Diboron calcium tetraoxide

Endpoint summary

Description of key information

Numerous studies have demonstrated the toxicokinetics of boric acid and borate salts in humans and experimental animals. At physiological pHs in the aqueous layer of mucosal surfaces, prior to absorption, simple inorganic borated salts are hydrolysed to undissociated boric acid, which are readily absorbed via oral and inhalation exposure. Boric acid is not expected to hydrolyse/react further due to the high energy required to break the B – O bond. Therefore, it is expected that there will be negligible parent compound, calcium metaborate, available systemically and boric acid will be the dominant and common compound in humans and experimental animals. Therefore, a read-across approach using boric acid data is considered appropriate to use, refer to Section 13.

In a read-across 2-year dietary study in Sprague Dawley rats (35/sex/treated group and 70 controls/sex) with interim kills of 5/sex/group at 6 and 12 months, rats were fed 0, 33 (5.9), 100 (17.5), 334 (58.5) mg boric acid (B)/kg bw/day. No adverse effects were observed in the low and mid-dose group. In the top dose group clinical signs, such as coarse hair coats, hunched position, swollen pads and inflamed bleeding eyes were reported. Survival at 6, 12 and 24 months was comparable in all groups including controls. Reduced body weight gain and reduced food intake were identified in the top dose group and significantly decreased red cell volume and haemoglobin were reported in top-dose males at 3, 6, 12, 18 and 24 months. Testes weights and the testes/bodyweight ratios were significantly lower compared to the controls and microscopic examination of the tissue revealed atrophied seminiferous epithelium and decreased tubular size in the testes. Based on these effects a NOAEL of 100 mg/kg bw/day (17.5 mg B/kg bw/day (nominal)) was identified for the source substance, boric acid.

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Reference 1

Endpoint:

chronic toxicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to justification attached in section 13.

Reason / purpose for cross-reference:

read-across source

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

Dose descriptor:

LOAEL

Effect level:

334 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based on testicular atrophy in males and reduced body weight in females

Dose descriptor:

NOAEL

Effect level:

17.5 mg/kg bw/day (nominal)

Based on:

element

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

Dose descriptor:

LOAEL

Effect level:

58.5 mg/kg bw/day (nominal)

Based on:

element

Sex:

male/female

Basis for effect level:

other: Based on testicular atrophy in males and reduced body weight in females.

Critical effects observed:

not specified

Conclusions:

Endpoint Effect level
NOAEL 100 mg/kg bw/day (17.5 mg boron/kg bw/day (nominal))
LOAEL 334 mg/kg bw/day (58.5 mg boron/kg bw/day (nominal))

Testicular atrophy and seminiferous tubule degeneration was observed at 6, 12 and 24 months at the highest dose level only. No treatment related effects were observed in the mid and low dose groups.

Reference 2

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: no data

Deviations:

not specified

Principles of method if other than guideline:

2 year dietary feeding study in Sprague Dawley rats, 35 per sex per treated group and 70 controls per sex with interim kills of 5/sex/group at 6 and 12 months at 0; 670 (117); 2000 (350); 6690 (1170) ppm boric acid (ppm as boron equivalents) equivalent to 0, 33 (5.9), 100 (17.5), 334 (58.5) mg boric acid (B)/kg bw per day.

GLP compliance:

no

Remarks:

Study pre-dates GLP

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: Males 93 - 129 g; females 86 - 128 g

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

No data

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No data

Duration of treatment / exposure:

2 years

Frequency of treatment:

Daily; ad libitum.

Remarks:

Doses / Concentrations:
0; 670 (117); 2000 (350); 6690 (1170) ppm boric acid (ppm as boron equivalents) equivalent to 0, 33 (5.9), 100 (17.5), 334 (58.5) mg boric acid (B)/kg bw per day
Basis:
nominal in diet

No. of animals per sex per dose:

35/sex/group

Control animals:

yes, plain diet

Details on study design:

No data

Positive control:

No data

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: recorded weekly for the first 52 weeks, then 4 weekly


BODY WEIGHT: Yes
- Time schedule for examinations: recorded weekly for the first 52 weeks, then 4 weekly


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): recorded weekly for the first 52 weeks, then 4 weekly
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data


WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No
- Time schedule for examinations:


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood:at 1, 2, 3, 6 ,12, 18 and end of study
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: on 5/sex/group
- Parameters examined: Haematocrit, haemoglobin concentration, erythrocyte count, total and differential leukocyte count


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at interim sacrifice at 6, 18 and 24 months for blood pH, sodium, potassium, chloride and carbon dioxide combining power; and at 6, 12 and 24 months for SGOT and SGPT
- Animals fasted: No data
- How many animals: 2/sex/group except SGOT and SGPT which were in 5/sex/group in the hihg and control dose groups
- Parameters: blood pH, sodium, potassium, chloride, carbon dioxide combining power, SGOT and SGPT


URINALYSIS: Yes
- Time schedule for collection of urine: at 6 months
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters examined: appearance, volume, osmolality, specific gravity, pH, protein, glucose, blood, acetone, bilirubin and microscopy

Sacrifice and pathology:

GROSS PATHOLOGY: Yes at 6 and 12 months 5 rats per sex per group, all interim deaths and at termination in 10 per sex per group in controls and high dose surviving animals.
Organs: Brain, pituitary, thyroid, stomach, small and large intestines, liver, pancreas, kidneys, adrenals, spleen, heart, lungs, gonads, urinary bladder, sternum, rib junction and all unusual lesions.

HISTOPATHOLOGY: Yes 10 rats per sex per group from the mid and low dose groups had gonads examined histologically

Other examinations:

Samples of blood, brain, liver and kidney were taken at 6, 12 and 24 months and frozen for boron analysis.

Statistics:

As appropriate.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Details on results:

CLINICAL SIGNS AND MORTALITY
No signs in the low and mid dose groups. Coarse hair coats, hunched position, swollen pads and inflamed bleeding eyes were observed in animals receiving the highest dose of boric acid.
Survival at 6, 12 and 24 months was comparable in all groups including controls.


BODY WEIGHT AND WEIGHT GAIN
No difference from controls in the low and mid dose group. Retarded body weight gain in animals receiving the highest dose of boric acid.


FOOD CONSUMPTION AND COMPOUND INTAKE
No difference from controls in the low and mid dose group. Reduced food intake in the highest dose group during weeks 1-13 in males, and in weeks 1-13 and 42-52 in females.


HAEMATOLOGY
No difference from controls in the low and mid dose groups. Significantly decreased red cell volume and haemoglobin were observed in the high dose group males at 3, 6, 12, 18 and 24 months. Hemoglobin values for the males in the high level test group were consistently below the normal range for adult male rats. Cell volume values for this group were, at most periods of determination, also below normal or within low normal range. The total leukocyte counts for the high level males were lower than those for the male controls at each determination but generally within normal limits. The hematological values determined during the first year for the low and intermediate level males and the females at all three test levels were generally within normal limits and comparable with the control values.


CLINICAL CHEMISTRY
No significant differences between groups.

URINALYSIS
No significant differences between groups.


ORGAN WEIGHTS
The testes weights and the testes/bodyweight ratios were significantly lower in the high dose group than those of control animals. The brain- and thyroid-to-bodyweight ratios in the high dose females were significantly higher than those of controls. This was thought to relate to the reduced bodyweight of the animals.

GROSS PATHOLOGYAND HISTOPATHOLOGY
Atrophic testes were found in all males exposed to the high dose 334 (58.5) mg boric acid (B)/kg bw) of boric acid at 6, 12 and 24 months. Microscopic examination of the tissue revealed atrophied seminiferous epithelium and decreased tubular size in the testes. Cysts in the eyelids, probably in the Meiobomian glands were observed in 4 high dose females, probably related to treatment. There was no treatment related increase in tissue masses.

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

Dose descriptor:

LOAEL

Effect level:

334 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based on testicular atrophy in males and reduced body weight in females

Dose descriptor:

NOAEL

Effect level:

17.5 mg/kg bw/day (nominal)

Based on:

element

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

Dose descriptor:

LOAEL

Effect level:

58.5 mg/kg bw/day (nominal)

Based on:

element

Sex:

male/female

Basis for effect level:

other: Based on testicular atrophy in males and reduced body weight in females.

Critical effects observed:

not specified

 

Parameter	Control		Low dose		Medium dose		High dose		Dose- response +/-
	m^a	f^a	m^a	f^a	m^a	f^a	m^a	f^a	m	f
number of animals examined	70	70	35	35	35	35	35	35
Mortality at 104 weeks	25/60	20/60	6/25	8/25	9/25	10/24	7/25	5/25	N	N
clinical signs*
body weight gain 0-104 weeks (g)	557	405	546	318	499	359	449	238	Y	Y
food consumption at week 52 (g/kg/day)	33.3	43.7	35.4	42.9	35.3	44.6	39.7	52.7
clinical chemistry*	no differences
haematology*	see separate  table
urinalysis*	No differences
testes weight*(g) at 26 weeks	3.76+0.29		3.67+0.29		3.81+0.14		0.95+0.06 sig low
testes weight (g) at 104 weeks	3.65+0.84		3.65+0.63		3.30+0.60		0.99+0.24 sig low
microscopic pathology* Testes atrophy at 24 months	3/10		1/10		4/10		10/10

 

 

Summary of haematological data from 2 year rat study boric acid:

Months	Cell Volume (%)
	Male
	Control	0.067%	0.2%	0.67%
	0	5.9 mg B/kg	17.5 mg B/kg	58.5 mg B/kg
1	42.6	45.3	42.7	39.0
2	44.1	44.9	45.5	40.8*
3	45.9	46.7	45.7	39.7*
6	45.4	45.9	46.5	44.6
12	47.3	45.5	44.8	41.4*
18	47.8	43.2*	42.8*	39.2*
24	46.4	36.4*	43.8	41.68
	Female
1	42.1	44.5	42.4	43.3
2	41.7	43.7	43.0	40.8
3	44.2	47.2	45.1	42.0
6	43.3	44.7	Data missing
12	42.8	43.9	41.8	40.6
18	43.0	43.0	42.8	39.3*
24	46.2	45.6	44.4	41.6

 

 

Months	Hb Value (g/100 mL)
	Male
	Control	0.067%	0.2%	0.67%
	0	5.9 mg B/kg	17.5 mg B/kg	58.5 mg B/kg
1	14.5	14.2	14.2	12.6*
2	14.7	14.1	14.4	13.2
3	15.7	15.2	14.9	13.3*
6	15.4	15.0	14.2	13.7*
12	14.1	13.2	13.4	12.6*
18	15.6	14.9	13.8*	12.7*
24	14.7	11.9	13.6*	12.8*
	Female
1	14.6	15.3	14.3	14.0
2	14.9	15.2	14.4	14.7
3	14.9	15.7	14.0	14.2
6	14.5	14.8	Data missing
12	12.9	13.2	13.2	12.6
18	14.8	13.9	14.6	13.6
24	14.4	13.2*	13.0*	12.5*

 

 

Months	WBC Count (x10^3/cm^2)
	Male
	Control	0.067%	0.2%	0.67%
	0	5.9 mg B/kg	17.5 mg B/kg	58.5 mg B/kg
1	18.1	13.6	15.3	8.0*
2	19.3	18.4	16.8	14.7
3	20.9	23.4	19.4	16.7
6	19.4	15.6	14.3	15.3
12	10.9	10.9	10.9	10.5
18	23.4	22.9	19.5	18.4
24	19.8	18.1	14.3	13.2*
	Female
1	19.8	20.9	17.3	14.7
2	16.6	28.9	17.1	17.4
3	26.6	19.0	18.6	21.1
6	14.6	14.1	Data missing
12	9.5	13.5	7.3	11.4
18	10.9	11.5	16.4	11.6
24	17.6	12.8	11.3	10.5

 

 

Months	RBC Count (x10^3/cm^2)
	Male
	Control	0.067%	0.2%	0.67%
	0	5.9 mg B/kg	17.5 mg B/kg	58.5 mg B/kg
1
2	8.2	7.68	7.98	7.00*
3	7.14	6.72	7.47	6.47
6
12
18	5.16	5.46	5.55	4.92
24	7.09	5.72	7.35	7.90
	Female
1
2	7.36	7.44	7.46	7.57
3	5.64	7.03	6.47	6.52
6
12
18	6.58	6.11	5.69	5.73
24	6.22	6.24	6.22	5.92

* Significantly different from controls

Missing data not thought to be significant according to the summary of the study

 

Conclusions:

Endpoint Effect level
NOAEL 17.5 mg Boron/kg bw/day (nominal)
LOAEL 58.5 mg Boron/kg bw/day (nominal)

Testicular atrophy and seminiferous tubule degeneration was observed at 6, 12 and 24 months at the highest dose level only. No treatment related effects were observed in the mid and low dose groups.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

100 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

The read-across study is reliable with restrictions

System:

male reproductive system

Organ:

seminiferous tubules

testes

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

In accordance to Regulation (EC) No 1272/2008, the source substance, boric acid, is classified as Repr. 1B H360FD and is considered a suitable analogue; therefore, it is concluded the target substance is also classified as Repr. 1B H360FD and does not warrant an additional classification for STOT-RE.