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The toxicity of sodium methanolate to aquatic organisms is mediated by its degradation products due to the rapid reaction with water yielding sodium hydroxide and methanol.

The limited data available for sodium methanolate are consistent with the aquatic toxicity of the alkali hydroxides. Information on sodium methanolate is available for fish, algae and microorganisms, where microorganisms were most sensitive. The EC50 values for sodium methanolate ranged from 96.9 to 346 mg/L. Similar to information on sodium methanolate, information on sodium hydroxide was of restricted reliability ("invalid" or "not assignable"), mostly due to unknown pH and alkalinity of the test solutions. Sodium hydroxide is assumed to affect aquatic organisms mainly via the shift in pH. The range of the available toxicity values with sodium hydroxide was rather small and varied between 40.4 and 189 mg/L, with microorganisms and daphnids among the more sensitive specimen.

Reliable data was available for the effects of methanol to all levels of organisms, with the highest sensibility with microorganisms and daphnids and EC50 values of > 1000 mg/L and > 10000 mg/L respectively. A long-term test on fish determined a NOEC(8d) of 7900 mg/L.

Based on the available data it is not considered useful to derive a risk assessment for the sodium methanolate or the metabolite sodium hydroxide as their effect is based on hydroxide ions or a pH change. Major arguments to support this approach were the significant variation of the natural pH in aquatic ecosystems, the differences in sensitivity of ecosystems to pH change and the different buffer capacities of ecosystem and hence different responses to change in pH in exposed ecosystems due to addition through methanolate release. Each respective release will require the need to assess the environmental effect of a release through sodium methanolate into the environment or a sewage treatment plant. 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).