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Boron (Boron and Borates only)
CASRN 7440-42-8
Contents
0410
Boron (Boron and Borates only); CASRN 7440-42-8
Health assessment information on a chemical substance is included in IRIS only
after a comprehensive review of chronic toxicity data by U.S. EPA health
scientists from several Program Offices and the Office of Research and
Development. The summaries presented in Sections I and II represent a
consensus reached in the review process. Background information and
explanations of the methods used to derive the values given in IRIS are
provided in the Background Documents.
STATUS OF DATA FOR Boron (Boron and Borates only)
File On-Line 10/01/1989
Category (section) Status Last Revised
----------------------------------------- -------- ------------
Oral RfD Assessment (I.A.) on-line 06/01/1995
Inhalation RfC Assessment (I.B.) no data
Carcinogenicity Assessment (II.) no data 05/01/1993
_I. CHRONIC HEALTH HAZARD ASSESSMENTS FOR NONCARCINOGENIC EFFECTS
__I.A. REFERENCE DOSE FOR CHRONIC ORAL EXPOSURE (RfD)
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
Last Revised -- 06/01/1995
The oral Reference Dose (RfD) is based on the assumption that thresholds exist
for certain toxic effects such as cellular necrosis. It is expressed in units
of mg/kg-day. In general, the RfD is an estimate (with uncertainty spanning
perhaps an order of magnitude) of a daily exposure to the human population
(including sensitive subgroups) that is likely to be without an appreciable
risk of deleterious effects during a lifetime. Please refer to the Background
Document for an elaboration of these concepts. RfDs can also be derived for
the noncarcinogenic health effects of substances that are also carcinogens.
Therefore, it is essential to refer to other sources of information concerning
the carcinogenicity of this substance. If the U.S. EPA has evaluated this
substance for potential human carcinogenicity, a summary of that evaluation
will be contained in Section II of this file.
NOTE: The Oral RfD for boron may change in the near future pending the
outcome of a further review now being conducted by the RfD/RfC Work Group.
___I.A.1. ORAL RfD SUMMARY
Critical Effect Experimental Doses* UF MF RfD
-------------------- ----------------------- ----- --- ---------
Testicular atrophy, NOAEL: 350 ppm 100 1 9E-2
spermatogenic arrest (8.8 mg/kg/day) mg/kg/day
2-Year Dog Study
Oral Exposure (diet) LOAEL: 1170 ppm
(29 mg/kg/day)
Weir and Fisher, 1972
*Conversion Factors: 1 ppm = 0.025 mg/kg/day (assumed dog food consumption).
Author converted borax and boric acid doses to boron equivalents.
___I.A.2. PRINCIPAL AND SUPPORTING STUDIES (ORAL RfD)
Weir, R.J., Jr. and R.S. Fisher. 1972. Toxicological studies on borax and
boric acid. Toxicol. Appl. Pharmacol. 23: 351-364.
Groups of 4 male and 4 female dogs were fed borax and boric acid in the diet
for 2 years. The NOAEL was established at 350 ppm of boron equivalents (8.8
mg/kg/day), highest dose tested. In an additional study, dogs were fed 1170
ppm (29 mg/kg/day) for 38 weeks. At this dose, severe testicular atrophy and
spermatogenic arrest occurred.
Groups of 35 male and 35 female rats were fed borax and boric acid in the diet
for 2 years at boron-equivalent doses of 117, 350, and 1170 ppm (5.9, 17.5 or
58.5 mg B/kg/day). No treatment-related effects were seen at 5.9 or 17.5
mg/kg/day, so the highest NOAEL is 17.5 mg/kg/day. The LOAEL is 58.5
mg/kg/day, based on the following: significantly decreased testes weights and
testes-to-body weight ratios; atrophied seminiferous epithelium; and decreased
tubular size in the testes. Brain and brain-to-body weight ratios were also
significantly decreased.
Schroeder and Mitchener (1975) reported a lifetime study in which mice were
administered boron in drinking water at 5 mg/L (equivalent to 8.1 mg
B/kg/day). No effects were observed with regard to body weight, longevity or
survival. The NOAEL in this study was 8.1 mg/kg/day.
___I.A.3. UNCERTAINTY AND MODIFYING FACTORS (ORAL RfD)
UF -- Used in accordance with Agency guidelines for a NOAEL from a lifetime
animal study.
MF -- None
___I.A.4. ADDITIONAL COMMENTS (ORAL RfD)
The two principal studies indicate that the dog is more sensitive than the
rat, with more severe testicular effects occurring at half the dose level in
the dog vs. the rat (29 mg/kg/day vs. 58 mg/kg/day).
Other studies reviewed:
1) 70-Day Study - rats: Groups of 15 rats were exposed to boron in drinking
water. LOAEL=23.7 mg/kg/day (150 mg B/L) (LDT: decreased body weights;
decreased weights of testes, seminal vesicles, spleens, and right femurs;
lower fat content of bones; and lower plasma triglycerides and protein
concentrations). At 300 mg B/L (44.7 mg/kg/day), spermatogenesis was
impaired. There was no NOAEL in this study (Seal and Weeth, 1980).
2) 13-Week Study - mice: Male and female mice were fed boric acid. LOAEL=
34-47 mg/kg/day (1200 ppm) (LDT: extramedullary hematopoiesis of spleen of
minimal to mild severity was observed in all groups). At the higher doses, 68
mg/kg/day (2500 ppm) to 544 mg/kg/day (20,000 ppm), degeneration or atrophy of
seminiferous tubules was observed in males (NTP, 1987).
3) 90-Day Study - rats: Boric acid and borax were administered in the diet at
52.5, 175, 525, 1750, and 5250 ppm (2.6, 8.8, 26, 88, and 260 mg B/kg/day.
The low dose caused an increase in the weight of the brain, spleen, kidneys,
liver, and ovaries in females. Increased kidney weight occurred at 175 ppm in
males. No organ weight changes were seen at 525 ppm in either sex. Severe
effects in both sexes were seen at 1750 ppm and above (organ and body weight
decreases) (Weir and Fisher, 1972).
4) 90-Day Feeding Study - dogs: Fed boron at levels of 17.5, 175, and 1750
ppm (0.44, 4.4, or 44 mg/kg/day). The lowest dose resulted in decreased
spleen/body weight ratio in male dogs; 175 ppm resulted in decreased
testes/body weight ratio; the highest dose produced severe testicular atrophy.
No changes in female organ weights were observed at 17.5 or 175 ppm. No
histologic changes were seen in dogs fed 175 ppm or below. Severe testicular
atrophy seen at highest dose (Weir and Fisher, 1972).
5) Multigeneration Reproductive Study - rats: Dosed at 117, 350, and 1170 ppm
(5.9, 17.5, 58.5 mg/kg/day). NOAEL=17.5 mg/kg/day; LOAEL=58.5 mg/kg/day;
(HDT: males showed lack of spermatazoa in atrophied testes; females showed
decreased ovulation) (Weir and Fisher, 1972).
6) 90-Day Reproductive Study - rats: Males were dosed with 0.3, 1.0, or 6.0
mg B/L (0.02, 0.072, or 0.426 mg/kg/day). NOAEL=0.426 mg/kg/day (HDT) (Dixon
et al., 1976).
7) 60-Day Reproductive Study - rats: Doses were 0, 500, 1000, or 2000 mg/kg
diet (equivalent to 25, 50, or 100 mg/kg/day). NOAEL=25 mg/kg/day; LOAEL=50
mg/kg/day; (decreased weights in liver, testes, and epididymis, and reduced
fertility) (Dixon et al., 1979).
___I.A.5. CONFIDENCE IN THE ORAL RfD
Study -- Medium
Data Base -- Medium
RfD -- Medium
The referenced lifetime dog study provides both a NOAEL and a LOAEL and
examines many biological endpoints, but has a limited number of experimental
animals; it rates a medium confidence. Several sub-chronic, chronic and
reproductive toxicity studies provide supportive data, but developmental data
do not exist; hence the data base rates a medium level of confidence. Medium
confidence in the RfD follows.
___I.A.6. EPA DOCUMENTATION AND REVIEW OF THE ORAL RfD
Source Document -- This assessment is not presented in any existing U.S. EPA
document.
Other EPA Documentation -- None
Agency Work Group Review -- 06/23/1988, 07/20/1989, 06/15/1993, 08/03/1994, 05/09/1995
Verification Date -- 07/20/1989
___I.A.7. EPA CONTACTS (ORAL RfD)
Please contact the Risk Information Hotline for all questions concerning this
assessment or IRIS, in general, at (513)569-7254 (phone), (513)569-7159 (FAX)
or RIH.IRIS@EPAMAIL.EPA.GOV (internet address).
__I.B. REFERENCE CONCENTRATION FOR CHRONIC INHALATION EXPOSURE (RfC)
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
Not available at this time.
_II. CARCINOGENICITY ASSESSMENT FOR LIFETIME EXPOSURE
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
Not available at this time.
_VI. BIBLIOGRAPHY
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
Last Revised -- 10/01/1989
__VI.A. ORAL RfD REFERENCES
Dixon, R.L., I.P. Lee and R.J. Sherins. 1976. Methods to assess reproductive
effects of environmental chemicals - Studies of cadmium and boron administered
orally. Environ. Health Perspec. 13: 59-67.
Dixon, R.L., R.J. Sherins, and I.P. Lee. 1979. Assessment of environmental
factors affecting male fertility. Environ. Health Perspec. 30: 53-68.
Seal, B.S. and H.J. Weeth. 1980. Effect of boron in drinking water on the
male laboratory rat. Bull. Environ. Contam. Toxicol. 25: 782-789.
Schroeder, H.A. and M. Mitchener. 1975. Life-term effects of mercury, methyl
mercury and nine other trace metals in mice. J. Nutr. 105: 452-458.
NTP (National Toxicology Program). 1987. Toxicology and carcinogenesis
studies of boric acid in B6C3F1 mice (feed studies). NTP Technical Report
Series No. 324. Research Triangle Park, NC.
Weir, R.J., Jr. and R.S. Fisher. 1972. Toxicologic studies on borax and boric
acid. Toxicol. Appl. Pharmacol. 23: 351-364.
__VI.B. INHALATION RfD REFERENCES
None
__VI.C. CARCINOGENICITY ASSESSMENT REFERENCES
None
_VII. REVISION HISTORY
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
-------- -------- --------------------------------------------------------
Date Section Description
-------- -------- --------------------------------------------------------
10/01/1989 I.A. Oral RfD summary on-line
10/01/1989 VI. Bibliography on-line
11/01/1989 I.A.6. Work group review date corrected
08/01/1990 I.A. Text edited
01/01/1992 IV. Regulatory Action section on-line
01/01/1993 II. Carcinogenicity assessment now under review
05/01/1993 II Work group review date added
07/01/1993 I.A. Oral RfD noted as pending change
07/01/1993 I.A.6. Work grp. rev. date added; mtg. & verif. date corrected
09/01/1994 I.A.6. Work group review date added
06/01/1995 I.A.6. Work group review date added
VIII. SYNONYMS
Substance Name -- Boron (Boron and Borates only)
CASRN -- 7440-42-8
Last Revised -- 10/01/1989
7440-42-8
BORON
Last updated: 5 May 1998
URL: http://www.epa.gov/iris/SUBST/0410.HTM
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