Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
154 mg/L
Assessment factor:
100
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
1 540 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
15.4 mg/L
Assessment factor:
1 000

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
100 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
570.4 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Hazard for air

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
23.5 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Additional information

The toxicity of sodium methanolate and potassium methanolate to aquatic organisms is mediated by their degradation products due to the rapid reaction with water yielding sodium or potassium hydroxide and methanol. The aquatic toxicity of methanol is low with acute EC50 or LC50 values > 10000 mg/L and therefore its contribution to the methanolate toxicity is considered negligible. The limited data available for sodium methanolate are consistent with the aquatic toxicity of the alkali hydroxides. For sodium methanolate the acute toxicity to fish (48-h LC50) forLeuciscus idus melanotus was 346 mg/L (equivalent to 256 mg/L of sodium hydroxide). The corresponding 48-h LC50 value for sodium hydroxide was 189 mg/L, the 96-h LC50 for Gambusia officinalis was 125 mg/L for sodium hydroxide. For invertebrates a 48-h LC50value of 40 mg/L (Ceriodaphnia dubia) and toxicity threshold concentrations (TTC) between 40 and 240 mg/L (Daphnia magna) were reported for sodium hydroxide. Lethal concentrations to molluscs of sodium hydroxide started from 150 mg/L (Bulinus truncatus, Lymnea caillaudi), the 48-h LC50 values for Ophryotrocha (marine polychaete) were between 33 and 100 mg/L. The 24-h EC50 for algae (assimilation inhibition) was 302 mg/L for sodium methanolate.

Aquatic PNECs

However, as concluded for 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.

 

Normally 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 methanolate 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 methanolate 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, 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 methanolate 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 10th percentile and the 90th 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 methanolate would be 1.4 mg/L and 8.2 mg/L (corresponding to 1.0 and 6.1 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 methanolates in water is methanol. Hence, a PNECaquatic was calculated on the basis of the effects of the organic dissociation product of the test substance.

PNEC STP 

Sodium methanolate was moderately toxic to bacteria with a 24-hour EC50 of 97 mg/L. The toxicity is likely mediated through a pH effect by the release of hydroxide ions. With postulated adaptation/neutralisation of hydroxide ions to the conditions in the STP, only methanol could affect microbial organisms in the plants. The relevant IC50(3h) value for methanol was > 1000 mg/L.

 

Terrestrial PNEC

There is only one study with potassium hydroxide available indicating a low level of terrestrial toxicity (90-day EC50 in Enchytraeus sp. (> 95% Cogentia sphagnetorium) of 850 mg/L (artificial soil)). The terrestrial toxicity will depend on the buffer capacity of the soil. Using that study for PNEC derivation based on an assessment factor of 100, a PNEC soil of 8.5 mg/kg soil dw would be derived, in the same range as the outcome of the calculation based on the partition coefficient.

Conclusion on classification

The presented data is conclusive, but not sufficient for classification according to UN-GHS and DSD-DPD.