o-chlorobenzenethiol

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:

From January 28th to February 25th, 2016.

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source: A sample of activated sludge was taken from the aeration tank of Sewage Treatment Plant ”Czajka” , Warsaw, receiving predominantly domestic sewage.
- Preparation of inoculum: The coarse particles were removed by settling and the supernatant was discarded. The sludge was washed in the mineral medium. The concentrated sludge was suspended in mineral medium to yield a concentration of 3-5 g suspended solids/l and it was aerated, at the test temperature of 22 °C, until application next day. A sample was withdrawn just before use for the determination of the dry weight of the suspended solids.
- Amount of inoculum suspended: 30 mg/L.

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- pH: 7.4 ± 0.2
- pH adjusted: no
- Test temperature: 22 ± 2°C
- Volume of test solution in flask, V: 0.164 L
- Initial test item concentration: 100 mg/L (51.3 mg/L of organic carbon)
- Calculated ThOD(NH4): 1.88 mgO2/mg of test item.
- Suspended solids concentration: 30 mg/L.
- Composition of medium: 10ml of solution (A) in 800 ml water, plus 1 ml solutions (B), (C), (D) and 11ml water. The following stock solutions were used, prepared with analytical grade reagents:
- Solution (A) contains: 8.50 g monopotassium dihydrogen orthophosphate (KH2PO4), 21.75 g dipotassium monohydrogen orthophosphate (K2HPO4), 33.40 g disodium monohydrogen orthophosphate dihydrate (Na2HPO4·2H2O), 0.50 g ammonium chloride (NH4Cl), in 1 L double-distilled water.
- Solution (B) contains: 27.50 g calcium chloride, anhidrous (CaCl2) in 1L water.
- Solution (C) contains: 22.50 g magnesium sulphate heptahydrate (MgSO4·7H2O) in 1L water.
- Solution (D) contains: 0.25 g iron(III) chloride hexahydrate (FeCl3·6H2O) in 1L water.
- The water used is double-distilled, containing 3mg/L of organic carbon (< 10% of the organic carbon content introduced by the test item), checked by DOC analysis using spectrophotometer Hach DR 3900 and Hach-Lange reagents.

TEST SYSTEM
- Number of culture flasks/concentration: triplicates were used, flasks #19, 20, 21 containing test item (100 mg/l) and inoculum 30mg/L SS.
- Measuring equipment: closed WTW OxiTop OC 110 repirometer for BOD determination. The data were read out every 112 min during the 28 day test (40 320 min that is 360 readings) and were recorded and stored in the measuring heads of the sample bottles.

CONTROL AND BLANK SYSTEM
- Inoculum blank: flasks #7, 8, 9, containing only inoculum 30mg/L SS.
- Procedure control: flasks #10, 11, 12 containing reference item (sodium acetate 100 mg/l) and inoculum 30mg/L SS.
- Toxicity control: flasks #22, 23, 24 containing test item, reference item and inoculum 30mg/L SS.

STATISTICAL METHODS: The calculations and the graphs were performed using SigmaPlot 9.0 software of SYSTAT Software, Inc., USA purchased from GAMBIT CoiS Ltd, Poland.

Reference substance:

acetic acid, sodium salt

Remarks:

CAS No.: 127-09-3, purity ≥ 98.5%, source: Eurochem

Key result

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

28 d

Details on results:

- At the 28th day of the test the measured aerobic biodegradation of the test item attained 0.0%. The pH values of all flasks were inside the range 7.19-8.92.
- In the toxicity test, the biodegradation was equal to 16.0% in 14 days. Therefore, the test item may have a toxic effect on the incoculum (inhibitory).

Results with reference substance:

The reference item reached 78.4% (>60%, pass level for ready biodegradability) by day 5.

Table 2. Sample oxygen uptake: biodegradability.

		time, days
		3	5	7	9	12	14	16	18	21	23	25	28
Test item O2uptake, mg/l	a1	0.0	0.0	0.0	1.3	3.1	10.6	32.0	32.1	34.2	34.2	36.9	35.1
	a2	0.0	0.0	0.0	0.0	2.8	10.4	31.4	29.2	31.3	31.2	33.5	33.7
	a3	0.0	0.3	3.2	6.0	6.4	10.1	28.5	30.0	30.5	31.6	33.6	33.8
	am. avg	0.0	0.1	1.1	2.4	4.1	10.3	30.6	30.4	32.0	32.3	34.7	34.2
Blank test O2uptake. mg/l	b1	6.7	13.8	17.7	22.9	25.6	33.3	51.6	53.5	56.2	56.3	56.3	59.7
	b2	3.3	8.8	13.3	17.4	19.7	27.8	45.0	46.2	48.1	48.2	50.6	50.6
	b3	9.0	13.6	17.5	19.7	25.6	30.3	46.8	47.8	50.8	50.6	51.0	54.1
	bm. avg	6.3	12.1	16.2	20.0	23.6	30.5	47.8	49.2	51.7	51.7	52.6	54.8
Reference item O2uptake. mg/l	w1	52.0	64.0	73.6	79.3	87.9	95.3	113.2	113.5	115.0	115.7	118.2	118.8
	w2	44.6	57.2	67.9	73.5	79.9	90.7	107.2	107.0	110.8	113.0	113.0	115.4
	w3	48.6	61.7	71.1	76.7	82.1	90.3	107.2	107.5	109.8	110.0	110.0	113.6
	wm. avg	48.4	61.0	70.9	76.5	83.3	92.1	109.2	109.3	111.9	112.9	113.7	115.9
Toxicity control O2uptake. mg/l	tox1	48.6	53.8	56.3	59.1	62.2	69.3	89.2	92.5	94.9	96.2	99.0	101.0
	tox2	48.6	54.1	59.5	62.1	65.0	72.4	92.7	95.5	98.8	99.0	101.4	101.4
	tox3	54.1	59.6	61.9	64.7	70.6	77.2	92.9	95.2	97.5	98.5	99.1	101.4
	toxm. avg	50.4	55.8	59.2	62.0	65.9	73.0	91.6	94.4	97.1	97.9	99.8	101.2
Corrected test item O2uptake, mg/l	(a1-bm)	-6.3	-12.1	-16.2	-18.7	-20.6	-19.9	-15.8	-17.0	-17.5	-17.5	-15.8	-19.7
	(a2-bm)	-6.3	-12.1	-16.2	-20.0	-20.8	-20.1	-16.4	-20.0	-20.4	-20.5	-19.1	-21.1
	(a3-bm)	-6.3	-11.8	-13.0	-14.0	-17.2	-20.4	-19.3	-19.2	-21.2	-20.1	-19.0	-21.0
Reference item % degradation ThOD = 0.78 mgO2/mg C = 100 mg/l	R1(w1)	58.5	66.5	73.7	76.1	82.3	83.1	83.9	82.5	81.2	82.0	84.1	82.0
	R1(w2)	49.1	57.8	66.3	68.6	72.2	77.3	76.2	74.1	75.8	78.6	77.4	77.7
	R3(w3)	54.2	63.7	70.4	72.7	75.0	76.8	76.2	74.8	74.5	74.7	73.5	75.4
	Rwavg	54.0	62.7	70.2	72.4	76.5	79.1	78.8	77.2	77.2	78.5	78.3	78.4
Test item % degradation ThOD = 1.88 mgO2/mg C = 100 mg/l	R1(a1)	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	R1(a2)	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	R3(a3)	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
	Raavg	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Toxicity control % degradation	R1(tox1)	15.9	15.7	15.1	14.7	14.5	14.6	15.6	16.3	16.3	16.7	17.4	17.4
	R2(tox2)	15.9	15.8	16.3	15.8	15.5	15.8	16.9	17.4	17.7	17.8	18.3	17.5
	R3(tox3)	18.0	17.8	17.2	16.8	17.6	17.6	16.9	17.3	17.2	17.6	17.5	17.5
	Rtoxavg	16.6	16.4	16.2	15.8	15.9	16.0	16.5	17.0	17.1	17.4	17.7	17.5

In the toxicity control, O2 uptake was less than the uptake of the blank test. This result may indicate that the test item has a toxic effect on the inoculum and inhibits its respiration.

Table 3. pH values of the test flasks.

flask #	19	20	21	7	8	9	10	11	12	22	23	24
	Test item			Control			Reference item			Toxicity test
initial	7.40	7.38	7.39	7.48	7.50	7.54	7.57	7.47	7.46	7.37	7.37	7.37
final	7.94	8.02	7.95	7.27	7.19	7.20	8.37	8.43	8.60	8.64	8.87	8.92

Validity criteria fulfilled:

yes

Remarks:

See 'overall remarks'.

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

Based on the test results (0% biodegradation in 28 days), the test item is not readily biodegradable.

Executive summary:

The study of ready biodegradability of the test item in an aerobic aqueous medium with manometric respirometry method was carried out according to OECD 301F/EC / C.4 – D manometric respirometry methods, under GLP conditions. 100 mg/l of test item were inoculated with adapted activated sludge (30 mg/L SS) and incubated under aerobic conditions in a closed respirometer flask at 22ºC for 28 days. A blank test, a procedure test with reference substance (sodium acetate) and a toxicity test were run in parallel. In the toxicity test, only 16% biodegradation was attained after 28 days, which may indicate that the test item is inhibitory. Under test conditions, no biodegradation was observed, and therefore the test substance cannot be considered readily biodegradable.

Description of key information

Key study. Method according to OECD 301F / EU C.4-D (manometric respirometry), GLP study. No biodegradation was observed after 28 days, and the toxicity control attained a 16% biodegradation (inhibitory). Therefore, the test item is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

The study of ready biodegradability of the test item in an aerobic aqueous medium with manometric respirometry method was carried out according to OECD 301F/EC / C.4 – D manometric respirometry methods, under GLP conditions. 100 mg/l of test item were inoculated with adapted activated sludge (30 mg/L SS) and incubated under aerobic conditions in a closed respirometer flask at 22ºC for 28 days. A blank test, a procedure test with reference substance (sodium acetate) and a toxicity test were run in parallel. In the toxicity test, only 16% biodegradation was attained after 28 days, which may indicate that the test item is inhibitory. Under test conditions, no biodegradation was observed, and therefore the test substance cannot be considered readily biodegradable.