Di-tert-dodecyl disulphide

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:

07-06-2016 to 06-09-2016

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

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Chemical name: di-tert-dodecyl disulphide
CAS number: 27458-90-8
Batch number: E10L036048
Purity: 96.06%
Date of reception
in the test facility: 23 November 2015
Expiration date: 02 November 2017
Internal identification: 0074-15
Appearance: Light yellow liquid
Water solubility: <0.03 mg/L
Relative density: 0.911 g/cm3 (according to the SDS)
Storage conditions: well-ventilated place, ambient temperature and obscurity

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

The inoculum was obtained on 07 June 2016 from the activated sludge of the biological wastewater treatment plant from Mourenx (France, 64) which handles predominantly domestic sewage.

On arrival at the laboratory, the sludge (around 800 mL) was centrifuged at room temperature for 12 min at 1000 g. The solid sewage inoculant portion was re-suspended in dilution water in order to keep the concentration unchanged with respect to the sample. The inoculum was preconditioned 72 hours (aeration) until the flasks were inoculated.

Sub-samples of the homogenised sludge were dried in an oven at approximately 105°C and the suspended solids content determined to be 4.4 g/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:

A total of 7 bioreactors were used: one for the toxicity control group and two for each of the following groups: test item, emulsifying agent control, reference item control. Details of bioreactors preparation are given in the table hereafter:

pH was measured in all flasks at the start and the end of the test period.
Note: as the test item is slightly dissolved it was decided to measure pH in an additional test item flask in order to avoid a test item quantity modification. This flask was not used for the test item biodegradation assessment.

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

0

Sampling time:

28 d

Details on results:

THEORETICAL OXYGEN DEMAND
The theoretical oxygen demand of the test item is ThOD = 3.138 mg O2/mg (based on its molecular formula C24H50S2 provided by the Sponsor). This calculation does not take into account any other constituents/impurities within the substance as supplied and is calculated by assuming formation of ammonium, water and carbon dioxide (no nitrification).
The theoretical oxygen demand of sodium benzoate is 1.666 mg O2/mg.

OXYGEN CONSUMPTION AND PERCENTAGE OF BIODEGRADATION
Raw data are presented in Table 1 and Table 2.
With regard to the oxygen consummation, the emulsifying agent could be considered as not toxic to bacteria and not biodegradable under test conditions.
The maximum degradation level of the test item was 0% at day 28 (a negative value was calculated. However, due to the low accuracy of this method, this result could be considered as non-significative).
The test item did not inhibit the micro-organisms as shown by the toxicity control flask where biodegradation percentage is already 30.4%, higher than 25%, after 14 days.

Results with reference substance:

The percentage degradation of the reference compound has reached the pass level by day 14: 90.6%

Table1: Cumulated Biological Oxygen Demand (mg/L)

Cumulated Biological Oxygen Demand (mg/L)
Day	Fa1	Fa2	Average Fa	Fc1	Fc2	Average Fc	Ft1	Ft2	Average Ft	Fi
0	0	0	0	0	0	0	0	0	0	0
1	1.7	0	0.85	14.7	14.6	14.65	0	0	0	9.8
2	2.6	0	1.3	22.8	22.4	22.6	0	0	0	19.4
3	4.1	0.6	2.35	30.3	30.9	30.6	1.4	0	0.7	26.6
4	4.8	1.6	3.2	120.2	119.1	119.65	1.9	0.9	1.4	115.1
5	6.4	2.7	4.55	127.1	125.5	126.3	3.1	2.2	2.65	121.8
6	6.4	2.7	4.55	130.5	128.9	129.7	3.1	2.3	2.7	126.3
7	8.7	4.2	6.45	134.7	133.1	133.9	5.3	4.1	4.7	129.9
8	14.1	8.6	11.35	140.4	139.6	140	9.5	10.4	9.95	133.5
9	14.1	8.6	11.35	143.2	140	141.6	9.5	10.4	9.95	137.3
10	14.1	8.6	11.35	148.7	146.6	147.65	10.1	10.4	10.25	141.9
11	14.1	8.6	11.35	154.2	150.7	152.45	11	10.4	10.7	146.2
12	14.8	10	12.4	159.6	156.5	158.05	12.5	10.4	11.45	150.8
13	16.7	10.8	13.75	164.2	161.5	162.85	13.9	10.4	12.15	156.2
14	18.8	11.9	15.35	167.4	165.2	166.3	15.6	10.4	13	161.5
15	20.3	12.7	16.5	169.7	167.4	168.55	17.6	10.4	14	166.3
16	22	14	18	172.7	169.9	171.3	19.8	11.3	15.55	170.5
17	23	15	19	175.9	172.1	174	21.3	11.9	16.6	174.2
18	25.2	15.7	20.45	178.5	174.3	176.4	22.1	12.9	17.5	177.2
19	25.2	16.5	20.85	180	176.7	178.35	22.8	12.9	17.85	179.1
20	25.2	17.6	21.4	181.6	180.1	180.85	23.6	14.1	18.85	181.1
21	26	18.4	22.2	183	182.5	182.75	24.1	14.5	19.3	182.7
22	27.1	19.9	23.5	184.5	184.5	184.5	25.1	15.5	20.3	184.1
23	27.7	20.5	24.1	185.7	186.2	185.95	25.3	16.5	20.9	185.2
24	29.1	21.4	25.25	186.4	187.2	186.8	26.3	17.5	21.9	185.8
25	29.1	22.6	25.85	187.2	188.2	187.7	26.3	17.5	21.9	186.9
26	29.1	23.8	26.45	188.2	189.6	188.9	26.3	17.5	21.9	187.7
27	29.1	24.8	26.95	188.8	190.4	189.6	26.8	18.4	22.6	188.4
28	30	25.3	27.65	189.4	191.3	190.35	27.4	18.7	23.05	189

Ft: Test item

Fc: Reference control

Fa: Emulsifying agent control

Fi: Toxicity control

Table2: Biodegradation (%)

Biodegradation (%)
Day	Fc1	Fc2	Average Fc	Ft1	Ft2	Average Ft	Fi
0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
1	8.3	8.3	8.3	-0.3	-0.3	-0.3	1.9
2	12.9	12.7	12.8	-0.4	-0.4	-0.4	3.8
3	16.8	17.1	17.0	-0.3	-0.7	-0.5	5.0
4	70.2	69.6	69.9	-0.4	-0.7	-0.6	23.3
5	73.6	72.6	73.1	-0.5	-0.7	-0.6	24.4
6	75.6	74.6	75.1	-0.5	-0.7	-0.6	25.3
7	77.0	76.0	76.5	-0.4	-0.7	-0.6	25.7
8	77.5	77.0	77.2	-0.6	-0.3	-0.4	25.4
9	79.1	77.2	78.2	-0.6	-0.3	-0.4	26.2
10	82.4	81.2	81.8	-0.4	-0.3	-0.4	27.2
11	85.7	83.6	84.7	-0.1	-0.3	-0.2	28.1
12	88.4	86.5	87.4	0.0	-0.6	-0.3	28.8
13	90.3	88.7	89.5	0.0	-1.1	-0.5	29.7
14	91.3	89.9	90.6	0.1	-1.6	-0.7	30.4
15	92.0	90.6	91.3	0.4	-1.9	-0.8	31.2
16	92.9	91.2	92.0	0.6	-2.1	-0.8	31.7
17	94.2	91.9	93.0	0.7	-2.3	-0.8	32.3
18	94.9	92.3	93.6	0.5	-2.4	-0.9	32.6
19	95.5	93.5	94.5	0.6	-2.5	-1.0	32.9
20	96.2	95.3	95.7	0.7	-2.3	-0.8	33.2
21	96.5	96.2	96.4	0.6	-2.5	-0.9	33.4
22	96.6	96.6	96.6	0.5	-2.5	-1.0	33.4
23	97.0	97.3	97.1	0.4	-2.4	-1.0	33.5
24	96.7	97.2	97.0	0.3	-2.5	-1.1	33.4
25	96.8	97.4	97.1	0.1	-2.7	-1.3	33.5
26	97.1	97.9	97.5	0.0	-2.9	-1.4	33.6
27	97.1	98.1	97.6	0.0	-2.7	-1.4	33.6
28	97.1	98.2	97.7	-0.1	-2.9	-1.5	33.6

Ft: Test item

Fc: Reference control

Fi: Toxicity control

Validity criteria fulfilled:

yes

Remarks:

The pH value for the test item bioreactors was outside the range (9.1 at day 28). As the test item biodegradation is clearly low, it was decided to not conduct an additional test with a lower cc of test item as recommended in the OECD test guideline.

Interpretation of results:

not readily biodegradable

Conclusions:

In this OECD 301F study a mean total of 0% degradation was achieved by day 28 (a negative value was calculated. However, due to the low accuracy of this method, this result could be considered as non-significative).
As a consequence the test item di-tert-dodecyl disulphide was not readily biodegradable under the conditions of the test.

Executive summary:

The study was conducted in accordance with procedures outlined in OECD Guideline 301F (1992). The ready biodegradability of di-tert-dodecyl disulphide was assessed over a 28-day period.

The test was conducted at a nominal loading rate of 100 mg/L. As test item is known to be difficult to dissolve, its dispersibility was improved by use of an emulsifying agent (Symperonic P103) as described in IS standard.

A total of 7 bioreactors were used: one for the toxicity control group and two for each of the following groups: test item, emulsifying agent control,reference item control.

The results of the test were as follows:

 

% biodegradation (28 days)	Test item (mean of replicates)	Reference item (mean of replicates)	Toxicity Control
	0%*	97.7%	33.6%

*a negative value was calculated. However, due to the low accuracy of this method, this result could be considered as non- significative.

 

The test item was not readily biodegradable under the conditions of the test as it failed to achieve a transition from 10% to 60% degradation in a 10-day window during the 28-day test.

The test item was not considered to be inhibitory to the microbial inoculum since the biodegradation observed in the toxicity control bioreactor was not less than 25% occurred within 14 days.

The definitive test met the validity criteria of the test guideline detailed as follows:

-  the difference of extremes of replicate values of the removal of the test item at the end of the test was less than 20%

- the percentage degradation of the reference compound has reached the pass level by day 14: 90.6%

- the biodegradation observed in the toxicity control bioreactor was not less than 25%:30.4% within 14 days,

- the oxygen uptake of the inoculum blank was not greater than 60 mg/l in 28 days: 27.7 mg/L

 

The following validity criteria of the test guideline was not respected: the pH value for the test item bioreactors was outside the range 6- 8.5: 9.1 at day 28

As the test item biodegradation is clearly low, it was decided to not conduct an additional test with a lower concentration of test item as recommended in the OECD test guideline. The test is thus considered as valid

Description of key information

Di-tert-dodecyl disulfide is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed