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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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When release in the atmosphere boron trifluoride (BF3) molecules in contact with atmospheric humidity form a 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 dihydrate form of boron trifluoride and those of its breakdown products in water: boric acid and fluoboric acid.

The abiotic degradation (hydrolysis) of tetrafluoroborate in water are ionic species and finally boric acid . Therefore it can be reasonably assumed that they will not be characterized by a high potential of bioaccumulation.

The WHO (1998) review of boron noted that highly water soluble materials are unlikely to bioaccumulate to any significant degree and that borate species are all present essentially as undissociated and highly soluble boric acid at neutral pH. The available data indicate that both experimental data and field observations support the interpretation that borates are not significantly bioaccumulated

For inorganic chemicals, estimates of bioaccumulation potential are not reliably predicted by octanol/water partitioning data. Although boric acid has a low measured Pow value (log Pow = - 1.09, Cordia, 2003a), the result should not be considered an appropriate model system.Laboratory data in oysters and salmon demonstrate low Bioconcentration Factors (BCF) for boron, although the tests pre-date current protocols.Thompson et al.(1976) reported BCF values of 0.7 to 1.4 L/kg for Pacific oysters (Crassostrea gigas) and showed that boron levels in tissue of sockeye salmon (Oncorhynchus nerka) were not significantly different from test water concentrations. Tissue concentrations in the oyster returned to background in 25 days. Hamilton and Wiedmeyer (1990) reported BCF < 0.1 in Chinook salmon fed boron-supplemented diets for 60 to 90 days. Suloway et al. (1983) reported a bioconcentration factor of 0.3 L/kg for fathead minnow (Pimephales promelas) and green sunfish (Lepomis cyanella), when exposed to components of coal fly ash extract containing boron at concentrations ranging from 1.23 to 91.7 mg/L.

Saiki et al.(1993) measured boron levels in aquatic food chains in the Lower San Joaquin River (California, United States) and its tributaries. They observed the highest concentrations of boron in detritus and filamentous algae, and lower concentrations in invertebrates and fish. Saiki et al did not calculate accumulation factors and many of their analytical values were below their detection limits. Using only measurements above detection limits, the average BCF for filamentous algae was 137 L/kg (standard deviation of 224). Bioaccumulation factors (BAF) for plankton and invertebrates were less than 20 L/kg; BAF for fish were < 5 L/kg. (Since these are field data, the body concentrations reflect uptake via both food and from water; BCF values theoretically reflect uptake from water only.) If measurements below detection limits are taken to be equal to the detection limit value, the estimated values are: algae-BCF ca.190 L/kg, plankton and invertebrates-BAF <20 L/kg, and fish-BAF ca. 8 L/kg.