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The alkyl ether sulfates grouped within the AES category show similar structural, physico-chemical, environmental and toxicological properties. The approach of grouping different AES for the evaluation of their effects on human health and the environment was also made by the Danish EPA (2001) and HERA (2008), supporting the read across approach between structurally related AES. The aquatic toxicity of the alkyl ether sulfates has been evaluated in studies on fish, invertebrates and algae as well as microorganisms. In most of the given studies AES were tested as sodium salts. As the kation counterpart of the AES anions is not expected to influence the ecotoxicological profile of the substance, read-across is possible between all comparable mixtures independent from the kation.

For AES (C12-14, 1-2.5EO) Na (CAS 68891-38-3) short-term studies on freshwater species of three trophic levels (fish, invertebrates and algae) are available. For fish one long-term study is available for C12-14 alcohol ethoxysulfates (CAS 68891-38-3) resulting in a NOEC-value of 0.14 mg/L (TEGEWA, 1995). The results of that key study are supported by investigations with the pure AES homologue (C14, 2EO) Na and with the similar alcohol ethoxysulfate mixture (C14-16, 2EO) Na. In the supporting studies NOEC-values of 0.18 mg/L and 1 mg/L were reported (P&G, 2004 and P&G, 1979a/b). For daphnids one chronic study is available for the mixture alcohol C12 -14 ethoxysulfates (2.25 EO) resulting in a NOEC-value of 0.27 mg/L (P&G, 1977a). The result of that key study is further supported by data available for other alcohol ethoxysulfates. In the supporting studies NOEC-values of 0.18 mg/L and 0.730 mg/L were reported for a C14 -C15 AES with 2.25 EO (P&G, 1987 and P&G, 1997). A chronic algae endpoint is reported in (Sasol, 1993c). In this study a NOEC-value of 0.95 mg a.s./L for growth rate is given.

For the environmental risk assessment further data were taken into account as different AES-homologues are expected to differ in their toxicity. That means in theory that a PNEC could be derived for each AES and the resulting quotients summed to determine the risk of an alcohol ethoxysulfate mixture as a toxic unit approach. Choosing an average structure approach, a toxic unit approach or some combination (for example consideration of individual carbon chain lengths but with average EO-concentration) requires consideration of toxicity QSAR (HERA, 2008).

Such a QSAR is developed by Dyer et al. (2000) on the basis of chronic data available from 7 -days toxicity tests conducted with Ceriodaphnia dubia. In that experiments daphnids were exposed to twelve different alcohol ethoxysulfates at different concentrations. In addition a mixture study with four AES structures was conducted to determine if the components were additive in toxicity.

The chronic QSAR estimates a parabolic relationship between carbon number and toxicity increasing from C12 to C15 and then decreasing. The QSAR is based on an extrapolation for carbon chain lengths longer than C15.

The QSAR developed by Dyer et al. (2000) is used to determine a NOEC-value for alcohol C12 -14 ethoxysulfates. Therefore mean-values of the amounts of C12 and C14 were used in the model considering different degrees of ethoxylation (in case of C12: 20% EO1 and 50% EO2 and in case of C14: 7% EO1 and 18%EO2). In addition, as a worst-case assumption C15 EO1 and EO2 were used for NOEC calculation at amounts of 10% EO1 and 15% EO2. The resulting NOEC-value could thus be predicted to be 1.211 mg/L. This value is used with an assessment factor of 5 for the PNEC-calculation.

 

References:

Danish EPA (2001): Environmental and Health Assessment of Substances in Household Detergents and Cosmetic Detergent Products. Environmental Project No. 615, pp. 24-28

Dyer, S. D., Stanton, D. T., Lauth, J. R. and Cherry, D. S. (2000): Structure-activity relationship for acute and chronic toxicity of alcohol ether sulfates. Environmental Toxicology and Chemistry, Vol. 19, No. 2, pp. 608 -616, 2000

HERA - Human & Environmental Risk Assessment on ingredients of European household cleaning products (2008). Alcohol Ethoxysulphates (AES).