Registration Dossier

Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

Currently viewing:

Administrative data

Link to relevant study record(s)

Referenceopen allclose all

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2013-2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: According to TG 308, under GLP, no deviations
Qualifier:
according to guideline
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of sediment:
Two freshly sampled water/sediment systems were used in this study: Swiss Lake (SL) and Schoonrewoerdsewiel (SW). They were significantly different based on the texture and percentage organic carbon of the sediment.

SL:
This shallow lake is fed by surface water run-off that mainly originates on moorland and woodland with a small contribution from upland pasture. Swiss Lake is located in Chatsworth, Derbyshire, England (Grid Reference SK 27177 69993). Water and sediment from Swiss Lake were sampled on 05 March 2014. Water was scooped from the lake. Oxygen content, pH and water temperature were measured at sampling. The water was clear, non-turbid with a pale brown colour. The sediment was sampled from the top 5 cm and was brown with dark patches, and some twigs, leaves and stones. The sediment was passed through a 2 mm sieve. The sediment was kept covered with water and shipped to the laboratory on the sampling day (overnight delivery). Upon arrival in the laboratory, the water and sediment (water-logged) were stored refrigerated under aerobic conditions (open lid) in the dark, prior to use.
Properties were determined by CEMAS, UK, under GLP conditions
SL water
pH (at sampling) 6.8
Temperature (at sampling) 5°C below water surface and 5°C 5 cm above sediment
Oxygen (at sampling) 97% below water surface and 97% 5 cm above sediment
Total N 0.97 mg/L
Total P <0.1 mg/L
Water hardness 34 mg/L as CaCO3
DOC 6.5 mg/L
TOC 3.8 mg/L (end of test)

SL sediment
Sand (50µm-2mm) 98 %
Silt (2µm-50µm) 0 %
Clay (<2µm) 2 %
Texture (USDA) Sand
CEC 1.7 meq/100g
Total N 0.04 % w/w
Total P 169 mg/kg
% organic carbon 0.6 %; 0.3 % (end of test)
pH (KCl) 5.6; 6.2 (end of test)

SW:
This surface water originated as a result of a dike (levee) failure in the 16th century. The force of the water flowing through the dike created a low area behind the dike. After closure of the dike, a small pond remained. "Schoonrewoerdse Wiel" is located in the province Zuid-Holland, in Leerdam, the Netherlands (N51.9168, E005.1331). Water and sediment from the Schoonrewoerdsewiel location were sampled on 05 March 2014. Water was taken from the upper layer (up to 1 meter depth) at the centre of the pond. Oxygen content, pH and water temperature were measured at sampling. The sediment was sampled from the upper layer (0-10 cm) from the middle of the pond (depth 8 m). The sediment was black in colour with a distinctive light sulphur smell, indicating reducing conditions. The sediment was kept covered with water and transported to the laboratory at ambient temperature.
Upon arrival in the laboratory, water from the Schoonrewoerdsewiel location was sieved through a 150 µm sieve and the sediment was wet-sieved through a 2 mm sieve. Sieved water and sediment (water-logged) were stored refrigerated under aerobic conditions (open lid) in the dark until use.

SW water
pH (at sampling) 9.0
Temperature (at sampling) 7°C
Oxygen (at sampling) 14.1 mg/L (115%)
Water hardness 152 mg/L as CaCO3
Total N 2.2 mg/L
Total P <0.1 mg/L
DOC 11.2 mg/L
TOC -0.59 mg/L (end of test)

SW sediment
Sand (50µm-2mm) 12 %
Silt (2µm-50µm) 53 %
Clay (<2µm) 35 %
Texture (USDA) Silty Clay Loam
CEC 33.0 meq/100g
Total N 0.65 % w/w
Total P 1673 mg/kg
% organic carbon 9.9 % ; 3.3 % (end of test)
pH (KCl) 7.5 ; 7.4 (end of test)
Details on inoculum:
At the beginning of the incubation period, microbial biomass was determined to be 160 µg C/g dry sample for the SL system and 1934 µg C/g dry sample for the SW system. These values are equivalent to 2.7% and 2.0% of organic carbon, respectively.
At the end of the incubation period, microbial biomass was 130 µg C/g dry sample for the SL system and 2759 µg C/g dry sample for the SW system. These values are equivalent to 2.2% and 2.8% of organic carbon, respectively.
The results indicate sufficiently viable conditions for both water/sediment systems.
Duration of test (contact time):
98 d
Initial conc.:
100 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
other: TDM content
Details on study design:
For the SL system, approximately 110 g wet sediment and 330 mL water and for the SW system, approximately 110 g wet sediment and 330 mL water were weighed into 500 mL amber glass jars. The wet sediment weights and water volumes were chosen such that a sediment layer of approximately 2 cm and a water layer of approximately 6-8 cm were obtained at the end of equilibration. For SL, a total of 41 metabolism flasks and for SW a total of 45 metabolism flasks were prepared.
The target initial concentration in the water phase was 100 µg/L, equivalent to 30 µg per test system and sufficiently high for adequate quantification of TPS 32 (polysulfides, di-tert-dodecyl) in both water and sediment
Spiking of the SL system took place on 03 April 2014 and spiking of SW system took place on 08 April 2014 by addition of 250 µL of the spike solution to 12 jars of each system. Four jars of each system were spiked four or seven days later and served as day 3 and day 0 samples, respectively. Of the day 0 jars, only the water layer was spiked (the water layer was decanted prior to spiking). The spike volume was chosen based on a water layer volume of 300 mL and a maximum percentage organic solvent of 0.1%.
The average volume (measured) of the water layer after equilibration was 290 mL (SL) and 298 mL (SW). The resulting TPS 32 (polysulfides, di-tert-dodecyl) concentrations in the jars were 104 µg/L and 101 µg/L in the water layer of respectively the SL and SW system. Additionally, six (SL) and eight (SW) metabolism flasks were spiked with solvent (250 µL tetrahydrofuran per jar).
Immediately after spiking, the jars were placed in a climatised room (20 ± 2°C) in the dark. During incubation, aeration took place continuously. The ingoing air was allowed to bubble gently – in order not to disturb the sediment layer – through the upper part of the water layer before leaving the metabolism flasks.
The incubation lasted 98 days for both the SL and SW system. Incubation took place in the dark at 20 ± 2°C. The temperature in the climatised room was continuously monitored.
During incubation, dissolved oxygen, pH, and redox potential were determined once a week in the water layer of two untreated flasks for each system. The redox potential in the sediment was determined at least once in the week of sampling in two untreated flasks per system.
Two metabolism flasks of each system were sampled 0, 3 (SL) or 4 (SW), 7, 14, 28, 63 and 98 days after spiking. Hereto the jars were disconnected from the aeration system and brought to the laboratory for analysis.
The water layer was carefully decanted from the jar in a weighed glass container. The total weight of the water layer was determined. Approximately 70 g of the water layer was transferred to a 100 mL glass jar and weighed. The remaining water layer was reduced to 200 g (weighed) and the rest was discarded.
The sediment layer was weighed and mixed. Approximately 10 g of the sediment layer was transferred to a 100 mL Erlenmeyer flask. Approximately 30 g of the sediment was transferred to a 50 mL glass jar and weighed.
The water and sediment layer were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and its (expected) major transformation product (Tertiododecylmercaptan) at each sampling interval (at day 0 only the water layer was analysed). The extraction/concentration procedures and the following LC-MS method are described in the summary's section describing details on analytical methods.
On the last sampling day, blank water and sediment were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and Tertiododecylmercaptan. In addition, the concentration of Tertiododecylmercaptan in a freshly prepared spike solution was determined.
Reference substance:
not required
Test performance:
TPS 32 (polysulfides, di-tert-dodecyl) was incubated under aerobic conditions in the laboratory in two water/sediment systems (Swiss Lake [SL] and Schoonrewoerdsewiel [SW]) at 20 ± 2 °C in the dark for 98 days. The initial test substance concentration in the water layer of the test systems was 0.1 mg/L. Redox potential and oxygen concentration measurements indicated aerobic conditions in the water layer and anaerobic conditions in the sediment throughout the test.
Duplicate samples of each water/sediment system were collected immediately after spiking and after 3 (SL) or 4 (SW), 7, 14, 28, 63 and 98 days. The water and sediment layer were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and its (expected) major transformation product (Tertiododecylmercaptan) at each sampling interval (at day 0 only the water layer was analysed).
Compartment:
water
DT50:
6.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SL water
Key result
Compartment:
entire system
DT50:
180 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SL total system
Compartment:
water
DT50:
6.6 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SW water
Key result
Compartment:
entire system
DT50:
158 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SW entire system
Transformation products:
not specified
Details on transformation products:
The anticipated transformation product tert-dodecyl mercaptan (TDM), resulting from a cleavage of the polysulfide chain has been followed through the incubation phase.
The results show significant concentration of TDM(4,8 % regarding to TPS 32) as soon as t=0, suggesting its presence in TPS 32, which is contradictory to the known composition of the test substance (TDM content in TPS 32 is known to be in the ppm range by the Sponsor having provided the test item batch). Consequently, further investigations have been carried out by the Sponsor which had provided the Sponsor having provided the test item batch, making use of a substance of close composition, below named [confidential].
The quantification method developed for the water/sediment study involves a derivatization step using dansyl chloride. The derivatized TDM (TDM-dansyl) is then analysed using LCMS/MS. Comparing results obtained with both TPS 32 and [confidential], analyzed under the same conditions (dansylation + LC/MS/MS analysis), it was demonstrated that a side reaction occurs between dansyl chloride and the higher congeners of polysulfides (S6+), with the production of TDM-dansyl.
The different behaviour of TPS 32 and [confidential] is resulting to the great nucleophilic properties of high ranking polysulfide (S6+), but also mainly by the decrease in steric hindrance (accessibility of sulfur atoms in the polysulfide), which allows for TPS 32 a reaction with dansyl chloride. This is not possible with the low ranks polysulfide, hence the lack of reaction with [confidential].
Finally, as there is no increase of the peak attributed to TDM along the incubation, is the sediment compartment, it cannot be concluded that TDM is a stable metabolite of polusulfide, di-tert-dodecyl.
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
not specified
Details on results:
The DT50 and DT90 values were calculated using the amounts of TPS 32 (polysulfides, di-tert-dodecyl) as determined by LC-MS. The models to which the data were fitted are described in the study report appendix 5 (Figure 10 and Figure 11). The choice of models is based on the FOCUS guidance document on estimating degradation kinetics [1].
Calculations were performed for:
- TPS 32 (polysulfides, di-tert-dodecyl) in SL and SW water layer;
- TPS 32 (polysulfides, di-tert-dodecyl) in SL and SW total system (i.e. the sum of parent in water and sediment compartment).
For sediment alone, no meaningful calculations could be performed.

DT50and DT90of TPS 32 (polysulfides, di-tert-dodecyl) in water/sediment systems

Compartment

Kinetics

Visual fit

c2

DT50

(days)

DT90

(days)

SL water

SFO

good

12.8

6.4

21.1

SL total system

SFO

moderate

10.9

180

600

SW water

SFO

good

11.6

6.6

21.9

SW total system

SFO

moderate

11.5

158

526

Detailed results on recovery of TPS 32 and TDM are shown below:

Table1      Recovery of TPS 32 (polysulfides, di-tert-dodecyl) in SL system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Parent

[µg]

Weight

[g]

Concentr.

[µg/g]

Parent

[µg]

Parent

[µg]

0

317.89

78.3

24.9

na

na

na

24.9

0

321.27

60.9

19.6

na

na

na

19.6

3

323.05

63.2

20.4

114.36

0.080

9.1

29.6

3

315.62

56.5

17.8

122.65

0.073

9.0

26.8

7

316.52

35.0

11.1

121.90

0.116

14.1

25.2

7

324.07

37.2

12.1

113.27

0.118

13.4

25.4

14

321.52

8.7

2.8

117.27

0.186

21.8

24.6

14

321.00

8.6

2.8

118.18

0.192

22.7

25.5

28

317.40

4.9

1.6

119.08

0.250

29.8

31.3

28

319.37

4.1

1.3

115.83

0.218

25.3

26.5

63

312.34

1.9

0.6

116.48

0.214

24.9

25.5

63

313.75

1.9

0.6

117.51

0.193

22.7

23.3

98

308.72

0.9

0.3

117.95

0.108

12.7

13.0

98

309.74

1.0

0.3

120.22

0.127

15.3

15.6

Blank

303.38

0.0*

0.0

121.81

nd

0.0

0.0

Blank

305.66

0.0*

0.0

126.04

nd

0.0

0.0

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

 

 

Table2      Recovery of TPS 32 (polysulfides, di-tert-dodecyl) in SW system

 

Water

Sediment

Total

Time

[days]

Volume [ml]

Concentr.[µg/l]

Parent

[µg]

Weight

[g]

Concentr.

[µg/g]

Parent

[µg]

Parent

[µg]

0

310.81

75.6

23.5

na

na

na

23.5

0

314.18

62.2

19.5

na

na

na

19.5

4

305.18

42.4

12.9

90.73

0.155

14.1

27.0

4

312.61

58.2

18.2

93.25

0.072

6.7

24.9

7

313.65

30.5

9.6

94.59

0.184

17.4

27.0

7

314.35

37.1

11.7

93.02

0.151

14.0

25.7

14

316.38

8.9

2.8

90.28

0.172

15.5

18.4

14

317.94

11.3

3.6

87.31

0.147

12.8

16.4

28

312.17

7.5

2.3

92.38

0.237

21.9

24.2

28

311.93

10.2

3.2

94.20

0.222

20.9

24.1

63

304.97

4.2

1.3

90.11

0.247

22.3

23.5

63

276.73

5.0

1.4

94.32

0.177

16.7

18.1

98

297.35

2.2

0.6

93.18

0.130

12.1

12.8

98

280.52

0.3

0.1

105.47

0.135

14.2

14.3

Blank

284.36

nd

0.0

102.20

0.002#

0.2

0.2

Blank

289.95

nd

0.0

106.71

0.002#

0.2

0.2

na   not applicable

nd    not detected

#      < LOQ (0.01 µg/g)

 

Table3      Recovery of Tertiododecylmercaptan in SL system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Metabolite

[µg]

Weight

[g]

Concentr.

[µg/g]

Metabolite

[µg]

Metabolite

[µg]

0

317.89

11.7

3.7

na

na

na

3.7

0

321.27

12.2

3.9

na

na

na

3.9

3

323.05

0.96

0.3

114.36

0.014

1.6

1.9

3

315.62

0.80

0.3

122.65

0.012

1.4

1.7

7

316.52

0.77

0.2

121.90

0.031

3.8

4.0

7

324.07

1.07

0.3

113.27

0.044

4.9

5.3

14

321.52

0.48

0.2

117.27

0.038

4.4

4.6

14

321.00

2.13

0.7

118.18

0.047

5.6

6.3

28

317.40

0.17

0.1

119.08

0.049

5.8

5.9

28

319.37

0.08

0.0

115.83

0.030

3.5

3.5

63

312.34

0.03

0.0

116.48

0.023

2.7

2.7

63

313.75

0.21

0.1

117.51

0.035

4.2

4.2

98

308.72

0.07

0.0

117.95

0.045

5.2

5.3

98

309.74

0.02

0.0

120.19

0.040

4.8

4.8

Blank

303.38

0.00*

0.0

121.81

nd

 

0.0

Blank

305.66

0.01*

0.0

126.04

nd

 

0.0

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

 

 

Table4      Recovery of Tertiododecylmercaptan in SW system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Metabolite

[µg]

Weight

[g]

Concentr.

[µg/g]

Metabolite

[µg]

Metabolite

[µg]

0

310.81

2.55

0.8

na

na

na

0.8

0

314.18

3.11

1.0

na

na

na

1.0

4

305.18

0.94

0.3

90.73

0.169

15.3

15.6

4

312.61

2.00

0.6

93.25

0.087

8.1

8.7

7

313.65

1.14

0.4

94.59

0.170

16.1

16.4

7

314.35

1.06

0.3

93.02

0.162

15.1

15.4

14

316.38

0.94

0.3

90.28

0.284

25.6

25.9

14

317.94

1.82

0.6

87.31

0.255

22.3

22.8

28

312.17

0.19

0.1

92.38

0.257

23.7

23.8

28

311.93

0.27

0.1

94.20

0.281

26.5

26.6

63

304.97

0.06

0.0

90.11

na

na

na

63

276.73

0.06

0.0

94.32

0.222

20.9

21.0

98

297.35

0.05

0.0

93.18

0.280

26.1

26.1

98

280.52

0.01

0.0

105.47

0.254

26.8

26.8

Blank

284.36

0.01*

0.0

102.20

0.003#

0.3

0.3

Blank

289.95

0.03*

0.0

106.71

0.001#

0.1

0.2

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

#      < LOQ (0.01 µg/g)

Validity criteria fulfilled:
yes
Remarks:
according to analytical reports
Conclusions:
Upon addition of to the water layer, TPS 32 (polysulfides, di-tert-dodecyl) partitioned between the water and sediment. At the start of incubation, 20-25 µg of the nominally applied 30 µg was recovered in the water layer which decreased to < 1 µg at the end of the incubation period. In the sediment layer, the concentration increased to 21-30 µg after 28 days of incubation and then decreased to approximately 12-15 µg.

In both test systems, Tertiododecylmercaptan (TDM), a possible degradation product of TPS 32 (polysulfides, di-tert-dodecyl) was detected. In the SL system, the initial amount of 4 µg Tertiododecylmercaptan did not significantly decrease or increase during the timeframe of the study; only a shift from the water to the sediment layer was observed. Further investigation showed that a side reaction occurs between dansyl chloride and the higher congeners of polysulfides (S6+), with the production of TDM-dansyl, mistakenly quantified as TDM in the system.

Similarly, In the SW system, the initial amount of 1 µg Tertiododecylmercaptan (recovered in the water layer) significantly increased to >20 µg (recovered in the sediment layer) within 14 days of incubation. Based upon the stability of TPS 32 (polysulfides, di-tert-dodecyl) during this period, no significant amounts of Tertiododecylmercaptan were to be expected in the water/sediment system.

The DT50 and DT90 values of TPS 32 (polysulfides, di-tert-dodecyl) in both water/sediment systems are shown in the table below. The half-life calculated for the water layer is not a degradation DT50 but a dissipation half-life because transfer from water to sediment is included in the dissipation process. The half-life calculated for the total system is a true degradation half-life because dissipation from the total system is only the result of degradation and irreversible bonding. For the sediment, no meaningful calculations could be performed; degradation should be assessed from the maximum onwards at a time no parent is present in the water layer so that transfer from water to sediment is excluded.
Executive summary:

Biodegradation of tert-dodecyl polysulfides in freshwater sediments has been evaluated through an OECD TG 308 compliant study. Two water/sediment systems with duly characterised different properties were used ("SL" is Organic Carbon poor, "SW" is OC rich). Test substance being poorly soluble was spiked in the overlying water phase through a tetrahydrofuran solution. Initial concentration was 0.1 mg/L.

The 2 water/sediment systems were incubated during 98 days in the dark at 20°C. Periodically (t = 0, 3, 7, 14, 28, 63 and 98 days), samples were removed in duplicates in order to measure concentration of TPS 32 in each phase.

It was shown that the substance migrates rapidly from water to sediment. Dissipation half-life DT50 in water was 6.4 days in "SL" water/sediment system and 6.6 days in "SW".

It was further shown that, after an increase of its concentration in the sediment phase, resulting from the partitioning (in agreement with the high Koc), the concentration decreased from 28 days onwards in both sediments. A DT50 could be calculated as being = 180 days in "SL" and 158 days in "SW" sediment. DT90 are respectively 600 and 526 days.

The anticipated degradation product, tert-dodecyl mercaptan, TDM, which could be produced from cleavage of the polysulfide chain was also analysed. The results are not fully conclusive as some TDM seemed to be present since the beginning, and even in the TPS 32 tested sample, which is contradictory with what is known of the composition of TPS 32. An interference has been suspected and further investigation has been carried out, showing that certain congeners of the test material endure a side reaction with the derivatising agent (dansyl chloride) in the sample preparation before analysis, leading to TDM-dansyl.

This doesn't challenge the main conclusions: tert-dodecyl polysulfide partitions rapidly from water to sediment compartment, where it undergoes a true degradation with DT50 =< 180 days.

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
2013-2015
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study used for read across
Justification for type of information:
Both source and target substances are tertiary-alkyl polysulfide UVCBs and contain multiple constituents with different sulfur contents and degrees of branching in the alkyl chain. The main difference between the two substances is the chain length of the alkyl chain; the target substance is C8 – 10 branched, C9 rich, whereas the source substance is C11 – 13 branched, C12 rich. Both substances have branched alkyl chains, therefore there are numerous potential constituents present in each substance. Read across between these substances is considered to be appropriate for environmental endpoints based on structural similarity; although there will be some differences in physico-chemical properties, and therefore fate in the environment due to the different chain lengths, these differences are likely to be predictable. Both substances contain branched alkyl chains, therefore the degree of branching is not considered to have an impact on the read across approach.

Please see the read across justification attached in the IUCLID robust study summary for a full justification of the read across approach
Reason / purpose for cross-reference:
read-across source
Qualifier:
according to guideline
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of sediment:
Two freshly sampled water/sediment systems were used in this study: Swiss Lake (SL) and Schoonrewoerdsewiel (SW). They were significantly different based on the texture and percentage organic carbon of the sediment.

SL:
This shallow lake is fed by surface water run-off that mainly originates on moorland and woodland with a small contribution from upland pasture. Swiss Lake is located in Chatsworth, Derbyshire, England (Grid Reference SK 27177 69993). Water and sediment from Swiss Lake were sampled on 05 March 2014. Water was scooped from the lake. Oxygen content, pH and water temperature were measured at sampling. The water was clear, non-turbid with a pale brown colour. The sediment was sampled from the top 5 cm and was brown with dark patches, and some twigs, leaves and stones. The sediment was passed through a 2 mm sieve. The sediment was kept covered with water and shipped to the laboratory on the sampling day (overnight delivery). Upon arrival in the laboratory, the water and sediment (water-logged) were stored refrigerated under aerobic conditions (open lid) in the dark, prior to use.
Properties were determined by CEMAS, UK, under GLP conditions
SL water
pH (at sampling) 6.8
Temperature (at sampling) 5°C below water surface and 5°C 5 cm above sediment
Oxygen (at sampling) 97% below water surface and 97% 5 cm above sediment
Total N 0.97 mg/L
Total P <0.1 mg/L
Water hardness 34 mg/L as CaCO3
DOC 6.5 mg/L
TOC 3.8 mg/L (end of test)

SL sediment
Sand (50µm-2mm) 98 %
Silt (2µm-50µm) 0 %
Clay (<2µm) 2 %
Texture (USDA) Sand
CEC 1.7 meq/100g
Total N 0.04 % w/w
Total P 169 mg/kg
% organic carbon 0.6 %; 0.3 % (end of test)
pH (KCl) 5.6; 6.2 (end of test)

SW:
This surface water originated as a result of a dike (levee) failure in the 16th century. The force of the water flowing through the dike created a low area behind the dike. After closure of the dike, a small pond remained. "Schoonrewoerdse Wiel" is located in the province Zuid-Holland, in Leerdam, the Netherlands (N51.9168, E005.1331). Water and sediment from the Schoonrewoerdsewiel location were sampled on 05 March 2014. Water was taken from the upper layer (up to 1 meter depth) at the centre of the pond. Oxygen content, pH and water temperature were measured at sampling. The sediment was sampled from the upper layer (0-10 cm) from the middle of the pond (depth 8 m). The sediment was black in colour with a distinctive light sulphur smell, indicating reducing conditions. The sediment was kept covered with water and transported to the laboratory at ambient temperature.
Upon arrival in the laboratory, water from the Schoonrewoerdsewiel location was sieved through a 150 µm sieve and the sediment was wet-sieved through a 2 mm sieve. Sieved water and sediment (water-logged) were stored refrigerated under aerobic conditions (open lid) in the dark until use.

SW water
pH (at sampling) 9.0
Temperature (at sampling) 7°C
Oxygen (at sampling) 14.1 mg/L (115%)
Water hardness 152 mg/L as CaCO3
Total N 2.2 mg/L
Total P <0.1 mg/L
DOC 11.2 mg/L
TOC -0.59 mg/L (end of test)

SW sediment
Sand (50µm-2mm) 12 %
Silt (2µm-50µm) 53 %
Clay (<2µm) 35 %
Texture (USDA) Silty Clay Loam
CEC 33.0 meq/100g
Total N 0.65 % w/w
Total P 1673 mg/kg
% organic carbon 9.9 % ; 3.3 % (end of test)
pH (KCl) 7.5 ; 7.4 (end of test)
Details on inoculum:
At the beginning of the incubation period, microbial biomass was determined to be 160 µg C/g dry sample for the SL system and 1934 µg C/g dry sample for the SW system. These values are equivalent to 2.7% and 2.0% of organic carbon, respectively.
At the end of the incubation period, microbial biomass was 130 µg C/g dry sample for the SL system and 2759 µg C/g dry sample for the SW system. These values are equivalent to 2.2% and 2.8% of organic carbon, respectively.
The results indicate sufficiently viable conditions for both water/sediment systems.
Duration of test (contact time):
98 d
Initial conc.:
100 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
other: TDM content
Details on study design:
For the SL system, approximately 110 g wet sediment and 330 mL water and for the SW system, approximately 110 g wet sediment and 330 mL water were weighed into 500 mL amber glass jars. The wet sediment weights and water volumes were chosen such that a sediment layer of approximately 2 cm and a water layer of approximately 6-8 cm were obtained at the end of equilibration. For SL, a total of 41 metabolism flasks and for SW a total of 45 metabolism flasks were prepared.
The target initial concentration in the water phase was 100 µg/L, equivalent to 30 µg per test system and sufficiently high for adequate quantification of TPS 32 (polysulfides, di-tert-dodecyl) in both water and sediment
Spiking of the SL system took place on 03 April 2014 and spiking of SW system took place on 08 April 2014 by addition of 250 µL of the spike solution to 12 jars of each system. Four jars of each system were spiked four or seven days later and served as day 3 and day 0 samples, respectively. Of the day 0 jars, only the water layer was spiked (the water layer was decanted prior to spiking). The spike volume was chosen based on a water layer volume of 300 mL and a maximum percentage organic solvent of 0.1%.
The average volume (measured) of the water layer after equilibration was 290 mL (SL) and 298 mL (SW). The resulting TPS 32 (polysulfides, di-tert-dodecyl) concentrations in the jars were 104 µg/L and 101 µg/L in the water layer of respectively the SL and SW system. Additionally, six (SL) and eight (SW) metabolism flasks were spiked with solvent (250 µL tetrahydrofuran per jar).
Immediately after spiking, the jars were placed in a climatised room (20 ± 2°C) in the dark. During incubation, aeration took place continuously. The ingoing air was allowed to bubble gently – in order not to disturb the sediment layer – through the upper part of the water layer before leaving the metabolism flasks.
The incubation lasted 98 days for both the SL and SW system. Incubation took place in the dark at 20 ± 2°C. The temperature in the climatised room was continuously monitored.
During incubation, dissolved oxygen, pH, and redox potential were determined once a week in the water layer of two untreated flasks for each system. The redox potential in the sediment was determined at least once in the week of sampling in two untreated flasks per system.
Two metabolism flasks of each system were sampled 0, 3 (SL) or 4 (SW), 7, 14, 28, 63 and 98 days after spiking. Hereto the jars were disconnected from the aeration system and brought to the laboratory for analysis.
The water layer was carefully decanted from the jar in a weighed glass container. The total weight of the water layer was determined. Approximately 70 g of the water layer was transferred to a 100 mL glass jar and weighed. The remaining water layer was reduced to 200 g (weighed) and the rest was discarded.
The sediment layer was weighed and mixed. Approximately 10 g of the sediment layer was transferred to a 100 mL Erlenmeyer flask. Approximately 30 g of the sediment was transferred to a 50 mL glass jar and weighed.
The water and sediment layer were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and its (expected) major transformation product (Tertiododecylmercaptan) at each sampling interval (at day 0 only the water layer was analysed). The extraction/concentration procedures and the following LC-MS method are described in the summary's section describing details on analytical methods.
On the last sampling day, blank water and sediment were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and Tertiododecylmercaptan. In addition, the concentration of Tertiododecylmercaptan in a freshly prepared spike solution was determined.
Reference substance:
not required
Test performance:
TPS 32 (polysulfides, di-tert-dodecyl) was incubated under aerobic conditions in the laboratory in two water/sediment systems (Swiss Lake [SL] and Schoonrewoerdsewiel [SW]) at 20 ± 2 °C in the dark for 98 days. The initial test substance concentration in the water layer of the test systems was 0.1 mg/L. Redox potential and oxygen concentration measurements indicated aerobic conditions in the water layer and anaerobic conditions in the sediment throughout the test.
Duplicate samples of each water/sediment system were collected immediately after spiking and after 3 (SL) or 4 (SW), 7, 14, 28, 63 and 98 days. The water and sediment layer were analysed for the presence of TPS 32 (polysulfides, di-tert-dodecyl) and its (expected) major transformation product (Tertiododecylmercaptan) at each sampling interval (at day 0 only the water layer was analysed).
Compartment:
water
DT50:
6.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SL water
Key result
Compartment:
entire system
DT50:
180 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SL total system
Compartment:
water
DT50:
6.6 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SW water
Key result
Compartment:
entire system
DT50:
158 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: SW entire system
Transformation products:
not specified
Details on transformation products:
The anticipated transformation product tert-dodecyl mercaptan (TDM), resulting from a cleavage of the polysulfide chain has been followed through the incubation phase.
The results show significant concentration of TDM(4,8 % regarding to TPS 32) as soon as t=0, suggesting its presence in TPS 32, which is contradictory to the known composition of the test substance (TDM content in TPS 32 is known to be in the ppm range by the Sponsor having provided the test item batch). Consequently, further investigations have been carried out by the Sponsor which had provided the Sponsor having provided the test item batch, making use of a substance of close composition, below named [confidential].
The quantification method developed for the water/sediment study involves a derivatization step using dansyl chloride. The derivatized TDM (TDM-dansyl) is then analysed using LCMS/MS. Comparing results obtained with both TPS 32 and [confidential], analyzed under the same conditions (dansylation + LC/MS/MS analysis), it was demonstrated that a side reaction occurs between dansyl chloride and the higher congeners of polysulfides (S6+), with the production of TDM-dansyl.
The different behaviour of TPS 32 and [confidential] is resulting to the great nucleophilic properties of high ranking polysulfide (S6+), but also mainly by the decrease in steric hindrance (accessibility of sulfur atoms in the polysulfide), which allows for TPS 32 a reaction with dansyl chloride. This is not possible with the low ranks polysulfide, hence the lack of reaction with [confidential].
Finally, as there is no increase of the peak attributed to TDM along the incubation, is the sediment compartment, it cannot be concluded that TDM is a stable metabolite of polusulfide, di-tert-dodecyl.
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
not specified
Details on results:
The DT50 and DT90 values were calculated using the amounts of TPS 32 (polysulfides, di-tert-dodecyl) as determined by LC-MS. The models to which the data were fitted are described in the study report appendix 5 (Figure 10 and Figure 11). The choice of models is based on the FOCUS guidance document on estimating degradation kinetics [1].
Calculations were performed for:
- TPS 32 (polysulfides, di-tert-dodecyl) in SL and SW water layer;
- TPS 32 (polysulfides, di-tert-dodecyl) in SL and SW total system (i.e. the sum of parent in water and sediment compartment).
For sediment alone, no meaningful calculations could be performed.

DT50and DT90of TPS 32 (polysulfides, di-tert-dodecyl) in water/sediment systems

Compartment

Kinetics

Visual fit

c2

DT50

(days)

DT90

(days)

SL water

SFO

good

12.8

6.4

21.1

SL total system

SFO

moderate

10.9

180

600

SW water

SFO

good

11.6

6.6

21.9

SW total system

SFO

moderate

11.5

158

526

Detailed results on recovery of TPS 32 and TDM are shown below:

Table1      Recovery of TPS 32 (polysulfides, di-tert-dodecyl) in SL system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Parent

[µg]

Weight

[g]

Concentr.

[µg/g]

Parent

[µg]

Parent

[µg]

0

317.89

78.3

24.9

na

na

na

24.9

0

321.27

60.9

19.6

na

na

na

19.6

3

323.05

63.2

20.4

114.36

0.080

9.1

29.6

3

315.62

56.5

17.8

122.65

0.073

9.0

26.8

7

316.52

35.0

11.1

121.90

0.116

14.1

25.2

7

324.07

37.2

12.1

113.27

0.118

13.4

25.4

14

321.52

8.7

2.8

117.27

0.186

21.8

24.6

14

321.00

8.6

2.8

118.18

0.192

22.7

25.5

28

317.40

4.9

1.6

119.08

0.250

29.8

31.3

28

319.37

4.1

1.3

115.83

0.218

25.3

26.5

63

312.34

1.9

0.6

116.48

0.214

24.9

25.5

63

313.75

1.9

0.6

117.51

0.193

22.7

23.3

98

308.72

0.9

0.3

117.95

0.108

12.7

13.0

98

309.74

1.0

0.3

120.22

0.127

15.3

15.6

Blank

303.38

0.0*

0.0

121.81

nd

0.0

0.0

Blank

305.66

0.0*

0.0

126.04

nd

0.0

0.0

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

 

 

Table2      Recovery of TPS 32 (polysulfides, di-tert-dodecyl) in SW system

 

Water

Sediment

Total

Time

[days]

Volume [ml]

Concentr.[µg/l]

Parent

[µg]

Weight

[g]

Concentr.

[µg/g]

Parent

[µg]

Parent

[µg]

0

310.81

75.6

23.5

na

na

na

23.5

0

314.18

62.2

19.5

na

na

na

19.5

4

305.18

42.4

12.9

90.73

0.155

14.1

27.0

4

312.61

58.2

18.2

93.25

0.072

6.7

24.9

7

313.65

30.5

9.6

94.59

0.184

17.4

27.0

7

314.35

37.1

11.7

93.02

0.151

14.0

25.7

14

316.38

8.9

2.8

90.28

0.172

15.5

18.4

14

317.94

11.3

3.6

87.31

0.147

12.8

16.4

28

312.17

7.5

2.3

92.38

0.237

21.9

24.2

28

311.93

10.2

3.2

94.20

0.222

20.9

24.1

63

304.97

4.2

1.3

90.11

0.247

22.3

23.5

63

276.73

5.0

1.4

94.32

0.177

16.7

18.1

98

297.35

2.2

0.6

93.18

0.130

12.1

12.8

98

280.52

0.3

0.1

105.47

0.135

14.2

14.3

Blank

284.36

nd

0.0

102.20

0.002#

0.2

0.2

Blank

289.95

nd

0.0

106.71

0.002#

0.2

0.2

na   not applicable

nd    not detected

#      < LOQ (0.01 µg/g)

 

Table3      Recovery of Tertiododecylmercaptan in SL system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Metabolite

[µg]

Weight

[g]

Concentr.

[µg/g]

Metabolite

[µg]

Metabolite

[µg]

0

317.89

11.7

3.7

na

na

na

3.7

0

321.27

12.2

3.9

na

na

na

3.9

3

323.05

0.96

0.3

114.36

0.014

1.6

1.9

3

315.62

0.80

0.3

122.65

0.012

1.4

1.7

7

316.52

0.77

0.2

121.90

0.031

3.8

4.0

7

324.07

1.07

0.3

113.27

0.044

4.9

5.3

14

321.52

0.48

0.2

117.27

0.038

4.4

4.6

14

321.00

2.13

0.7

118.18

0.047

5.6

6.3

28

317.40

0.17

0.1

119.08

0.049

5.8

5.9

28

319.37

0.08

0.0

115.83

0.030

3.5

3.5

63

312.34

0.03

0.0

116.48

0.023

2.7

2.7

63

313.75

0.21

0.1

117.51

0.035

4.2

4.2

98

308.72

0.07

0.0

117.95

0.045

5.2

5.3

98

309.74

0.02

0.0

120.19

0.040

4.8

4.8

Blank

303.38

0.00*

0.0

121.81

nd

 

0.0

Blank

305.66

0.01*

0.0

126.04

nd

 

0.0

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

 

 

Table4      Recovery of Tertiododecylmercaptan in SW system

 

Water

Sediment

Total

Time

[days]

Volume [mL]

Concentr.[µg/L]

Metabolite

[µg]

Weight

[g]

Concentr.

[µg/g]

Metabolite

[µg]

Metabolite

[µg]

0

310.81

2.55

0.8

na

na

na

0.8

0

314.18

3.11

1.0

na

na

na

1.0

4

305.18

0.94

0.3

90.73

0.169

15.3

15.6

4

312.61

2.00

0.6

93.25

0.087

8.1

8.7

7

313.65

1.14

0.4

94.59

0.170

16.1

16.4

7

314.35

1.06

0.3

93.02

0.162

15.1

15.4

14

316.38

0.94

0.3

90.28

0.284

25.6

25.9

14

317.94

1.82

0.6

87.31

0.255

22.3

22.8

28

312.17

0.19

0.1

92.38

0.257

23.7

23.8

28

311.93

0.27

0.1

94.20

0.281

26.5

26.6

63

304.97

0.06

0.0

90.11

na

na

na

63

276.73

0.06

0.0

94.32

0.222

20.9

21.0

98

297.35

0.05

0.0

93.18

0.280

26.1

26.1

98

280.52

0.01

0.0

105.47

0.254

26.8

26.8

Blank

284.36

0.01*

0.0

102.20

0.003#

0.3

0.3

Blank

289.95

0.03*

0.0

106.71

0.001#

0.1

0.2

na   not applicable

nd    not detected

*       < LOQ (0.1 µg/L)

#      < LOQ (0.01 µg/g)

Validity criteria fulfilled:
yes
Remarks:
according to analytical reports
Conclusions:
Upon addition of to the water layer, TPS 32 (polysulfides, di-tert-dodecyl) partitioned between the water and sediment. At the start of incubation, 20-25 µg of the nominally applied 30 µg was recovered in the water layer which decreased to < 1 µg at the end of the incubation period. In the sediment layer, the concentration increased to 21-30 µg after 28 days of incubation and then decreased to approximately 12-15 µg.

In both test systems, Tertiododecylmercaptan (TDM), a possible degradation product of TPS 32 (polysulfides, di-tert-dodecyl) was detected. In the SL system, the initial amount of 4 µg Tertiododecylmercaptan did not significantly decrease or increase during the timeframe of the study; only a shift from the water to the sediment layer was observed. Further investigation showed that a side reaction occurs between dansyl chloride and the higher congeners of polysulfides (S6+), with the production of TDM-dansyl, mistakenly quantified as TDM in the system.

Similarly, In the SW system, the initial amount of 1 µg Tertiododecylmercaptan (recovered in the water layer) significantly increased to >20 µg (recovered in the sediment layer) within 14 days of incubation. Based upon the stability of TPS 32 (polysulfides, di-tert-dodecyl) during this period, no significant amounts of Tertiododecylmercaptan were to be expected in the water/sediment system.

The DT50 and DT90 values of TPS 32 (polysulfides, di-tert-dodecyl) in both water/sediment systems are shown in the table below. The half-life calculated for the water layer is not a degradation DT50 but a dissipation half-life because transfer from water to sediment is included in the dissipation process. The half-life calculated for the total system is a true degradation half-life because dissipation from the total system is only the result of degradation and irreversible bonding. For the sediment, no meaningful calculations could be performed; degradation should be assessed from the maximum onwards at a time no parent is present in the water layer so that transfer from water to sediment is excluded.
Executive summary:

Biodegradation of tert-dodecyl polysulfides in freshwater sediments has been evaluated through an OECD TG 308 compliant study. Two water/sediment systems with duly characterised different properties were used ("SL" is Organic Carbon poor, "SW" is OC rich). Test substance being poorly soluble was spiked in the overlying water phase through a tetrahydrofuran solution. Initial concentration was 0.1 mg/L.

The 2 water/sediment systems were incubated during 98 days in the dark at 20°C. Periodically (t = 0, 3, 7, 14, 28, 63 and 98 days), samples were removed in duplicates in order to measure concentration of TPS 32 in each phase.

It was shown that the substance migrates rapidly from water to sediment. Dissipation half-life DT50 in water was 6.4 days in "SL" water/sediment system and 6.6 days in "SW".

It was further shown that, after an increase of its concentration in the sediment phase, resulting from the partitioning (in agreement with the high Koc), the concentration decreased from 28 days onwards in both sediments. A DT50 could be calculated as being = 180 days in "SL" and 158 days in "SW" sediment. DT90 are respectively 600 and 526 days.

The anticipated degradation product, tert-dodecyl mercaptan, TDM, which could be produced from cleavage of the polysulfide chain was also analysed. The results are not fully conclusive as some TDM seemed to be present since the beginning, and even in the TPS 32 tested sample, which is contradictory with what is known of the composition of TPS 32. An interference has been suspected and further investigation has been carried out, showing that certain congeners of the test material endure a side reaction with the derivatising agent (dansyl chloride) in the sample preparation before analysis, leading to TDM-dansyl.

This doesn't challenge the main conclusions: tert-dodecyl polysulfide partitions rapidly from water to sediment compartment, where it undergoes a true degradation with DT50 =< 180 days.

Description of key information

This endpoint is completed by read across from polysulfides di-tert-dodecyl. For further information please see the read across justification attached in the IUCLID robust study summary.

The study shows rapid migration of the test item from the water to sediment phase (half-life DT50 6.4 days in “SL” system and 6.6 days in “SW”). In sediment, DT50 values of 180 days in “SL” and 158 days in “SW” sediment were calculated.

Key value for chemical safety assessment

Additional information

This endpoint is completed by read across from polysulfides di-tert-dodecyl. For further information please see the read across justification attached in the IUCLID robust study summary.

A study following OECD guideline 308 is available to assess the biodegradation potential of the source substance in freshwater sediments (Brands 2015, Baltussen 2015), using two sediment systems, “SL” (organic carbon poor) and “SW” (organic carbon rich). The test substance was spiked at an initial concentration of 0.1 mg/L in a tetrahydrofuran solution into the overlying water. The incubation period was 98 days, at 20°C in the dark. Analysis of the different phases was conducted using UPLC-MS/MS. The results show rapid migration of the test item from the water to sediment phase (half-life DT50 6.4 days in “SL” system and 6.6 days in “SW”). In sediment, after an initial concentration increase from 28 days onwards the concentrations decreased in both systems, with DT50 values of 180 days in “SL” and 158 days in “SW” sediment calculated. Tert-dodecyl mercaptan (TDM), the expected degradation product was assessed, but the analysis was not conclusive. Some TDM was detected at the start of the study, suggesting interference. It was determined that certain congeners of the test material undergo a side reaction with the derivatising agent (dansyl chloride) when the samples are prepared before analysis, which leads to TDM-dansyl being present. The study met all of the validity criteria and is therefore considered to be reliable without restrictions.