Do inhaled ultrafine particles cause acute health effects in rats? II: exposure system

J. Aemsol Sci. Vol. 29, Suppl. I, pp. S67%S680. 1998 8 1998 Published by Elsevier Science Ltd. All tights reserved Printed in Great Britain

Pergamon

0021-8502/98

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DO INHALED ULTRAFINE PARTICLES CAUSE ACUTE HEALTH EFFECTS IN RATS? I: PARTICLE PRODUCTION C. ROTH, E. KARG AND J. HEYDER GSF-National Research Center for Environment and Health, Institute for Inhalation Biology, PO Box 1129, D-85758 Neuherberg/Munich, Germany

KEYWORDS:

Ultrafine Particles, Inhalation, Spark Discharge Generator

Introduction Acute exposure to inhaled ambient particles has been found to be associated worldwide with adverse health effects. In order to find a uniform explanation for these observations, the number of ultrafine particles has been proposed as a major factor contributing to the adverse health effects of particulate air pollution (Seaton 1995). Evidence for the involvement of chemically inert, very small particles in eliciting health effects comes from animal experiments (Oberdorster, 1997). The hypothesis that the number of ultrafine particles is more closely associated with health effects than the mass of tine particles was recently supported in an epidemiological study (Peters et al., 1997). However, this hypothesis still stimulates controversial discussions. Therefore, in this acute animal exposure study the question was challenged whether or not ultratine particles are able to cause acute health effects due to their generic nature as particles. Chemically inert ultrafine particles without any surface contamination were generated by spark discharging and rats were exposed to them over various periods of time at various concentrations in whole body chambers (Karg et al., 1998). Biological responses of these exposures are discussed by Ziesenis et al., 1998. Methods Ultrafine particles can be produced by various processes. By spark discharging the purity of both particle material and aerosol gas can be controlled and therefore pure particles without any surface contamination can be produced. Other advantages of the spark generator are the high number concentrations of generated particles and the adjustment of particle size by the discharge frequency. For the production of ultrafine particles in a size range between 10 and 30 nm a commercially available spark generator (Palas, GFG 1000, Karlsruhe, FG) has been modified: Supplied with graphite (EC), silver, and iron electrodes (Alfa, Karlsruhe, FG) it is operated at a low mass output and a low discharge frequency. Two graphite electrodes of 6 mm resp. metal electrodes of 2 mm diameter are mounted in brass collets at a distance of about 2 mm and are adjusted automatically to keep the breakdown voltage constant. A 20 nF capacitor connected to one of the electrodes is charged by a high-voltage supply with adjustable output current to vary spark repetition frequency. Currents between 0.13 and 20 mA correspond to spark frequencies between 3 and 300 set-l. An argon flow is focussed through a narrow slit into the space between the electrodes. In case of iron oxide the argon was mixed with 02 up to a concentration of 3 %. The outlet is positioned about 15 mm downstream of the electrodes where the aerosol is diluted by pure nitrogen. To stop coagulation the aerosol is mixed homogenously with an air flow of 40 Ipm in a dilution device. To avoid losses of the highly charged particles the aerosol is neutralized by a 85Kr source. S619

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Abstracts

of the 5th International

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1998

Results The particle size distribution and number concentration of the generated particles measured with a differential mobility analyser @MA 150, Hauke, Gmunden, Austria) and a concensation particle counter (CPC model 3022A, TSI) depend on the particle material, the discharge frequency, and the flow rates of argon, nitrogen and dilution air. When discharge frequency is increased both size and concentration increases. Fig. 1 shows size distributions for the 3 different materials. The discharge frequencies and the flow rates of the generator gases are different for the 3 materials. The frequencies are 80, 3, and 20 set-J for Ag, EC, and Fe,03 respectively. The corresponding argon flow rates are 3.0, 6.3, and 5.8 lpm, whereas the flow rate of nitrogen is zero for silver and 20 Ipm for the 2 other materials. After dilution with air a particle number concentration of ca. 5 x lo6 cm-3 is obtained. In Fig. 2 the dependence of the count mode diameter of the particle size distributions on the discharge frequency is plotted. Electronmicroscopy showed different shapes and porosity of the particles for the 3 materials. Porosity increases from silver over iron oxide to graphite. dN/dlog d, l/ccm

count mode diameter, nm

F

‘owoo3-l

14

1

1

1

““..

,

10'

‘.....L+

10 diameter d, nm

100

0

50 100150200250300350 discharge frequency, l/set

Fig. I: Particle size distributions for 3 materials. Fig. 2: Dependence of particle size on frequency (particle number concentration:5 x 1O6cm3). References: Karg, E., Roth, C., Heyder, J. (1998) Do inhaled ultratine particles cause acute health effects: II. Exposure atmospheres and exposure system.J. Aerosol Sci.29: Suppl. 1.

OberdiSrster,G. (1997) J. Aerosol Medicine 10, 237. Peters, A., Wichmann, HE., Tuch, T., Heinrich, H., Heyder, J. (1997) Respiratory effects are associated with the number of ultrafine particles. Am. J Respir. Crit. Carehfed.

155: 1376-1383.

Seaton, A., MacNee, W., Donaldson, K., Godden, D. (1995) Particulate air pollution and acute health effects. Luncet 345:176-178. Ziesenis, A., Karg, E., Korbel, R.E., Kreyling, W.G. Maier, K.L., Ostermaier, S., Roth, C., Schulz, H., Taker&a, S., Heyder, J. (1998) Do inhaled ultrafine particles cause acute health effects: III. Biological Responses.Aerosol Sci.29: Suppl. 1.