Triboron trimethyl hexaoxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Peer-reviewed technical publication. Data not presented.

Principles of method if other than guideline:

Test organisms were exposed during 72h in petri dishes

GLP compliance:

not specified

Analytical monitoring:

not specified

Vehicle:

no

Test organisms (species):

other: Opercularia bimarginata

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Nominal and measured concentrations:

Nominal concentrations : 10, 15, 20, 50 and 110 mg B/l

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

growth inhibition

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

20 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

growth inhibition

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

not specified

Analytical monitoring:

yes

Details on sampling:

- Sampling method: a portion of a reaction mixture was transferred to a standard BOD dilution bottle.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Stock solutions (0.5 to 5.0 g/L) of the test chemical were prepared in deionized water. When necessary, the stock solutions were adjusted to pH 7.5 ± 0.5 by the addition of 1N H2SO4 or 1N NaOH as required

Test organisms (species):

other: activated sludge from domestic and industrial sewage treatment plants

Details on inoculum:

Activated sludge was obtained on the day prior to the first day of each series of inhibition tests. On return to the laboratory, the solids were allowed to settle and the waste liquor was discarded. The solids were then transferred into a 9-liter laboratory-scale, semi-continuous activated sludge cylinder and diluted to approximately 8.5 liters with deionized water. The system was initially mixed by aerating at a rate of approximately 0.5 L/min, and the concentration of mixed liquor suspended solids was determined by gravimetric analysis. The solids were then allowed to settle in the cylinder and the upper layer of waste liquor was discarded. The activated sludge was washed three times with appropriate volumes of deionized water. After washing, the system was adjusted to contain 4000 ± 400 mg of mixed liquor suspended solids (dry weight) per liter. The system was then aerated continuously at a rate of 0.5 L/min and incubated at ambient temperature (21°C).
The system was supplemented daily with 50 mL of a synthetic sewage stock solution per litter of activated sludge. The synthetic sewage stock solution was composed of, per liter: Bacto-Peptone, 16.0 g; Bacto-Beef extract, 11.0 g; urea 3.0 g; K2HPO4, 28 g; MgSO4 • 7H2O, 0.2 g; CaCl2 • 2H2O, 0.4 g; and NaCl, 0.7 g. Final pH of the stock solution was adjusted to pH 7.0 with H3PO4. Fresh stock solution was prepared as required and stored for not more than two days at 5°C.
When the same source of inoculum was to be used for testing on a subsequent day (maximum of 7 days). an additional 50 mL of synthetic sewage stock solution was added per liter of activated sludge. The system was incubated overnight.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

21°C

pH:

7.4 - 8.0

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 1L-bottle, final volume 500 mL
- Aeration: 0.5 - 1.0 L/min

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionized water

OTHER TEST CONDITIONS
- Adjustment of pH: yes, 7.5 ± 0.5

Reference substance (positive control):

yes

Remarks:

3,5-dichlorphenol

Duration:

3 h

Dose descriptor:

IC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

not specified

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Details on results:

During a number of preliminary inhibition studies, it was observed that the pH of a test reaction often changed during the 3-hour incubation period. Thus, decreases in the respiration rate may have been due to a combination of both the effects of pH and toxicity of the test chemical. As a consequence, the buffering capacity of the synthetic sewage nutrient medium was increased to prevent changes in pH of reaction mixtures.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: IC50 for 3,5-dichlorphenol: 12.2 ± 2.2 mg/L (18% variance) (municipal sewage), 11.4 ± 1.5 mg/L (13% variance) (industrial sewage)

Reported statistics and error estimates:

Inhibition data were analyzed using Thompson's method of moving averages to estimate IC50 values. The experimental data were also analyzed using a probit-transformation model similar to that described by Larson and Schaeffer (1982). A nonlinear curve-fitting program (Procedure NLIN of SAS) was used to estimate IC50 values and associated 95% confidence intervals.

Description of key information

TMBX is hydrolytically unstable and breaks down to form methanol and boric acid in the presence of water, these species can be expected to be found following release to the environment. Therefore, an assessment of ecotoxicological potential was conducted taking account of the effects of the hydrolysis breakdown products of TMBX upon the different trophic levels.

Testing of Respiration inhibition of Activated sludge by methanol was conducted by Klecka et al 1985. The IC50 was in excess of 1000 mg/L based on nominal test material concentrations.

Taking into account the extensive information on the toxicity of boron to microorganism in STP, i. e. - 4 respiration studies using activated sludge, showing NOEC between 17.5 and >10000 mg B/L, - 1 nitrification study in a fixed bed reactor, showing no effect up to 500 mg B/L, and - 3 studies of growth of protozoans relevant for the functioning of STPs, show NOEC data between 10 and 20 mg B/L. Therefore, it was decided to base the PNECstp on the lowest NOEC from the available toxicity data. The lowest NOEC for the protozoan Opercularia bimarginata on growth is 10 mg B/L (Guhl. 2000). Since the studies of STP functioning showed no adverse effects at higher concentrations, no additional assessment factor was used, therefore resulting in e PNECstp of 10 mg B/L.

Based on the above results, the NOEC value for boron were used to calculate equivalent values for TMBX:

Respiration inhibition NOEC=10 x (173.5/32.4) = 53.5 mg/L

 

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

53.5 mg/L