عنوان مقاله [English]
The present study aimed at investigating the effect of potential ecological risk of metals emitted from traffic on Street-side trees within Sep. 2012 and Sep. 2014 based on geochemical indices. The economic and political conditions of Iran during the years 2010-2011 caused foreign countries to refuse to engage in fuel deals with Iran. This forced the country to supply the required fuel of vehicles from domestic petrochemical plants. After that, in the winter of 2013, with the announcement of relevant institutional bodies, including the Department of Environment(DoE)and Ministry of Petroleum(MoP), the fuel quality of the vehicles was improved. It should be recalled that, until the publication of this paper, no official reports on the new content of the fuel distributed by the relevant organizations have been published. The present research investigated the changes in the heavy metal content of the fuel within two time intervals, i.e. Sept. 2012 and Sept. 2014. Since plants function as natural filters, they can decompose the dust particle due to their morphological features (Daylam-jafarabad et al. 2013; Naderizadeh et al. 2016; Chrabąszcz and Mróz. 2017. Hatami-Manesh et al.,2019). In the present study, for the ease of sampling, the leaves of the street-side trees were used as particle collector surfaces.
2. Materials and Methods
For the current investigation, two different sites were selected in the center and west of Tehran (Fig. 1).
The Site 1 was Azadi Square in the west of Tehran and Site2 was Gisha Bridge (conjunction of Jalal Al Ahmad and Chamran highways) in the center of Tehran. Azadi square is an area with heavy traffic. This area is the closest study station in the present research to the Tehran – Karaj Highway. In this area, presence of wide streets and various walking passages and subsequent to it reduction of the density of business and residential structures have led to a better conditioning and air flow in comparison with the area of site 2 in this region. In site 2, presence of overpass bridges for transportation vehicles and the intersection of the two highways and closeness to the business and residential structures and higher education institutes and offices in this area have led to the increase of the traffic volume and the volume of the pollutants increase and air conditioning reduces. Standards have not yet been set for determining the concentrations of metals in air (pre-industrial background levels) in Tehran and Iran.Therefore, the levels of metal concentrations were determined in one the largest forest parks in west of Tehran i.e. Chitgar Park (control site) and were used as background levels for estimating geochemical indices. Given the application of Chitgar forest park, in this site, traffic of cars in the sampling areas have been very little. The horizontal distance of the sampling place in this site to the Tehran – Karaj Highway (the most traveled highway of Iran) is approximately 1000 meters; nevertheless, due to the location being in the west of Tehran and the large number of small and large industries and special topographical conditions and wind in Tehran, this region is influenced by the consequences of air pollutants. Since a large portion of the particles produced by the traffic of cards in the shortest distance from the source of production of sediment, thus samples of tree leaves in the monitoring site have been collected from inside of the dense coating of the green space of the margin of the passages inside the park.
Regarding the pollution emitted from industries in the west and southwest of Tehran, it was indicated that the trends of metal concentrations in sites 1 and 2 were mainly caused by traffic in comparison to the control site (Fig.1).
In the area of Chitgar Park, there was no active air monitoring station. The closed air pollutant monitoring stations to the site 1 and 2 were 500 meters from the sampling location.
In each site, the tree leaves were collected randomly from the leaves of three types of trees sycamore, elm and acacia in the shortest distance from the street. The location of the trees from the street and sunlight and the direction of the wind blow and height from the street level have been considered to be equal. Samples were collected from trees within two time intervals in the late growing season i.e. Sept. 2012 and Sept. 2014. It had been almost one moth that passed the latest rainfall, storm and wind in these sites by two periods. Completely healthy leaves have been collected from the canopy of each tree from the street. With the least touch of hands, the leaves were put into the ice tank and were transferred to the laboratory in the shortest time. 0.5 grams of each sample was put in 12cc of nitric acid in a Teflon polymer coated with aluminum foil for one hour in the room temperature. Then it was put on an asbestos heater with indirect heat. After drying up with paper in a 50cc balloon, it reached its desirable volume and was smoothened with a 42 whatman filter and then it was read in an ICP-MS. For calibration of amounts of element in the reference material was used used to read the concentration levels of cadmium, lead, zinc, nickel, copper and cobalt. Several studies have considered these metals as the main metals emitted from traffic and highlighted their toxicity (Kermani et al. 2016; Maher et al. 2008).
The present study used Contaminatio factor (Cf), Modified degree of contamination (mDf), Pollution load index (PLI), potential ecological risk index (RI) indices to determine the likelihood of potential ecological risks of each metal element in the intended sites (Muller 1979; Thomilson et al. 1980; Salmanzadeh et al. 2015; Xu et al. 2015; Yu et al. 2014; Yuan et al. 2014; Hakanson. 1980; Suryawanshi et al. 2016; Herath et al, 2016; Han et al. 2017. Chen et al.,2021).
The metal concentrations, determined in Chitgar Park, was used as background value while Aluminum was used as reference metal.
The present study intended to investigate the potential trend of ecological risk of metals, including Cd, Zn, Pb, Co, Ni and Cu, in two high-traffic areas of Azadi Square and Gisha Bridge in Tehran, Iran, within two time intervals i.e. September 2012 and September 2014, using Contaminatio factor (Cf) ,Modified degree of contamination (mDf),Pollution load index (PLI), potential ecological risk index (RI) indices. In general, the purpose of the current study was to investigate the effect of fuel quality on the contamination and potential ecological risk of metals in high-traffic areas. To this end, leaves of street-side tress were used as particle collectors. The results indicated that the improvement of fuel quality reduced the emission of metal pollutants in 2014. These trends had a significant effect on the reduction of potential risks of Lead and Cadmium. According to the results, despite the improvement of fuel quality in 2014, there was yet a moderate likelihood of potential ecological risk of metals in the aforesaid areas. Thus, considerations should be given to not only fuel quality but also fuel consumption. In 2014, copper significantly increase due to the wear and tear of vehicles. It was found that the influential factors on the concentrations of metal pollutants include the mean age of vehicles, wear and tear of vehicles, automotive alloys, and the type of platform of vehicle compatible with fuel. Furthermore, the vehicle traffice volume, frequent use of brake and the composition of automotive fleet have significant effects of the emission of metal pollutants. In 2014, metal rise and the degree of contamination emitted from these metals in environment signified the role of influential factors including wear and tear of vehicles, particularly after the high-risk period of 2012, and the increased wear of the interior parts of vehicles. The other influential factor which should be considered in pollution management is the role of natural factors, such as wind and air conditioning, on the severity or stability of metal pollutants at local levels in Tehran. It seems that in the cases of fuel quality reduction, the degree of contamination becomes more critical in Azadi. Whereas once the fuel quality improves, other factors such as fuel consumption, wear and tear of vehicles, erosion of construction materials and street asphalt as well as climate conditions cause more severe contamination in Gisha. Consequently, in addition to considering fuel quality and consumption in Tehran, the improvement of the fuel of polluting industries should be ensured