Acetylcysteine

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:

2018-01-30 to 2018-03-08

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of activated sludge: sewage treatment plant Rossdorf, Germany
- Conditioning: washed by centrifugation, supernatant liquid phase decanted after 15 minutes of deposition; solid material re-suspended in test water and centrifuged again (procedure done three times); aliquot of final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined; 3.5 g dry material per litre were mixed with test water and aerated overnight. This suspension was used for the experiment.
- Concentration of sludge: 3.5 g dry material per litre

Duration of test (contact time):

28 d

Initial conc.:

101 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: reconstituted test water according to guideline
- Additional substrate: no
- Test temperature: 22 °C +/- 1 °C
- pH: 6.6 - 7.7
- pH adjusted: yes (adjusted to 7.4 to 7.5 at the start of the test)
- Aeration of dilution water: no
- Continuous darkness: yes

TEST SYSTEM
- Preparation of test solutions: The amounts of test item and reference item were directly weighed into the test flasks. No emulsifiers or solvents were used for the test item flasks, but the solutions were dispersed by stirring to achieve a homogeneous solution of the test item. Silicone oil AR20 was used as a distribution agent in the sodium benzoate flask of the parallel control.
- Culturing apparatus: manometric test system (sorrounding type: climatised chamber)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: activated sludge was aereated prior to preparation of test solutions
- Measuring equipment: BSB/BOD-Sensor-System, Aqualytic Dortmund, Germany
- Test performed in closed vessels: yes
- CO2 trap: Potassium hydroxide solution (45%)

SAMPLING
- Sampling frequency for measurement of oxygen: The change of pressure in the test flasks was measured by means of a manometric method each day.
- Sampling method: BSB/BOD-Sensor

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 flasks
- Abiotic sterile control: 1 flask
- Toxicity control: 1 flask
- reference (procedure) control: 1 flask

Reference substance:

benzoic acid, sodium salt

Preliminary study:

No

Key result

Parameter:

% degradation (O2 consumption)

Value:

76

Sampling time:

28 d

Remarks on result:

other: nitrification (ThODNO3) considered

Details on results:

The difference of duplicate values for the degradation of the test item at the end of the test and at the end of the 10-day window was less than 20%. The difference of duplicate values at day 28 differed by 0%. The mean biodegradation of 10% of the test item was reached at day 4 (ThODNH4) and at day 5 (ThODNO3). At the end of the 10-day window at day 14 and day 15, the mean degradation of the test item were 84% (ThODNH4) and 65% (ThODNO3) and therefore the 10 day window criterion was passed. The mean biodegradation at test end after 28 days was 103% (ThODNH4) and 79% (TIIODNO3). In the case of a nitrification, or transformation of ammonium to nitrate the degradation of the test item was 76% after 28 days.

Results with reference substance:

The reference item sodium benzoate was degraded to more than 60% after 4 days of incubation.

Table: Correction of percentage biodegradation of the test item based on ThOD under consideration of nitrification on day 28

	Nitrite-N				Nitrate-N				Total ^3	Measured ^4	Corrected ^5	Day 28
	Day 0	Day 28	∆ nitrite-N^1	O2 Equi.^2	Day 0	Day 28	∆ nitrite-N^1	O2 Equi.^2	O2 Equi.	ThODNH4	ThODNH4	Degradation ^6
	mg NO2-N/L			mg	mg NO3-N/L			mg	mg	mg	mg	%
Test Item Rate 1	0.002	0.002	0.000	0.000	0.026	9.236	9.21	8.089	8.089	32.330	24.241	77.300
Test Item Rate 2	0.002	0.002	0.000	0.000	0.026	10.072	10.046	9.021	9.021	32.330	23.309	74.000
Control (mean)	0.002	0.002	0.000	-	0.026	1.982	1.956	-	-	-	-	-
Test Item (mean)	0.002	0.002	0.000	0.000	0.026	9.654	9.628	8.555	8.555	32.330	23.775	75.650

-: Not applicable

¹: ∆ nitrite-N / ∆ nitrate-N: Difference of Nitrite-N / Nitrate-N between day 28 and day 0

²: ∆ nitrite-N/ ∆ nitrate-N multiplied by empirically determined conversion factor (NH4-N to NO2-N: 3.43; NH4-N to NO3-N: 4.57), corrected by test volume (0.244 L) and concentration of control

³: Sum of nitrite-N O2-equivalent and nitrate-N O2-equivalent

⁴: BOD value test item day 28 [mg/L] - BOD value control day 28 [mg/L] multiplied with test vessel volume [0.244L]

⁵: Corrected ThODNH4 = ThODNH4- O2-Equivalent

⁶: Degradation = Corrected ThODNH4 / Calculated ThODNH4* 100

Limits of quantification:

nitrite: 0.002 mg nitrite-N/L

nitrate: 0.026 mg nitrate-N/L

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

In a manometric test according to OECD TG 301 F and EU Method C.4-D the test item was determined to be readily biodegradable in a ten days window and after 28 days of exposure (76% ThODNO3).

Executive summary:

The ready biodegradability of the test item was assessed in a GLP-compliant manometric respirometry test according to OECD TG 301 F and EU Method C.4 -D using aerobic activated sludge from a domestic wastewater treatment plant. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure to 101 mg/L test item (corresponding to an oxygen demand of about 128.8 mg/L ThOD_NH4 and 168.4 mg/L ThOD_NO3). As a reference item sodium benzoate was tested (1 replicate) simultaneously under the same conditions as the test item, along with an inoculum control (2 replicates), a toxicity control (containing both, the test item and the reference item sodium benzoate; 1 replicate) and an abiotic control (without inoculum, 1 replicate). All validity criteria of the guidelines were met. The nitrate concentration in the controls after 28 days of incubation was 19.982 mg/L (mean). The nitrate concentration in the test item treated vessels was 9.654 mg/L (mean). Thus, a nitrification occured. The mean biodegradation of 10% of the test item was reached at day 4 (ThODNH4) and at day 5 (ThODNO3). At the end of the 10-day window at day 14 and day 15, the mean degradation of the test item were 84% (ThOD_NH4) and 65% (ThOD_NO3) and therefore the 10 day window criterion was passed. The mean biodegradation at test end after 28 days was 103% (ThOD_NH4) and 79% (ThOD_NO3). In the case of a nitrification, or transformation of ammonium to nitrate the degradation of the test item was 76% after 28 days. Based on these results, the test item can be regarded as readily biodegradable according to OCED criteria.

Description of key information

In a manometric test according to OECD TG 301 F and EU Method C.4-D the test item was determined to be readily biodegradable in a ten days window and after 28 days of exposure (76% ThODNO3) (reference 5.2.1 -1).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

The ready biodegradability of the test item was assessed in a GLP-compliant manometric respirometry test according to OECD TG 301 F and EU Method C.4 -D using aerobic activated sludge from a domestic wastewater treatment plant. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure to 101 mg/L test item (corresponding to an oxygen demand of about 128.8 mg/L ThOD_NH4 and 168.4 mg/L ThOD_NO3). A reference control (with the reference substance sodium benzoate, 1 replicate), an inoculum control (without the test item or reference substance, 2 replicates), a toxicity control (containing both, the test item and the reference item sodium benzoate; 1 replicate) and an abiotic control (with the test item but without inoculum, 1 replicate) ran in parallel. In the test a nitrification occured as the nitrate concentration in the controls after 28 days of incubation was 19.982 mg/L (mean). In result, the test item was determined to be readily biodegradable in a ten days window and after 28 days of exposure (76% ThOD_NO3). All validity criteria of the guidelines were met (reference 5.2.1 -1).