Sodium octane-1-sulphonate monohydrate

Endpoint summary

Description of key information

There are no in vivo data for acute toxicity on Sodium octane-1-sulphonate, this is because the test item is corrosive to the skin category 1B according to the CLP regulation. This is a conservative approach taken since cell viability of 87.9% and 4.2% was observed following exposure to the test item at up to 3 minutes and 60 minutes respectively. The test item also caused severe eye damage i.e. Category 1, according to the CLP regulation. Thus in vivo acute and local toxicity study is not required under Regulation (EC) 1907/2006, Annex VIII, Part 8.3/8.5, Column 2.  

There are no long-term toxicity studies on the test item directly, however, read across was used to assess the potential for subacute/chronic exposure via oral route in rats (OECD 408 & 414).  In the OECD 408 study, no mortality was reported and no effect on body weight, food consumptions, or overt clinical signs were observed. Increases in absolute organ weights were confined to the highest test group (5000 ppm) however only the increased liver weights from the females were found to be statistically significant (p ≤ 0.05). The increase in organ weights at the highest tested concentration (5000 ppm) was unaccompanied by any pathological effects, as a result, 5000 ppm (430 mg/kg bw/day) is considered a no-observed effect level (NOAEL) for the test item. In the OECD 414 study, mortality was observed in the highest dose group, maternal toxicity was also observed in the form of disturbance of the gastrointestinal tract, resulting in diarrhoea, anorexia, weight loss and cachexia prior to death. Furthermore, there was an increase in foetal loss and reduced litter size, due almost entirely to total litter losses, these factors were deemed to be a secondary consequence of the maternal reaction to the test item. NOAEL that could be determined for maternal toxicity was 300 mg/kg bw/day and > 600 mg/kg bw/day for developmental toxicity.

Absorption

The physicochemical properties of the test item i.e., a dry solid with n-octanol/water partition coefficient of <0.0, melting point of >300°C, critical micelle concentration of 9.836 g/l and surface tension of 44.93 mN/m are suggestive of favourable absorption via oral route. Although the corrosive nature of the test item and its physicochemical properties make uptake from the dermal route possible, the surface tension of 44.93 mN/m may restrict transfer between the stratum corneum and the epidermis and therefore overall systemic bioavailability via this route would be significantly reduced. Based on the vapour pressure and the melting point of the substance, uptake via inhalation route is likely to be insignificant based on physical chemical properties alone.

Distribution

Given the surface active nature of the substance, penetration will be enhanced and subsequent uptake of the test item into the circulatory system is likely. As an anionic surfactant, the test item is readily absorbed from the gastrointestinal tract and widely distributed. Dermal distribution is mainly confined to the skin, specifically in the dermis as the test item could simply form more micelles which could not readily penetrate further due their supra-molecular large size, this is implicated by the local toxicity of the test item.

Metabolism

Anionic surfactants are extensively metabolized mainly through the liver via phase I and II enzymes as demonstrated by increased liver weight and enzyme activities such as serum alkaline phosphatase (ALP) in both sexes following repeated exposure to the substance. Desulfonation via hydrolysis of the n-alkyl sulfate by enzymes such as sulfatases resulting in acidic derivatives, ω-oxidation of the hydrophobic part followed by β-oxidation is also possible resulting in carboxylic acid, sulfate ester derivatives as well as sulphite.

Excretion

The presumed metabolites of the test item are expected to be more polar than the parent compound and therefore suggestive of elimination via urine which is supported by the hydronephrosis observed in the kidney of exposed animal in the repeated dose toxicity studies. Based on the effect observed in the stomach of exposed animals, some percentage of the test item may be excreted in faeces as parent compound. Based on the low toxicity and no major changes in biochemical blood parameters, it is expected that elimination is rapid with low potential for bioaccumulation in tissues.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

1

Absorption rate - inhalation (%):

100

Additional information

The Anionic Surfactants Category

The anionic surfactants (ANS) category includes three structurally related classes of substances: Alkyl sulfates, which are sulfate salts consisting of a predominantly linear alkyl chain bearing a terminal sulfate ester anion, neutralised with a base (single chain length or a defined chain length distribution); primary alkane sulfonates, the salt of a linear saturated alkyl chain, bearing a terminal sulfonate anion, neutralized with sodium hydroxide; and alpha-olefin sulfonates, a mixture of sodium alkene sulfonate and hydroxyl alkane sulfonate salts, with the sulfonate group in the terminal position and the double bond, or hydroxyl group, located at various positions along a linear aliphatic chain in the vicinity of the sulfonate group.

The most important common structural feature of the category member is the presence of a predominantly linear aliphatic hydrocarbon chain with a polar sulfate or sulfonate group, neutralized with a counter ion. The hydrophobic hydrocarbon chain and the polar sulfate or sulfonate groups confer surfactant properties and enable the commercial use of these substances as anionic surfactants. Common physical and/or biological pathways result in structurally similar breakdown products and are, together with the surfactant properties, responsible for the essentially identical hazard profiles with regard to human health.

The toxicological properties of the ANS category were assessed under the high production volume (HPV) chemicals program of the Organisation for Economic Cooperation and Development (OECD) in 2007 at the OECD SIDS Initial Assessment Meeting (SIAM) 25 using a category approach (a grouped approach, in which data for individual members are presented and discussed together as part of a category, rather than substance-by-substance). In total, 61 anionic surfactants were assessed: 46 alkyl sulfates, 6 primary alkane sulfonates (including 1-Octanesulfonic acid, sodium salt), and 9 alpha-olefin sulfonates. For the ANS category members, a comprehensive data set was collected from many sources, which is fully described in the peer-reviewed Screening Information Dataset (SIDS) documentation and discussed in the SIDS Initial Assessment Report (SIAR) [OECD, 2007]. For those members of the category where reliable data were not available for all obligatory endpoints required according to the Manual for Investigation of HPV Chemicals, read across of toxicological data from closely related chemicals of the category was applied to address their properties.

Toxicokinetics, metabolism and distribution

There are several studies available for members of the ANS category.

The data for experimental animals as well as studies with human volunteers demonstrate that the alkyl sulfates, alkane sulfonates and alpha-olefin sulfonates are well absorbed after oral uptake, as up to 98% of the applied doses were excreted rapidly via urine [Denner et al. (1969); Burke et al. (1975, 1976); Merits (1975); Taylor et al. (1978); Black & Howes (1980); Inoue et al. (1982) ]. Hence, oral absorption is assumed to be 100%.

On the other hand, the penetration through intact skin with < 1% of the applied doses is poor [Howes (1975); Prottey & Ferguson (1975); Minegishi et al. (1977); Black & Howes (1980) ]. Based on the experimental data, a default assumption of 1% dermal absorption was taken for deriving the DNEL. Since dermal absorption decreases with increasing concentration of a solution, this percentage can also be used for workers as a worst case approach.

After absorption, these chemicals are distributed mainly to the liver (Denner et al. (1969); Burke et al. (1975, 1976); Merits (1975); Taylor et al. (1978); Inoue et al. (1982) ] and the alkyl sulfates, alkane sulfonates and most probably also alpha-olefin sulfonates are metabolized by cytochrome P450-dependent omega-oxidation and subsequent beta-oxidation of the aliphatic fatty acids. End products of the oxidation are a C4 sulfate or sulfonate (even numbered chain lengths) and a C3 or C5 sulfate or sulfonate (odd numbered chain lengths). For the alkyl sulfates, sulfate is also formed as a metabolite (Denner et al. (1969); Ottery et al. (1970); Burke et al. (1975, 1976); Merits (1975); Taylor et al. (1978); Greb & Wingen (1980); Black & Howes (1980); Inoue et al. (1982) ]. Several reasons for a lack of concern regarding bioaccumulation exist including rapid excretion of metabolites via urine, limited dermal absorption (main route of consumer exposure) and the low concentration of substances in consumer products.

It is considered relevant to adopt the absorption rates defined for the ANS (of which the read-across source substance is a member) to the substance being registered, i.e. oral absorption rate = 100 %, dermal absorption rate = 1 %, inhalation absorption rate = 100 %.

References

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Burke B, Olavesen AH, Curtis CG, Powell GM (1975) The biodegradation of some anionic detergents in the rat. A common metabolic pathway. Xenobiotica 5, 573–584.

Burke B, Olavesen AH, Curtis CG, Powell GM (1976) The biodegradation of the surfactant undecyl sulphate. Xenobiotica 6, 667–678.

Denner WHB, Olavesen AH, Powell GM, Dodgson KS (1969) The metabolism of potassium dodecyl [35-S]sulphate in the rat. Biochem. J. 111, 43–51.

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

Inoue S, O’Grodnick JS, Tomizawa S (1982) Metabolism of alpha-olefin sulfonate (AOS) in rats. Fundam. Appl. Toxicol. 2, 130–138.

Merits I (1975) The metabolism of labelled hexadecyl sulphate salts in the rat, dog and human. Biochem. J. 148, 219–225.

Minegishi K-I, Osawa M, Yamaha T (1977) Percutaneous absorption of alpha-olefin sulfonate (AOS) in rats. Chem. Pharm. Bull. (Tokyo) 25, 821–825.

OECD (2007) Category of Alkyl sulfates, Alkane sulfonates and a-Olefin sulfonates. SIDS Initial Assessment Report for SIAM 25, Organization for Economic Cooperation and Development, Paris. OECD Integrated HPV database online at /http: //cs3-hq. oecd. org/scripts/hpvS.

Prottey C, Ferguson TF (1975) Factors which determine the skin irritation potential of soaps and detergents. J. Soc. Cosmet. Chem. 26, 29–46.

Taylor AJ, Olavesen AH, Black JG, Howes D (1978) The metabolism of the surfactants dodecyl sulfonate and hexadecyl sulfonate in the rat. Toxicol. Appl. Pharmacol. 45, 105–117.

Wibbertmann A, Mangelsdorf I, Gamon K, Sedlak R (2011) Toxicological properties and risk assessment of the anionic surfactants category: Alkyl sulfates, primary alkane sulfonates, and alpha-olefin sulfonates, Ecotoxicology and Environmental Safety, 74, 1089–1106.