Sodium ethanolate

Endpoint summary

Additional information

The toxicity of sodium ethanolate to aquatic organisms is mediated by its degradation products due to the rapid reaction with water yielding sodium hydroxide and ethanol. The aquatic toxicity of ethanol is low with acute EC50 or LC50 values clearly exceeding 100 mg/L and therefore its contribution to the ethanolate toxicity is considered negligible. For sodium hydroxide no data are available since the substance completely dissociates in water and effects are related to a shift in pH values only.

The limited data available for sodium ethanolate are consistent with the aquatic toxicity of the alkali hydroxides. For ethanol the acute toxicity to fish (96-h LC50) for Pimephales promelas exceeded 10000 mg/L. The acute toxicity of ethanol to aquatic invertebrates was tested in a guideline study according to ASTM E729 -80. The LC50 value (based on nominal concentrations) was determined to be 5012 mg/L. In another study a NOEC (10d) of 9.6 mg/L was determined for the reproduction of Daphnia magna. The EC50 (4d) of ethanol to Chlorella vulgaris was deter­mined to be 1000 mg/L (nominal value).

Aquatic PNECs

However, as concluded for sodium hydroxide and as read across sodium hydroxide, acute toxicity data cannot be used to derive a PNEC or a PNECadded for the compounds releasing hydroxide on the basis of the hydroxide component. Aquatic ecosystems are characterized by an alkalinity/pH and the organisms of the ecosystems are adapted to these specific natural conditions. Based on the natural alkalinity of waters, organisms will have different optimum pH conditions, ranging from poorly buffered waters with a pH of 6 or less to very hard waters with pH values up to 9. A lot of information is available on the relationship between pH and ecosystem structure and also natural variations in the pH of aquatic ecosystems have been quantified and reported extensively in ecological publications and handbooks. 

Usually a PNEC or a PNECadded has to be derived from available ecotoxicity data. A PNECadded is a PNEC which is based on the added concentrations of a chemical (added risk approach). Based on the available data it is not considered useful to derive a PNEC or PNECadded for the sodium ethanolate as their effect is based on hydroxide ions or a pH change, because:

-The natural pH of aquatic ecosystems can vary significantly.

-The sensitivity of aquatic ecosystems to a change of the pH can vary significantly between aquatic ecosystems.

-The change in pH due to anthropogenic-addition through ethanolate releases is influenced significantly by the buffer capacity of the exposed ecosystem.

Based on the pH and the buffer capacity of the effluent and receiving water and the dilution factor of the effluent, the pH of the receiving water after discharge can be calculated or its pH can be measured. The change in pH should be compared with the natural variation in pH of the receiving water. Based on this comparison it should be assessed if the pH change is acceptable (see OECD SIDS 2006). To illustrate the effects of sodium hydroxide with an example calculation and to get an idea about the order of magnitude for a maximum anthropogenic addition, the maximum sodium ethanolate concentration will be calculated for two representative cases. According to Dir. 78/659/EEC, the pH of surface water for the protection of fish should be between 6 and 9. The 10^th percentile and the 90^th percentile of the bicarbonate concentration of 77 rivers of the world were 20 and 195 mg/L respectively. If it is assumed that only bicarbonate is responsible for the buffer capacity of the ecosystem and that an increase of pH to a value of 9 would be the maximum accepted value, then the maximum anthropogenic addition of sodium ethanolate would be 1.4 mg/L and 13.1 mg/L (corresponding to 0.86 and 8.3 mg NaOH/L) for bicarbonate concentrations of 20 and 195 mg/L respectively (SIDS Category of methanolates 2006).

In conclusion, sodium hydroxide and substances dissociating into sodium hydroxide respectively, should not be released into the environment, but has to be adapted to the buffering capacities and natural pH of the receiving waters or STP.

Postulating that measures to mitigate the effects of hydroxide ions in the receiving environment are taken, the remaining component released from sodium ethanolates in water is ethanol. Hence, a PNECaquatic was calculated on the basis of the effects of the organic dissociation product of the test substance.

 

PNEC STP 

The results with the dissociation product ethanol were used for PNEC derivation. The PNEC STP was based upon an EC50 of 5.8 g/L determined for Paramaecium caudatum and an assessment factor of 10. For sodium hydroxide no data are available since the substance completely dissociates in water and effects are related to a shift in pH values only.

 

Terrestrial PNEC

The results with the dissociation product ethanol were used for PNEC derivation for freshwater sediment as well as marine water sediment. In the absence of any sediment toxicity data, both PNEC sediment values were derived by using the equilibrium partitioning method. The results with the dissociation product ethanol were used for the derivation of PNEC soil. Data are available for toxicity to plants. The results in the available studies are not in a form that can be directly used for PNEC calculation but have been converted into an appropriate mg/kg format using default data for the composition of soil. The starting point therefore becomes an EC50 of 633 mg/kg, with a conservative assessment factor of 1000 as normally used when only acute toxicity data is available.