Toxicity of Ambient Particulate Matter. III. Acute toxicity study in asthmatic mice following 3-day exposure to ultrafine and fine ammonium nitrate, a model compound for secondary aerosol fraction of PM10

Ammonium nitrate is the most prominent component of secondary PM10 in the Netherlands. In our study, healthy and asthmatic mice were exposed to fine (CMD = 0.3 mum; 4 x 10 exp. 3 particles per cm3) and ultrafine (CMD = 0.03 mum; 2 x 10. exp. 5 particles per cm3) ammonium nitrate. The mean mass concentrations were 140 and 250 mug/m3, respectively. At exposure levels comparable to previous studies with ammonium bisulfate and ammonium ferrosulfate, pulmonary effects were observed in both healthy and asthmatic mice. The effects were mainly found after exposure to fine rather than to ultrafine nitrate. In view of the mass concentration of fine aerosols being even lower than that of the ultrafine aerosols, we conclude that not only are mass concentrations important for the development of adverse effects but also the specific size of the particles. Dosimetry models will be useful in confirming this conclusion. There were no signs of asthmatic mice being more sensitive to secondary aerosols than healthy mice