Docusate sodium

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The study is compliant with ISO 14593 (CO2 Headspace-Test) wichh is equivalent to OECD 310. This test is suitable to assess ready biodegradation of surfactants according to 648/2004/EEC.

Qualifier:

according to guideline

Guideline:

other: ISO 14593

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure):
Activated sludge from STP "Hochdahl" (mainly municipal)
- Laboratory culture: NA
- Method of cultivation: NA
- Preparation of inoculum for exposure: No adaptation
- Pretreatment: None (non-adapted sludge was used)
- Concentration of sludge: 4 mg dry matter/L
- Water filtered: yes/no: NA
- Type and size of filter used, if any: NA

One paralell set of experiments was conducted using adapted sludge (SCAS procedure), but these results are irrevelant according to 648/2004/EEC and are hence not reported here (since adaptation is not allowed to assess ready biodegradability of surfactants).

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

other: TOC

Parameter followed for biodegradation estimation:

inorg. C analysis

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral medium (assumed according to the test guideline)
- Additional substrate: NA
- Solubilising agent (type and concentration if used): None reported
- Test temperature: 20 to 25°C
- Aeration of dilution water: No (closed bottle)
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: Closed bottles "serum flasks" 160 mL/L, 56 mL headspace
- Number of culture flasks/concentration: Submission substance (one concentration, 5 replicates), blank control (one replicate), reference substance (1 replicate)
- Method used to create aerobic conditions: Shaking
- Method used to create anaerobic conditions: NA
- Measuring equipment: TOC analysis according to DIN 38409 Part 3
- Test performed in closed vessels due to significant volatility of test substance: Yes (although the submission substance is not volatile, closed systems were used to be consistent with the test system for other (volatile) ring test substances)
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: NA

SAMPLING
- Sampling frequency: 14 days (reference substance) and 28 days (blank control and submission substance)
- Sampling method: Total volume was taken (assumption since not reported)
- Sterility check if applicable: NA- Sample storage before analysis: No information provided

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes (one replicate)
- Abiotic sterile control: No
- Toxicity control: Yes (dodecyl benzene sulhonate)

STATISTICAL METHODS: Due to replications of docusate sodium test group, calculation of average and standard deviation is possible

Reference substance:

other: Dodecyl benzene sulfonate

Test performance:

No events are reported, which might have affected the quality of the study

Parameter:

% degradation (inorg. C analysis)

Remarks:

(TIC)

Value:

91.2

St. dev.:

0.67

Sampling time:

28 d

Details on results:

On day 15 after incubation initiation, 93% of the reference substance, based on DOC removal was degraded. Hence the test is rendered valid.

Validity criteria fulfilled:

yes

Remarks:

biodegradation of reference substance > 60%

Interpretation of results:

readily biodegradable

Conclusions:

The submission substance is considered ready biodegradable accoding to criteria for surfactants, as laid down in 648/2004/EEC

Executive summary:

The test item was exposed at 10 mg C/L in a valid study to a solution composed of suitable mineral medium and activated sludge as obtained from a domestic STP (non-adapted). The sludge concentration in test solutions was 4 mg dry matter/L. Exposure was for 28 days in the dark, under shaking conditions, in closed bottles of 160 ml, with 56 ml headspace volume. Three test groups were incubated: Test item (one concentration), blanc control and reference substance (one concentration of dodecyl benzene sulphonate). Each test group had 5 replicates. Biodegradation was determined by measuring the TIC (total inorganic carbonic, carbon fixation method) within 14 days (reference substance) and 28 days (test item and blanc control). The results show that 91.1% of the test item were degraded within 28 days. The test was valid since biodegradation was > 60% after 14 days for the reference substance.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2005

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:

no

Remarks:

The study was conducted under ISO/EC 17025. This certification standard is accepted according to 648/2004/EEC to assess the biodegradation of surfactants

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure):
Sludge obtained from municipal STP Werhölzli
- Laboratory culture: No
- Method of cultivation: NA
- Preparation of inoculum for exposure: Sludge was washed twice with tap water and used immediately for the test
- Pretreatment: None (non-adapted sludge was used)
- Concentration of sludge: 30 mg/L (it is not stated whether dry matter or not), concentration is that of the final mixture
- Water filtered: NA
- Type and size of filter used, if any: NA

Duration of test (contact time):

28 d

Initial conc.:

107 mg/L

Based on:

act. ingr.

Parameter followed for biodegradation estimation:

DOC removal

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: Aerobic mineral salts medium acc. to OECD 301 F/A. Conductivity: > 1.5USi; DOC: < 0.3 mg/L
- Additional substrate: None reported
- Solubilising agent (type and concentration if used): none reported
- Test temperature: 22 +/- 2 °C
- Aeration of dilution water: No
- Suspended solids concentration: 30 mg/L (it not stated whether this is referring to dry mass or wet weight)
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: OxiTop-C (WTW Wissenschaftlich-Technische Werkstätten GmbH & Co KG, D-82362 Weilheim). This is 500 mL glass bottles (tightly closed with manometric BOD measureing devices, OxiTop-C) contaning a total volume of test solution of 200 ml. The bottles were equipped with stirring rods and butyl rubber quivery which contain 2 pellets of sodium hydroxide each to adsorb the produced CO2 from the head space. Test system were exposed to 22 plus/minus 0.5°C, in the dark. Each bottel was filled with 200 mL test solution.
- Number of culture flasks/concentration: submission substance (107 mg/L, 2 replicates), blanc control (one replicate), reference substance (100 mg/L sodium benzoate, two replicates), abiotic control (0.2 mM HgCl2, one replicate)
- Method used to create aerobic conditions: stirring
- Method used to create anaerobic conditions: NA
- Measuring equipment: BOD: OxiTop-C (WTW Wissenschaftlich-Technische Werkstätten GmbH & Co KG, D-82362 Weilheim); DOC: Shimadzu 5060 TOC-Analyzer
- Test performed in closed vessels due to significant volatility of test substance: NA
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: NA

SAMPLING
- Sampling frequency: DOC: days 0 and 28; BOD: Continuous measuerments, evaluation points: daily during 28 days
- Sampling method: DOC: Test solutions were centrifuges (15 min at 4500 g) and acidified to pH < 2. Prior to analysis the samples were sparged with CO2 free high purity air for 5 min to remove inorganic carbon

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes (two replicates)
- Abiotic sterile control: Yes (sterilized with 0.2 mM HgCl2, one replicate)
- Toxicity control: Yes (100 mg/L sodium benzoate, 2 replicates)

STATISTICAL METHODS: NA

Reference substance:

benzoic acid, sodium salt

Test performance:

No events are reported, which might have affected the quality of the study

Parameter:

% degradation (DOC removal)

Value:

100

Sampling time:

28 d

Parameter:

other: BOD

Value:

73.6 - 78.3

St. dev.:

3.3

Remarks on result:

other: Continuous measurement, evaluation daily

Details on results:

The procedure control (sodium benzoate) reached 78% biodegradation after 14 days, thus confirming suitability of inoculum and test conditions.

Validity criteria fulfilled:

yes

Remarks:

Biodegradation of reference substance was 78% within 28 days of exposure

Interpretation of results:

readily biodegradable

Conclusions:

The test item exceeded the pass level of 60% for ultimate ready biodegradability (average 76% +/-3%) within 28 days and can therefore be regarded asready biodegradable, accoding to criteria for surfactanta, as laid down in 648/2004/EEC

Executive summary:

The biodegradability of docusate sodium (98.5% of the test item) was performed in a valid study, by exposing the test item at 107 mg /L to a mixture of appropriate mineral medium and activated sludge (domestic STP, non-adapted, 30 mg/L concentration in test solutions). Although the test was not conducted under GLP, application of ISO/IEC 17025 is appropriate for the determination of surfactant ready biodegradation, according to 648/2004/EEC. Exposure was for 28 days in the dark, under shaking conditions, in 500 mL closed bottles with 200 mL solution and 300 mL headspace (OxiTop system with BOD measuring device). Four test groups were incubated: Test item (one concentration, 2 replicates), blank control (activated sludge only, one replicate), reference substance (one concentration of dodecyl benzene sulphonate 100 mg/L, 2 replicates) and an abiotic controls (medium only, one replicate). Biodegradation was determined by measuring DOC (day 0 and day 30) and the BOD continuously (daily evaluations) during 28 days. The results show that 73.6 and 78.3% of the test item was degraded within 28 days, based on BOD determinations. DOC measurement showed that degradation reached 100% after 28 days. Biodegradation of the reference substance was 78% within 28 days of exposure, thus confirming suitability of inoculum and test conditions.

 

Reference 3

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

14.05.2003 to 12.06.2004

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The test item is a formulation containing 74.6% of the submissin substance. The precise composition of the formulation is unknown.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure):
Sludge obtained from municipal STP "Breisgauer Bucht" (30 mg dry mass/L ). The sludge was not adapted prior to use.
- Laboratory culture: NA
- Method of cultivation: NA
- Storage conditions: NA
- Storage length: Sludge was incubated under test conditions on the day of removal
- Preparation of inoculum for exposure: The activated sludge was washed twice by settling the sludge, decanting the supernatant and re-suspending the sludge in aerated tap water.
- Pretreatment: None
- Concentration of sludge: 30 mg dry solids/L
- Initial cell/biomass concentration: NA
- Water filtered: NA
- Type and size of filter used, if any: NA

Duration of test (contact time):

29 d

Initial conc.:

20 mg/L

Based on:

other: Organic Carbon

Parameter followed for biodegradation estimation:

other: Total Inorganic Carbon (TIC)

Details on study design:

A solution of the test item in a mineral medium (acc. to OECC 301), corresponding to 10-20 mg TOC/L, was inoculated with activated sludge (30 mg dry matter per L. the test vessels were aerated by the passage of carbon dioxide-free air and are incubated under aerobic conditins in diffuse light for 28 days. Degradation is followed by determining the carbon dioxide produced and absorbed to sodium hydroxide via IC-measurement (TOC analyser). The amount of carbon dioxide produced from the test item less then amont derived from the blank inoculum is expressed as a percentage of ThCO2.
TEST CONDITIONS
- Composition of medium: Mineral medium according to OECD 301
- Solubilising agent (type and concentration if used): No information provided
- Test temperature: 22 to 24 °C
- pH adjusted: NA
- CEC (meq/100 g): No information provided
- Aeration of dilution water: Aeration with CO2 free air
- Suspended solids concentration: 30 mg dry mass/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Several bottles in series (reactor system): Two 1L gas wash bottles filled with dry soda lime (CO2 removal), one 1 L gas wash bottle (0.1 M NaOH), one 1 L gas wash bottel (0.5 M Ba(OH), one 1 L gas wash bottle (demineralized water), one 1 L gas wash bottle (empty), one glass bottle (r1.5 L test solution), two 250 mL gas wash bottles with 200 mL 0.2 M NaOH (CO2 trapping system).
- Number of culture flasks/concentration: test item (3 reactors), inocculum blanc (two reactors), reference substance (two reactors), toxicity control (one reactor)
- Method used to create aerobic conditions: Continuous aeration with CO2 free air, mixing of the test solutions by magnetic stirring
- Method used to create anaerobic conditions: NA
- Measuring equipment: TOC analyzer Shimadzu 3000
- Test performed in closed vessels due to significant volatility of test substance: No
- Test performed in open system: Seale, but aerated with CO2 free air
- Details of trap for CO2 and volatile organics if used: NA

SAMPLING
- Sampling frequency: days 0, 7, 10, 14, 21 and 20 after incubation initiation
- Sampling method: 4 mL aliquots of NaOH CO2 trapping solutions were removed to determine the TIC. On day 28 TOC was determined after removal of CO2 from test solutions by HCl. In addition TIC analysis of NaOH CO2 trapping systems was performed.
- Sterility check if applicable: NA

- Other:

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, two replicates
- Abiotic sterile control: No
- Toxicity control: Yes, once replicate
- Reference substance: Yes, one concentration (19.9 to 20.4 mg/L organic carbon, two replicates
- Other:

STATISTICAL METHODS: Average and SD calculation is possible due to replication of systems

Reference substance:

benzoic acid, sodium salt

Test performance:

No events are reported, which might have affected the quality of the study.

Parameter:

% degradation (inorg. C analysis)

Value:

83.5 - 103.6

St. dev.:

10.9

Sampling time:

29 d

Details on results:

Biodegradation of the reference substance reached 83 % within 28 days of incubation.

Results with reference substance:

Biodegradation of the reference substance reached 85.6 and 88.2 % within 14 days of incubation. Hence the test is rendered valid.

Interpretation of results:

readily biodegradable

Conclusions:

Docusate Sodium is readily biodegradable according to criteria for surfactantas, as laid down in 648/2004/EEC.

Executive summary:

In a valid study, the test item was exposed at a concentration of 20 mg C/L to a mineral medium and activated sludge obtained from a domestic STP ( non-adapted, at 30 mg dry matter/L), under aerobic conditions. Exposure was for 29 days in the dark, under stirring conditions. 2 L reactors with 1.5 L test solution was constantly aerated with CO2 free air. CO2 as produced by the inocculum was adsorbed in 0.2 NaOH solutions. Trapped C was determined by TOC analysis. Four test groups were incubated: Test item (20 mg TOC/L, 3 replicates), blank control (one replicate), reference substance (approx 20 mg TOC/L of sodium benzoate, two replicates). Biodegradation was determined by measuring CO2 (via IC) on days 4, 7, 10, 14, 21 and 28. In addition IC was determined in test solution after release by HCL and trapping of the CO2 in NaOH . The results show that 83.5 to 103.6% of the test item were degraded within 28 days (average 93.1 +/- 9%). Between 86 and 88% of the reference substance were degraded after 28 days.

Reference 4

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The test item is a formulation containing 85 % of the submission substance. The precise composition of the formulation is unknown. Some relevant details of the test design are not reported. Though the study was not performed under GLP, industry standards similar to GLP were used.

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, non-adapted

Details on inoculum:

- Source of inoculum/sewage (e.g. location, sampling depth, contamination history, procedure):
Sewage was used to conduct the test. It was taken from domestic STP Hochdahl.
- Preparation of inoculum for exposure: Filtration
- Pretreatment: None (no adaptation)
- Concentration of sewage: 1 ml sewage/L
- Water filtered: yes. The first 200 mL were discareded
- Type and size of filter used, if any: coarse paper filter.

Duration of test (contact time):

30 d

Initial conc.:

3 mg/L

Based on:

formulation

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Composition of medium: Deonized water as used for the test

- Test temperature: Ambient conditions are assumed
- pH: No information provided
- Aeration of dilution water: No

TEST SYSTEM
- Number of culture flasks/concentration: One replicate per test group
- Method used to create anaerobic conditions: NA
- Measuring equipment: Titration
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: NA

SAMPLING
- Sampling frequency: Samples were analyzed on day 28
- Sampling method: Removal of test solutions at test end
- Sterility check if applicable: NA

CONTROL AND BLANK SYSTEM
- Inoculum blank: No
- Abiotic sterile control: No
- Toxicity control: No
- Other: reference substance (one concentration 3 mg/L, one replicate

STATISTICAL METHODS: NA

Reference substance:

other: Sulfuric acid, mono dodecyl ester sodium salt

Test performance:

No events are reported, which might have affected the quality of the study.

Parameter:

% degradation (DOC removal)

Value:

93

Sampling time:

28 d

Details on results:

At the end of incubation, 93% of the reference substance, based on DOC removal, was degraded. Hence the test is rendered valid.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

Within 30 days post-treatment, 93% of the test item were degraded, in a valid study with respect to reference substance performance. Hence the substance is readily biodegradable.

Executive summary:

The test item was exposed at 3 mg/L to 1 mg/L domestic, non-adadpted STP sewage in deionized water , under aerobic conditions. Exposure was for 30 days. Two test groups were incubated: Test item (3 mg formulation/L) and reference substance (2 mg/L sulfuric acid, mono dodecyl ester sodium salt). Each test group had one replicate. Biodegradation was determined by measuring the DOC removal during 30 days (test item and reference substance). The results show that 93% of the test item were degraded within 30 days (reference substance 87% within 15 days). The test was valid since biodegradation of the reference substance was > 60% after 15 days.

Description of key information

The key study for this endpoint clearly demonstrates the ready biodegradability of Docusate Sodium, according to the criteria for surfactants, as defined under 648/2004/EEC. The study was conducted according to ISO 14593 (equivalent to OECD 310). Docusate Sodium passed the test specific 60% criterion for ready biodegradation, as set by the above guidelines. Totally average 91% had been degraded after 28 days of incubation. Although the 10 day window criterion is not relevant for surfactants according to 648/2004/EEC, the 10 day window was met in this study. Three other, reliable and appropriate studies support ready biodegradation of Docusate Sodium.  

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Docusate Sodium is an anionic surfactant and has the following physical-chemical characteristics, relevant for the selection of appropriate OECD test procedures to assess ready biodegradability.

Water solubility: 8.2 g/L.

Vapour Pressure: 1.63 10 ^-12Pa.

K_OC: 952.3 L/kg.

Based on these values, Docusate Sodium can be considered water soluble, non-volatile and not strongly adsorptive. Four reliable studies are available for the assessment of ready biodegradability, based on testing requirements for anionic surfactants, according to Annex III of 648/2004/EEC .

The study of Cognis, Borowivcz 1998 (GLP) is considered the key study, since it is using analytical grade Docusate Sodium (98% pure). Furthermore, it applied test guideline ISO 14593, i.e. the reference method of 648/2004/EEC. ISO 14593 is equivalent to OECD 310, the most appropriate test design for anionic surfactants. The results of this study indicate that more than 90% of the test substance was degraded within 28 days, respectively. The results indicate that Docusate Sodium is readily biodegradable.

Three of the studies are considered supportive.

The study of Dow, Häner 2008 was conducted with analytical grade Docusate Sodium (98.5% pure, i.e., within its specification). Furthermore, it used a suitable method according to Directive 67/548/EEC Annex V, i.e., C.4 -D, equivalent to OECD 301 F. As a result 76% (ThOD) or 100% (DOC) were degraded within 28 days, respectively. This finding supports the result of the key study, i.e., that Docusate Sodium is readily biodegradable, according to the criteria set by the above guideline.

Two other studies were conducted with formulations of Docusate Sodium containing 85 and 76.4% of it (Cognis, Richterich 2001a and Elementis, Brunswick-Titze 2003). Between 90 and 100% of the test item was degraded within 28 days, respectively.

 

In conclusion it can be stated that Docusate Sodium is readily biodegradable.

This conclusion is supported by findings of Cognis, Richterich 2001b, who reported primary biodegradation (98%) within 19 days of a 70% Docusate Sodium formulation exposed to a non-adapted, activated sludge.

Other available study results were non reliable to assess this endpoint, and were hence disregarded, for various reasons (sole or in combination):

1. The test materials contained up to 10% ethanol. Since ethanol is known to enhance biodegradation, the results of these studies might be false positive and are therefore not reliable.

2. The tests were conducted according to OECD 301 A and E, which are less suitable for the purpose or ready biodegradation assessment, according to 648/2004/EEC, due to the physical-chemical properties of Docusate Sodium, K_OC in particular.

3. Tests were conducted according to guidelines, which are not recommended by 648/2004/EEC for the assessment of ready biodegradation of surfactants.

4. Essential experimental details were not reported.

5. GLP was not applied.