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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 that corresponds to NOAEL of 56.3 mg Boric oxide /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

+/-

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

 

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
56.3 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
58.4 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 inhalation BMCL05 of 58.4 mg/m³ for boric oxide 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 56.3 mg B/kg bwday) from two 2-year studies in rats on boric acid and disodium tetraborate decahydrate (Weir, 1966a, b).


Justification for classification or non-classification

Boric oxide/ diboron trioxid is listed in Annex VI to Regulation (EC) No 1272/2008 under Index No 005 -008 -00 -8 with the following harmonised classification:

Repr. 1B, H360FD: C ≥ 3,1 % May damage fertility. May damage the unborn child

Boric oxide is classified under the 1stATP 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).

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 boric oxide than Repr. Category 1B H360FD.

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.

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

Regarding systemic target organ toxicity after repeated exposures (STOT-RE), boric oxide does not meet criteria for classification and labelling according to EU CLP Regulation (EC) No. 1272/2008) because no other than testis target organs were identified during the study (Weir, 1966).