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

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)

Effect of Boron on Human Health

“…Absorption of boron orally is very similar in both humans and animals [36]. Studies have shown that boron is also absorbed through inhalation exposure [42,43]. Culver et al reported that total estimated boron intake including both diet and environmental exposure had for the high-borax dust exposure group a mean daily boron intake of 27.90 mg/day [42].…”

“…Studies have shown that boron is also absorbed through inhalation exposure [42,43]. Culver et al reported that total estimated boron intake including both diet and environmental exposure had for the high-borax dust exposure group a mean daily boron intake of 27.90 mg/day [42]. In addition, it was determined that boron was absorbed by healthy skin only to a very limited extent [44], although absorption of boron that is present in liquid solution occurred in irritated skin [45].…”

The developmental toxicity of boric acid in mice, rats, and rabbits.

“…These data must be interpreted with respect to the level of human exposure and sensitivity in order assess potential risk to human health. In this regard, recent studies have shown that the highest exposures to boron achieved as a result of dietary intake plus worker exposure were 0.38 mg boron/kg/day or approximately 1.9 mg/kg/day of boric acid (22).…”

Borsäure und Tetraborate [MAK Value Documentation in German language, 2011]

“…Beschäftigte der Boraxverarbeitung mit Exposition gegen Stäube von wasserfreiem Dinatriumtetraborat sowie von Penta-und Decahydrat wiesen in Blut und Urin nach Schichtende höhere Borgehalte als bei Schichtbeginn auf (Culver et al 1994). Unklar ist, welcher Anteil über den Atemtrakt selbst aufgenommen wurde.…”

“…Bei Betrachtung der zeitgewichteten 6-Stunden-Werte war kein signifikanter Effekt zu erkennen (Hu et al 1992). In AGS (2006) ist eine unveröffentlichte Analyse zitiert, in der das von Wegman et al (1994) und Hu et al (1992) verwendete Messverfahren mit dem modernen "Inhalable Particulate Mass"-Sammler (IOM) verglichen wurde, bei dem die Menge einatembarer Partikel angemessener berücksichtigt wird (Culver et al 1994). Daraus wurde abgeleitet, dass die von Wegman et al (1994) und Hu et al (1992) gemessenen Konzentrationen um den Faktor 1,76 erhöht werden müssten, um sie mit dem IOM-Sammler vergleichen zu können (AGS 2006).…”