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Toxicity to microorganisms

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Description of key information

An OECD Guideline 209 was conducted on boric acid, the hydrolysis product of the reference substance, which is applicable to use in the evaluation of the reference substances ecotoxicological properties.  
The 3 hr EC50 (based on inhibition of respiration) was 1001 mg/l boric acid (equivalent to 175 mg B/L). The NOEC was 100 mg/l boric acid (equivalent to 17.5 mg B/L).

Key value for chemical safety assessment

EC50 for microorganisms:
175 mg/L
EC10 or NOEC for microorganisms:
17.5 mg/L

Additional information

The reference substance (BAGE) hydrolyses within less than an hour to its hydrolysis products: Boric acid and glycerol. Therefore, conducting a study on the reference substance itself was considered not to be feasible. If a study was conducted on the reference substance, it would give a result representative of the hydrolysis products mentioned above.

An assessment of boric acid has therefore been made based on available study data.

Boric acid data:

Hanstveit and Schoonmade 2000:

Study conducted to OECD Guideline 209.

Activated sludge was exposed to test concentrations of 0, 3.2, 10 32, 100, 320 and 1001 mg/L boric acid, with the addition of a synthetic sewage feed as a respiratory substrate.

The rate of respiration was determined after 10 minutes and 3 hours incubation.

Inhibition was observed only at extremely high concentrations (320 mg/L boric acid or more). No EC50 was observed. The maximum inhibition reported was 24%.However, the value at 1001 mg/l was reported as 13.3 mg O2, which is only 19% less than the average control respiration of 16.5.

Results were stated as follows:

EC50: >1001 mg/L Boric acid (>175 mg B/L)

EC20: 638 mg/L Boric acid (112 mg B/L)

EC80: >1001 mg/L Boric acid

NOEC stated as 100 mg/L Boric acid (17.5 mg B/L).

The reference substance (3,5-dichlorophenol) demonstrated inhibition with the expected range (EC50: 11.5 mg/L).


Glycerol is the other hydrolysis product of the reference substance, BAGE. It is not classified for the environment according to CLP or DSD.

Available data (see section 13) suggests that glycerol is of low toxicity to microorganisms.

Refer to section 13, Ecotoxicological expert report (BAGE: Evaluation of Environmental Fate and Ecotoxicity Properties) for further details of the evalaution of ecotoxicological properties of the reference substance and its hydrolysis products, especially for additional information on glycerol.