Dihydrogen bis(acetato-O)difluoroborate(1-)

Toxicity to aquatic algae and cyanobacteria

Description of key information

With high probability acutely not harmful to aquatic algae.

Additional information

In water, the acetic acid - boron trifluoride complex rapidly decomposes to form acetic acid and boron trifluoride dihydrate. The latter reacts further to boric acid and fluoroboric acid, which finally hydrolyses to yield hydrofluoric acid/ fluoride ions (BUA, 2005). The assessment of fish toxicity was therefore based on studies on the substance itself as well as on the products of hydrolysis.

In a GLP compliant, guideline 72 hr acute toxicity test of potassium acetate solution to the marine algal speciesSkeletonoma costatum, no significant effect was seen up to the highest test concentration of 1000 mg/L (Beslagic, 2005). Therefore the EC50 was determined to be >1000 mg/L for the test substance. The 72hr EC50 forSkeletonema costatumwas calculated to be >300.82 mg/l based on the effect of the acetate ion. The reported EC50 was recalculated, adjusting for the molecular weight of the acetate compared to the parent molecule and for the fact that the test substance is only 50% potassium acetate.Although it is preferable to have data from tests on freshwater algal species, this study is considered suitable for use as weight of evidence, as the results are within the same range as for freshwater studies in fish and Daphnia.

The toxicity of boron trifluoride dihydrate was investigated following the guideline of Directive 92/69/EEC, method C3 and according to GLP. The EC50 value based on growth rate was determined to be greater than 500 mg/L (Arkema, 2005).

The toxicity of boron to Spirodella polyrrhiza was determined by Davis et al. 2002 using standard methods. Frond production is apparently a more sensitive endpoint than either growth rate or the presence of abnormal fronds. Frond production in S. polyrrhizawas significantly reduced at 3.55 mg B/L. Significant reductions in growth rate and the percentage of abnormal (chlorotic, necrotic, and dead) fronds were observed at 18.9 and 22.4 mg B/L, respectively. The EC₅₀for frond production, frond growth rate, and abnormal fronds were 14.3, 11.7, and 17.7 mg B/L, respectively. Davis et al. (2002) reported a NOEC value of 6.1 mg- B/L for the duckweed Spirodella polyrhiza. They reported endogenous boron level of 0.9 mg- B/L from the various nutrient media used.

Another non published data, an OECD 201 study of Selenastrum capricornutum (Hanstveit and Oldersma 2000) reported a NOEC concentration of 17.5 mg-B/L..

Other studies reported NOEC values were obatined for Chlorella pyrenoidosa (10 mg-B/L), Scenedesmus subspicatus (24 mg-B/L), Anacystis nidulans (50 mg-B/L) and Lemna minor (60 mg-B/L) are also available.