Ammonium tetrafluoroborate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because there is no emission to a sewage treatment plant

other:

Justification for type of information:

There are results obtained by electrospray ionization mass spectrometry, NMR spectroscopy, and pH measurements that clearly indicate that hydrolysis is a process restricted to ([PF6]- and) [BF4]-, while imidazolium cation remains unchanged. Hydrolysis of [BF4]- was observed under all of the experimental conditions used, even at room temperature.

Since it is a salt it is not likely to pass biological membranes as ammonium tetrafluoroborate, but rather dissolve and be hydrolysed in the water. Even the BF4 cation is being hydrolysed in water at room temperature. Research has proven that the toxicity of ionic liquids come from the length of the alkyl chains. Ammonium tetrafluoroborate is an ionic liquid, but it does not contain any alkyl chains on the cation or the anion. The toxic effects of ionic liquids are directly related to disruption of cell membrane. This is due to long alkyl chains, often presented in the cationic part of ionic liquids, which increase the lipophilic character of the ionic liquids molecule. It has been confirmed that the toxicity of ionic liquids is associated with their lipophilic character and membrane damage.

Other researchers have discussed toxicity results considering the structural particularities of selected ionic liquids toward vibrio fischeri. Imidazolium, choline, pyridinium, and ammonium head groups were used in the toxicity evaluation. The impact of anions to V. fischeri was assessed through the analysis of five groups commonly used in ionic liquids methanesulfonate, bistriflimide, acetate, chloride, and Tetrafluoroborate. It was reported that ionic liquids with non-aromatic groups present generally lower toxicity than the ones incorporating aromatic rings.
Furthermore, since ammonium tetrafluoroborate does not contain a hydrophobic alkyl chain it should not be able to undergo micellization in aquatic solution very easily. The larger the hydrophobic domain, the greater the tendency to aggregate and the higher the rate of their transport through the soil matrix. Elongating the alkyl chain increases affinity for soil or sediment. Further, double layer sorption has been observed in the more hydrophobic, long-chain ILs. In contrast, the presence of a hydroxyl group in the alkyl chain causes the sorption ability of these ILs to be relatively poor. This means, again, that ammonium tetrafluoroborate as an ionic liquid should be relatively poor in sorption.
Publication shows that among a range of commonly used imidazolium, pyridinium and phosphonium ionic liquids, it was imidazolium and pyridinium ionic liquids that showed high toxicity to acetylcholinesterase at very low concentrations, whereas phosphonium ionic liquids were non-toxic within the test limits. This testing showed that toxicity of these ionic liquids lies in the cationic part and alkyl side chain and not in the anionic part.
The critical micelle concentration (CMC), which reflects the ionic and hydrophobic properties of quaternary ammonium compounds (QACs), has been determined for different QAC and used as a descriptor to develop quantitative structure-activity relationships to express their sorption affinity for biosolids and their Microtox toxicity. All QACs tested had a high sorption affinity for biosolids. QACs with low CMCs had a higher adsorption affinity for biosolids than QACs with relatively high CMCs, suggesting that QACs with high CMCs are more mobile than the ones with low CMCs. On the contrary, QACs with high CMCs were more toxic than the ones with lower CMCs. The QAC with the lowest acute Microtox toxicity was the compound with the smallest alkyl chain. The presence of counter-ions (anions) had no significant effect on the QAC toxicity, but natural organic matter decreased the QAC toxicity.
Hydrogen fluoride is probably formed when ammonium tetrafluoroborate is being dissolved in aquatic environment. In aqueous form it is called hydrofluoric acid. Hydrogen fluoride is only a weak acid in dilute aqueous solution. This is in part a result of the strength of the hydrogen-fluorine bond, but also of other factors such as the tendency of HF, H2O, and F− anions to form clusters.
Hydrogen fluoride is not included in Reproductive and Developmental Toxicants, a 1991 report published by the U.S. General Accounting Office (GAO) that lists 30 chemicals of concern because of widely acknowledged reproductive and developmental consequences. Fluoride crosses the placenta, and at low doses is thought to be essential for normal fetal development in humans. It is rarely excreted in breast milk. There have been rare cases of mottling of deciduous teeth in infants born to mothers who had high daily intakes of fluoride during pregnancy; skeletal abnormalities are considered unlikely. No reproductive effects due to hydrogen fluoride are known.
It has also bten concluded by Slooff (1998) that the limited data available indicate that accumulation through food chains (biomagnification) is of little significance in the aquatic environment.
In another study, the investigated compound BF4, which are the constituents of the room temperature ionic liquids, was not detected in water or wastewater samples.

Longer unbranched alkyl chains promote biodegradability and the presence of hydrolysable groups (i.e. esters) and groups easily oxidised (i.e. alcohols) and carboxylic acids are noted as being amongst the prominent features of the readily biodegradables ILs in another review. Again, ammonium tetrafluoroborate does not contain any alkyl chains, but is easily hydrolysed, i.e the cation is easily biodegradable.
Apart from ammonium ions, hydrogen fluoride is probably formed when ammonium tetrafluoroborate is being dissolved in aquatic environment. In aqueous form it is called hydrofluoric acid. Hydrogen fluoride is only a weak acid in dilute aqueous solution. This is in part a result of the strength of the hydrogen-fluorine bond, but also of other factors such as the tendency of HF, H2O, and F− anions to form clusters.
Hydrogen fluoride is not included in Reproductive and Developmental Toxicants, a 1991 report published by the U.S. General Accounting Office (GAO) that lists 30 chemicals of concern because of widely acknowledged reproductive and developmental consequences. Fluoride crosses the placenta, and at low doses is thought to be essential for normal fetal development in humans. It is rarely excreted in breast milk. There have been rare cases of mottling of deciduous teeth in infants born to mothers who had high daily intakes of fluoride during pregnancy; skeletal abnormalities are considered unlikely. No reproductive effects due to hydrogen fluoride are known.
It has also been concluded by Slooff (1998) that the limited data available indicate that accumulation through food chains (biomagnification) is of little significance in the aquatic environment.
In one study it was especially noted that in none of the animal carcinogenicity studies effects on morphology of any of the reproductive organs were found. Effects on on the reproduction are systemic and HF occurs in the systemic circulation only as a free ionic or as organically bound fluoride rather tan as HF or NaF. In several studies, the effect of fluoride on the testes of mice, rats and rabbits with respect to reproductive impairment was tested. In none of these studies the fluoride anion content of the control diet was stated. In natural water, fluoride ions form strong complexes with aluminium, and fluorine chemistry in water is largely regulated by aluminium concentration and pH. Below pH 5, fluorine is almost entirely complexed with aluminium and consequently, the concentration of free F- is low. As the pH increases, Al-OH complexes dominate over Al-F complexes and the free F level increases. The dominant Al-F complex at pH <5 is AlF2+) is of little significance in the aquatic environment.