Disodium octaborate

Endpoint summary

Description of key information

A number of sub-chronic and chronic studies on boric acid and disodium tetraborate decahydrate were carried out in rats, mice and dogs. In some cases these studies are research studies (Dixon et al, 1976; Seal and Weeth, 1980; Lee et al., 1978; Treinen and Chapin, 1991; Ku et al., 1993), but most support that boron can cause adverse haematological effects and that the main target organ of boron toxicity is the testis. The NOAEL for fertility effects is equivalent to 17.5 mg B/kg bw/day that corresponds to NOAEL of 83.3 mg disodium octaborate /kg bw (Weir, 1966).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

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:

other: Meets generally accepted scientific standards with acceptable restrictions.

Qualifier:

no guideline followed

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.

Dose / conc.:

0 mg/kg bw/day (nominal)

Dose / conc.:

33 mg/kg bw/day (nominal)

Remarks:

corresponds to 5.9 mg B/kg bw/day

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

corresponds to 17.5 mg B/kg bw/day

Dose / conc.:

334 mg/kg bw/day (nominal)

Remarks:

corresponds to 58.5 mg B/kg bw/day

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

83.3 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

The study meets generally accepted scientific standards with acceptable restrictions.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

BMCL05

86.6 mg/m³

Species:

rat

Quality of whole database:

The key developmental study provides BMDL05 which is based on results of two studies and therefore is more accurate and more precise than NOAEL established in one study. The oral BMDL05 has been extrapolated to the inhalation BMCL05 of 86.6 mg/m³ for disodium octaborate by route-to-route extrapolation (see section "DNEL derivation").

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

Additional information

A number of studies on boric acid or disodium tetraborate decahydrate in diet or via drinking water for periods of 30 days to two years in rats, mice and dogs are available, however, the majority of these studies do not comply with current test guidelines, and they lack essential information regarding e. g. histological descriptions and statistical evaluations of the results. Most studies support that boron can cause adverse haematological effects and that the main target organ of boron toxicity is the testis. Other effects observed at high doses include rapid respiration, hunched position, bloody nasal discharge; urine stains on the abdomen, inflamed bleeding eyes, desquamation and swollen paws and tail, reduced food consumption and body weight gain. Treatment with boric acid and disodium tetraborate decahydrate disrupted spermiation, induced degeneration of testicular tubules and caused testicular atrophy. For effects on the blood system extramedullary haematopoiesis, reduced red cell volume and haemoglobin values and deposition of haemosiderin in spleen, liver and proximal tubules of the kidney were described. Several cases of anaemia have been observed in human poisoning cases. However, although doses in these poisoning cases are difficult to define, the effects occurred generally at relatively high concentrations.

Groups of albino rats and dogs were exposed to aerosols of boron oxide for periods up to 24 weeks, 6 hours a day for 5 days a week. The highest concentration rats were exposed was 470 mg/cu m for a period of 10 weeks. There were no significant changes in tissues from rats or in chemical analyses of rats and dogs blood. No changes or toxic signs were noted in the mature female dogs exposed for 23 weeks to a concentration of 57 mg/cu m (Wilding et al. 1959; 1960).

Boric acid, the main species present under physiological conditions, acts as a Lewis acid and as such owns the ability to complex with hydroxyl, amino and thiol groups from diverse biomolecules, like e. g. carbohydrates and proteins (BfR, 2006). Such a mechanism could be involved in effects of boron on different enzyme activities (Huel et al., 2004).

A NOAEL for effects on testes and the blood system of 17.5 mg B/kg bw/day can be derived (with a LOAEL of 58.5 mg B/kg bw/day) from two 2-year studies in rats on boric acid and disodium tetraborate decahydrate (Weir, 1966a, b).

Please also refer to the read-across statement attached to section 13.

Justification for classification or non-classification

Disodium octaborate anhydrous and disodium octaborate tetrahydrate are listed in Annex VI to Regulation (EC) No 1272/2008 under Index No 005 -020 -00 -3 with the following harmonised classification:

Repr. 1B, H360FD May damage fertility. May damage the unborn child

Also boric acid and disodium tetraborates are classified under the 1^stATP to CLP as Repr. 1B; H360FD.

Data for disodium octaborate tetrahydrate for reproductive toxicity is based on read-across from other tested borates (e.g. boric acid) and borate salts (borax or disodium tetraborate decahydrate) because its hydrolysis results in the formation of the same substances.

While boron has been shown to adversely affect male reproduction in laboratory animals, there was no clear evidence of male reproductive effects attributable to boron in studies of highly exposed workers (Whorton et al. 1994; Sayli 1998, 2001; Robbins et al. 2010; Scialli et al. 2010). Not only are these the most exposed workers, but the Chinese worker study is the most sensitive study that has been carried out as semen analysis was performed, a very sensitive detection system for testicular damage. There is no evidence of developmental effects in humans attributable to boron in studies of populations with high exposures to boron (Tuccar et al 1998; Col et al. 2000; Chang et al. 2006).

Several studies in laboratory animals and in vitro studies have recently been completed that demonstrate the protective effect of zinc against boric acid related developmental and fertility toxicity of boric acid. Humans have intrinsically higher levels of zinc than laboratory animals that explain in part the absence of boric acid related reproductive toxicity effects in humans. These studies provide important mechanistic data on the effects of zinc on boric acid related reproductive toxicity that raises doubt about the relevance of the effects for humans. These data provide further justification that classification of Repr. Category 2 H361d is more appropriate for disodium octaborate than Repr. Category 1B H360FD.

Nonetheless, the harmonised classification according to Annex VI to Regulation (EC) No 1272/2008 applies:

Repr. 1B, H360FD May damage fertility. May damage the unborn child