Dipotassium tetraborate

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 (Weir and Fisher, 1972; 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 (Weir, 1966) that corresponds to a NOAEL of 94.6 mg dipotassium tetraborate/kg bw (anhydrous, and 123.7 mg dipotassium tetraborate tetrahydrate/kg bw).

Based on the sub-acute inhalation study on boron oxide conducted in rats (Wilding, 1960), the NOAEC for systemic effects is equivalent to 146 mg B/m³ that corresponds to a NOAEC of 789 mg dipotassium tetraborate/m³ (anhydrous, and 1032 mg dipotassium tetraborate tetrahydrate/m³).

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

94.6 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

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

November 1957 - July 1958

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable well documented study report (no GLP) which meets basic scientific principles.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Groups of albino rats and dogs were exposed to aerosols of boron oxide in dynamic chambers. The rats were individually caged in racks, 10 cages each, which were randomly changed for each exposure. The animals were exposed for 6 hours a day for 5 days a week.
70 rats exposed for 24 weeks 77 mg/m³,
4 rats exposued for 12 weeks, 175 mg/m³
20 rats exposed for 10 weeks, 470 mg/m³
3 dogs exposed for 23 weeks , 57 mg/m3.

GLP compliance:

no

Limit test:

no

Species:

other: rats and dogs (only females)

Strain:

other: rats (albino)

Sex:

male/female

Details on test animals or test system and environmental conditions:

No further data available

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

not specified

Vehicle:

air

Remarks on MMAD:

MMAD / GSD: Rats:
Dose group of 77 mg/m³: 2.5 microns;
Dose group of 175 mg/m³: 1.9 microns;
Dose group of 470 mg/m³: 2.4 microns;
Dogs:
Dose group of 57 mg/m³: 2.4 microns.

Details on inhalation exposure:

Groups of albino rats and dogs were exposed to aerosols of boron oxide in four dynamic chambers having volumes of 20, 100, 1000, and 1000 liters, respectively. The rats were individually caged in racks, 10 cages each, which were randomly changed for each exposure. The animals were exposed for 6 hours a day for 5 days a week.
Boron oxide, which was presized, was dispersed from modified Wright dust dispersers into the chambers at a fairly constant rate throughout the exposure period. Large particles were eliminated by means of a settling column between the disperser and the mixing bowl, where air entered the top of the chamber. A flow of room air of about half of the chamber volume per minute was maintained.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples for determination of airborne concentrations of boron oxide were withdrawn from the chambers every hour and collected by means
of a filter paper sampler containing 5/ 8-inch disc s of Knowlton filter paper, Grade 100. The boron oxide was dissolved in water and the amount estimated by the carmine sulfuric-acid method. Standard solutions of boron oxide were run with every set to reduce possible errors in time of color development, acid concentration, or temperature. Samples for particle-size determinations of the aerosol were collected by means of a modified Cascade impactor, and mass median diameters (MMD) were derived by use of predetermined stage calibrations for boron oxide.

Duration of treatment / exposure:

Rats:
Dose group of 77 mg/m³: 24 weeks;
Dose group of 175 mg/m³: 12 weeks;
Dose group of 470 mg/m³: 10 weeks;
Dogs:
Dose group of 57 mg/m³: 23 weeks

Frequency of treatment:

6 hours a day for 5 days a week

Dose / conc.:

57 mg/m³ air (nominal)

Dose / conc.:

77 mg/m³ air (nominal)

Dose / conc.:

175 mg/m³ air (nominal)

Dose / conc.:

470 mg/m³ air (nominal)

No. of animals per sex per dose:

Rats:
Dose group of 77 mg/m³: 70 animals;
Dose group of 175 mg/m³: 4 animals;
Dose group of 470 mg/m³: 20 animals;
Dogs:
Dose group of 57 mg/m³: 3 animals.

Control animals:

yes

Details on study design:

No data

Positive control:

No data

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS: Yes

BODY WEIGHT: Yes

HAEMATOLOGY: Yes (see table 6 in "Results)

CLINICAL CHEMISTRY: Yes (see table 2 and 3 in "Results")

URINALYSIS: Yes
- Metabolism cages used for collection of urine: Yes
The urine of control and exposed rats was analyzed for boron by spectrographic methods.

OTHER:
- The fragilition of rat femurs, as measured by the breaking point, is shown in table 5. The ratio of the fracture weight in kg to the least diameter in mm was taken as the index for comparison of bone fragilition.
- Roentgenograms of control rats and those exposed to 77 mg/m³ were made.

Sacrifice and pathology:

- Tissues of the lungs, trachea, pancreas, thyroids, adrenals, eyes, femurs, ribs, bone marrow, liver, heart, spleen, kidneys, brain, stomach, intestines, ovaries, testes, lymph nodes, and muscles have been examined histologically for evidence of pathology.
Samples of the above tissues of exposed and control animals were dissolved in 20% sodium hydroxide and analyzed spectrographically for boron content.

- The percentage of body weight of heart, lungs, liver, and kidneys from five rats exposed to the aerosol for 20 weeks was compared with control rats.

Other examinations:

No data

Statistics:

No data

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

a slight reddish exudate from the nose (470 mg/m³)

Mortality:

mortality observed, treatment-related

Description (incidence):

a slight reddish exudate from the nose (470 mg/m³)

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

considerable differences in the pH, volume, and creatinine coefficient.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

considerable amounts of boron were excreted by the exposed rats and averaged 11.90 mg/kg/day

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY
At no time were any toxic signs noticed, nor were there any deaths from inhalation of the boron-oxide aerosol. However, some of the rats exposed to a concentration of 470 mg/m³ had a slight reddish exudate from the nose. Since these animals were covered with the dust there was probably local irritation of the external nares and some irritation from scratching. This concentration produced a dense cloud of fine particles. Workers experienced in the aerosol field expressed their belief that visibility in such a cloud would probably be limited to 10 to 12 feet.

BODY WEIGHT AND WEIGHT GAIN
The weight changes of control and exposed aniamls are shown in figure 2 (please see attached). Since female rats bad almost reached full growth at the time of initiation of therre exposures, whereas males far from their peak growth were used, the different growth rates of the two sexes are not believed to be attributable to the exposure.The control rats grew about 9% faster than those exposed to a concentration of 470 mg/m³, whereas those exposed to 77 mg/m³ gained the same amount or slightly more than their controls for the same period of time. The mature dogs showed slight fluctuations in weight but no general trend in either direction.

HAEMATOLOGY
There was a slight and probably insignificant rise in the leucocyte counts of the exposed dogs that may suggest a slight response to poisoning
by the aerosol. There were no other changes, except for the usual fluctuations, and no significant difference from the control (table 6).


CLINICAL CHEMISTRY
There were no modifications in the sugar or albumin content of the urine of the exposed rate and the controls. There were considerable
differences, however, in the pH, volume, and creatinine coefficient, as shown in table 2. The changes were analyzed by the T-test and found to be significantly different, with the following values of probability: volume P = 5%, pH and creatinine coefficient P = 1%. The formation of boric acid by hydration in the body probably caused the greater acidity of the urine of the exposed rats. The increased volume is undoubtedly accounted for by the known diuretic property of boric acid. The cause of increased creatinine excretion is not known. These values returned to normal a week after termination of the exposure.
Chemical analyses of six common blood constituents are given in table 3, for groups of rats exposed for 24 weeks to two concentrations of aerosols. There were no constant changes in either direction and no significant difference from the control values. Since no control values were determined
for the female rats the possible significance of apparent changes in sugar and lactic acid were undetermined.

In table 7 are given the results of the chemical analyses of some constituents of the dog blood. As with the rat blood, there were no changes from the pre-exposure values nor from those of the control dog. Sulfobromophthalein retention tests, for liver damage, were also negative as compared to the control.

URINALYSIS
The urine of control and exposed rats was analyzed for boron by spectrographic methods. The data show that considerable amounts of boron were excreted by the exposed rats and averaged 11.90 mg/kg/day. The controls excreted 0.24 mg/kg/day, or about 10 µg/mL. The data are presented
in table 4.

ORGAN WEIGHTS
The percentage of body weight of heart, lungs, liver, and kidneys from five rats exposed to the aerosol for 20 weeks was compared with control
rats. The differences were not significant.

HISTOPATHOLOGY: NON-NEOPLASTIC
No differences were noted between the tissues of the exposed and control animals. There were no signs of pneumoconiosis. Samples of the tissues of exposed and control animals were dissolved in 20% sodium hydroxide and analyzed spectrographically for boron
content. Standard solutions of boron oxide in water were aaalyzed and showed that by the method a minimum of 2.5 µg/mL of boron could be detected. The use of the method would have detected 0.011% of boron in the lung sample analyzed and a thid that amount in the other tissues. The rats had been exposed for 6 weeks to a concentration of 77 mg/m³ of boron oxide. There was no boron found in any of the samples. The rats were, however, in metabolism cages for 60 hours after exposure and before being killed. If boron had been present, it is possible that it was eliminated during that time.

OTHER FINDINGS
The fragilition of rat femurs, as measured by the breaking point, is shown in table 5. The ratio of the fracture weight in kg to the least diameter in mm was taken as the index for comparison of bone fragilition. There was no significant difference between the controls and those exposed to the aerosol, as shown by the t- test.
Roentgenograms of control rats and those exposed to 77 mg/m³ of boron oxide for 10 weeks showed no detectable effects.

Dose descriptor:

NOAEC

Remarks:

systemic (rats)

Effect level:

470 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No systemic effects were noted at this dose level

Dose descriptor:

NOAEC

Remarks:

local (rats)

Effect level:

175 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: due to local effects (slight reddish exudate from the nose) observed in animals at 470 mg/m³

Dose descriptor:

NOAEC

Remarks:

systemic (dogs)

Effect level:

57 mg/m³ air (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: No changes or toxic signs were noted.

Critical effects observed:

not specified

Table 1. Exposure animals to aerosols of boron oxide

Species	No.	Chamber size	Average concentration	Duration of exposure	Particle size, MMD
		litters	mg/m³	weeks	microns
Rat	70	1000	77	24	2. 5
Rat	4	20	175	12	1.9
Rat	20	100	470	10	2.4
Dog	3	1000	57	23	2. 4

 

Table 2. The pH, volume and creatinine coefficient for urine of control and of exposed rats (concentration 77 mg/m³)

 

Weeks of exposure	pH		Volume		Creatinine coefficient
	Exposed	Control	Exposed	Control	Exposed	Control
			ml/kg/day		mg/kg/day
4	8.66	8.94	30	12	14.7	2.2
6	-		33	43	9.3	4.0
8	8.30	8.85	44	20	13. 9	1.6
10	-	-	52	24	18. 1	3. 6
12	-	-	41	21	17. 2	3.8
14	-	-	55	22	12. 1	10.8
16	8.24	8.94	28	13	18. 1	7.6
18	8.16	8.78	23	11	16.3	11.8
20	7.38	9.05	17	11	17. 9	11.2
22	8.24	8.90	24	17	14. 9	7.2
Average	8.16	8.91	34.7	19.4	15.3	6.4

 

Table 3. Chemical analyses of the blood of rats exposed to aerosols of boron oxide

Time of exposure	Sugar	Lactic acid	Protein	Inorganic phosphorus	Creatinine	Cholesterol
weeks	mg	%	g %		m %
Females exposed to 470 mg/m³
2	119	29	5.9	10. 5	1.0	-
4	53	50	5. 5	8.4	1.2	-
6	52	52	7. 5	-	-	-
8	* 78	30	6. 6	4. 7	-	-
10	55	60	7.4	5.1	-	-
Males exposed to 77 mg/m³
2	116	37	7.2	5.6	-	-
4	120	14	9.6	4.4	-	-
6	87	47	5.8	4.2	0.8	-
8	80	39	6.5	5.0	1.2	-
10	120	32	6.2	4.4	0.9	-
12	59	28	4.5	5.4	0.8	-
14	88	29	7. 3	5.1	0.9	-
16	104	30	6. 7	5.2	1.0	83
18	86	27	6.8	4.4	0. 6	-
20	161	13	7.4	4.6	1.0	91
22	138	37	6.8	5. 1	0.8	121
24	82	55	7.5	4. 7	0.5	127
Average	103	32	6.8	4.8	0.94	101
Male controls (13 samples)
Average	104	37	6.8	5.5	1.04	100

 

Table 4. Boron content of urine control rats and of rats exposed to aerosols of boron oxide

Weeks of exposure	Urinary boron content* (mg/kg/day)
	Controls	Exposed
2	-	16.6
4	0.7	12.3
6	0.2	7.4
8	0.3	1.9
10	0.2	5.5
12	0.1	23.2
14	0.2	2.8
16	0.1	20.7
18	0.1	20.7
20	0.3	7.0
22	0.2	12.7
Average	0.24	11.9

* When the urine of the rats was analyzed a week after the end of the period of exposure, the boron content in the urine of the control rats and exposed rats was 0.3 mg/kg/day. After a 2-week interval, the boron content in the urine of the control rats wae 0.5 mgjkglday; in the urine of the exposed rats, it was 0.9 mg/kg/day.

 

Table 5. Fragility of femurs of control rats and rats exposed to an aerosol of boron dioxide

Group	No.	Least diameter	Fracture weight	Fracture weight least diameter	Standard deviation
		mm	kg	av*
Controls	14	2.68	6.6	2.43	0.69
Exposed*	8	2.70	6.2	2.30	0.87

* Arerages of groups that had been exposed for 6 and 10 weeks to a concentraam of 470 mg/m³

Conclusions:

No toxic signs were evident in any of the animals. NOAEC of 470 mg/m³ for systemic toxicity in rats is established based on the study results. NOAEC of 175 mg/m³ is appropriate for local effects due to irritation of noses of rats. NOAEC of 57 mg/m³ for dogs is based on the absence of any toxic effect.

Executive summary:

Groups of albino rats and dogs were exposed to aerosols of boron oxide in dynamic chambers. The rats were individually caged in racks, 10 cages each, which were randomly changed for each exposure. The animals were exposed for 6 hours a day for 5 days a week. 70 rats were exposed for 24 weeks (77 mg/m³), 4 rats were exposued for 12 weeks (175 mg/m³), 20 rats were exposed for 10 weeks (470 mg/m³) and 3 dogs were exposed for 23 weeks to 57 mg/m³. The test concentrations were verified analytically and mass median diameters (MMAD) were derived.

No toxic signs were evident in any of the animals. All groups of rats exposed to concentrations of 77 and 470 mg/m³ gained weight at about the same rate as their controls. Chemical analyses of dog and rat blood, and urine showed no changes from control values, except for an increased urinary excretion of creatinine in the rats, and lower pH, increased volume, and increased boron content in the rat urine. No changes were found as a result of aerosol exposures in the following:

1. rat tissues and organs

2. bone fragility

3. roentgenograms of rat bones

4. hematology of dog blood

5. sulfobromophthalein retention

6. rat organ weight.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

789 mg/m³

Study duration:

subacute

Species:

rat

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

Boric acid and disodium tetraborate are classified under the 1^stATP to CLP as Repr. 1B; H360FD.

However, text of the 30th ATP as published in the EU Official Journal, 15 September 2008 stated that “The classification and labelling of the substances listed in this Directive should be reviewed if new scientific knowledge becomes available. In this respect, considering recent preliminary, partial and not peer-reviewed information submitted by industry, special attention should be paid to further results of epidemiological studies on the Borates concerned by this Directive including the ongoing study conducted in…”

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).

A weight of evidence approach was used in evaluating numerous independent studies on the determination of the hazard of boric acid to humans. Information that was considered together included results of in vitro tests, animal data, occupational exposure data, epidemiological studies and mechanistic data.

Extensive evaluations of sperm parameters in highly exposed workers in Turkey and China have demonstrated no effects on male fertility. No evidence of developmental effects in humans attributable to boron (B) has been observed in studies of populations with high exposures to boron. Although the epidemiological studies have methodological deficiencies, collectively these studies consistently show an absence of effects in highly exposed populations.

Workers in boron mining and processing industries represent the maximum possible human exposure. However, a comparison of blood, semen and target organ boron levels in studies of laboratory animals and human studies shows that boron industry worker exposures are lower than untreated control rats.

Mechanistic data provide possible explanations for the absence of developmental and reproductive effects in humans exposed to high levels of boron. Recent studies provide evidence that boric acid may act by similar mechanisms in causing developmental effects in mice as sodium salicylate (the natural deacetylated form of aspirin and a rodent teratogen) including effects on Hox gene expression and inhibition of embryonic histone deacetylases. Although aspirin is known to cause developmental effects in laboratory animals, controlled human studies have not demonstrated developmental effects in humans. Similar mechanisms of action of boric acid and aspirin, and the absence of developmental effects in humans ingesting aspirin suggest that boric acid related developmental effects in humans are unlikely. 

Additionally, zinc levels in soft tissue in humans is over 2 times greater than in comparative tissues in rats (King et al. 2000; Yamaguchi et al. 1996), which explain in part the absence of fertility and developmental effects in humans. Zinc has been shown to protect against testicular toxicity of cobalt and cadmium (Anderson et al. 1993), and the developmental effects of cadmium (Fernandez et al. 2003). There is evidence that zinc interacts with boric acid in the body reducing the toxicity of boric acid. The interaction of zinc and boric acid is evident by the low acute toxicity of zinc borate (absorbed as boric acid and zinc) with a LD50 value greater than 10,000 mg/kg-body weight in rats (Daniels 1969) compared to disodium tetraborate pentahydrate (similar % boron composition as zinc borate) with a LD50 value of 3300 mg/kg-body weight. Furthermore, no toxic effects were observed in the testes of males (a target organ of boric acid) administered 1000 mg zinc borate/kg/day in a 28-day repeated dose oral gavage toxicity study, equivalent dose of boron of 50 mg B/kg bodyweight (Wragg et al. 1996). The LOAEL for testicular effects is 26 mg B/kg body weight. 

Based on the total weight of evidence, the data show that it is improbable that boric acid or dipotassium tetraborate will cause reproductive or developmental effects in humans.

Therefore, based on a total weight of evidence, Category 2 H361d: suspected human reproductive toxicant, suspected of damaging the unborn child is considered the appropriate classification. Extensive evaluations of sperm parameters in highly exposed workers have demonstrated no effects on male fertility. While no developmental effects have been seen in highly exposed populations, epidemiological studies of developmental effects are not as robust as the fertility studies, warranting the Category 2 H361d.