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Environmental fate & pathways

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Potassium tetrafluoroborate is soluble in water and with a melting point of >300 °C its vapour pressure may be considered negligible. In aqueous solution, inorganic salts such as potassium tetrafluoroborate may be anticipated to dissociate rapidly and fully into the respective cation and anion. Potassium tetrafluoroborate released into the environment will thus be distributed into the water compartment in the form of potassium (K+) and boron tetrafluoride (BF4 -) ions. Subsequent stepwise hydrolysis of BF4- occurs under formation of BF3OH-, BF2(OH)2-, BF(OH)3- and ultimately B(OH)4- accompanied with the formation of hydrofluoric acid. Due to the strong affinity of boron for fluoride, complete hydrolysis of BF4- occurs at low concentrations, yet with a slow initial step, especially at normal temperature and at a neutral or alkaline pH. Biodegradation does not apply to inorganic substances. Given its ionic nature, potassium tetrafluoroborate is expected to partition favourably to water rather than organic and fatty media and bioaccumulation is therefore not to be expected. With regards to transport and distribution in the environment, the basic parameters used in the exposure assessment (log Kow, Henry's law constant, adsorption/desorption coefficients) are not applicable to the ionised form of substances (TGD, part II (2003)). Furthermore, the determination of Koc for the intact molecule is not technically possible to perform, as the required test methods are not applicable to molecules which dissociate. Potassium is usually the most abundant of the major nutrient elements for plants and animals in soil (the total potassium content of soils are reported to vary from <0.01% to about 4% with a typical content of about 1%. Potassium content of sediments is about 2%). Therefore potassium emissions originating from uses of KBF4 are probably small compared to other sources and unlikely to contribute significantly to background concentrations in soil and sediment. The BF4- ion and the different anionic hydrolysis products are expected to have low potential for adsorption based on their negative charge. Although some non-specific and specific processes of anion attraction (e.g electrostatic, Al-Fe-oxides interaction) occur in soil, the organic carbon content of the soils is not anticipated to play a significant role in adsorption because soluble organic compounds and organic particulate phases (i.e. humus) generally have large amounts of negative surface charge. Therefore, the actual test endpoint, that of an organic carbon normalised adsorption coefficient (Koc), is probably not actually valid/relevant for this type of substance. Typical fugacity modeling is also not applicable as the ions exert zero partial pressure and fugacity in air. Furthermore, standard computer models to estimate the distribution of this substance in the environment cannot be applied because these programs are designed specifically for organic chemicals, not for inorganic salts.