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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 ecotoxicity, 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.

 

Aquatic toxicity of alkyl sulfates:

For the alkyl sulfate category many mono-species tests are available on the acute, sub-chronic and long-term toxicity to fish, invertebrates, and algae, conducted with single-chain homologues as well as with technical mixtures.The available data for the different category members as well as for dodecyl sulfate demonstrate that invertebrates are the most sensitive trophic level, followed by fish and algae. The most important influencing parameter for fish and invertebrate toxicity within the alkyl sulfates category is the chain length of the alkyl group.

Short-term toxicity to fish is well studied for the category of alkyl sulfates and includes the tests with substances ranging from C8 to C18 covering a variety of both freshwater and marine species. Alkyl sulfates of chain lengths from C8 to C12 seem to have low to moderate toxicity. Homologues from C13 to C15 are more toxic than C8 to C12. Toxicity of the chain lengths from C16 and higher is inconsistent, but in general these substances are less toxic than C13 to C15. This most probably can be explained by variable bioavailability as a consequence of reduced water solubility.

The influence of the chain length of alkyl sulfates on the acute toxicity fish is comparable to invertebrate toxicity (OECD SIDS, 2007). Also in this case a clear correlation can be shown since the available database includes the studies for the alkyl sulfates ranging from C8 to C18. Short-term toxicity to aquatic invertebrates increases with increasing length of the hydrocarbon chain up to C16 and then decreases.

Available long-term tests on fish with alkyl sulfates show that the toxicity depends again on the substance chain length. The same pattern as in the acute tests was observed - homologues C12 and C18 are less toxic than the chain lengths C14-C15 (OECD SIDS, 2007).

Available information on the long-term toxic effects of alkyl sulfates to Ceriodaphnia dubia includes the substances with a carbon chain length from C10 to C18. A clear response curve was observed - toxicity increase with chain length from C12 to C14 and then decreased up to C18. Since C18-AS is insoluble in calcium-containing water (i.e., Ceriodaphnia test waters), the effects are due to physical interactions, not the classic uptake into the organism and then elicit toxicity. Chronic toxicity testing with Daphnia magna using the technical product C14 -15 proved that these are the most toxic chain lengths for aquatic invertebrates (OECD SIDS, 2007).

Several reliable experimental studies with algae are available for alkyl sulfates. It seems that algae react less sensitive to alkyl sulfate exposure than fish and invertebrates. The results do not allow the clear prediction of a chain length dependency of algal toxicity because most of the studies were conducted with technical products. Nevertheless, it seems that the most toxic chain lengths are C10 and also C14 - C15 (OECD SIDS, 2007).

Activated sludge respiration inhibition tests and Pseudomonas putida tests are available for the alkyl sulfates of chain lengths from C12 to C18. In Pseudomonas putida testing a tendency of increasing toxic effects with increasing carbon chain length could be observed (OECD SIDS, 2007).

 

Acute toxicity key values for Sodium dodecyl sulfate (CAS 151-21-3):

Fish

96h-LC50 = 29 mg/L (measured concentration, freshwater) for Pimephales promelas (OECD 203)

96h-LC50 = 4.1 mg/L (measured concentration, marine water) for Cyprinodon variegatus (ASTM E-35 1980)

 

Invertebrates

48h-EC50 = 5.55 mg/L (freshwater) for Ceriodaphnia dubia (similar to OECD 202)

48h-LC50 = 3.15 mg/L (nominal concentration, marine water) for Artemia salina (acute toxicity test)

 

Algae

72h-EC50 > 120 mg/L (nominal concentration) for growth rate of Desmodesmus subspicatus (DIN 38412, part 9)

 

Chronic toxicity key values for Sodium dodecyl sulfate (CAS 151-21-3):

Fish

42d-NOEC ≥ 1.357 mg/L (measured concentration) for juvenile mortality and growth of Pimephales promelas

 

Invertebrates

7d-NOEC = 0.88 mg/L (measured concentration) for reproduction of Ceriodaphnia dubia, (EPA-600/489/001)

 

Algae

72h-EC10 = 30 mg/L (nominal concentration) for yield of Desmodesmus subspicatus (DIN 38412, part 9)

 

Microorganism

3h-EC50 = 135 mg/L (nominal concentration) for respiration inhibition of non-adapted domestic activated sludge (similar to OECD 209)

 

Since aquatic invertebrates showed to be the most sensitive trophic group the chronic effect value obtained in a 7d chronic toxicity test with Ceriodaphnia dubia was used for derivation of the PNEC values of the substance (for more details about the PNEC derivation see CSR chapter 7.2 or the justification document for using an assessment factor of 5/50 for derivation of PNEC freshwater/marine water attached in IUCLID chapter 13).