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In water, diethyl ether - boron trifluoride rapidly decomposes to form diethyl ether and boron trifluoride dihydrate. The latter reacts further to boric acid and fluoroboric acid, which finally hydrolyses to yield hydrofluoric acid/ fluoride ions (BUA Report 261, 2005). Due to the reactivity of diethyl ether – boron trifluoride in water, a weight of evidence approach was chosen for the assessment of aquatic toxicity, including studies on the submission substance itself as well as studies on decomposition/hydrolysis products. For this purpose all public data described in the EU Risk Assessment Report for boric acid was used. Fluoride was not included in the assessment, since it is not assumed to significantly contribute to the toxic effect. The EU Risk assessment report on hydrofluoric acid indicates for fluoride ions a PNEC of 0.9 mg/L (or 3.3 mg/L derived with SSD), whereas a PNEC of 0.56 mg/L (or 1.9 mg/L derived with SSD) was estimated for boric acid. We can, therefore, assume that the toxicity of BF3 is dominated by the toxicity of H3BO3.

Short-term fish studies are available for all main hydrolysis products. Diethyl ether showed very low fish toxicity, with EC50 values greater than 2000 mg/L (Geiger et al., 1986; Könemann, 1981). With boron trifluoride dihydrate, the observed effects were due to the decreased pH only. No mortality or sublethal effects occured in the neutralised sample at 100 mg/L (BASF AG, 1988). The most reliable literature studies with boric acid and fluoroborate report LC50 values between 125 and 600 mg/L (Hamilton, 1997; Curtis and Ward, 1981).

Also the effects observed with Daphnia magna were only due the low pH, when testing diethyl ether – boron trifluoride. No effects were observed in the neutralised sample at 100 mg/L (BASF AG, 1992). In the EU Risk Assessment Report for boric acid, 24 – 48 h EC50 values for Daphnia magna range from 73 to 226 mg B /L. Expressed as concentration of diethyl ether – boron trifluoride, all values are above 100 mg/L. Also diethyl ether showed low toxicity on daphnia, with an EC50 value of 165 mg/L.

No growth inhibition of Scenedesmus subspicatuswas observed with diethyl ether – boron trifluoride at the highest concentration tested 10 mg/L, nor with boron trifluoride dihydrate at 500 mg/L (BASF AG, 1991). In the EU Risk Assessment Report for boric acid, only an EC50 value of 52 mg B /L is reported, which corresponds to 690 mg/L diethyl ether – boron trifluoride.

Long-term data is only available for boric acid and borax (disodium tetraborate). Reliable NOEC values for fish and daphnia range between 5 and 27 mg B /L.

No long-term studies are available for diethyl ether, probably due to its high volatility. From surface waters diethyl ether will evaporate more or less rapidly depending on the hydrographic conditions, and will be subject to photolysis in the atmosphere (BUA report 49, 1991).