The possible impact of “sequential co-exposure” on ozone associated adverse health effects. Preliminary data from cumulative cross sectional and prospective studies in Milan

Two monitoring campaigns (July-September 2008) (January - March 2009) covering the entire City arwere performed in Milan, Italy. In particular, gaseous pollutants, (O3, NO2, CH6H6) were monitored using passive samples in 50 different urban sites. Recorded values were processed by a GIS based geostatistical software to give the concentration profiles for the 3 selected pollutants. Fine particulate matter (PM10) concentrations were measured by gravimetric samplers in 5 urban sites representative of different areas of the City. Benzene and NO2 were representative of traffic emission. Both showed high values in sites with intense vehicular traffic, as in the highly congested city centre and along the heavy-traffic roads. Ozone showed an opposite behaviour, being higher inside the city gardens and parks. In fact, in vegetation-rich areas, the absence of traffic scavenging is summed-up to the vegetation-released ozone precursors. However, ozone average concentrations seldom reached values of more than 90 μg/m3. Clinical effects from environmental pollution can be considered as the final result of a complex mixture, including variable concentrations of various pollutants. In the occurrence of the health outcome, not only PM2,5 and/or PM10, but also gaseous pollutants (ozone, NOx, SO2) and biological components cooperate together by concomitant or sequential co-exposure. It is suggested that ozone could be responsible for a "sequential coexposure", i.e. it could fill the gap and damage even during "the summer window", which could otherwise permit logical and physiological repair of previous damages. In this way, ozone is responsible for a continuous damage to human tissues, that will have no time left for re-epithelization, cell or tissue repair, due to the uninterrupted activity of multiple pollutants, each one having a preferred season, but also all acting together and in ordered sequence.