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Reference
Endpoint:
basic toxicokinetics in vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See attached Read-across justification
Reason / purpose:
read-across source
Type:
absorption
Results:
at least 65%
Type:
metabolism
Results:
extensive (e.g. 2-ethylhexanol)
Type:
excretion
Results:
in the urine (within 24h) and feces
Details on absorption:
Table 1 shows the results of the analysis of the urine from these animals using the 2-ethylhexanol distillation procedure. Since the percent of dose excreted in the urine after intravenous dosage was comparable to the excretion after oral dosage, it is concluded that the orally administered compound is well absorbed by the rat. Since 2-ethylhexanol derivatives recovered in the urine after administration of the alcohol are appreciably lower than those recovered after DSS administration, it is concluded that the mechanism of absorption of DSS does not include prior hydrolysis of the ester groups in the gastrointestinal tract. This is further substantiated by the finding that the 2-ethylhexanol forming compound in urine after administration with DSS is largely not the free alcohol or its glucuronide conjugate.
Details on excretion:
The male animal given radioactive compound showed that the urine excreted during the first 24 hours accounted for 64.1% of the radioactivity; the feces for 37.4%. The animal was further found to eliminate 1.0% of the dose in the 24-48h urine and 0.9% of the dose in the 24-48h feces.
Metabolites identified:
yes

Table 1. 24 hour excretion of 2-ethylhexanol-forming compounds by the rat after oral dosage with DSS and 2-ethylhexanol

Rat No.

Compound

Dose (mg)

Route

% of dose excreted

Urine

Faeces

1

DSS

5

oral

18.6

0.9

3

DSS

10

oral

15.5

8.7

4

DSS

10

I.V.

12.3

-

5

DSS

10

I.V.

15.5

-

2

2-ethyl-hexanol

5.8

oral

3.1

3.9

-: not determined

Conclusions:
Interpretation of results: no bioaccumulation potential based on study results of read-across substance DSS.
The read-across compound was well absorbed, metabolised and excreted after oral administration (two thirds were oberved in the 24 hours urine; one third was found in the feces).
Executive summary:

The absorption, excretion and metabolism of read-across substance dioctyl sodium succinate (DSS) have been investigated. Unlabeled DSS and radiolabeled compound (carbon-14) were used. Using a gas chromatographic procedure, a similarity in percent excretion of dose into urine was observed in rats dosed orally and intravenously, indicating a high degree of absorption of the oral dose. Confirmation of extensive absorption of DSS was obtained through oral dosage of 10 mg/kg carbon-14 labeled compound. Two thirds of the administered radioactivity was found in the urine at 24 hours after dosage. All of the activity was in the form of metabolites (2-ethylhexanol forming compounds).

.

Description of key information

The toxicokinetics of registered product was assessed based on the physicochemical parameters
and information from toxicokinetic literature from structural analogue substances.
In summary, the substance is anticipated to be orally absorbed to a high extent, whereas inhalation

or dermal uptake is very unlikely. The substance may be distributed within the organism, but
accumulation is unlikely. Major suggested metabolites are 2-ethylhexanol derivatives, water, CO2
and sulfur. The major path of excretion seems to be via kidney, although some excretion via the
bile is also possible. This was confirmed by experimental study of read-across substance Docusate
sodium (CAS 577-11-7), demonstrating rapid and extensive metabolism and excretion in the urine in
the form of metabolites. As more than 90% of the radioactivity was detected in the urine both after oral
and intravenous application, oral absorption was considered to be relevant and therefore also the
most relevant route of testing. Literature data for other anionic surfactants (e.g. alkyl sulfates, alkane
sulfonates and α-olefin sulfonates) demonstrated a similar toxicological and toxicokinetic/metabolic
profile as for the sullfosuccinate esters/amides. For these surfactants high oral absorption rates (90%)
and low dermal absorption rates (<1%) were observed. For risk characterisation of the registered
substance, conservative absorption rates of 90, 10 and 10% were taken into account for oral,
dermal and inhalation routes, respectively.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
90
Absorption rate - dermal (%):
10
Absorption rate - inhalation (%):
10

Additional information

The absorption, distribution, metabolism and excretion of registred product is assessed on three levels:

1) Based on the physicochemical properties of the compound itself

2) Read-across to Docusate sodium (CAS 577 -11 -7)

3) Literature review of other anionic surfactants

 

Part 1: physicochemical properties

Absorption was assessed as follows based on physicochemical/toxicological data following ECHA guidance 7c (ECHA Guidance on information requirements and chemical safety assessment. Chapter R.7c: Endpoint specific guidance, November 2012 Version 1.1). The substance is a solid material with molecular weight of 584.83 g/mol and water solubility > 170 g/L. The log Pow is around 0.47 and the mean particle size is 30000-40000 µm. The vapour pressure is 0.0048 Pa. The structure of the substance shows ionisable groups, the surface tension of a watery solution is 25.2 mN/m. The substance is not readily biodegradable, but strongly binding and hence removed from the environment.

-Oral/GI absorption:

Based upon the molecular weight above 500g/mol, the ionisable and hydrophilic properties, oral absorption might be considered to be limited, however the good solubility in GI fluids and a logPow between -1 and 4 are factors in favor of oral absorption. Furthermore the observed toxicity in acute oral toxicity studies indicated a systemic availability of the substance underlining an oral absorption. Nevertheless the extent of absorption stays unclear.

-Respiratory absorption:

The respiratory absorption is limited by the amount of inhalable substance and the fraction reaching the lower respiratory system. Due to the large particle size and low vapour pressure (0.0048 Pa) inhalation and/or deposition of significant amount of the substance seems unlikely. Additionally the high hydrophilic properties of the substance may retain the substance in the upper mucosa. As a result the respiratory uptake and absorption is assumed to be very limited.

-Dermal absorption:

Due to the molecular weight of above 500, the high water solubility (>100 mg/mL) dermal absorption is not expected to be a favorable route. However the LogPow between -1 and 4 makes it possible for the substance to cross the lipophilic areas of the stratum corneum. The surface tension is above 10mN/m pointing to no enhanced absorption, however due to the low vapor pressure a dermally attached substance may stay on the skin for a longtime. No skin irritations were observed for structural analog substances or with in vitro tests performed with the target substance. Therefore a limited dermal absorption is expected from this information. Also QSAR information (Dermwin) shows a very slow dermal absorption. The dermal penetration coefficient Kp was calculated to be 1.68.10-6 cm/h. In summary, the dermal absorption is assumed to be very limited due to the high hydrophilicity and based on the irritation test information received.

 

For the assessment of distribution, metabolism and excretion physicochemical and toxicological properties are taken into account according to ECHA guidance 7c (ECHA Guidance on information requirements and chemical safety assessment. Chapter R.7c: Endpoint specific guidance, November 2012 Version 1.1).

-Metabolism:

Hydrolysis will take place at the ester site of the substance causing it to split in a polar and apolar part. Eventually, it is expected that these parts will break down to water, CO2 and sulfur.

-Distribution:

Based on the molecular size of above 500g/mol and the high hydrophilicity a less wide distribution is expected but cannot be excluded. Nevertheless the LogPow is very close to 0 which indicates that a distribution into cells is less likely. However from the clinical signs observed after oral acute toxicity testing, distribution in the body is expected to take place. 

-Accumulation:

Based on the hydrophilicity and the large diameter of the substance, the substance is not expected to accumulate in the lung. Based on the low log Pow the accumulation in adipose tissues is also unlikely as well as accumulation in the stratum corneum. As the substance is no metal, accumulation in bones is also not expected. Taken together there is no direct indication of bioaccumulation potential.

-Excretion:

Derived from the high hydrophilicity and low logPow excretion in the urine is expected to be the favourable route. Nevertheless also excretion via bile is expected to occur after oral absorption but in less amounts than via urine. As the substance has a low vapour pressure, exhalation is not expected. Nevertheless the cleavage products of the substance may be included in the energy cycle and exhalation as CO2 may be possible.

 

Part 2: Read-across to Docusate sodium

No test data were available for current substance, however read across data were available from Docusate sodium. Justification for read across with the category of Di-ester sulphosuccinates is documented in a separate document attached in Section 13.

-The absorption, excretion and metabolism of read across substance Docusate sodium have been investigated in rats, rabbits, dogs and man (Kelly, 1973). Radiolabelled compound carbon-14 was used in animal studies and unlabelled Docusate sodium in certain studies in rats, dogs and man. Both studies show a good absorption of the compound. From the studies with unlabelled Docusate sodium in the rat, the percent excretion of metabolites (2-ethylhexanol derivatives) seem to be similar after oral and intravenous administration demonstrating the good oral absorption of the compound. Confirmation of extensive absorption was obtained through oral dosage of 10 mg/kg carbon-14 labelled compound.

A comparison of an intravenous and an oral dose of 4 mg/kg of radiolabeled Docusate sodium in the rabbit also indicated a high degree of absorption following oral dosage in this species. Each route of administration resulted in the excretion of over 90% of the radioactivity in the urine after 48 hours. After 24 hours 89.4% and 72.8% are found after intravenous and oral administration respectively. As in the case of the rat, extensive metabolism was observed in the rabbit. A comparison of an oral and an intravenous dose of 4 mg/kg carbon-14 Docusate sodium in the dog yielded remarkably similar excretion patterns and metabolic profiles. However compared to the rat and rabbit, excretion via feces is higher than via urine. After 96 hours around 25% is excreted in the urine (20% after 24 hours), while around 71% is excreted in the feces (65-70% after 48 hours). Countercurrent distribution curves on the urine of these animals were almost identical.

-In man, peak concentrations of Docusate sodium in serum occurred at 2 hours after dosage with 200 mg. These values, in two men, were 7.9 and 5.5 µg/mL, similar in magnitude to the plasma concentration seen at 1 hour in the orally dosed dog (7.4 µg/mL) which received 4 mg/kg. The analysis of human serum was done by gas chromatography and that of dog plasma by the radiometric method. The excretion of 2-ethylhexanol derivatives in the urine of man accounted for only a very small amount of the administered dose of Docusate sodium, a finding similar to that seen in the urine of the dog. An attempt to compare the urine of man and the dog by analysis of 2-ethylhexanol forming compounds in countercurrent distribution fractions did not yield fruitful results. The metabolites found in dog urine are assumed to be incompletely hydrolysed ester derivatives of docusate sodium.

Reference:

-Kelly R. G. (1973). The pharmacokinetics and metabolism of dioctyl sodium sulfosuccinate in several animal species and man. Testing laboratory: American Cyanamid. Report no.: 07066. Owner company: Cytec. Study number: 7235-03. Report date: 1973-04-10.

 

Part 3: literature review of anionic surfactants (alkyl sulfates, alkane sulfonates and α-olefin sulfonates)

Anionic surfactants, including alkyl sulfates and alkane sulfonates and α-olefin sulfonates, have been assessed under the HPV program. These chemicals were shown to have low acute and repeated dose toxicity, no evidence of genetic or reproductive toxicity or carcinogenicity. The toxicological profile was similar to the sulfosuccinate esters/amides, and the absorption rate was high in both situations (90% absorption was demonstrated for a sulfosuccinate ester). Therefore, the toxicokinetic profile of the anionic surfactants can also be used for the sulfosuccinate esters and amides, with special emphasis on the low dermal absorption rate (<1%) and the common metabolic breakdown after oral absorption. The common physiological pathways result in structurally similar breakdown products ((butyric-, propionic-and pentanoic acid-5-sulfate fragments) for the various chain lengths, leading to fairly rapid excretion and low hazard for human health.

 

For risk characterisation, conservative absorption rates of 90, 2 and 10% were taken into account for oral, dermal and inhalation routes, respectively. See also Section 7.0: attached Justification for DNEL calculation & Annexes for support of absorption rates.

 

References:

-Wibbertmann et al., Ecotoxicolog   y and Environmental Safety 74 (2011) 1089-1106, Toxicological properties and risk assessment of the anionic surfactants category: alkyl sulfates, primary alkane sulfonates andα-olefin sulfonates.

-SIDS Initial Assessment Report for SIAM 25, Category of Alkyl sulfates, Alkane sulfonates andα-Olefin sulfonates, 2007

-Howes, D., J. Soc. Cosmet. Chem. 26 (1975) 47-63, The percutaneous absorption of some anionic surfactants.