Sensory and Associated Reactions to Mineral Dusts: Sodium Borate, Calcium Oxide, and Calcium Sulfate

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.

Medical image of the week: acute pneumonitis secondary to boric acid exposure

“…The Cain et al (2004 studies were selected over the Wegman et al (1991Wegman et al ( , 1994 studies as the basis of the acute-duration inhalation MRL for boron because they identified a NOAEL based on observations from carefully-controlled exposures of volunteers. The Wegman et al (1991Wegman et al ( , 1994 data are problematic for identifying a NOAEL or LOAEL because the average irritation intensity level reported prior to a work shift was very close to the average intensity level reported for all incidents of nasal irritation.…”

“…Further, the best 0.25-hour TWA data (confirmed by worker response and simultaneous air sampling by a study technician) suggest that the probability of workers reporting incidences of nasal irritation occurred when estimated boron concentrations reached 0.8-1.2 mg boron/m 3 , which is very similar to the laboratory findings of Cain et al ( , 2008. Cain et al (2004 trained male and female volunteers to recognize the difference in chemesthetic feel (pungency or irritancy) of various levels of CO 2 offered to the eyes, nose, and throat. Exposures of ≥17.7% CO 2 resulted in a "feel" described by the volunteers as irritating.…”

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

“…In zwei experimentellen Studien (Cain et al 2004(Cain et al , 2008 (Wise und Wysocki 2002). Eindeutige Dosis-Wirkungs-Beziehungen konnten in dieser Studie nicht ermittelt werden, da ähnliche Intensitätsangaben für 10 und 40 mg Dinatriumtetraborat-Pentahydrat/m 3 gemacht wurden (Cain et al 2004).…”

“…Eindeutige Dosis-Wirkungs-Beziehungen konnten in dieser Studie nicht ermittelt werden, da ähnliche Intensitätsangaben für 10 und 40 mg Dinatriumtetraborat-Pentahydrat/m 3 gemacht wurden (Cain et al 2004). Basierend auf den physiologischen Messungen kann für Dinatriumtetraborat-Pentahydrat eine NOAEC von 5 mg/m 3 abgeleitet werden.…”

“…Von anderen Autoren wurde ein entsprechender durchschnittlicher Umrechnungsfaktor von 2,5 für Stäube aus verschiedenen Industriezweigen und für Borate und Borsäure ein Umrechnungsfaktor von 2,2 ermittelt (Werner et al 1996). Unter Berücksichtigung dieser Korrektur widersprechen die Befunde von Hu et al (1992) und Wegman et al (1994 nicht der NOAEC von 5 mg/m 3 aus der Probandenstudie mit Dinatriumtetraborat-Pentahydrat (Cain et al 2004(Cain et al , 2008. In der Studie von Wegman et al (1994) wurde die Lungenfunktion von 303 Beschäftig-ten (von ursprünglich 629, weshalb ein "Healthy-Worker-Effekt" nicht auszuschließen ist) nach ihrer ersten Untersuchung in der Studie von Garabrant et al (1985) (Garabrant et al 1984).…”