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Toxicological information

Repeated dose toxicity: oral

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Administrative data

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: see 'Remark'
Remarks:
Meets generally accepted scientific standards with acceptable restrictions. This study is conducted on an analogue substance. Read-across is justified on the following basis: In aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic borates such as boric acid, disodium tetraborate decahydrate, disodium tetraborate pentahydrate, boric oxide and disodium octaborate tetrahydrate will predominantly exist as undissociated boric acid. At about pH 10 the metaborate anion (B(OH)4-) becomes the main species in solution (WHO, 1998). This leads to the conclusion that the main species in the plasma of mammals and in the environment is un-dissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as un-dissociated boric acid under the same conditions. For comparative purposes, exposures to borates are often expressed in terms of boron (B) equivalents based on the fraction of boron in the source substance on a molecular weight basis. Some studies express dose in terms of B, whereas other studies express the dose in units of boric acid. Since the systemic effects and some of the local effects can be traced back to boric acid, results from one substance can be transferred to also evaluate the another substance on the basis of boron equivalents. Therefore data obtained from studies with these borates can be read across in the human health assessment for each individual substance. Conversion factors are given in the table below. Conversion factor for equivalent dose of B Boric acid H3BO3 0.175 Boric Oxide B2O3 0.311 Disodium tetraborate anhydrous Na2B4O7 0.215 Disodium tetraborate pentahydrate Na2B4O7•5H2O 0.148 Disodium tetraborate decahydrate Na2B4O7•10H2O 0.113 Disodium octaborate tetrahydrate Na2B8O13•4H2O 0.210 Sodium metaborate (anhydrous) NaBO2 0.1643 Sodium metaborate (dihydrate) NaBO2•2H2O 0.1062 Sodium metaborate (tetrahydrate) NaBO2•4H2O 0.0784 Sodium pentaborate (anhydrous) NaB5O8 0.2636 Sodium pentaborate (pentahydrate) NaB5O8∙5H2O 0.1832 References: WHO. Guidelines for drinking-water quality, Addendum to Volume 1, 1998.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
1966
Report Date:
1966
Reference Type:
study report
Title:
Unnamed
Year:
1967
Report Date:
1967
Reference Type:
publication
Title:
Toxicologic studies on borax and boric acid.
Author:
Weir RJ & Fisher RS
Year:
1972
Bibliographic source:
Toxicology and Applied Pharmacology 23: 351 - 364.

Materials and methods

Test guideline
Qualifier:
according to
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

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material: Boric acid
- Physical state: Fine white powder with no odour
- Analytical purity: > 99 %
- Stability under test conditions: Stable

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Weight at study initiation: Males 93 - 129 g; females 86 - 128 g

Administration / exposure

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.
Doses / concentrations
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

Examinations

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.

Results and discussion

Results of examinations

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.

Effect levels

open allclose all
Dose descriptor:
NOAEL
Effect level:
100 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
clinical signs
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:
clinical signs
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.

Target system / organ toxicity

Critical effects observed:
not specified

Any other information on results incl. tables

 

Parameter

Control

Low

dose

Medium

dose

High

dose

Dose-

response

+/-

ma

fa

ma

fa

ma

fa

ma

fa

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 (x103/cm2)

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 (x103/cm2)

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

 

Applicant's summary and conclusion

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.
Read-across is justified on the basis detailed in the rationale for reliability above. This study is therefore considered to be of sufficient adequacy and reliability to be used as a supporting study and no further testing is justified.