Tissue disposition of boron in male Fischer rats

Ku, Warren W.; Chapin, Robert E.; Moseman, Robert F.; Brink, Robert E.; Pierce, Katherine D.; Adams, Kelly Y.

doi:10.1016/0041-008x(91)90143-3

Cited by 101 publications

(53 citation statements)

References 16 publications

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“…Our observations that progressive accumulation does not occur are consistent with the experimental work at much higher doses in which animals that were fed diets containing up to 1575-ppm boron (67.9 mg boron/kg/day) did not demonstrate progressive increases in tissue levels once a plateau had been reached following the first day of dosing (10).…”

Section: Rationalesupporting

confidence: 78%

The Relationship of Blood- and Urine-Boron to Boron Exposure in Borax-Workers and the Usefulness of Urine-Boron as an Exposure Marker

Culver¹,

Shen²,

Taylor³

et al. 1994

Environmental Health Perspectives

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Daily dietary-boron intake and on-the-job inspired boron were compared with blood-and urine-boron concentrations in workers engaged in packaging and shipping borax. Fourteen workers handling borax at jobs of low, medium, and high dust exposures were sampled throughout full shifts for 5 consecutive days each. Airborne borax concentrations ranged from means of 3.3 mg/mi3 to 18 mg/m3, measured gravimetrically. End-of-shift mean blood-boron concentrations ranged from 0.1 1 to 0.26 pg/g; end-of-shift mean urine concentrations ranged from 3.16 to 10.72 pg/mg creatinine. Creatinine measures were used to adjust for differences in urine-specific gravity such that 1 ml of urine contains approximately 1 mg creatinine. There was no progressive increase in end-of-shift blood-or urine-boron concentrations across the days of the week. Urine testing done at the end of the work shift gave a somewhat better estimate of borate exposure than did blood testing, was sampled more easily, and was analytically less difficult to perform. Personal air samplers of two types were used: one, the 37-mm closed-face, two-piece cassette to estimate total dust and the other, the Institute of Occupational Medicine (IOM) sampler to estimate inspirable particulate mass. Under the conditions of this study, the IOM air sampler more nearly estimated human exposure as measured by blood-and urine-boron levels than did the sampler that measured total dust. The highest mean blood-and urine-boron levels in the workers were approximately an order of magnitude lower than blood and urine values found by others in dogs during feeding studies conducted as part of reproductive toxicity studies at the no-observed-adverse-effect level (NOAEL). The mean dietary intake of the workers was 1.35 mg boron/day, close to the 1.521 mg boron/day reported recently for the standard U.S. diet. Total estimated boron intake, which is diet plus environmental exposure, had for the high-borax dust exposure group a mean daily boron intake of 27.90 mg/day or, based on the body weights of the subjects, 0.38 mg boron/kg/day. These subjects had a mean blood-boron level of 0.26 pg boron/g blood, a factor of 10 lower than found in the dog or rat at NOAEL exposure levels. -Environ Health Perspect 102(Suppl 7): 133-137 (1994)

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Section: Rationalesupporting

confidence: 78%

The Relationship of Blood- and Urine-Boron to Boron Exposure in Borax-Workers and the Usefulness of Urine-Boron as an Exposure Marker

Culver¹,

Shen²,

Taylor³

et al. 1994

Environmental Health Perspectives

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“…Using the analytical method as described above, several hundred rat tissue samples from two studies (28,29), were analyzed for boron. A summary of the results of the analyses are presented in Tables 7 and 8.…”

Section: Resultsmentioning

confidence: 99%

Chemical disposition of boron in animals and humans.

Moseman¹

1994

Environ Health Perspect

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Elemental boron was isolated in 1808. It typically occurs in nature as borates hydrated with varying amounts of water. Important compounds are boric acid and borax. Boron compounds are also used in the production of metals, enamels, and glasses. In trace amounts, boron is essential for the growth of many plants, and is found in animal and human tissues at low concentrations. Poisoning in humans has been reported as the result of accidental ingestion or use of large amounts in the treatment of burns. Boron as boric acid is fairly rapidly absorbed and excreted from the body via urine. The half-life of boric acid in humans is on the order of 1 day. Boron does not appear to accumulate in soft tissues of animals, but does accumulate in bone. Normal levels of boron in soft tissues, urine, and blood generally range from less than 0.05 ppm to no more than 10 ppm. In poisoning incidents, the amount of boric acid in brain and liver tissue has been reported to be as high as 2000 ppm. Recent studies at the National Institute of Environmental Health Sciences have indicated that boron may contribute to reduced fertility in male rodents fed 9000 ppm of boric acid in feed. Within a few days, boron levels in blood and most soft tissues quickly reached a plateau of about 15 ppm. Boron in bone did not appear to plateau, reaching 47 ppm after 7 days on the diet. Cessation of exposure to dietary boron resulted in a rapid drop in bone boron. The analytical methodology developed and validated for these tissues consisted of microwave digestion of samples in concentrated nitric acid, followed by inductively coupled argon plasma emission spectroscopy analyses. The recovery of added boron from tissue samples was quantitative. The precision and accuracy were typically better than 6% and 12%, respectively. The method detection limit is typically 0.02 to 0.04 ppm of boron, depending on the sample matrix. -Environ Health Perspect 102 (Suppl 7): 113-117 (1994)

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“…Blood samples were collected retroorbitally at the end of weeks 1 and 2 to correlate with urine levels. A previous disposition study (7) had shown that testis boron levels were the same as blood levels. Table 1 shows that boric acid effectively inhibited reproduction in mice.…”

Section: Male Pathogenesis Studymentioning

confidence: 89%

The reproductive toxicity of boric acid.

Chapin

1994

Environ Health Perspect

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Previous studies on the reproductive toxicity of boric acid have indicated that male rodents suffer testicular atrophy after treatment. There were, however, no studies of the potential effects on female fertility or on the neonate. In addition, no study described the development of the testicular lesion, thought to be related to the mechanism of toxicity. A Reproductive Assessment by Continuous Breeding (RACB) study using mice exposed to boric acid at 1000, 4500, and 9000 ppm in the diet indicated that there are probably multiple sites of action, although male fertility appears very sensitive. Possible effects on female fertility cannot be separated from potential developmental toxicity and need additional investigation.Decrements in sperm motility were observed at all exposure levels, and testicular atrophy was confirmed in high-and middle-dose-group males.This was investigated further by timed serial-sacrifice studies using 9000 ppm in the diet of rats, which found that the first lesion seen in the testis was an inhibition of spermiation (release of mature spermatids). With continued dosing, this was followed by a disorganization of the normal ordered layering of the seminiferous epithelium, germ cell sloughing and death, and finally, atrophy. Subsequent studies using additional doses (2000, 3000, 4500, 6000, and 9000 ppm) found that it was possible to observe inhibited spermiation that did not progress to atrophy (4500 ppm and below) within the 9-week exposure period. Also, once atrophic (from 9000-and 6000-ppm exposures), there was no return of spermatogenesis after refeeding of normal diet for 8, 16, 24, or 32 weeks, despite the presence of a normal-sized population of spermatogonia that was seen to divide. No effects were observed in rats treated with 2000 ppm. Testicular boron concentrations remained steady during exposure at the same level as found in blood, and declined to background levels within 72 hr after cessation of exposure. Bone boron levels were greater than those found in blood, and maintained slightly elevated levels even 32 weeks after the cessation of exposure. These studies document the effects of boric acid on functional and structural aspects of the male reproductive system; demonstrate that the tissue concentration of boron, and not total dose, is important for the testicular toxicity; and show that there is a threshold for these effects. These studies also suggest that the potential for recovery from boric acidinduced testicular atrophy should be examined in other species to evaluate the significance of the persistent atrophy seen in the rats. -Environ Health Perspect 102(Suppl 7): 87-91 (1994)

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Tissue disposition of boron in male Fischer rats

Cited by 101 publications

References 16 publications

The Relationship of Blood- and Urine-Boron to Boron Exposure in Borax-Workers and the Usefulness of Urine-Boron as an Exposure Marker

The Relationship of Blood- and Urine-Boron to Boron Exposure in Borax-Workers and the Usefulness of Urine-Boron as an Exposure Marker

Chemical disposition of boron in animals and humans.

The reproductive toxicity of boric acid.

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