No abstract

Occupational exposure limits (OELs) for irritant dusts have had no quantifiable bases. This study (1) charted chemosensory feel, denoted chemesthesis here, to dusts of calcium oxide (1 to 5 mg/m(3)), sodium tetraborate pentahydrate [sodium borate] (5 to 40 mg/m(3)), and calcium sulfate (10 to 40 mg/m(3)); (2) examined correlates of the chemesthetic sensations; and (3) sought to illuminate the basis for potency. Twelve screened men exercised against a light load while they breathed air in a dome fed with controlled levels of dust for 20 min. Measured parameters included nasal resistance, nasal secretion, minute ventilation, heart rate, blood oxygenation, mucociliary transport time, and chemesthetic magnitude, calibrated to pungency of carbon dioxide. Subjects registered time-dependent feel from exposures principally in the nose, secondarily in the throat, and hardly in the eyes. Calcium oxide had the greatest potency, followed by sodium borate, with calcium sulfate a distant third. Of the physiological parameters, amount of secretion showed the best association with chemesthetic potency. That measure, as well as mucociliary transport time and minute ventilation, went into calculation of mass of dust dissolved into mucus. The calculations indicated that the two alkaline dusts increased in equal molar amounts with time. At equal molar concentrations, they had, to a first approximation, equal chemesthetic magnitude. On the basis of mass concentration in air or dissolved into mucus, calcium oxide and sodium borate differed in potency by a factor just above five, equal to the difference in their molecular weights. This relationship could inform the setting of OELs for a critical effect of irritation.

No abstract

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)

Literature from the first half of this century report concern for toxicity from topical use of boric acid, but assessment of percutaneous absorption has been impaired by lack of analytical sensitivity. Analytical methods in this study included inductively coupled plasma-mass spectrometry which now allows quantitation of percutaneous absorption of 10B in 10B-enriched boric acid, borax, and disodium octaborate tetrahydrate (DOT) in biological matrices. This made it possible, in the presence of comparatively large natural dietary boron intakes for the in vivo segment of this study, to quantify the boron passing through skin. Human volunteers were dosed with 10B-enriched boric acid, 5.0%, borax, 5.0%, or disodium octaborate tetrahydrate, 10%, in aqueous solutions. Urinalysis, for boron and changes in boron isotope ratios, was used to measure absorption. Boric acid in vivo percutaneous absorption was 0.226 (SD = 0.125) mean percentage dose, with flux and permeability constant (Kp) calculated at 0.009 microgram/cm2/h and 1.9 x 10(-7) cm/h, respectively. Borax absorption was 0.210 (SD = 0.194) mean percentage of dose, with flux and Kp calculated at 0.009 microgram/cm2/h and 1.8 x 10(-7) cm/h, respectively. DOT absorption was 0.122 (SD = 0.108) mean percentage, with flux and Kp calculated at 0.01 microgram/cm2/h and 1.0 x 10(-7) cm/h, respectively. Pretreatment with the potential skin irritant 2% sodium lauryl sulfate had no effect on boron skin absorption. In vitro human skin percentage of doses of boric acid absorbed were 1.2 for a 0.05% solution, 0.28 for a 0.5% solution, and 0.70 for a 5.0% solution. These absorption amounts translated into flux values of, respectively, 0.25, 0.58, and 14.58 micrograms/cm2/h and permeability constants (Kp) of 5.0 x 10(-4), 1.2 x 10(-4), and 2.9 x 10(-4) cm/h for the 0.05, 0.5, and 5.0% solutions. The above in vitro doses were at infinite, 1000 microliters/cm2 volume. At 2 microliters/cm2 (the in vivo dosing volume), flux decreased some 200-fold to 0.07 microgram/cm2/h and Kp of 1.4 x 10(-6) cm/h, while percentage of dose absorbed was 1.75%. Borax dosed at 5.0%/1000 microliters/cm2 had 0.41% dose absorbed, flux at 8.5 micrograms/cm2/h, and Kp was 1.7 x 10(-4) cm/h. Disodium octaborate tetrahydrate (DOT) dosed at 10%/1000 microliters/cm2 was 0.19% dose absorbed, flux at 7.9 micrograms/cm2/h, and Kp was 0.8 x 10(-4) cm/h. These in vitro results from infinite doses (1000 microliters/cm2) were 1000-fold greater than those obtained in the companion in vivo study. The results from the finite (2 microliters/cm2) dosing were closer (10-fold difference) to the in vivo results. General application of infinite dose percutaneous absorption values for risk assessment is questioned by these results. These in vivo results show that percutaneous absorption of boron, as boric acid, borax, and disodium octaborate tetrahydrate, through intact human skin, is low and is significantly less than the average daily dietary intake. This very low boron skin absorption makes it apparent that, for the borates tes...

No abstract

Boron occurs most frequently in nature as borates and boric acid, never as the free element. Its largest uses are in glass, detergents, and agriculture. Essential for higher plants, there is growing evidence for essentiality in vertebrates. Humans consume daily about a milligram of boron, mostly from fruit and vegetables. At high doses, boron is a developmental and reproductive toxin in animals. Pregnant rats were the most sensitive. An oral NOAEL of 9.6 mg B/kg/day was established for developmental toxicity in Sprague-Dawley rats fed boric acid. To extrapolate from the large, animal boron toxicity database to humans, especially to pregnant women, information on renal clearance of boron was needed. This study's purpose was to measure renal clearance of boron in pregnant and nonpregnant woman. In 16 second trimester women and 15 nonpregnant age-matched referents, dietary boron provided the blood and urine boron concentrations used for calculating boron clearance. The pregnant and nonpregnant boron intake was 1.35 and 1.31 mg boron/24 h, respectively. Blood for boron, creatinine, and urea was collected at the start, at 2 h, and at 24 h. Urine was collected during the first 2 h in the Clinical Research Center and during a 22-h period outside the center for measurement of volume, boron, and creatinine. Renal boron clearance measured over the initial 2 h, the most complete urine collection period, was 68.30ml/min/1.73 m(2) for pregnant subjects and 54.31ml/min/1.73 m(2) for nonpregnant subjects. Comparison of renal boron clearance with creatinine clearance indicated that tubular reabsorption of boron occurred in both pregnant and nonpregnant women.

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/m3 to 18 mg/m3, measured gravimetrically. End-of-shift mean blood-boron concentrations ranged from 0.11 to 0.26 microgram/g; end-of-shift mean urine concentrations ranged from 3.16 to 10.72 micrograms/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.(ABSTRACT TRUNCATED AT 250 WORDS)