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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
other: OECD 314
Deviations:
no
GLP compliance:
yes
Remarks:
The P&G Environ Science Lab is in the process of attaining formal GLP status. This expt was conducted in accordance with GLP's, by scientists with years of environ testing expertise. P&G helped develop and write the OECD protocol for this test method.
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural sediment
Details on source and properties of sediment:
Sediment was collected from Lytle Creek located in Wilmington, Ohio. Surficial (top 2-3 cm) sediment and overlying water was collected using a plastic scoop at a site immediately below the Wilmington Wastewater Treatment Plant outfall. The plant services a population of about 17,000 and receives about 90% of its waste from domestic sources. The sediment was placed in plastic jars and kept on ice during transport, and then stored in a 4 C cold room prior to the test. The sediment was characterized by the University of Wisconsin, Madison Soil & Plant Analysis Laboratory. The sediment type was sandy comprised of 95% sand, 2% silt, and 3% clay. Organic content was 2.1%, total nitrogen content was 0.02%, and pH was 7.9.
Details on inoculum:
Source of inoculum: see description of source and properties of sediment above
Duration of test (contact time):
148 d
Initial conc.:
1.5 other: mg/Kg dry weight
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
test mat. analysis
other: Metabolites... (see attached file)
Details on study design:
OVERVIEW of EXPERIMENTAL DESIGN
The radiolabeled test substance was incubated with biotic and abiotic sediment samples under static conditions. The sediment for the abiotic treatment was autoclaved for 90 min and amended with mercuric chloride at 1 g/L to inhibit microbial activity. The test systems consisted of replicate 1 ml samples of sediment with 0.1 ml overlying water in test tubes, which were individually dosed with the test substance at a final added concentration of 4.1 mg/Kg dry weight.
Four replicate samples for the biotic treatment were prepared per sampling interval and all the biotic samples were incubated together in a sealed dessicator, which contained a 50 ml beaker containing 20 ml of 1.5 N KOH to trap any evolved 14CO2 in the headspace. In addition, the dessicator was continuously purged with CO2-free air to maintain aerobic conditions, and the effluent gas was passed through a gas trapping system consisting of one empty trap followed by three base traps containing 100 ml of 1.5 N KOH to recover any 14CO2 not collected by the internal trap. See the study report for diagrams of the test system and the analysis scheme.

TEST CONDITIONS
- Volume of test solution/treatment: 1 ml sediment with 0.1 ml overlying water
- Composition of medium: natural sediment, overlying water
- Additional substrate: no
- Solubilising agent: not used
- Test temperature: not specified in the study report
- pH: not specified in the study report
- pH adjusted: no
- Aeration of dilution water: N/A
- Suspended solids concentration: N/A
- Continuous darkness: not specified in the study report
- Any indication of the test material adsorbing to the walls of the test apparatus: no

TEST SYSTEM
- Culturing apparatus: test tubes
- Number of culture flasks/concentration: 4 at each time point
- Method used to create aerobic conditions: CO2-free air continuously pumped through test system
- Measuring equipment: see details on analytical methods
- Test performed in closed vessels: yes (CO2-free air purged through system to measure evolved 14CO2 in traps)
- Details of trap for CO2: see overview of experimental design above.

SAMPLING
- Sampling frequency: Biotic treament sampled after 15 min, and after 1, 2, 3, 6, 9, 14, 33, 92, and 148 days. The abiotic treatment was sampled less frequently.
- Sampling method: At each sampling, the dessicator was opened to change the internal base trap, and to recover sufficient samples for dissolved 14CO2, and for characterizing residual radioactivityf.
- Sample storage before analysis: not specified in study report

STATISTICAL METHODS: The parent loss and mineralization data were fit to a variety of first order decay and production equations using nonlinear regression. Regression analysis was performed using Jandel Table Curve 2D software (version 4.01).
Compartment:
other: sediment, material (mass) balance
% Recovery:
101
St. dev.:
0.3
% Degr.:
60.8
St. dev.:
0.3
Parameter:
CO2 evolution
Sampling time:
148 d
Remarks on result:
other: Mean of biotic flasks; aerobic
% Degr.:
14.4
St. dev.:
0.7
Parameter:
other: associated with solids
Sampling time:
148 d
Remarks on result:
other: Mean of biotic flasks; aerobic
% Degr.:
1.4
St. dev.:
0.6
Parameter:
other: metabolites
Sampling time:
148 d
Remarks on result:
other: Mean of biotic flasks; aerobic
% Degr.:
24.5
St. dev.:
0.05
Parameter:
other: parent
Sampling time:
148 d
Remarks on result:
other: Mean of biotic flasks; aerobic
Compartment:
sediment
DT50:
0.4 d
St. dev.:
0.1
Type:
other: two compartment first order model
Remarks on result:
other: Primary biodegradation; aerobic; compartment 1
Compartment:
sediment
DT50:
99 d
St. dev.:
4.2
Type:
other: two compartment first order model
Remarks on result:
other: Primary biodegradation; aerobic; compartment 2
Compartment:
sediment
DT50:
11.6 d
St. dev.:
1.5
Type:
other: first order
Remarks on result:
other: Mineralization; aerobic
Other kinetic parameters:
first order rate constant
Transformation products:
yes
No.:
#1
Details on transformation products:
Metabolites were not identified, other than by position on RAD-TLC:
Rf 0.36 parent
Rf 0.57 metabolite
Evaporation of parent compound:
no
Volatile metabolites:
not measured
Residues:
yes
Details on results:
Primary degradation was best described by a two compartment first order model (r2 > 0.99). The process was biphasic with two pools (compartments) of material exhibiting different degradation rates. Pool A (compartment 1) presumably was readily bioavailable test material, in the aqueous phase. Pool B (compartment 2) presumably was less bioavailable test material, bound to solids (sorbed).

Amount in pool A: 42.2%
Amount in pool B: 64.8%

Mineralization (14CO2 production) was best described by a First Order Model (r2 > 0.99), indicating that parent and metabolites were equally bioavailable to undergo mineralization.

Mass balance of abiotic flasks was 110.6% (107.5% parent, 3.0% associated with solids).

Fate of C12-LAS (C12-linear alkylbenzene sulfonate) in Aerobic Sediment: Die-Away Study using Lytle Creek Sediment (study 68316)

Time (days)

Parent (Rf 0.36)

Non-Polar Metabolite (Rf 0.57)

Solids

CO2

Total Recovery

0.01

108.6

1.4

4.0

Not sampled

113.2

1

72.9

5.7

22.9

10.4

108.9

2

69.5

0.0

20.3

20.2

110.0

3

60.9

1.3

23.9

18.8

104.9

6

61.8

4.0

22.8

19.4

106.0

9

64.5

1.7

19.8

21.5

106.7

14

56.7

1.9

18.9

31.9

108.4

33

39.5

1.0

18.6

46.5

105.4

61

26.7

0.7

16.9

53.5

97.8

148

24.5

1.4

14.4

60.8

101.0

 

 

 

 

 

 

Abiotic (n=5)

107.5

ND

3.0

Not analyzed

110.6

% of dosed radioactivity recovered as parent, metabolites, associated with extracted solids, or mineralized to CO2 as a function of time in Lytle Creek aerobic sediment.

Sediment dosed with [14C-U-ring] C12 linear alkylbenzene sulfonate.

Standard deviations are available in the study report.

ND = not detected.

Validity criteria fulfilled:
yes
Conclusions:
C12LAS (linear alkylbenzene sulfonate) was aerobically biodegraded in sediment (Lytle Creek). After 148 days, 60.8% was mineralized, 14.4% was associated with solids, 1.4% was metabolites, and 24.5% remained as parent. The rate constants for primary biodegradation and mineralization were 1.5 day-1 and 0.06 day-1, respectively.
Executive summary:

The biodegradation of C12LAS (linear alkylbenzene sulfonate) in sediment was evaluated in an aerobic die-away study using sediment from Lytle Creek, Wilmington, Ohio. Radiolabeled test material (14C) was used in a test design that was similar to OECD 308 and OECD 314. The test material was added to the sediment at 1.5 mg/Kg dry weight. The die-away study continued for 148 days. The test material was comprised of C10 -C13 alkyl chainlengths with an average chainlength of 11.6.

C12 -LAS was aerobically biodegraded in sediment from Lytle Creek. After 148 days:

60.8% was mineralized,

14.4% was associated with solids,

24.5% remained as parent, and

1.4% was metabolites.

Primary degradation was best described by a two compartment first order model (r2 > 0.99). The process was biphasic with two pools of material exhibiting different degradation rates. Pool A was presumably the more readily bioavailable test material in the aqueous phase. Pool B was presumably the less bioavailable test material bound to solids (sorbed). The rate constants for primary degradation were:

1.5 day-1 (pool A)

0.007 day-1 (pool B)

Mineralization (14CO2 production) was best described by a First Order Model (r2 > 0.99), indicating that parent and metabolites were equally bioavailable to undergo mineralization. The rate constant for mineralization was 0.06 day-1.

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
other: OECD 314
Deviations:
no
GLP compliance:
yes
Remarks:
The P&G Environ Science Lab is in the process of attaining formal GLP status. This expt was conducted in accordance with GLP's, by scientists with years of environ testing expertise. P&G helped develop and write the OECD protocol for this test method.
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural sediment
Details on source and properties of sediment:
Sediment was collected from the Ohio River near Cincinnati, Ohio at approximately river mile 476-477. The sediment was collected using a dredge and the (top 2-3 cm layer of sediments was retained. The sediment was placed in plastic jars and kept on ice during transport, and then stored in a 4 C cold room prior to the test. The sediment was characterized by the University of Wisconsin, Madison Soil & Plant Analysis Laboratory. The sediment consisted of 55% sand, 36% silt, and 9% clay. Organic content was 2.4%, total nitrogen content was 0.1%, and pH was 7.6.
Details on inoculum:
Source of inoculum: see description of source and properties of sediment above.
Duration of test (contact time):
92 d
Initial conc.:
1.5 other: mg/Kg dry weight
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
CO2 evolution
test mat. analysis
other: Metabolites... (see attached file)
Details on study design:
OVERVIEW of EXPERIMENTAL DESIGN
The radiolabeled test substance was incubated with biotic and abiotic sediment samples under static conditions. The sediment for the abiotic treatment was autoclaved for 90 min and amended with mercuric chloride at 1 g/L to inhibit microbial activity. The test systems consisted of replicate 1 ml samples of sediment with 0.1 ml overlying water in test tubes, which were individually dosed with the test substance at a final added concentration of 4.1 mg/Kg dry weight.
Four replicate samples for the biotic treatment were prepared per sampling interval and all the biotic samples were incubated together in a sealed dessicator, which contained a 50 ml beaker containing 20 ml of 1.5 N KOH to trap any evolved 14CO2 in the headspace. In addition, the dessicator was continuously purged with CO2-free air to maintain aerobic conditions, and the effluent gas was passed through a gas trapping system consisting of one empty trap followed by three base traps containing 100 ml of 1.5 N KOH to recover any 14CO2 not collected by the internal trap. See the study report for diagrams of the test system and the analysis scheme.

TEST CONDITIONS
- Volume of test solution/treatment: 1 ml sediment with 0.1 ml overlying water
- Composition of medium: natural sediment, overlying water
- Additional substrate: no
- Solubilising agent: not used
- Test temperature: not specified in the study report
- pH: not specified in the study report
- pH adjusted: no
- Aeration of dilution water: N/A
- Suspended solids concentration: N/A
- Continuous darkness: not specified in the study report
- Any indication of the test material adsorbing to the walls of the test apparatus: no

TEST SYSTEM
- Culturing apparatus: test tubes
- Number of culture flasks/concentration: 4 at each time point
- Method used to create aerobic conditions: CO2-free air continuously pumped through test system
- Measuring equipment: see details on analytical methods
- Test performed in closed vessels: yes (CO2-free air purged through system to measure evolved 14CO2 in traps)
- Details of trap for CO2: see overview of experimental design above.

SAMPLING
- Sampling frequency: Biotic treament sampled after 15 min, and after 1, 2, 3, 7, 10, 15, 36, and 92 days. The abiotic treatment was sampled less frequently.
- Sampling method: At each sampling, the dessicator was opened to change the internal base trap, and to recover sufficient samples for dissolved 14CO2, and for characterizing residual radioactivityf.
- Sample storage before analysis: not specified in study report

STATISTICAL METHODS: The parent loss and mineralization data were fit to a variety of first order decay and production equations using nonlinear regression. Regression analysis was performed using Jandel Table Curve 2D software (version 4.01).
Compartment:
other: sediment, material (mass) balance
% Recovery:
75.8
St. dev.:
2
% Degr.:
42.1
St. dev.:
2.7
Parameter:
CO2 evolution
Sampling time:
92 d
Remarks on result:
other: Mean of biotic flasks; aerobic; normalized to 100% mass balance.
% Degr.:
28.5
St. dev.:
3.7
Parameter:
other: associated with solids
Sampling time:
92 d
Remarks on result:
other: Mean of biotic flasks; aerobic; normalized to 100% mass balance.
% Degr.:
0
Parameter:
other: metabolites
Sampling time:
92 d
Remarks on result:
other: Mean of biotic flasks; aerobic
% Degr.:
29.8
St. dev.:
6.7
Parameter:
other: parent
Sampling time:
92 d
Remarks on result:
other: Mean of biotic flasks; aerobic; normalized to 100% mass balance.
Compartment:
sediment
DT50:
1.4 d
St. dev.:
0.2
Type:
other: two compartment first order model
Remarks on result:
other: Primary biodegradation; aerobic; compartment 1
Compartment:
sediment
DT50:
77 d
St. dev.:
0.001
Type:
other: two compartment first order model
Remarks on result:
other: Primary biodegradation; aerobic; compartment 2
Compartment:
sediment
DT50:
11.6 d
St. dev.:
1.9
Type:
other: first order
Remarks on result:
other: Mineralization; aerobic
Other kinetic parameters:
first order rate constant
Transformation products:
yes
No.:
#1
No.:
#2
Details on transformation products:
Metabolites were not identified, other than by position on RAD-TLC:
Rf 0.45 parent
Rf 0.70 non-polar metabolite
Rf 0.90 non-polar metabolite
Evaporation of parent compound:
no
Volatile metabolites:
not measured
Residues:
yes
Details on results:
Primary degradation was best described by a two compartment first order model (r2 > 0.99). The process was biphasic with two pools (compartments) of material exhibiting different degradation rates. Pool A (compartment 1) presumably was readily bioavailable test material, in the aqueous phase. Pool B (compartment 2) presumably was less bioavailable test material, bound to solids (sorbed).

Amount in pool A: 49.3%
Amount in pool B: 49.9%

Mineralization (14CO2 production) was best described by a First Order Model (r2 > 0.99), indicating that parent and metabolites were equally bioavailable to undergo mineralization.


Mass balance of abiotic flasks was 105.8% (99.5% parent, 5.5% associated with solids).

Fate of C12-LAS (C12-linear alkylbenzene sulfonate) in Aerobic Sediment: Die-Away Study using Ohio River Sediment (study 68315)

Time (days)

Parent (Rf 0.45)

Non-Polar Metabolite (Rf 0.70)

Non-Polar Metabolite (Rf 0.90)

Solids

CO2

Total Recovery

0.01

91.2

1.4

2.6

6.6

1.2

102.7

1

60.1

0.8

1.6

22.8

5.9

91.2

2

64.8

0.9

2.4

24.6

7.9

100.5

3

60.7

0.9

1.5

24.1

9.0

96.1

7

58.0

0.4

1.3

25.8

10.0

95.5

10

45.6

0.0

0.9

28.7

11.7

86.9

15

31.4

4.7

0.0

23.7

19.1

78.8

36

36.7

0.0

0.0

23.9

27.9

88.4

92

22.6

0.0

0.0

21.6

31.6

75.8

 

 

 

 

 

 

 

Abiotic (n=10)

99.5

ND

ND

5.5

Not analyzed

105.8

% of dosed radioactivity recovered as parent, metabolites, associated with extracted solids, or mineralized to CO2 as a function of time in Ohio River aerobic sediment.

Sediment dosed with [14C-U-ring] C12 linear alkylbenzene sulfonate.

Standard deviations are available in the study report.

ND = not detected.

Biodegradation results in biotic flasks at 92 days were normalized to 100% mass balance as follows:

Mineralization: 31.6% to 42.1%

Solids: 21.5% to 28.5%

Metabolites: 0% to 0%

Parent: 22.6% to 29.8%

Mass Balance: 75.8% to 100%

Validity criteria fulfilled:
yes
Conclusions:
C12LAS (linear alkylbenzene sulfonate) was aerobically biodegraded in sediment (Ohio River). After 92 days, 42.1% was mineralized, 28.5% was associated with solids, 0% was metabolites, and 29.8% remained as parent. The rate constants for primary biodegradation and mineralization were 0.5 day-1 and 0.06 day-1, respectively.
Executive summary:

The biodegradation of C12LAS (linear alkylbenzene sulfonate) in sediment was evaluated in an aerobic die-away study using sediment from the Ohio River, Cincinnati, Ohio. Radiolabeled test material (14C) was used in a test design that was similar to OECD 308 and OECD 314. The test material was added to the sediment at 1.5 mg/Kg dry weight. The die-away study continued for 92 days. The test material was comprised of C10 -C13 alkyl chainlengths with an average chainlength of 11.6.

C12 -LAS was aerobically biodegraded in sediment from the Ohio River. After 92 days (normalized to 100% mass balance):

42.1% was mineralized,

28.5% was associated with solids,

29.8% remained as parent, and

0% was metabolites.

Primary degradation was best described by a two compartment first order model (r2 > 0.99). The process was biphasic with two pools of material exhibiting different degradation rates. Pool A was presumably the more readily bioavailable test material in the aqueous phase. Pool B was presumably the less bioavailable test material bound to solids (sorbed). The rate constants for primary degradation were:

0.5 day-1 (pool A)

0.009 day-1 (pool B)

Mineralization (14CO2 production) was best described by a First Order Model (r2 > 0.99), indicating that parent and metabolites were equally bioavailable to undergo mineralization. The rate constant for mineralization was 0.06 day-1.

Endpoint:
biodegradation in water and sediment: simulation testing, other
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Qualifier:
no guideline followed
Principles of method if other than guideline:
The bioassay was run according to established scientific methods. Radiolabeled LAS tracer in an LAS mixture with an average chain length of 11.4 carbons was used in a 28-d Lumbriculus (oligochaete) sediment exposure assay with sediment spiked from 50-600 mg LAS/kg dry weight sediment.
GLP compliance:
yes
Specific details on test material used for the study:
Test material is a radiolabeled LAS tracer in an LAS mixture with an average chain length of 11.4 carbons (Proctor & Gamble). 14C-LAS radio tracer was spiked into the sediment along with non-labelled LAS. The 14C-labelled LAS used for the Lumbriculus test was 3-dodecylbenzene sulphonate (3-DOBS 95% purity, specific activity of 2,686,200 Bq/mg) with the 14C-labelled carbon atom included in the benzene ring. The non-labelled LAS compound was a mix of internal and external isomers and alkyl chains, with an average alkyl chain length of 11.4 carbon atoms (Nansa HS 80 S, provided by Unilever).
Radiolabelling:
yes
Remarks:
14C-labelled carbon atom included in the benzene ring
Oxygen conditions:
aerobic
Inoculum or test system:
other: Distilled water with natural and artificial sediments
Details on source and properties of sediment:
The natural uncontaminated sediment used for the study was collected on 21th of November 1997 from the ARC Study Centre, Wolverton Road, Great Linford, Milton Keynes, UK. It contained 44% sand, 48% silt and 8% clay, with a total organic carbon content of 1.7% and a cation exchange capacity of 104.5 +/- 6.7 meq/kg (n ¼ 6) and the pore water dissolved organic carbon concentration was 28 +/- 1.3 mg/l (n = 20). The sediment particle size ranged from 0 to 500 mm with the bulk of the particles being less than 63 mm (68%). The wet sediment contained 51 +/- 2% by mass of water (n = 6).
As the natural sediment that was used for the Lumbriculus assay was not available for the nematode assay, an artificial sediment, matching the grain size and organic content of the natural sediment was used. The artificial sediment consisted of the following components: quartz sand (Millisil W4, Quarzsandwerke GmbH, Frechen, Germany), calzitic sand (Pitti Heimtierprodukte, Recklinghausen, Germany), kaolin (Sigma-Aldrich, Taufkirchen, Germany), Dolomite 5T (Carl Ja¨ger Tonindustriebedarf GmbH, Hilgert, Germany), Humus (Sphagnum peat; Terra Plant Service, Wiefelstede, Germany), Fe2O3 (Sigma-Aldrich, Taufkirchen, Germany), Al2O3 (Sigma-Aldrich, Taufkirchen, Germany). The dry sediment was mixed with M9-medium (6 g/l Na2HPO4, 3 g/l KH2PO4, 5 g/l NaCl, 0.25 g/l MgSO4$7H2O, and 5 mg/l cholesterol) yielding an overall dry weight of 60%. The artificial sediment was characterized by (as dry weight) 44% sand, 48% silt, 8% clay, with 2% organic matter.
Duration of test (contact time):
28 d
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on study design:
A 28 day chronic study was conducted using sediment spiked with radiolabelled material. The test species, Lumbriculus variegatus, is a true sediment feeder (i.e., subsurface ingestion of sediment particles). The nominal concentrations were 50, 75, 100, 150, 300, 600 mg/kg/dry weight and controls. The test sediment contained 44% sand, 48% silt, and 8% clay. Twenty grams (wet weight) of the prepared sediment was added to clean 60 mL glass vessels followed by 30 mL of groundwater drawn from an aquifer. After 24 hours of equilibration, 10 mature Lumbriculus (ca. 15 mm in length, 8 mg dry weight) were added to each vessel. Vessels were aerated for 5 minutes every day and the overlying water replenished with distilled water every two days. Each test concentration was replicated 6 times. LAS concentrations were measured at 0 and 28 days. After 28 days the sediment was removed and all live worms counted, blotted dry, and wet weighed prior to air drying for 48 hours to a constant dry weight. Toxicity endpoints included survival, reproduction and biomass. The mode of reproduction (architomy) necessitates the treatment of survival and reproduction as a single endpoint, i.e., number of organisms at test termination.
Key result
Compartment:
entire system
DT50:
>= 17.5 - <= 22.6 d
Temp.:
22 °C
Details on results:
There was a loss of between 15 and 78% of the LAS radioactivity over the duration of the test, which was attributed to mineralization of LAS by the worms and microorganisms present in the sediment (biodegradation). Results are therefore based on the average of day 0 and day 28 measured sediment concentrations.
Executive summary:

Biodegradation of LAS in sediments has been reported in a study conducted using a radiolabeled LAS tracer in an LAS mixture with an average chain length of 11.4 carbons. A 28-d Lumbriculus (oligochaete) sediment exposure assay with sediment spiked from 50-600 mg LAS/kg dry weight sediment resulted in LAS half lives in sediment of 17.5-22.6 days.

Description of key information

A study by Comber et al. (2006) was conducted using a radiolabeled LAS tracer in an LAS mixture with an average chain length of 11.4 carbons. A 28-d Lumbriculus (oligochaete) sediment exposure assay with sediment spiked from 50-600 mg LAS/kg dry weight sediment resulted in LAS half lives in sediment of 17.5-22.6 days.

Biodegradation was investigated in a study using radiolabeled LAS added to sediment from Lytle Creek, Wilmington, Ohio at 1.5 mg/kg dry weight. Primary degradation was best described by a two compartment first order model. The process was biphasic, with two compartments of material exhibiting different degradation rates. The first compartment was presumed to be readily bioavailable test material in the aqueous phase. The second compartment was less bioavailable test material sorbed to solids. Calculated half-lives (DT50) of the parent LAS were 0.4 days (primary biodegradation, compartment 1), 99 days (primary biodegradation, compartment 2), and 11.6 days (first order aerobic mineralization). In a study using the same methodology, but with sediment collected from the Ohio River near Cincinnati, Ohio, calculated half-lives (DT50) of the parent LAS were 1.4 days (primary biodegradation, compartment 1), 77 days (primary biodegradation, compartment 2), and 11.6 days (first order aerobic mineralization).

Key value for chemical safety assessment

Additional information

Biodegradation of LAS in sediments has been reported. A study by Comber et al. (2006) was conducted using a radiolabeled LAS tracer in an LAS mixture with an average chain length of 11.4 carbons. A 28-d Lumbriculus (oligochaete) sediment exposure assay with sediment spiked from 50-600 mg LAS/kg dry weight sediment resulted in LAS half lives in sediment of 17.5-22.6 days.

In addition, the biodegradation of C12-LAS in natural sediments was evaluated in two aerobic die-away studies. In the first, radiolabeled LAS was added to sediment from Lytle Creek, Wilmington, Ohio at 1.5 mg/kg dry weight. Primary degradation was best described by a two compartment first order model. The process was biphasic, with two compartments of material exhibiting different degradation rates. The first compartment was presumed to be readily bioavailable test material in the aqueous phase. The second compartment was less bioavailable test material sorbed to solids. Mineralization was best described by a first order model, indicating that parent and metabolites were equally bioavailable to undergo mineralization. After 148 days, 60.8% was mineralized, 14.4% was associated with solids, 1.4% was metabolites, and 24.5% remained as parent LAS. Calculated half-lives (DT50) of the parent LAS were 0.4 days (primary biodegradation, compartment 1), 99 days (primary biodegradation, compartment 2), and 11.6 days (first order aerobic mineralization). Rate constants for primary degradation and mineralization were 1.5 day-1and 0.06 day-1, respectively.

The second die-away study used the same methodology as above but with sediment collected from the Ohio River near Cincinnati, Ohio. Again, primary degradation was best described by a two compartment first order model and the process was biphasic, with two compartments of material exhibiting different degradation rates. After 92 days, 42.1% was mineralized, 28.5% was associated with solids, 0% was metabolites, and 29.8% remained as parent LAS. Calculated half-lives (DT50) of the parent LAS were 1.4 days (primary biodegradation, compartment 1), 77 days (primary biodegradation, compartment 2), and 11.6 days (first order aerobic mineralization). Rate constants for primary degradation and mineralization were 0.5 day-1and 0.06 day-1, respectively.