Potassium methanolate

Endpoint summary

Additional information

Potassium methanolate is a white to yellowish organic solid salt that decomposes above 300 °C (OECD SIDS 2006). Potassium methanolate has a calculated vapour pressure of 1.05 x 10-6 Pa (study director 2003). On contact with water the substance decomposes rapidly and exothermically under formation of methanol and potassium hydroxide (OECD SIDS, 2006). Due to the fast decomposition the hydrolysis products are relevant for the evaluation of the partitioning in the environmental compartments.

Potassium hydroxide
Potassium hydroxide is a strong alkaline substance that dissociates completely in water to K⁺ and OH^-. In the majority of natural waters pH levels are between 6 and 10, which illustrates that OH^- is a widely occurring chemical in nature. Also K⁺ is widely found in natural waters. Atmospheric emissions in the form of aerosols are rapidly neutralized by carbon dioxide as occurs with other bases (US EPA, 1988) and the salts will be washed out by rain. For this reason, potential atmospheric emissions of KOH are considered of no concern. (OECD SIDS, 2002)

High water solubility and low vapour pressure indicate that potassium hydroxide will be found predominantly in aqueous environments. The substance characteristics imply KOH will not adsorb on particulate matter or surfaces and will not accumulate in living substances (OECD SIDS, 2002). Significant emissions to the terrestrial environment are not expected during normal handling and use of KOH. Small terrestrial emissions will be neutralized by the buffer capacity of the soil. For this reason, the environmental assessment can be limited to the aquatic compartment. (OECD SIDS, 2002)

An addition of KOH to an aquatic ecosystem may increase the pH depending on the buffer capacity of the receiving water. In general, the buffer capacity is regulated by the equilibrium between CO2, HCO3- and CO32-:

CO2 + H2O * HCO3- + H+ (pKa1 = 6.35)

HCO3- * CO32- + H+ (pKa2 = 10.33)

 

The pH of effluents is normally measured very frequently, can be adapted easily and these effluents are commonly neutralised, and therefore a significant increase of the pH of the receiving water is not expected.

Emissions of potassium originating from the use of potassium hydroxide are small compared to other sources (natural and anthropogenic) of potassium. KCl is a very large volume fertiliser (global production of 24 million tons K in 1989).

Methanol
If released to the environment methanol is readily biodegradable (76 – 82% BOD-removal after 5 days). The log Pow of methanol is -0.77, indicating a low bioaccumulation potential and low potential for adsorption (study director, 2009). The low potential for bioaccumulation was confirmed by experimental BCF-values of < 10 that have been determined in different fish species (Freitag et al., 1985, Gluth et al., 1985). Gaffney et al. (1987) published a Henry’s law constant of 0.461 Pa m³/mol for methanol indicating a low potential for volatilisation. If released to the air compartment, methanol will be photodegraded by hydroxyl radicals with a half-life of 17 - 18 days (Atkinson, 1989).