Sodium 2-methylpropan-2-olate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.11 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

1.1 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.011 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.419 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.042 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.019 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The toxicity ofsodiumtert.-butanolate to aquatic organisms is mediated by its degradation products due to the rapid reaction with water yieldingsodiumhydroxideand tert.-butanol. Theaquatic toxicity of tert.-butanol is low with acute EC50or LC50values >110 mg/L and therefore its contribution to the sodium tert.-butanolatetoxicity 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 forsodium tert.-butanolateare consistent with the aquatic toxicity of the alkali hydroxides. Fortert.-butanoltheacute toxicity to fish (96-h LC50) forPimephales promelasexceeded 1000 mg/L. The acute toxicity of tert.-butanol to aquatic invertebrates was tested in a guideline study according to OECD 202. The EC50 value was determined to exceed the highest nominal test concentration of 1000 mg/L. The toxicity of tert.-butanol to Pseudokirchnerella subcapitatawas tested in a GLP guideline study according to OECD 201. The EC50 value (based on measured concentrations) on the growth was determined to be greater than 110 mg/L.

Aquatic PNECs

As concluded forsodiumhydroxide, acute toxicity data cannot be used to derive a PNEC or a PNECaddedfor 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 PNECaddedhas to be derived from available ecotoxicity data. A PNECaddedis 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 PNECaddedfor thesodiumtert.-butanolateas itseffect 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-additionthrough sodiumtert.-butanolatereleasesis 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 ofsodiumhydroxide with an example calculation and to get an idea about the order of magnitude for a maximum anthropogenic addition, the maximum sodiumtert.-butanolateconcentration 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 10thpercentile and the 90thpercentile 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 ofsodium tert.-butanolatewould be 2.5 mg/L and 14.6 mg/L (corresponding to 1 and 6.1 mg NaOH/L) for bicarbonate concentrations of 20 and 195 mg/L respectively (see also 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 fromsodiumtert.-butanolates in water is tert.-butanol. 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 tert.-butanol were used for PNEC derivation. The PNEC STP was based upon the EC50 > 1000 mg/L determined in a study according to OECD 209. 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 tert.-butanol were used for PNEC derivation. In the absence of any terrestrial toxicity data, the PNEC soil was derived by using the equilibrium partitioning method.

Conclusion on classification

Due to all available data on environmental fate and aquatic toxicology the substance does not need to be classified according to EU GHS CLP and DSD-DPD.