Boric acid

Repeated dose toxicity: inhalation

Administrative data

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.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1960

Materials and methods

Test guideline

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

Test material

Test material information

Constituent 1

Reference substance name:

Boric oxide

IUPAC Name:

Boric oxide

Test animals

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

Administration / exposure

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

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

57 mg/m³ air (nominal)

Doses / concentrations 2

Dose / conc.:

77 mg/m³ air (nominal)

Doses / concentrations 3

Dose / conc.:

175 mg/m³ air (nominal)

Doses / concentrations 4

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

Examinations

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

Results and discussion

Results of examinations

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.

Effect levels

1

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

2

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

3

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.

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 1. Exposure animals to aerosols of boron oxide

Species	No.	Chamber size	Average concentration	Duration of exposure	Particle size, MMD
		liters	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

Applicant's summary and conclusion

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. rattissues and organs

2. bone fragility

3. roentgenograms of rat bones

4. hematology of dog blood

5. sulfobromophthalein retention

6. rat organ weight.