Assessment of Environmental Pollution of Heavy Metals Deposited on the Leaves of Trees in Yazd Bus Terminals


 There is a lack of information about urban transport activity in adding heavy elements to the environment. This research assesses concentration some of heavy elements in the deposited atmospheric dust in Yazd bus terminals. Dust samples were collected from the green space in the bus terminals of urban transportation. Following the digestion by nitric acid, determination of the total metal concentration of cadmium(Cd), cobalt(Co), copper(Cu), nickel(Ni), lead(Pb), zinc(Zn), chromium (Cr), and manganese(Mn) in the dust were performed via Atomic Absorption Spectrometry. The map representing the spatial distribution of metals was plotted and their source was identified using Pearson correlation coefficients, Principal Component Analysis(PCA), and Cluster Analysis(CA). The findings indicated that the mean concentration of heavy metals in the deposited dust on the leaves of the trees was in the following order; Cd < Co < Ni < Pb < Cu < Zn < Cr < Mn. The map representing the spatial distribution of heavy metal concentrations indicated that the abundance of metals in different stations varies according to their location. Two important sources for the concentration of heavy metals in the deposited dust on the leaves were identified. The sources of Co, Cd, Mn, and Ni were anthropogenic and lithogenic, and the sources of Pb, Zn, Cr and Cu were the traffic and industrial activities. The amounts of EF, CF, IPI and, RI Indicators in residential, commercial, green space and environmental uses were estimated at low to extremely high levels of pollution. The findings showed that the growth of industrialization and human activities had caused contamination of the environment by heavy metals emitted into the atmosphere of Yazd.


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Heavy metals cause and severely impact on the health of local residents (Ahn et al. 2020). The 30 prolonged exposure to the various well-known environmental factors including heavy metals, air 31 pollutants (particulate matter), nanoparticles containing metals, results in accelerating the progression 32 some of diseases such as Alzheimer (Mir et al. 2020). Air pollution is becoming an increasingly essential 33 environmental issue in today's societies, particularly in developing countries. It poses severe risks to the 50 environmental dust on the leaf surface. Tree leaves are of low sampling costs, most useful and most widely used

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The results indicated that urban soils were at moderate to the high levels of contamination with Cd and Pb.

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Rapid industrialization has made Yazd, a city in the center of Iran, to face sever air, soil and water pollutions,

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Yazd has a cold and dry climate and is with 31° N and 54° E, located in the Pediment of Yazd-Ardakan Plain.

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The region is at an average altitude of 1216 meters above sea level. According to the 15-year data of Yazd 75 Synoptic Station, the mean precipitation, average temperature and relative humidity in this period are 67.7 76 millimeters, 19.9 and 27%, respectively (Fathizad et al, 2020). Yazd covers an area of 6336 square kilometers.

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The population of Yazd is 586,276 people.Yazd can be considered as one of the cities with high traffic. The

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In this study, trees in the green space in the bus terminals were used as a biological indicator and natural 88 collector of falling dust. In this study, deposited samples of falling dust were obtained from the leaves of trees 89 that were 1.5 -2 meters tall. The collected leaf samples in paper bags were transported to the laboratory and 90 rinsed with distilled water. To estimate the amount of deposited dust, the resulting solutions were centrifuged at 91 5000 rpm for 5 min. The water was then pipetted off the dust and the samples were placed in an oven at 55 °C 92 for 24 hours. Finally, the dry particles were weighed with a digital scale with an accuracy of 0.001 g, and acid 93 digestion was performed on the dust samples using the ISO method. Then, the Atomic Absorption Spectrometer 94 (model 330) was used to determine the concentration of the given elements.

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All statistical analyses, including the correlation between variables and multivariate analysis, were performed 97 using SPSS software. The (PCA) and (CA) methods were used to determine the relationship between HMs and 98 their potential sources. In this study, the heavy metal concentrations were standardized through the Z method,

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and Euclidean intervals were used to calculate similarities in variables. Then, hierarchical clustering was 100 employed using the Ward method of the standardized data set. Due to the lack of specific background standards 101 to assess the degree of pollution in Iran, the average concentration of HMs in the earth's crust was used as the 102 background concentration (Taylor 1995

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To determine the status of contamination in the study area in terms of commercial use, residential area, green 105 space, and environmental protection, the , and in terms of integration, the EF, IPI, RI, and mean of mCd were 106 calculated.

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Where mCd represents the mean of contamination degree and n is the number of examined trace elements (mg 119 kg -1 ).

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The potential environmental risk factor has been calculated to assess the contamination of heavy metals in soil 137 and the ecological and environmental effects of heavy metals. RI is calculated according to Eq. (6) and (7): 138 ) 6 ( 139 (7)

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Where represents the risk factor for each metal, refers to the toxicity response to heavy metals (Table 3) Table 4 shows the classification of the index and potential environmental risk levels. 143

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The enrichment factor and contamination indices were used to assess the contamination, which is briefly 149 described here.

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EF is an important factor that indicates the degree of human intervention in the natural environment. The 151 passive element is used to calculate this factor. The reference element for calculating the enrichment coefficient 152 is an element that has a strictly geological basis. The reference element, which is necessary to calculate the 153 enrichment factor, has a purely geological origin. In environmental research, the following components are most

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The amount of Cu metal in the study area was calculated between 0.33-3.63 (mg kg -1 ). The highest amount of 179 Cu is associated with Emam Ali and Golzar-e Shohada bus stations. There was no significant difference 180 between them and Darvazeh-e Quran. The lowest amount of Cu is associated with a non-polluted area (Yazd

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Mn concentration in the studied samples was between 13160-53600 mg kg -1 , the highest amount was related to 185 Doulat Abad bus terminaland the lowest amount with Atlasi bus station, which there was no significant 186 difference between them and the non-polluted area (Yazd University).

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The density of spatial distribution of Zn and Cr metals is also associated with Qadir bus station. This station is

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The spatial distribution of Cu metal is around the city, such as the Emam Ali bus terminal. In the southeastern 228 part, the distribution of Mn metal is more visible in the central part of the town.

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In general, compared with other bus terminal located in the city of Yazd, the two stations of Qadir and Quran

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Relationships between HMs in dust were investigated using the Pearson correlation matrix (Table 6).

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The relationships between elements could provide information on sources and pathways of heavy metals in the

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The Principle Component Analysis method by applying a varimax rotation to determine the sources of HMs in 283 the falling dust resulting from using the factor analysis method to the data is shown in Table 7. In this Table, the 284 results for the first to eighth main components are given. Also, the factor load of each variable before and after 285 the rotation is presented in Table 8. The results indicate that the total variance of two of the specific amounts is 286 more than one, and these two factors justify 57.93% of the total variance

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The three different analyses used to identify the sources of pollutant emissions produced almost the same 295 results.

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The source of these pollutants is most likely human activities. According to the studies, the most prominent

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The results of the Contamination Factor (CF) for heavy metals in the air showed that the metals Co, Ni, Cu, Zn,

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Cd, Cr, for all four residential, commercial, green space and environmental protection uses were in the range of 325 low pollution. In the case of lead metal, the level of pollution for the residential area was in the range of 326 moderate pollution. As it is shown in Figure 6, the highest contamination is associated with manganese metal in 327 city of Yazd. Mn was classified in the very high pollution range for all four uses.

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Evaluating the general status of ecological risk of atmospheric heavy metals in the urban atmosphere of Yazd 338 city showed that the region ranged from non-polluted to safe in different functional areas (Fig. 7).

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Examining the general status of pollution in the study area using the integration of indices (IPI, mCd and RI),

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showed that the level of pollution in the urban atmosphere of Yazd ranges from low to extremely high ( fig. 8).

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This study aims to evaluate the role of transportation in the production of some heavy metals cadmium (Cd),

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The highest concentration of heavy metals is associated with Qadir bus terminal and Quran Gate bus terminal 375 because these two stations are more exposed to winds that enter Yazd city from the west. In addition to the

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In this study in addition to office and residential buildings located in the city the canopies constructed in stations 381 that are made of metal can produce heavy metals. The main sources of heavy metals are the wear and tear of the 382 tire and various vehicle parts, car battery and building materials. Human activities determined the severity of 383 these contaminants. The results showed that the emission sources of Cr, Zn, Pb and Cu metals in addition to the 384 combustion of fossil fuels, also originated from other emission sources in the second major cluster of Cd, Ni,

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Mn, and Co. Ni metal is emitted from heavy fossil fuels and gas oil. There is also the possibility that some

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According to the obtained results, though currently the average concentration of Ni, Co, Cd, Cu, in the samples 398 of dry atmospheric deposition in Yazd is lower than the permitted limit, the lack of continuous monitoring of 399 heavy metal concentrations in dust and particles suspended in the air can lead to the emission of harmful 400 pollutants such as heavy metals into the atmosphere. Public health is affected by heavy metals through 401 inhalation, ingestion, skin contact and absorption of toxic metals. To this end and to support general health, it is 402 suggested to study the radioactive substances, bacteria fungi in the dust and particles suspended in the air.