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Environmental fate & pathways

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The emissions of NaOH mainly apply to (waste)water. Furthermore, the high water solubility and very low vapour pressure indicate that NaOH will be found predominantly in water. In water (including soil or sediment pore water), NaOH is present as the sodium ion (Na+) and hydroxyl ion (OH-), as solid NaOH rapidly dissolves and subsequently dissociates in water (EU RAR 2007 of sodium hydroxide, section 3.1.3, page 24).

If emitted to the air as an aerosol in water, NaOH will be rapidly neutralised as a result of its reaction with CO2 (or other acids), as follows (EU RAR 2007, section 3.1.3.4, page 26):

NaOH + CO2 -> HCO3- + Na+

Subsequently, the salts (e.g. sodium(bi)carbonate) will be washed out from the air (US EPA, 1989; OECD, 2002 ). Thus, atmospheric emissions of neutralised NaOH will largely end up in soil and water.

If emitted to soil, sorption to soil particles will be negligible (EU RAR 2007, section 3.1.3.3, page 26). Depending on the buffer capacity of the soil, OH- will be neutralised in the soil pore water or the pH may increase.