Experimental study of the long-term impact of asbestos prohibition mandate in tunnels, subway, and urban environments in Tehran

Airborne asbestos has been a concerning pollutant in many high-traffic and industrial megacities such as Tehran. In 2011, the Department of Environment in Iran approved the prohibition of asbestos usage in industries. Since 2009, Tehran Air Quality Control Company has monitored fibrous pollutants using phase contrast microscopy. However, this method is not sufficient for asbestos monitoring. To assess the significance of asbestos prohibition law and the current levels of ambient airborne asbestos, the combination of this method with scanning electron microscopy was used in a high-traffic area, a subway station, a construction zone, and two urban tunnels. In the following, the effectiveness of the asbestos ban law was investigated using these investigations and the ten-year archive of fibrous pollutant concentrations provided by the Tehran Air Quality Control Company. Scanning electron microscopy showed that most of the fibers in different regions are not asbestos (while some exceptions showed less than 0.0001 (f/ml) of actinolite), and other types of fiber particles exist in the ambient air of Tehran. The average concentrations of fibers in tunnels and subway were 0.00161 and 0.001774 (PCM f/ml), respectively. The statistical analysis indicated no significant difference between the average concentrations in working days and holidays (p > 0.05). No linear relationships were observed between the fiber concentrations and meteorological parameters. Moreover, the average fiber concentration and actinolite observed at the construction site were estimated roughly at 0.000605 and 0.0001 (f/ml), respectively. Such evidence indicates the effectiveness of the Asbestos Prohibition Act, as the average concentration of 11 monitored stations has decreased by about 53% in 2020 compared to 2012. As a result, this research emphasizes that asbestos should be totally banned in private and public locations, not only in Tehran; but also throughout the country. In addition, the findings suggest that the monitoring network should expand the partial investigation of various fibrous contaminants as a strategic part of the air pollution monitoring program.