Heavy Metals Accumulation in Trees Grown in Urban and Rural Areas ()
1. Introduction
Pollution is the spread of pollutants in natural environments that negatively affect the components of the ecosystem soil, water, plants and human health ( 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/cm3. 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.
2. Materials and Methods
2.1. 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).
2.2. 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). All samples were saved in box during transporting back to the laboratory at the Department of Biology, University of Thi-Qar. plant samples were washed with tap water to remove soil particles twice with distilled water and deionized water. The plant leaves of Eucalyptus, Olea, Zizphus and Conocarpus were cut into small pieces, and then oven dried at 60˚C for 48 h ( AOAC, 1984).
2.3. 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 HNO3:HCIO4 (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.
2.4. 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).
3. Results and Discussion
3.1. 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 Table 1. Significant differences (p < 0.05) in Zn concentration in leaves of Eucalyptus, Olea, Zizphus and Conocarpus were found among the different growing location. Olea leaves gave the highest Zn content (45.52 mg/kg DW) in urban area of (Nasiriyah city) when compared with rural area (farms north of Nasiriyah) city (8.67 mg/kg DW). The results showed that Olea leaves was had significantly (p < 0.05) in Zn content compared to Eucalyptus,
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Table 1. Zinc content in trees leaves extracts, (mg /kg DW).
L.S.D = 3.20.
Zizphus and Conocarpus. Among all trees of Eucalyptus, Conocarpus Zizphus and Conocarpus species showed the highest Zn content in Eucalyptu followed by Conocarpus and Zizphus respectively. These results indicated that for all plant species and growing environment had influence on Zn content. Comparing Zn content from this study and other study data is difficult because of the fact that concentration of Zinc can be influenced by method, extracting solvent, species and growing location ( Shrrog et al., 2015; Dayang & Che, 2013; Azim et al., 2017) reported that zinc content of 24 mg/kg medicinal plants samples and zinc values ranged from 17.70 to 87.55 mg/kg.
3.2. 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 Table 2. For trees leaves the maximum Cu content were obtained for Eucalyptu and Olea leaves 25.72 to 21.70 mg/kg DW respectively. The leaves from Conocarpus contained the lowest Cu content as compared to all other samples. Significant difference (p < 0.05) in Cu content were found among the different leaves and among the grown locations. Among all grown locations urban and rural area in all trees species showed the lowest Cu content in Conocarpus and Zizphus leaves 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).
3.3. The Lead Content of Eucalyptus, Olea, Zizphus and Conocarpus Leaves
Lead content (expressed as mg/kg dw) in Eucalyptus, Olea, Zizphus and Conocarpus
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Table 2. Copper content in trees leaves extracts (mg /kg DW).
L.S.D = 1.53.
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Table 3. Lead content in trees leaves extracts (mg/kg DW).
L.S.D = 0.019.
leaves is presented in Table 3. A significant amount of lead was found in Conocarpus leaves and Eucalyptus leaves. Whereas the content of Pb in Olea leaves to be lower in rural area than in urban area. For urban and rural area, the maximum Pb were obtained for Conocarpus and Eucalyptus leaves (0.197 and 0.194 mg/kg DW) in Nasiriyah city respectively. Between within grown location, urban area showed the higher (Pb) then rural area. Table 3 showed significant difference (p < 0.05) in the Pb content of Eucalyptus, Olea, Zizphus and Conocarpus between urban and rural Conocarpus and Eucalyptus leave for Nasiriyah city gave the highest lead content when compared with farms north of Nasiriyah areas. Low content of Pb (0.015 mg/kg DW) were obtained from Olea leaves in rural area. After Olea leaves, leaves of Zizphus (0.032 mg/kg DW) had low content of Pb in extract. One possible reason for the increased Pb content with the urban areas might be due to the increase in organic matter and topography of the land. Pb content for the Eucalyptus, Olea, Zizphus and Conocarpus leaves t in this study were lower than that of ( Dayang & Che, 2013; Livia et al., 2015; Taghred et al., 2017) for different plants. The Pb concentration in this research showed that leaves were lower than that of Kamaruzzaman et al. (2009).
4. 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.
Acknowledgements
This research was supported by University of Thi-Qar, Faculty of Education for Pure Science, Department of Biology, Iraq.