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The category consists of alkyl sulfates with a predominantly linear alkyl chain length of C8-C18. Most chemicals of this category are not defined substances, but mixtures of homologues with different alkyl chain lengths (UVCBs). The most important common structural feature of the category members is the presence of a predominantly linear aliphatic hydrocarbon chain with a polar sulfate group, neutralized with a counter ion (i.e., Na+, K+, NH4+, or an alkanolamine cation). The hydrophobic hydrocarbon chain (with a length between C8 and C18) and the polar sulfate group confer surfactant properties and enable the commercial use of these substances as anionic surfactants. Common physical and biological pathways result in structurally similar breakdown products, and are, together with the surfactant properties, responsible for similar environmental behavior and essentially identical hazard profiles with regard to human health. The counter ion will not influence chemical reactivity and classification for the purpose of this assessment is not expected to be affected by the difference in counter ion (ref. OECD SIDS 2007, HERA Report 2002, Koennecker et al. 2011).

In aqueous environments the salts will dissociate, so that the counter ions will not fundamentally alter pathways of tissue disposition, metabolism, excretion, or target organs of toxicity. Accordingly no major differences were found in most of the endpoints between the compounds with different counter ions (ref. OECD SIDS 2007, HERA Report 2002, Koennecker et al. 2011). Moreover, several of the counter-ions have also been assessed in the OECD HPV Program and/or according to REACH Regulation (EC) No 1907/2006: triethanolamine (CAS 102-71-6), the ammonia category (CAS 7664-41-7; 1336-21-6; 7783-18-8; 12593-60-1) and ammonium salts, like ammonium sulfate (CAS 7783-20-2), chloride (CAS 12125-02-9) and bicarbonate (CAS 1066-33-7).

In accordance with Article 13 (1) of Regulation (EC) No 1907/2006, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met. In particular for environmental fate and eco-toxicity, information shall be generated whenever possible including the use of information from structurally related substances. In this particular case the similarity of the alkyl sulfates category members is justified, in accordance with the specifications listed in Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances and read-across, is based on the scope of overlapping of composition, similar molecular structure, physico-chemical properties, toxicological, ecotoxicological profiles and supported by various QSAR methods.

 

Physico-chemical properties relevant for environmental toxicity of alkyl sulfates:

Physico-chemical characteristics of the substances in the category are similar, or follow regular patterns. The most important parameter influencing PC-properties is the varying length of the alkyl chain.

- Vapour pressure - as ionic substances, category members are characterized by low vapour pressures.

- Partition coefficient - as surfactants concentrate at hydrophilic/hydrophobic boundaries and do not equilibrate between phases, Pow is not a good descriptor of surfactant hydrophobicity and only of a limited predictive value for the partitioning of these compounds in the environment. Nevertheless, experimental Pow values have been obtained, usually as quotients of solubilities in octanol and in water. Partition coefficients are low (mostly negative values of log Pow) and they increase with the alkyl chain range.

- Water solubility - the solubility in water of the category members is high, in the range of 100-1000 g/L. Particular values decrease with the alkyl chain range.

 

Environmental fate and pathways of alkyl sulfates:

- The substances are readily biodegradable. Abiotic degradation (e.g. hydrolysis) is not a relevant for environmental pathway due to the chemical structure of the substances.

- All the substances in this category are essentially non-volatile, which implies that atmospheric photodegradation is irrelevant.

- As the log Pow-value is below 3, a potential for bioaccumulation can be excluded.

- Due to the low to moderate log Koc-value, it can be predicted that the sorption to sludge, sediments and soils will be relatively low. Alkyl sulfates are unlikely to persist in the aquatic environment.

 

Terrestrial toxicity of alkyl sulfates:

The substance exhibits an adsorption coefficient (log Koc) below 5 and is readily biodegradable. Moreover, the substance is not acutely toxic in the aquatic compartment (EC/LC50 for fish, Daphnia and algae above 1 mg/L). In case of exposure to soil, the substance is expected to rapidly degrade, thus the hazard to terrestrial organisms is negligible. Hence, the Equilibrium Partitioning Method is sufficient to calculate the PNECs values for the terrestrial compartment according to the “Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance”, Section 7.11.6 Integrated Testing Strategy for Effects on Terrestrial Organisms (ECHA 2008).