This paper offers a study case using the WHO approach to assess the impact of atmospheric pollution on human health for people living in Tehran, one of the most populated areas in the world, where the geographical features make the air quality among the worst in the world. The impact was estimated as the increase in all-causes, cardiovascular and respiratory mortality, and hospital admissions for cardiovascular and respiratory diseases, COPD and acute myocardial Infarction for short-term exposure.
Considering short-term effects, PM10 had the greatest health impact on the 8,700,000 inhabitants of Tehran city, causing an excess of total mortality of 2,194 out of 47,284 people in a year. The effect of SO2, NO2 and O3 on total mortality was an excess of about, respectively, 1458, 1050 and 819 cases in a year.
The AirQ software has been used by other investigators to assess the human health impact of PM2.5
] or PM10
] estimated the human health risk in relation to air quality in two municipalities in an industrialized area of Northern Italy, the authors found that PM2.5
had the highest health impact on the 24,000 inhabitants of the two small towns, causing an excess of total mortality of 8 out of 177 in a year; also Ozone and nitrogen dioxide each caused about three excess cases of total mortality. [30
] focused on short-term effects of PM10
in Trieste (about 200,000 inhabitants), a city in north-east Italy; For PM10
concentrations above 20 μg/m3
, 52, 28 and 6 cases in excess, respectively, were estimated for total, cardiovascular and respiratory mortality. These figures, if normalized to the population in Tehran (8,700,000 inhabitants), would result in a number of excess cases very similar to those reported for PM10
in Table .
In another study, [31
] found in Milan (1,308,000 inhabitants), a big industrial city in the Po Valley, the central estimate of the number of excess cases attributable to PM10
was 677 for total mortality. In a study of PM10
impact on human health in 13 Italian cities, with about nine million inhabitants during the period 2002–2004, [32
] it was reported that on average 8220 deaths a year, excluding accidental causes, were attributable to PM10
above 20 μg/m3
. For O3
the effect was estimated at 516 extra deaths yearly. For short-term effects exposure to PM10
above 20 μg/m3
was responsible for 1372 extra deaths.
Results obtained from studies of health effects of air pollution in various parts of the world differ. Particulate matter is the pollutant with the biggest health effects in all of these papers, including the present study.
This study has several limitations. One of the limitations of this approach is that the health impact focuses on individual compounds without considering the simultaneous exposure to several, which is what actually occurs [15
]. The health effects of atmospheric pollution are indeed the consequence of interactions between different air contaminants, and between these and other compounds of natural origin. Generally, in quantitative assessments of health effects, the interactions between different contaminants are not investigated as it would require a good knowledge of the mechanisms of toxicity for the different compounds, which is rarely available. In order to take account of co-exposure to different pollutants, it is often assumed that the health effects of individual compounds are additive. However the simple addition of the effects of the single pollutants would not be right because atmospheric pollutants are usually positively related.
A further limitation related to the exposure assessment is that the approach assumes that concentrations measured in specific sampling points are representative of the average exposure suffered from people living in Tehran. Another limitation is due to the RR estimates derived in studies of different populations in comparison to the one under investigation. In particular, while for PM10
the RRs were mainly based on studies on the European population. The transferability of the mortality effect estimates from the evidentiary (e.g., the US cohort) to the target population, however, is feasible if no compelling evidence that the target population and the evidentiary population differ in the response to the air pollution [33