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Toxicological information

Toxicity to reproduction: other studies

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Administrative data

Endpoint:
toxicity to reproduction: other studies
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
No data
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Does not meet important study design or analytical criteria. 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

Reference
Reference Type:
publication
Title:
Effect of boric acid on the generative function in males.
Author:
Tarasenko NY, Kasparov AA & Strongina OM
Year:
1972
Bibliographic source:
Gigiena Truda y Professionalnye Zabolevaniya 16 (11): 13 - 16.

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: No data
Deviations:
not specified
Principles of method if other than guideline:
Groups of 12 male rats were exposed to aerosols of 9.6 ± 0.5mg/m3 and 48.6 ± 1.46mg/m3 boric acid for 4 hours/day for four months. When treatment was ended six males from the test and control groups were mixed (in separate cages) with an equal number of healthy oestrous females. Histological examinations of the testes were later performed.
GLP compliance:
no
Remarks:
Study pre-dates GLP.
Type of method:
in vivo

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material: Boric acid

Test animals

Species:
rat
Strain:
not specified
Sex:
male

Administration / exposure

Route of administration:
inhalation
Type of inhalation exposure (if applicable):
not specified
Vehicle:
not specified
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
4 hours per day
Frequency of treatment:
Daily
Duration of test:
4 months
Doses / concentrations
Remarks:
Doses / Concentrations:
aerosols of 9.6 ± 0.5mg/m3 and 48.6 ± 1.46mg/m3
Basis:
no data
No. of animals per sex per dose:
12 males per group
Control animals:
yes
Details on study design:
Groups of 12 male rats were exposed to aerosols of 9.6 ± 0.5 mg/m3 and 48.6 ± 1.46mg/m3 boric acid for 4 hours/day for four months. When treatment was ended six males from the test and control groups were mixed (in separate cages) with an equal number of healthy oestrous females. After a single and double mating vaginal smears of females were examined for spermatozoa.

Results and discussion

Effect levels

Dose descriptor:
LOAEL
Effect level:
9.6 mg/m³ air
Based on:
test mat.
Sex:
male
Basis for effect level:
other: Animals exposed to 9.6 ± 0.5 mg/m3 boric acid exhibited atrophied testis, reduced numbers and lifetime of spermatozoa, with pathological changes in the testis, including desquamation of the epithelium and necrotic cells.

Observed effects

Animals exposed to 9.6 ± 0.5 mg/m3 boric acid exhibited atrophied testis, reduced numbers and lifetime of spermatozoa, with pathological changes in the testis, including desquamation of the epithelium and necrotic cells. The effects were more severe in the 48.6 ± 1.46 mg/m3 dose group, this group also exhibiting a persistent retardation in growth as compared to the controls. Effects on the liver, kidneys, spleen and lungs were also observed.

Any other information on results incl. tables

There are a number of criticisms of this study, which prevent its use in the risk assessment of boric acid. Limitations were as follows:
1.
 No indication of the type of inhalation chamber is given. It was not clear as to whether exposure was to the whole body or nose only. There was no indication of aerosol size.
2.
 The methodology of investigation of the testis was not recognised.
3.
 There were no units given for spermatogenic index, nor for the numbers of spermatozoa. The term "lifetime" was not understood, and it was not clear what has been measured.
4.
The histological criteria used in the table of morphological characteristics were not indicators that are normally used.

Applicant's summary and conclusion

Conclusions:
Animals exposed to 9.6 ± 0.5 mg/m3 boric acid exhibited atrophied testis, reduced numbers and lifetime of spermatozoa, with pathological changes in the testis. The effects were more severe in the 48.6 ± 1.46 mg/m3 dose group. However, there were a number of limitations relating to the methodology and reporting.
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.