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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The inhibition of the degradation activity of activated sludge is not expected when introduced in appropriate low concentrations.
The substance may generate a shift in the pH.

Key value for chemical safety assessment

Additional information

In water, the tetrahydrofuran - boron trifluoride complex rapidly decomposes to form tetrahydrofuran 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). The assessment of toxicity to microorganisms is therefore based on studies on the hydrolysis products tetrahydrofuran and boric acid and on an analogy to the similar substance diethyl ether - boron trifluoride.

The acute toxicity of the similar substance diethyl ether – boron trifluoride on microorganisms was investigated, using Pseudomonas putida as test organism. The test was conducted according to the German national guideline (DIN 38412, Part 8) and GLP. The observed growth inhibition in the unneutralised samples was due to the decrease of pH at high test substance concentrations. In the neutralised sample, no effects were observed at the concentration of 100 mg/L (BASF AG, 1992).


In an OECD 209 study with tetrahydrofuran, an IC50 of 460 mg/L was obtained for three hours exposure (Talinli and Tokta, 1994).


Effects of boric acid on micro-organisms are reviewed in the EU Risk Assessment Report for boric acid. Inhibition was estimated using the standardized OECD 209 method, Hanstvelt and Schoonmade (2001) reported 24% inhibition at 175 mg-B/L, and an EC10 can be calculated from their data as 58 mg-B/L. A NOEC was reported by the study authors of 17.5 mg-B/L, but was not determined via any statistical means. In actuality, there was 4% inhibition at this exposure, so it is an EC4, thus more stringent than intended by the OECD 209 protocol. An EC10 value was calculated by linear regression from the data which showed a good fit (R2= 0.863) with a value of 58.0 mg-B/L. This study complies with GLP practice, is rated as highly reliable in quality, and is consistent with earlier tests of activated sludge, however they were not published.

Gerike et al.(1976), using an earlier version of the OECD activated sludge method reported LOEC and NOEC of 120 and 20 mg-B/L, respectively. Guhl (1992, 2000) reported activated sludge LOEC and NOEC of 50 and 20 mg-B/L, respectively.

Other reports include tests of the microbe,Pseudomonas putida, with NOEC values ranging from 7.6 to 1040 mg-B/L However, these study reports are of varying reliability and it appears that the high value (1040) is incorrect. The geometric mean value of the Henkel studies is 50.8 mg-B/L (EC10 values of 340 and 7.6 mg-B/L).

Guhl (1992, 2000) reported on ciliate growth inhibition toEntosiphon sulcatum, Opercularia bimarginata,andParamecium caudatum,with NOEC values of 10, 15, and 20 mg-B/L, respectively. Bringmann and Kuehn (1980b) reported a toxicity threshold (EC5) to the ciliateUronema pardacziof 23 mg-B/L.

The data on sewage treatment plants appears consistent, specifically that no effects are seen at boron exposures of 8 to 20 mg-B/L.