Boron trifluoride

Endpoint summary

Additional information

When released in the atmosphere boron trifluoride (BF3), which is a strong Lewis' acid, forms in contact with atmospheric moisture the complex: dihydrated boron trifluoride (BF3, 2H2O). On the opposite if BF3 is directly brought into contact with water, it reacts violently. That is the reason why all the assessment of environmental fate and pathways is based on the properties of the more stable dihydrated form of boron trifluoride.

Measurement of fluoride ion production over a range of pH values (1.2 to 9), using both ion chromatography and an ion-selective electrode, indicated a hydrolytic half-life time of less than 30 minutes for boron trifluoride. Subsequent analysis of boric acid by titration confirmed the rapidity of the reaction. Consequently, the risk associated to dehydrated boron trifluoride when release into water can be assessed based upon the hazards of its breakdown products in water: boric acid and fluoboric acid.

With regards to boric acid,the preliminary study showed that at each of pH 1.2, 4, 7 and 9 and 50±0.5ºC, less than 10% hydrolysis had occurred after 5 days, equivalent to a half-life of greater than 1 year under environmental conditions (25°C). No further testing was considered necessary. Boric acid was determined to be hydrolytically stable under acidic, neutral and basic conditions.

Fluoroboric acid was determined to be hydrolytically unstable under similar conditions, reacting to form the ultimate degradation product boric acid and, predominantly, intermediate fluoroborate species. These latter components were not positively identified but, chromatographing as a very broad peak between the tetrafluoroborate and boric acid peaks, and increasing in concentration over the duration of the test, it was considered likely that these were the partially hydrolysed fluoroborate species.

Hydrolysis is also the most relevant process for the soil compartment. BF3 2H2O formed in moisture air may transfer into soil via dry and/or wet deposition, where in turn, it will undergo hydrolysis in moisture soils and in pore water. In addition, the sorption potential of boron on soils was widely described and assessed as low (European Risk Assessment of Boric acid, 2007).

Based on the uses inventoried for boron trifluoride, no direct application of the substance on the soil compartment is expected. The environmental risk of borates were evaluated by considering exposures resulting from wastewater entering rivers or being used for irrigation and from sewage sludge being applied to agricultural soil (Human and Environmental Risk Assessment on ingredients of Household Cleaning Products relative to boric acid, 2005). No significant risks were identified.