Calcium metaborate (Ca(BO2)2) and calcium tetraborate (CaB4O7), amorphous reaction products of boric acid with lime

Sediment toxicity

Administrative data

Endpoint:

sediment toxicity: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

17 June to 15 July 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 218 (Sediment-Water Chironomid Toxicity Test Using Spiked Sediment)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

10043-35-5

IUPAC Name:

10043-35-5

Constituent 2

Reference substance name:

Boric acid

EC Number:

233-139-2

EC Name:

Boric acid

Cas Number:

10043-35-3

Molecular formula:

H3BO3

IUPAC Name:

Boric acid

Details on test material:

Sigma Aldrich, Boric Acid, Lot No. 079k0115. Purity 99.9%

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

Analytical measurements were made on additional replicate systems at day 0 and day 28 for determination of test substance concentrations in overlying water, pore water and sediment.

Pore water was obtained by centrifugation of sediment at approx 4000 rpm for 20 min at 20 degrees C after removal of overlying water. Supernatant centrifuged at approx 9000 rpm for another 20 minute and analyzed for test substance.

Sediment concentration was measured after removal of pore water. Substance was extracted from sediment by mixing with reagent water then centrifugation and measurement of the supernatant.

Test substrate

Vehicle:

no

Details on sediment and application:

PREPARATION OF SPIKED SEDIMENT
- Formulated sediment consisting of fine industrial sand (75% w/w), kaolin clay (20%) and fine sphagnum peat moss (5%)
- Method of mixing: Stock solutions prepared in water, aliquots added to each treatment batch of sediment and mixed by hand.
- Equilibration time: Test chambers prepared 2 days before introduction of organisms, maintained under test conditions

Test organisms

Test organisms (species):

Chironomus riparius

Details on test organisms:

Laboratory cultures used to provide 1st instar (1-day old) individuals at test initiation. Age was confirmed by measurement of head capsule widths of a representative sample.

Breeding conditions: Cultured at room temperature (21-25 degrees C) in laboratory culture water.
Handling of egg masses and larvae: Egg masses collected and isolated in freshwater, maintained at 20 degrees C.
- Feeding during test: prepared invertebrate food- a suspension of commercial fish flake food
- Amount: Daily, 2.5-3 ml of 2.0 mg/ml during 1st 10 days, 6-8 ml for remainder

Study design

Study type:

laboratory study

Test type:

static

Water media type:

freshwater

Type of sediment:

artificial sediment

Limit test:

no

Exposure duration

Duration:

28 d

Exposure phase:

total exposure duration

Test conditions

Hardness:

176 to 230 mg CaCO3/L

Test temperature:

18.8 to 20.9 degrees C

pH:

7.4 to 8.5

Dissolved oxygen:

4.7 to 9.0 mg/L (55 to 101% saturation)

Ammonia:

0.00003 to 0.0145 micrograms/L (un-ionized)

Nominal and measured concentrations:

Nominal Sediment Concentrations: 0 (control), 6.5, 13, 25, 50, 100, and 200 mg B/kg dry sediment
The day 0 measured concentrations of boron in the sediment samples were 0.207, 1.56, 4.27, 10.0, 18.1, 32.6, and 81.0 mg/kg dry sediment
The day 28 measured concentrations of boron in the sediment samples were
The initial (day 0) measured concentrations of boron within the overlying water samples were 0.319, 0.536, 0.818, 1.44, 2.96, 6.89, 14.4 mg B/L
The termination (day 28) overlying water measured concentrations were 0.125, 0.574, 1.42, 2.53, 6.16, 13.9, and 30.5 mg B/L

Details on test conditions:

Spiked sediments were prepared by addition of boric acid solutions (484 mL of appropriate concentration) to 1500 g formulated sediment and thorough mixing. This resulted in a hydration level of approx. 35%.

Test chambers were 1-L glass jars containing approximately 200 g of formulated sediment (spiked with appropriate amount of test substance) Sediment depth was approximately 2 cm. Dilution water (600 mL) was added to each replicate chamber using a deflector to minimize disturbance of the sediment. Water depth was approx 8 cm, so the water: sediment volume ratio was approx 4:1. Polypropylene emergence traps with nylon mesh were used to monitor adult midge emergence. Chambers were left for 2 d to equilibrate before the test started.

At least 7 replicate chambers were prepared for each treatment level and control. Two were used to provide samples for chemical analysis and 3 chambers were used for biological observations. 20 midge larvae were added to each chamber for the chemical and biological observations. Seven different exposures were tested, a control and six treatments. Larvae were impartially added to cups, then the cups randomly assigned to a replicate chamber.

Overlying water was aerated during the test beginning 24 h after addition of the organisms by gentle bubbling. Midges were fed 2.5 to 3 ml of a commercial flake fish food suspension (2 mg/ml) for the first 10 d, then 6 to 8 ml daily for the remainder of the test. Lighting was 16 h: 8 h light:dark cycle with a 30 m transition period. Light intensity was 653 lux. Temperature was maintained at 20 +/- 2 degrees C by keeping the test chambers in a flowing water bath.

Emergence of adult flies was monitored from day 18. Presence of adults or exuviae in traps was monitored. Adult flies were identified by gender.

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

37.7 mg/kg sediment dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Basis for effect:

mortality

Remarks on result:

other: boron added

Effect concentrations 2

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

37.7 mg/kg sediment dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Basis for effect:

emergence rate

Remarks on result:

other: boron added

Effect concentrations 3

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

37.7 mg/kg sediment dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Basis for effect:

development rate

Remarks on result:

other: boron added

Effect concentrations 4

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

37.7 mg/kg sediment dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Basis for effect:

other: gender ratio

Remarks on result:

other: boron added

Effect concentrations 5

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

81 mg/kg sediment dw

Nominal / measured:

meas. (initial)

Conc. based on:

element

Basis for effect:

other: all endpoints

Effect concentrations 6

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 37.7 mg/kg sediment dw

Nominal / measured:

meas. (geom. mean)

Conc. based on:

element

Basis for effect:

other: all endpoints

Remarks on result:

other: boron added

Details on results:

Percent emergence in the controls was 90% which exceeded the minimum of 70% emergence specified in the OECD 218 guideline for valid results.

All chemical and physical parameters for the 28 day study were within expected ranges with the following exceptions:
Temperature: 18.8 to 20.9 degrees C, except for 15 h period where temperature rose to 25.4 degrees due to water bath heater malfunction.
Dissolved oxygen: 4.7 to 9.0 mg/L. Low oxygen (<60% saturation) occurred in one control and one high exposure replicate on day 21. The exceptions in temperature and dissolved oxygen were judged to have no effect on the test results.

Light intensity: 653 lux (day 0).

Reported statistics and error estimates:

Statistical analysis based on one-way ANOVA followed by Dunnett's test. ECx estimates obtained from probit method and trimmed Spearman-Karber method if poor fit in the probit approach.

Any other information on results incl. tables

Measured Sediment Concentrations and Endpoint Values

Group	Nominal Exposure (mg B/kg sediment dw)	Sediment Mean Measured Concentration (mg B/kg sediment dw)	Sediment Mean Concentration as added Boron (mg B-added/kg)	Survival	Emergence	Gender Ratio **	Development rate
Control	0	0.00	--	90%	90%	0.7	0.046
T1	6.5	1.18	1.10*	90%	88%	1.2	0.047
T2	13	2.83	2.76*	92%	92%	1.4	0.049
T3	25	6.07	6.00*	88%	88%	1.6	0.048
T4	50	11.3	11.2*	93%	93%	1.5	0.046
T5	100	19.4	19.3*	87%	85%	1.3	0.048
T6	200	37.8	37.7*	88%	88%	0.8	0.046

* Mean value for group minus mean control boron concentration (i.e., added boron), expressed as mg B-added/kg sediment dw.

**Ratio is males:females

The gender ratio was increased in all treatments above the control (more males than females). However, there was no dose-related pattern; the most highly exposed group (T6) was most similar to controls. In addition, the test with spiked water showed virtually the reversed pattern of gender ratio, again with no evident dose-response pattern.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

Based on all biological measurements, no significant effects were observed in any treatment. Therefore the NOEC for all endpoints (survival, emergence, development rate, and gender ratio) is stated as the maximum exposure tested. Expressed as the geometric mean concentration in sediment, the NOEC is 37.7 mg B-added/kg sediment dw.

Because no effects were observed, no ECx can be determined.

Analyses of the sediment, pore-water and overlying water at test initiation and termination documented that the boron concentrations decreased in the sediment and pore-water, while increasing in the overlying water. Virtually all added boron could be accounted for (85 to 107%) in the 4 highest treatments and slightly lesser fractions (49 to 63%) in the two smaller treatments.

The geometric mean pore-water and overlying water concentrations of the highest treatment group were 68 and 21 mg B/L respectively. These were associated with no observed effects.