Benzenesulfonamide, N-(4-hydroxyphenyl)-

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:

2019-2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

Adopted July 17, 1992

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Effluent freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage
- Laboratory culture: /
- Method of cultivation: /
- Storage conditions: The filtrate was kept aerated until inoculation.
- Storage length: /
- Preparation of inoculum for exposure: /
- Pretreatment: /
- Concentration of sludge: 4 mL filtrate of secondary effluent per litre of final volume.
- Initial cell/biomass concentration: /
- Water filtered: yes
- Type and size of filter used, if any: Secondary effluent was filtered through a coarse filter paper, the first 200 mL were discarded.

Duration of test (contact time):

28 d

Initial conc.:

21 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

Test duration 28 days for the inoculum blank and test suspension
14 days for the procedure and toxicity control
Test bottles 2 litre brown coloured glass bottles
Milli-RO water Tap-water purified by reverse osmosis (Millipore Corp., Bedford, Mass., USA).

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 1 litre Milli-RO water, pH 7.4 + 0.2
B) 22.50 g MgSO4.7H2O dissolved in 1 litre Milli-RO water.
C) 36.40 g CaCl2.2H2O dissolved in 1 litre Milli-RO water.
D) 0.25 g FeCl3.6H2O dissolved in 1 litre Milli-RO water.

Mineral medium 1 mL aliquots of solution (A) to (D) were mixed and made up to 1 litre with Milli-RO water. T
Barium hydroxide 0.0125 M Ba(OH)2 (Boom, Meppel, The Netherlands), stored in a sealed vessel to prevent absorption of CO2 from air.
Pre-incubation medium Before the start of the test (Day -1) mineral components, Milli- RO water (ca. 80 % of final volume) and inoculum were added to each bottle. This mixture was aerated with synthetic air overnight to purge the system of CO2.
Type and number of bottles Test suspension: containing test item and inoculum (2 bottles).
Inoculum blank: containing only inoculum (2 bottles)
Procedural control: containing procedural control item and inoculum (1 bottle).
Toxicity control: containing test item, procedural control item and inoculum (1 bottle).
Illumination The test bottles were protected from light.
Preparation At the start of the test (Day 0), test and procedural control item were added to bottles containing microbial organisms and mineral components.
Volumes were made up to 2 L with Milli- RO water, resulting in the mineral medium described before.
Three CO2-absorbers (bottles filled with 100 mL 0.0125 M Ba(OH)2) were connected in series to the exit aeration line of each test bottle.

Reference substance:

other: sodium acetate

Test performance:

The pH values stayed between 7.4 and 7.8.
The temperature recorded in a vessel with Milli-RO water in the same room varied between 22 and 23°C, and complied with the requirements as laid down in the study plan.

Parameter:

% degradation (CO2 evolution)

Value:

23

Sampling time:

21 d

Details on results:

Relative biodegradation values calculated from measurements performed during the test period revealed 23 % biodegradation of CH03951 (based on ThCO2) in both vessels. Thus, the criterion for ready biodegradability (at least 60 % biodegradation within a 10-day window) was not met.

In the toxicity control, 59 % biodegradation was observed. Therefore, CH03951 was found not to inhibit microbial activity at a concentration of 11 mg/L.
Functioning of the test system was checked by testing the procedural control item sodium acetate, which showed a normal biodegradation curve

Results with reference substance:

Procedural control item was biodegraded by at least 60 % (actual result: 75 % in) within 14 days.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

In conclusion, CH03951 was designated as not readily biodegradable.

Executive summary:

The objectiveofthe studywas to evaluate test item CH03951 for its ready biodegradability in an aerobic aqueous medium with microbial activity introduced by inoculation with activated sludge.

Procedures described in this report were in compliance with OECD guideline No. 301 B, 1992. In addition, procedures were designed to meet test methods of ISO standard 10634, 2018.

In total, two experiments were performed. In the first experiment a potentially inhibitory effect was found in the toxicity control. Therefore, a second experiment was performed at a 50 % decreased concentration.

CH03951 was an off-white powderwith a purity of approximately 96.85 w/w%. Test item was tested in duplicate at a concentration of 11 mg/L, corresponding to 6 mg TOC/L. Organic carbon content was based on the molecular formula. Theoretical CO₂ production (ThCO₂) of CH03951 was calculated to be 2.12 mg CO₂/mg.

The study consisted of six bottles:

·     2 inoculum blanks (no test item),

·     2 test bottles (CH03951),

·     1 procedural control (sodium acetate) and

·     1 toxicity control (CH03951 plus sodium acetate).

Since CH03951 was not sufficiently soluble to allow preparation of an aqueous stock solution at a concentration of 1 g/L, weighed amounts were added to 2 L test bottles containing medium with microbial organisms and mineral components. To this end, approximately 10 mL of Milli- RO water was added to each weighing bottle containing test item. After vigorous mixing (vortex) the resulting suspension was added quantitatively to the test medium. Test solutions were continuously stirred during the test, to ensure optimal contact between test item and test organisms. Furthermore, test medium was swirled around daily, since the test item tended to float on the water surface.Test duration was28 days for inoculum blank and test item (last CO₂measurement on Day 29) and 14 days for procedural and toxicity control (last CO₂measurement on Day 15).

Relative biodegradation values calculated from measurements performed during the test period revealed 23 % biodegradation of CH03951 (based on ThCO₂) in both vessels. Thus, the criterion for ready biodegradability (at least 60 % biodegradation within a 10-day window) was not met.

In the toxicity control, CH03951 was found not to inhibit microbial activity at a concentration of 11 mg/L.

Since all criteria for acceptability of the test were met, this study was considered to be valid.

In conclusion,CH03951 was designated as not readily biodegradable.

Description of key information

CH03951 was found to not be readily biodegradable in the OECD 301B test (CO2 evolution test).

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater