Zinc bis(hydroxymethanesulphinate)

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:

November 2009 - January 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-guideline study: The test was made in accordance with the „Revised OECD Principles of Good Laboratory Practice“ (Paris, 1997) as stated in the following guideline: OECD 301B resp. EU C.4.C

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES
- Melting point: no melting point, but a melting range (139.0 to 140.7 °C (412.2 to 413.9 K))
- Boiling point: no boiling point (decomposition)
- log Pow: < 0.3
- pKa: 9.61 ± 0.02 and 6.62 ± 0.01
- Stability in water: the substance is only used in aqueous solutions (water solubility: 636.4 ± 13.0 g/L)
- pH dependance on stability: the stability of the chemical in alkaline solution is usually better than in neutral or acid solution.

OTHER PROPERTIES (if relevant for this endpoint)
- Results of test for ready biodegradability: readily biodegradable

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge:
Activated sludge from a biological sewage treatment plant was used. The chosen plant is treating mostly domestic sewage.The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant, Im Altenschemel, NW-Lachen-Speyerdorf (date of collection: 06. Nov. 2009, batch no: 06112009).
- Preparation of inoculum for exposure: . The inoculum was taken from its source, washed, aerated and the dry matter was determined.
- Pretreatment: The sludge was filtrated, washed with tap water twice, then washed with and resuspended in test medium. It was then aerated for
>=12 hours.
- Concentration of sludge: 4600 mg suspended solids/litre
- Initial cell/biomass concentration: The test was performed with a nominal start concentration of 20 mg organic carbon/L
- Water filtered: yes

Duration of test (contact time):

28 d

Initial conc.:

20 mg/L

Based on:

other: organic carbon/L

Initial conc.:

25 mg/L

Based on:

other: dry matter/L, sludge used in inoculum

Initial conc.:

233 mg/L

Based on:

test mat.

Details on study design:

TEST CONDITIONS
- Composition of medium:
The medium was freshly prepared.
Composition:
Solution a 10 mL
Solution b 1 mL
Solution c 1 mL
Solution d 1 mL
H2O demin. ad 1000 mL

Solution a)
Potassium dihydrogenephosphate (KH2PO4) 8.5 g
Di-potassium hydrogenephosphate (K2HPO4) 21.75 g
Di-sodiumhydrogenephosphate dihydrate (Na2HPO4*2H2O) 33.4 g
Ammonia chloride (NH4Cl) 0.5 g
H2O demin. ad 1000 mL
The pH was adjusted to 7.4  0.1.

Solution b)
Calcium chloride dihydrate (CaCl2*2H2O) 36.4 g
H2O demin. ad 1000 mL

Solution c)
Magnesium sulfate heptahydrate (MgSO4*7H2O) 22.5 g
H2O demin. ad 1000 mL

Solution d)
Iron(III) chloride hexahydrate (FeCl3*6H2O) 0.25 g
Di-sodium-ethylendiamintetraacetate dihydrate (Na2EDTA*2H2O) 0.4 g
H2O demin. ad 1000 mL

- Test temperature: 22 +/- 2°C

- pH adjusted: yes ( Solution a: The pH was adjusted to 7.4 +/- 0.1)

TEST SYSTEM
- Number of culture flasks/concentration:
Controls: 2, containing mineral medium and inoculum
Positive control flasks: 2, containing positive control, mineral medium and inoculum
Test flasks: 2, containing test item, mineral medium and inoculum
Abiotic control: 1, containing test item, mineral medium and HgCl2
Toxicity control: 1, containing test item, positive control, mineral medium and inoculum
Incolum concentration: 25.0 mg dry matter/L
Flask Volume: 1500 mL

- Method used to create aerobic conditions: all flasks were aerated for 24 hours with purified, CO2-free, moistened air to purge the system of CO2

- Measuring equipment:
The following instruments and devices were used in the performance of the study:
• Data logger for temperature
• Analytical scales Mettler Toledo AB 184 SA
• Precision scales Sartorius 1403
• Adjustable pipettes with one-way tips Rainin® (for volumes 1 mL, 1 – 10 mL); LAUS-No.s 24; 29
• Carbon analyser TOC multi N/C 2100S, Analytik Jena
• Magnetic stirrers
• pH-meter 340i wtw
• Heating chamber Memmert 4

SAMPLING
From each front scrubber flask, ten samples were taken in order to determine the emitted CO2. (on days 0, 2, 4, 7, 9, 11, 14, 18, 23 and 29). The sample volume was 1 mL. The resulting change in the volume of the front flask was considered in the calculation of emit-ted CO2 (see also chapter 8.2.1).
On day 28, 5 mL HCl 2-m. were added to each test flask in order to drive off dissolved CO2. On day 29, samples from both scrubber flasks were taken.

STATISTICAL METHODS:
Analyses of the emitted CO2 were made by IC measurement using the carbon analyser TOC multi N/C 2100S, Analytik Jena. Each sample was measured at least in duplicate. The carbon analyser was calibrated with freshly prepared reference solutions once a week. After every start, quality control samples were measured.
Emitted Carbon in mg/L test solution at time t is calculated using the following equation:
emittC=(IC(t) - IC(0))* VolNaOH(t)/VolTestVessel
with
emittC emitted carbon in mg/L test solution
IC(t) net inorganic carbon in mg/L NaOH at time t
IC(0) inorganic carbon in mg/L NaOH at the start of the test
VolNaOH (t) remaining volume NaOH in L in the scrubber at time t
(Volume at t = 0 (here: 0.1 L) - ∑ (all sample volumes up to time t))
VolTestVessel test vessel volume in L (here: 1.5)

Reference substance:

aniline

Preliminary study:

No preliminary study was conducted.

Test performance:

The test was performed at 22+/- 2. No unusual observations during test or any other information affecting results.

Parameter:

other: biodegradation

Value:

67

Sampling time:

9 d

Parameter:

other: biodegradation

Value:

72

Sampling time:

10 d

Parameter:

other: biodegradation

Value:

77

Sampling time:

28 d

Remarks on result:

other: end of the test

Results with reference substance:

Degradation behaviour of positive control and toxicity control was normal. Abiotic degradation was less than 5 %. Both replicates of the test item showed very good correspondence.

Table 1 emmited carbon in mg/L:

Day	Control 1	Control 2	Positive Control 1	Positive Control 2	Test 1	Test 2	Abiotic Control	Toxicity Control
2	0.30	0.92	0.98	0.69	0.27	0.54	0.55	0.07
4	0.61	1.34	3.64	5.28	0.95	2.29	0.73	1.66
7	1.22	1.64	10.56	12.50	2.44	3.38	0.64	11.16
9	1.92	2.31	15.29	15.52	5.42	9.04	0.72	18.19
11	2.07	2.47	15.83	16.34	8.13	9.87	0.66	22.59
14	2.28	2.38	17.15	17.01	14.94	13.90	1.08	28.02
18	2.67	3.01	18.07	17.77	16.45	17.41	0.71	31.34
23	3.03	2.57	18.41	17.04	17.38	18.61	0.72	32.99
29	3.78	3.53	17.54	18.94	18.10	19.45	0.71	33.85

table 2 Degradation Values:

Day	Positive Control 1	Positive Control 2	Positive Control Mean	Test 1	Test 2	Test Mean	Abiotic Control	Toxicity Control
2	1.9	0.4	1.1	-1.8	-0.4	-1.1	2.8	-1.4
4	13.5	21.8	17.6	-0.1	6.7	3.3	3.7	1.7
7	46.2	56.0	51.1	5.1	10.0	7.6	3.3	24.8
9	66.7	67.8	67.2	16.9	35.5	26.2	3.7	40.9
11	68.6	71.2	69.9	30.0	38.9	34.5	3.4	51.7
14	75.0	74.3	74.6	64.6	59.3	61.9	5.5	65.4
18	77.1	75.6	76.3	69.7	74.6	72.1	3.6	72.5
23	79.0	72.0	75.5	74.6	80.9	77.8	3.7	76.8
29	70.2	77.3	73.8	73.9	80.9	77.4	3.6	76.8

table 3: Validity:

Parameter	Criterion	Found	Assessment
IC content of test item solution in medium	<=5% of TC	2.66%	valid
CO2emitted by the controls	< 70 mg/L	13.4mg/L	valid
Difference within replicates	<=20%	6.9%	valid
Degradation of positive control > 60%	< 14 days	9 days	valid
Degradation in the toxicity flask on day 14	> 25%	65.4 %	valid

All validity criteria were met. Degradation behaviour of positive control and toxicity control was normal. Abiotic degradation was less than 5 %. Both replicates of the test item showed very good correspondence. If degradation in the toxicity flask is below 25% after 14 days, the test item can be considered as toxic towards the inoculum. As degradation in the toxicity flask was 65.4% after 14 days, the test item can be stated as “not toxic towards the inoculum in a concentration of 233.4 mg/l”.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

• The test item is considered as “readily biodegradable“.
• The degree of biodegradation reached 77 % after 28 days.
• The 10-day-window began on day 8, at its end, 72 % were reached, surpassing the pass level of 60 % given in the OECD guideline.
• The abiotic degradation reached 3.6 %.

Executive summary:

The test item was tested using a concentration of nominally 20 mg organic carbon/L (corresponding to 233.4 mg test item/L) in test medium. Aniline was chosen as positive control. Activated sludge was used as inoculum (concentration

in the test 25 mg dry matter/L). The test was left running for 28 days. All validity criteria were met.

Degradation of the positive control was 67 % after nine days.

The following data were determined for the test item:

10-day-window: day 8-18

degradation at the end of 10-day-window: 72%

degradation at the end of the test: 77 %

pass level: 60% at the end of 10-day-window

Description of key information

The biodegradation of the substance is 77 % (28 d), respectively 72 % (10-day-window)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

According to the guideline study OECD 301 B, the substance was tested using a concentration of nominally 20 mg organic carbon/L in test medium. Activated sludge was used as inoculum. The test was left running for 28 days. All validity criteria were met. The biodegrading of the substance is 77 % (28 d), respectively 72 % (10-day-window). The test can be considered as valid.

A supporting study according to OECD 302 B proofed the biodegradability; however the given data are not sufficient for a terminal conclusion.

Another non GLP-Study according to OECD 301 B shows deficiencies and results that could not be reproduced. Therefore these results will not be taken into the further considerations.

Additionally the substance’s biodegradability was also estimated by a calculation using the software “Biowin”. The estimation resulted in a conclusion to consider the organic part of the substance as readily biodegradable.