thereby satisfying the validation criteria.

Key result

Parameter:

other: biodegradation

Value:

8

Sampling time:

28 d

Remarks on result:

other: not readily biodegradable

Details on results:

The test item attained 8% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301D. Variation in biodegradation rates on different sampling days was considered to be due to normal biological variation in respiration rates between control and test vessels. The toxicity control attained 35% biodegradation after 14 days and 39% biodegradation after 28 days therefore confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test.

Key result

Parameter:

ThOD

Value:

1.67 other: mg O2/mg

Key result

Parameter:

COD

Value:

>= 15 - <= 150 other: mg O2/L

Results with reference substance:

An aqueous solution of 600 mg sodium benzoate in 1 liter of deionized reverse osmosis water was prepared. This was diluted to give a 60 mg/L aqueous solution. Aliquots (2 mL) of this solution were dispensed to each of 3 reaction vials for the COD analysis. The reference item, sodium benzoate, attained 65% biodegradation after 14 days and 67% biodegradation after 28 days thereby confirming the suitability of the test method and culture conditions.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test item attained 8% biodegradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline No. 301D.

Executive summary:

The test item attained 8% biodegradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline No. 301D.

Description of key information

The oxygen depletion of the inoculated control did not exceed 1.5 mg O2/L after 28 days, the residual oxygen concentration in the test bottles remained at 4.45 mg O2/L or greater in all test vessels and the difference between the extremes of replicate oxygen depletion values at the end of the test was less than 20% in all vessels thereby satisfying the validation criteria.

The test item attained 8% biodegradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline No. 301D. Variation in biodegradation rates on different sampling days was considered to be due to normal biological variation in respiration rates between control and test vessels. The toxicity control attained 35% biodegradation after 14 days and 39% biodegradation after 28 days therefore confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test. The reference item, sodium benzoate, attained 65% biodegradation after 14 days and 67% biodegradation after 28 days thereby confirming the suitability of the test method and culture conditions.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable, fulfilling specific criteria

Additional information

Variation in biodegradation rates on different sampling days was considered to be due to normal biological variation in respiration rates between control and test vessels. The toxicity control attained 35% biodegradation after 14 days and 39% biodegradation after 28 days therefore confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test. The reference item, sodium benzoate, attained 65% biodegradation after 14 days and 67% biodegradation after 28 days thereby confirming the suitability of the test method and culture conditions.