Heavy Metals Accumulation in Trees Grown in Urban and Rural Areas

Since heavy metals are the big concerns for the 
public health today. Metals play a vital role as structural and functional 
components of proteins and enzymes in cell. The most important pathway of 
metals to transport into human is from soil to plant to human, so this study was carried out to measure the contents of heavy metals concentrations in 
plants leaves from their natural habitats of urban and rural area in Nasiriyah 
city, Iraq. The 
study was conducted to investigate the heavy metals content of four plant 
species of Eucalyptus, Olea, Zizphus and Conocarpus from urban (Nasiriyah city) and rural area 
(farms north of Nasiriyah). The concentration of heavy metals was 
tested, including the zinc, copper and lead. Heavy metals were detected using 
an atomic absorption spectrometer. The results showed that the highest 
concentration of heavy metals in Olea leaves and Eucalyptus leaves were found from the urban areas. Zn was the most dominant metal whereas 
Pb had the lowest concentration for all urban and rural area. Among the Eucalyptus, Olea, Zizphus and Conocarpus studied, showed higher heavy 
metals concentration (Zn, Cu and Pb) than rural area. The results indicated 
that the Zizphus and Conocarpus leaves of urban and rural area 
had the lowest heavy metals content compared with Eucalyptus and Olea. 
The results suggested that Eucalyptus and Olea leaves are good 
sources to treat the pollution of heavy metals. Our study provides a detailed 
examination of habitat location and plant species effects on potential of heavy 
metals in trees.


Introduction
Pollution is the spread of pollutants in natural environments that negatively af-  (Lone et al., 2008;Abdelhafez et al., 2014). Studies indicate that there are some factors that control the severity of the pollutant: its chemical nature, concentration and stability (Miller, 2007). Heavy metals have been widely spread as a result of human activities, leading to an excess accumulation that exceeds the permissible limits causing serious environmental disaster (Huseyinova et al., 2009). Heavy metals are relatively difficult to define, in spite of their shared physical properties. Therefore, the definition of heavy metals tends to be based on the toxicity of the compounds. Furthermore, they can be further classified based on their weight, hence why they are considered to be "heavy"; all heavy metals weigh over 5 g/cm 3 . Examples include lead (Pb), zinc (Zn), mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), copper (Cu) silver (Ag), iron (Fe), and the platinum group (Hawkes, 1997;Hutton & Symon, 1986). Taking in especially high concentrations of such heavy metals (Pb, Cd, Hg and As) can be toxic to the plants, thereby resulting in heavy metal poisoning although they continue to be toxic for humans, even when present at very low concentrations (Jansen et al., 1994). There are many properties of heavy metals that are unique to their classification. Plants used for treatment in urban areas with congested traffic have several benefits in addition to their aesthetic value and soil conservation, windbreakers, providing for humans and animals and use in medicine and reduce air pollution (Cetin, 2016). Plants are always used as biomonitors in the accumulation of heavy metals. Plants living in polluted areas show symptoms of accumulation of heavy metals in different parts of them (Kulshreshtha et al., 2010). Some plants have the ability to absorb heavy elements in different plant tissues more than others (Aksoy et al., 2012). Thus, the selection of plants is very important in pollution treatment programs in polluted areas (Malakootian et al., 2009). The aim of this study is to determine heavy metals concentrations plants leaves (Eucalyptus, Olea, Zizphus and Conocarpus) from urban and rural area in Nasiriyah city.

Study Area
Leaves of four different species of plants (Eucalyptus, Olea, Zizphus and Conocarpus) samples were collected from two sampling stations which were: 1) Nasiriyah city, 2) Farms north of Nasiriyah. For each sampling location, three samples replicate were taken (n = 3).

Plant Samples
For plant parts, leaves were collected at the same sites where the plant samples were taken. The leaves were carefully hand-picked from the trees at young stage (free diseases

Samples Digestion
Extraction of heavy metals from Eucalyptus, Olea, Zizphus and Conocarpus leaves were done by wet digestion according to the Monni et al. (2000). Dried samples were weighed in a conical flask with HNO 3 :HCIO 4 (2:1) for 3 -4 hours on a sand bath at a temperature of 100˚C until all brown fumes had changed to white.
Digested samples were filtered with a 0.45 µm pore size cellulose nitrate membrane filter paper and the volume was made up to 50 ml with deionized water.
Heavy metals concentrations were determined by atomic absorption spectrometer.

Statistical Analysis
All the analyses were conducted in triplicates for each location. The heavy metals for the leaves extracts were evaluated with the two-way ANOVA and L.S.D triplicates range test using SPSS software (SPSS ver.23). P values less than 0.05 were considered to be statistically significant. Values were expressed in means ± SD (Bryman & Cramer, 2012).

The Zinc Content of Eucalyptus, Olea, Zizphus and Conocarpus Leaves
The result showed that the Zn accumulation in rural area were less than urban area in all plant species. Regarding the Zn content in trees, accumulation of these metals by leaves also increased respectively in urban area compare with remote area. The effects of species and growing location (rural and urban areas) in Zn content is shown in

The Copper Content of Eucalyptus, Olea, Zizphus and Conocarpus Leaves
The copper content for four different species of trees (Eucalyptus, Olea, Zizphus and Conocarpus) at two areas of urban and rural is presented in from urban and rural area (4.60 and 10.67) mg/kg DW (3.59 and 9.69) mg/kg DW respectively. The Cu content obtained from Eucalyptus leaves was higher significantly (p < 0.05) than the extract obtained from Olea leaves in both grown location (urban and rural area). Significant differences (p < 0.05) in Cu content were found between the two growing locations. Both Nasiriyah city and farms north of Nasiriyah areas had higher Cu content. When comparing the data from this research with other study, results from different sources seriously differ. The Cu mean value in this research showed that leaves were higher than that of fruits (Dayang & Che, 2013;Shrrog et al., 2015;Ayden et al., 2018).

The Lead Content of Eucalyptus, Olea, Zizphus and Conocarpus Leaves
Lead content (expressed as mg/kg dw) in Eucalyptus, Olea, Zizphus and Conocarpus

Conclusion
Concentration of heavy metals in trees planted in urban areas is related to the location in the city. Plants near sources of pollution such as main roads increase the accumulation of heavy elements by about twice as much as those of remote areas from sources of pollution. The results indicated that all plants and growing location had influence on heavy metals concentration. Eucalyptu and Olea leaves gave the highest, Zn and Cu content in urban area when compared with rural area, so these trees (Eucalyptu and Olea) can be used to treat pollution in cities.