Damage to the nasopharyngeal mucosa induced by current levels of urban air pollution: a field study in lambs

This study concerns the effects of urban air pollution on the nasopharyngeal epithelium, with the aim of evaluating the possible harmful activity of levels of atmospheric pollution which are not currently considered to be dangerous. Over a 3 month period, 10 lambs kept in a zone characterized by numerous vehicles were sacrificed at regular intervals, and their nasopharyngeal mucosa was examined by scanning electron microscopy and image analysis. Two lambs kept in a rural area were used as controls. The local levels of some airborne contaminants (NO(x), NO2, NO, SO2, CO and particulate matter with aerodynamic diameter < or =10 microm (PM10)) were monitored throughout the experiment. The urban air had an irritating effect, inducing hypersecretion of mucus and morphological damage to the ciliated epithelium. These alterations increased with the duration of exposure to urban air and with increasing pollution levels, although the levels remained below current legal levels. We conclude that the harmful effects of airborne contaminants are probably underestimated. Moreover, physicochemical evaluation of pollution parameters should be complemented by morphological study of upper respiratory epithelium in exposed animals, since this mucosa is a sensitive target for irritating agents.