Comparing Inhaled Ultrafine versus Fine Zinc Oxide Particles in Healthy Adults

Abstract

Rationale: Zinc oxide is a common, biologically active constituent of particulate air pollution as well as a workplace toxin. Ultrafine particles (Ͻ 0.1 m diameter) are believed to be more potent than an equal mass of inhaled accumulation mode particles (0.1-1.0 m diameter). Objectives: We compared exposure-response relationships for respiratory, hematologic, and cardiovascular endpoints between ultrafine and accumulation mode zinc oxide particles. Methods: In a human inhalation study, 12 healthy adults inhaled 500 g/m 3 of ultrafine zinc oxide, the same mass of fine zinc oxide, and filtered air while at rest for 2 hours. Measurements and Main Results: Preexposure and follow-up studies of symptoms, leukocyte surface markers, hemostasis, and cardiac electrophysiology were conducted to 24 hours post-exposure. Induced sputum was sampled 24 hours after exposure. No differences were detected between any of the three exposure conditions at this level of exposure. Conclusions: Freshly generated zinc oxide in the fine or ultrafine fractions inhaled by healthy subjects at rest at a concentration of 500 g/m 3 for 2 hours is below the threshold for acute systemic effects as detected by these endpoints.Keywords: air pollution; metal fume fever; particulate matter, ultrafine; zinc Ambient air pollution particles occur in three major size distributions. Common combustion processes generate some primary ultrafine particles (Ͻ 0.1 m diameter), which can rapidly coalesce into larger accumulation mode particles (0.1-1.0 m diameter). The third fraction is the coarse mode particles, from 1 to 100 m in diameter, which are often generated by mechanical breakdown of the earth's crustal minerals. A given mass of ultrafine particles has a markedly higher ratio of total surface area to weight than does the same mass of accumulation mode particles. In experimental animals, inhaled ultrafine particles exhibit greater lung inflammatory and systemic activity than an equal mass of larger particles, and these particles may also have greater effects in adult human subjects (1-3). With ambient particle air pollution exposure, certain respiratory effects have been more closely associated with the number of ultrafine particles than with the total mass of particle exposure (4).Zinc is a common element in the earth's crust and an essential mineral in human nutrition. Zinc oxide may be found in ambient air particles from combustion sources (5-7), and it is generated in high concentrations in industrial processes, such as brass founding and welding or cutting galvanized sheet metal. Actual exposures of welders and others depend on the conditions in the workplace, but the permissible exposure limit for occupational exposure to zinc oxide in the United States is 5.0 mg/m 3 respirable dust. Zinc is one of several transition metals that have been proposed to contribute to the biological activity of ambient combustion particles. Freshly generated zinc oxide causes a selflimited, febrile, and inflammatory response known as metal fume fever, subtle findings ...

Human inhalation exposure to iron oxide particles

“…Two phases of clearance, a fast phase on the order of days representing mucociliary clearance in the tracheobronchial region and a slow phase on the order of years representing macrophage clearance in the alveolar region were defined. Studying 59 Fe labeled iron oxide dust, Albert and Arnett found that particle clearance rate was dependent on size [39]. When the same dose of 100 μCi was inhaled, clearance of ~47% was measured after 2.4 h for particles with diameters of 1.4-2.3 µm while ~87% of larger particles with diameters of 3.5-4.3 µm cleared after 2 h. Note that in this study and for about half of all studies reviewed, the methods used to characterize the aerosol content were not reported.…”

“…The authors are not aware of any published human inhalation studies using iron oxide nanoparticles. However, several controlled human inhalation studies have exposed volunteers to other ultrafine particles [57][58][59][60][61][62][63][64][65][66]. In addition, many human inhalation studies have been conducted using Technegas or 99m Tc labeled ultrafine carbon particles; however, this literature is beyond the scope of this review.…”

“…Beckett et al conducted a study comparing the physiological response to inhaling ultrafine and fine zinc oxide particles in healthy male and female volunteers [59]. Twelve volunteers were exposed for 2 h to ZnO generated by an electric arc discharge system brought to a concentration of 500 µg/m 3 , which consisted of either 4.6 × 10 7 particles for the ultrafine (~40 nm in aerodynamic diameter) particles or 1.9 × 10 5 particles for the fine (~300 nm in aerodynamic diameter) particles.…”

Toxic effects of nanoparticles - differences and similarities with fine particles

“…Freshly generated zinc oxide can cause an inflammatory response known as fume fever (Beckett et al, 2005).…”

Biological and chemical hazards in water-mix metalworking fluids and mists

“…However, in the research involving MWF, M.avium has only been detected in one/ two incidences (James et al, 2017). Whereas, the most commonly detected mycobacterial species in MWF are usually from the MCC group (Moore et al, 2000;Khan et al, 2003;Beckett et al, 2005). …”