Docusate sodium

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, and documentation / justification is limited

Justification for type of information:

1. SOFTWARE
EPISuite 4.11

2. MODEL (incl. version number)
BCFBAF (v3.01)

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
CAS 577-11-7
CCCCC(CC)COC(=O)CC(C(=O)OCC(CC)CCCC)S(=O)(=O)O([Na])

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: yes
- Unambiguous algorithm: yes
- Defined domain of applicability: yes (substance is within the training set)
- Appropriate measures of goodness-of-fit and robustness and predictivity: yes
- Mechanistic interpretation: no

5. APPLICABILITY DOMAIN
- Descriptor domain: substance is part of the training set (BCF 9.33 L/kg)
- Structural and mechanistic domains: substance is part of the training set (BCF 9.33 L/kg)
- Similarity with analogues in the training set: substance is part of the training set (BCF 9.33 L/kg)
- Other considerations (as appropriate): for surface active substances, the QSAR calculations which are based on the logKow are considered to be not appropriate by ECHA.

6. ADEQUACY OF THE RESULT
The result is used in the WoE approach.

BCFBAF™: Formerly called BCFWIN™, this program estimates fish bioconcentration factor and its logarithm using two different methods. The first is the traditional regression based on log KOW plus any applicable correction factors, and is analogous to the WSKOWWIN™ method. The second is the Arnot-Gobas method, which calculates BCF from mechanistic first principles. BCFBAF also incorporates prediction of apparent metabolism half-life in fish, and estimates BCF and BAF for three trophic levels.

Further information on the models, trainings sets and validation is provided in the attached background information.

Qualifier:

no guideline followed

Principles of method if other than guideline:

QSAR

Type:

BCF

Value:

56.2 L/kg

Basis:

whole body w.w.

Calculation basis:

steady state

Remarks on result:

other: regression based on log KOW plus any applicable correction factors

Type:

BAF

Value:

10.9 L/kg

Basis:

whole body w.w.

Calculation basis:

steady state

Remarks on result:

other: Arnot-Gobas (upper tropic)

Validity criteria fulfilled:

not applicable

Conclusions:

The QSAR tool BCFBAF (v3.01) predicts a BCF of 56.2 L/kg (regression based estimate for ionic substance)

Executive summary:

The QSAR tool BCFBAF (v3.01) predicts  a BCF of 56.2 L/kg (regression based estimate Ionic substance)

Reference 2

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Qualifier:

no guideline required

Principles of method if other than guideline:

Peer reviewed review article Reference to various studies made including the assessment of reliability.
Reference is made to http://qsar.cerij.or.jp/cgi-bin/DEGACC/index.cgi?e
However, that web page was not available at the time when the dossier was prepared. Therefore the information as provided in supplementary data of this review article is provided in this robust study summary.

GLP compliance:

no

Radiolabelling:

no

Test organisms (species):

Cyprinus carpio

Details on test organisms:

TEST ORGANISM
- Weight : 30 g
- Lipid content: 4.1%

Route of exposure:

aqueous

Test type:

flow-through

Water / sediment media type:

other: fresh water

Total exposure / uptake duration:

42 d

Test temperature:

25 °C

Nominal and measured concentrations:

mean measured: 50 and 500 µg/L

Lipid content:

4.1 %

Time point:

other: not reported

Conc. / dose:

50 µg/L

Temp.:

25 °C

Type:

BCF

Value:

9.33 L/kg

Basis:

whole body w.w.

Calculation basis:

steady state

Conc. / dose:

500 µg/L

Temp.:

25 °C

Type:

BCF

Value:

0.891 L/kg

Basis:

whole body w.w.

Calculation basis:

steady state

Validity criteria fulfilled:

yes

Conclusions:

BCF fish Cyprinus carpio 4.1 % lipid content: 9.33 and 0.891 L/kg at water concentrations of 500 and 50 µg/L

Executive summary:

The source of the experimental fish BCF data is actually cited by Arnot and Gobas (2006) as being from the Japanese National Institute of Technology and Evaluation (NITE) database for Biodegradation and Bioconcentration of Existing Chemical Substances under the Chemical Substances Control Law. In this study, non-radiolabelled sodium docusate was exposed to common carp (Cyprinus carpio) at concentrations of 0.5 and 0.05 mg/L under flow-through conditions for 42 days. At the end of the study, whole body fish BCF values of 9.33 and 0.891 L/Kg were obtained for fish exposed to 0.05 and 0.5 mg/L of sodium docusate, respectively.

The fish BCF data from this study was assigned a high overall quality and reliability rating in the publication by Arnot and Gobas (2006) (see spreadsheet in Annex I) and the data is included in the training set for ionisable chemicals in the BCFBAF v3.01 QSAR model as part of the US EPA Episuite software package.[1] This fish BCF data for sodium docusate is also included in the BCF gold standard database developed as a result of a CEFIC LRI project in 2006 (CEFIC, 2007). On this basis, the quality and reliability of this source data for sodium docusate is deemed sufficient to use for adressing this data requirement.

[1]The BCF values selected for the BCFBAF training and validation datasets are available in Appendix G and via Internet download at:http://esc.syrres.com/interkow/EpiSuiteData.htm

Reference 3

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 305 D (Bioaccumulation: Static Fish Test)

Deviations:

not specified

Principles of method if other than guideline:

static exposure for 72 hours

GLP compliance:

no

Specific details on test material used for the study:

14-C labelled Docusate Sodium with a specific activity of 35 µCi/mmol was obtained from Amersham International

Radiolabelling:

yes

Details on sampling:

- Sampling intervals/frequency for test organisms: 0, 2,4,12, 24, 48 and 72 hours
- Sampling intervals/frequency for test medium samples: 0, 2,4,12, 24, 48 and 72 hours
- Sample storage conditions before analysis: no
- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods):
Rainbow trout fingerlings were not fed for 24 h prior to their exposure to [14C]DSS nor were they fed during the uptake or elimination phase of the study. Thirty-six trout were split into two groups and exposed in glass covered 13L. seamless battery jars filled to 10L. An additional battery jar contained no fish and was used to assess any adsorption or volatilization of DSS. All jars were gently aerated via glass pipettes to assure a safe dissolved oxygen level. Temperature was maintained at 12°C during the study. The [14C]DSS solution was made up in one batch which was then divided to each of the battery jars. Triplicate 1 ml water samples were taken from each jar for scintillation counting after 0, 2, 4, 12, 24, 48 and 72h of exposure. The initial DSS concentration was 5.5 µg/L and there was no significant change in [14C]DSS concentration throughout the exposure phase of the study. A slight rise in concentration was observed in the jar containing no trout due to evaporation of the test water. Trout were sampled after 2, 4, 12, 24, 48 and 72 h of exposure and at the same times after transfer to DSS free fresh water. Tissues from three fish were sampled at each time point. The fish were rinsed in DSS free fresh water, blotted dry with paper toweling and weighed. The trout's pericardium was opened by making a dorsal cut posterior to the braincase with a scalpel. Ten microliters of blood was then collected in a graduated micropipet. Each pipet was placed in 15 ml of scintillation cocktail and broken to assure complete mixing. The peritoneal cavity of the trout was then opened and the gall bladder, with its contents, was removed and placed in a preweigbed scintillation vial containing 1 ml of tissue solubilizer. The viscera were then removed, weighed and placed in tissue solubilizer at a ratio of 1.0 ml per 0.1 g of tissue. The remaining carcass (head, skin, kidney, musculature and fins) was weighed and placed in tissue solubilizer at the same ratio as was the viscera. All of the tissue samples, except blood, were then placed in an oven at 60°C for 24 h. One milliliter aliquots of the cooled solubilized tissue samples were added to 15 ml of scintillation cocktail. Forty microliters of glacial acetic acid was added to each sample to reduce chemiluminescence. The prepared samples were placed in a refrigerator for 24 h and then counted at room temperature. The counts were corrected for quench and background and converted to nanograms of [14C]DSS. Temperature and the level of dissolved oxygen with each jar were measured every 24 h during the study. The pH of the [14C]DSS solution was measured at the onset of trout exposure and when the fish were removed for the depuration phase. The pH of DSS-free water was also measured at the time of transfer of the exposed trout. Total EDTA hardness and total alkalinity of the solution used for DSS exposure and the water used for the elimination phase were measured using the methods of APHA (1985). Unionized ammonia levels were measured in the battery jars, containing DSS, at the termination of exposure. Ammonia measurements were made following the methods of Bower and Holm-Hansen (1980) using the equilibrium equations of Emerson et al. (1979).

Vehicle:

no

Details on preparation of test solutions, spiked fish food or sediment:

see above

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

Rainbow trout (fingerlings, average weight 2.4 g/fish) were obtained from Silver Moon Springs Trout Farm (Elkhart, Wis.) and Wilderness Springs Trout Farm (New London, Wis.). The fish were held on a 12:12 photoperiod in flowing dechlorinated Milwaukee tap water at 12°C. During their acclimation to the laboratory conditions the trout were fed a commercially prepared pelleted food (Silvercup; Murry Elevators, Utah). The health of the fingerlings was well established during the laboratory acclimation period with no observed mortality or sickness.

Route of exposure:

aqueous

Justification for method:

aqueous exposure method used for following reason: no information provided

Test type:

static

Water / sediment media type:

natural water: freshwater

Total exposure / uptake duration:

72 h

Total depuration duration:

72 h

Hardness:

140 to 142 mg CaCO3/L

Test temperature:

12°C

Dissolved oxygen:

9.1 to 10.7 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass covered 13L. seamless battery jars filled to 10L
- Aeration: yes
- Renewal rate of test solution (frequency/flow rate): no renewwal, after 72 h the trout were placed in water without test item.
- No. of organisms per vessel: 18
- No. of vessels per concentration (replicates): 18
- No. of vessels per control / vehicle control (replicates): 1
- Biomass loading rate: not reported

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated Milwaukee tap water

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: 12:12

Nominal and measured concentrations:

control, 5.5 µg/L

Reference substance (positive control):

no

Details on estimation of bioconcentration:

Uptake
The uptake of [14C]DSS was measured in fingerling rainbow trout, averaging 2.40g in body weight, exposed to 5.5 µg/L DSS at 12°C. The trout were exposed under static conditions for 72 h. The concentration of [14C]DSS remained nearly constant throughout the exposure period and was found not to readily adsorb to glass nor volatilize. The uptake of DSS in rainbow trout is depicted in Fig. 1(a) and (b) (for figures see attached publication). DSS appearance in the bile proceeded rapidly, reaching a concentration of 638 ng/g, wet weight, after 2 h of exposure. Concentrations of [14C]DSS in trout bile did not reach steady state in 72 h and attained a concentration of 27,232 ng/g in that period. Uptake of the [14C]DSS in trout whole blood was rapid as well, with a peak concentration of 43 ng/ml at 4 h of exposure. After attaining 43 ng/ml the [14C]DSS concentration dropped in the blood to a steady state concentration of 19 ng/ml from 12 through 72 h of exposure. The uptake of [14C]DSS into the viscera and carcass of the trout were the same for the first 12 h of exposure, attaining 28 and 26 ng/g, respectively. After 12 h of exposure the [14C]DSS concentration within the trout carcass was at steady state, while uptake continued into the trout viscera with little change in the slope (rate) of uptake. The concentration of [14C]DSS within the trout viscera did not attain steady state by the end of 72 h of exposure and had reached 145 ng/g by that time. The bioconcentration factor (BCF) of DSS was calculated for the trout carcass and whole blood, as these compartments had reached steady state. The BCF is defined as the tissue concentration at steady state divided by the water concentration. BCFs could not be calculated for the trout viscera nor the bile as neither attained steady state by the end of the exposure phase. Uptake rate constants (Table 2) were calculated for all of the tissues sampled using the initial rate assumptions of Landrum and Giesy (1985).

Elimination
Elimination of DSS in rainbow trout is depicted in Fig. 2(a) and (b). The elimination of [14C]DSS from the bile of the trout was found to produce a nonsignificant log-linear regression [ct = 0.05, Fig. 2(b)]. Attempts to use curve stripping or feathering techniques (Landrum and Giesy, 1985; Spacie and Hamelink, 1985) proved not to be significant. The limination of [14C]DSS from the bile is then best described as following first order kinetics, which provides the best estimate of the depuration rate constant (K10 = 5.77 × 10-3/h). The [14C]DSS half-life of elimination from trout bile is calculated to equal 120 h.
The elimination of [14C]DSS from the blood was found to produce a highly significantly log-linear regression (ct = 0.01) and therefore prescribes the use of first order kinetics. The resultant depuration rate constant equals 3.71 × 10-2/h with an elimination half-life of 19 h.
The elimination of [14C]DSS from the carcass of the trout did not produce a significant log-linear regression (alpha = 0.05) and the variation attributed to deviations from the model was significant (alpha = 0.05). Examination of the data suggested a biphasic elimination which was then analyzed using curve stripping (Spacie and Hamelink, 1985) and by minimization of residuals (Sokal and Rohlf, 1981). The slow or terminal phase of elimination did not produce a significant regression yet the deviations from the regression model were not significant either (alpha = 0.05). To produce an estimate of the initial phase of elimination, the regression statistics for the terminal phase were used to remove the contribution of the second phase from the initial time points, as described by Spacie and Hamelink (1985). Log-linear regression analysis of the adjusted early time points was highly significant (alpha = 0.001). As there was no evidence that the biphasic elimination followed a particular second order kinetic model, the general model of Gibaldi and Perrier (1982) was used. The model illustrates the two phases of elimination with compartments where elimination of [14C]DSS is assumed to occur through the central compartment only (Gibaldi and Perrier, 1982). The peripheral compartment represents the second order of equations needed to approximate the elimination process. There are two elimination half-lives for the disappearance of DSS from trout carcass; that of the initial phase (t1/2 = 2 h) and that of the terminal phase (t1/2 = 172 h). The rate of flux from the central compartment into the peripheral compartment compartment (K12) equals 0.26 h. The rate of flux out of the peripheral compartment back into the central compartment (K21) equals 0.05/h. The central compartment depuration rate (K10) is calculated to equal 0.027/h. Elimination of [14C]DSS from the viscera of trout did not produce a significant log-linear regression (alpha=0.05) and as in the elimination from trout carcass produced significant deviations from the regression (ct = 0.05). Examination revealed a biphasic elimination pattern and a significant terminal or slow phase regression (alpha = 0.05). The regression, however, showed a positive slope representing uptake not elimination. The regression was statistically tested and found to have a slope significantly greater than zero ( alpha = 0.05). The initial phase of elimination was analyzed after removing the contribution from the terminal phase (Spacie and Hamelink, 1985) and found to not significantly deviate from the model (alpha = 0.05). The data were then fitted to the biphasic model of Gibaldi and Perrier (1982). The rate of flux from the central compartment into the peripheral compartment (K12) equals 0.67/h. The rate of flux out of the peripheral compartment back into the central compartment (K2~) equals 0.14/h. The rate constant for the elimination from the central compartment (K10), where it is assumed that the [14C]DSS elimination occurs, is equal to 0.035/h. The half-life for the initial phase of elimination is calculated to be 0.85 h. No half-life for the terminal phase of elimination could be calculated due to the positive slope. Table 3 summarizes the elimination rate constants.

Conc. / dose:

5.5 µg/L

Temp.:

12 °C

Type:

BCF

Value:

3.47 L/kg

Basis:

other: blood

Calculation basis:

kinetic

Conc. / dose:

5.5 µg/L

Temp.:

12 °C

Type:

BCF

Value:

3.78 L/kg

Basis:

other: Carcass

Calculation basis:

kinetic

Metabolites:

not determined in the BCF study. The BCF was based on total 14C activity.

Validity criteria fulfilled:

not specified

Executive summary:

Experimental fish BCF data are available for the closely related read-across analogue substance sodium docusate (CAS: 577-11-1) from a peer reviewed publication by Goodrich et al (1991). In this study, the bioconcentration and metabolism of ¹⁴C-radiolabelled sodium docusate was assessed in rainbow trout (Onchorynchus mykiss) and bioconcentration factor (BCF). The trout were exposed for 72h uptake followed by a 72h period for depuration with tissue sampling and analysis conducted at 2, 4, 12, 24, 48 and 72h during both phases. At the end of the study, sodium docusate was calculated to have bioconcentration factor values of 3.47 (blood) and 3.78 (carcass) in rainbow trout. Although this study was not conducted in accordance with current OECD 305 guidelines, it does indicate the bioaccumulation potential of the read-across substance is low and possibly even overestimated given the fact the use of radiolabelled test compound does not discriminate between parent and metabolites.

Sice the study period was shorter than requested by the guideline and no equilibrium was reached, the result is considered to be not fuly reliable.

Description of key information

BCF (42-day, carp, steady state, 4.1% lipid content): 9.33 L/kg

Key value for chemical safety assessment

BCF (aquatic species):

9.33 L/kg ww

Additional information

An experimental study (Arnot & Gobas 2006, 42 day exposure, steady state) resulted in a BCF of 9.33 L/kg in carp (4.1% lipid content). A further 72 -hour study (Goodrich et al. 1991) with rainbow trout resulted in a BCF of 3.78 L/kg in carcas. In addition to the experimental results, a QSAR using the BCFBAF (v3.01) module implemented in EPISuite 4.11 resulted in a BCF of 52.6 L/kg. Hence there was a good agreement between the experimental values and the QSAR.

For the risk assessment, a BCF of 9.33 L/kg will be used since this study is considered to be scientifically most relevant study. The use of the more conservative QSAR result would not have had a different outcome for e.g. the PBT assessment.