Quaternary Journal of Iran

"Spatial evaluation of heavy metal contamination in soils and alluvial sediments of urban parks in Shiraz using pollution indices and GIS-based analysis"

Document Type : Original Article

Author

Atefeh Nimroozi

Expert, Geology and Mineral Exploration Organization, Southern Geology, Shiraz, Iran

10.22034/irqua.2025.2069445.1052
Abstract
Introduction
Urban green spaces, particularly public parks, play a vital role in enhancing environmental quality and improving public health in rapidly expanding cities. However, these areas are increasingly exposed to contamination from anthropogenic sources, with heavy metal pollution being one of the most concerning threats. Urban soils, especially in parks, can accumulate potentially toxic elements (PTEs) due to vehicular emissions, industrial activities, atmospheric deposition, and inappropriate use of fertilizers and pesticides. Monitoring heavy metal concentrations in park soils is therefore essential to evaluate potential environmental risks and inform urban environmental management strategies.
This study focuses on the spatial assessment of heavy metal contamination in soils of selected urban parks using pollution indices and Geographic Information Systems (GIS). Heavy metals such as lead (Pb), cadmium (Cd), arsenic (As), chromium (Cr), copper (Cu), zinc (Zn), and nickel (Ni) are selected based on their toxicity, persistence in the environment, and potential health impacts on urban populations.
Sampling and Analytical Methods
Soil samples were systematically collected from different locations within each urban park to capture spatial variability. The topsoil layer (0–20 cm) was targeted, as it is most susceptible to anthropogenic contamination. Samples were air-dried, sieved, and subjected to acid digestion based on USEPA standard protocols. Heavy metal concentrations were then measured using atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS), depending on the element and required detection limits.
Application of Pollution Indices
To assess contamination levels, multiple pollution indices were employed:
1. Geoaccumulation Index (Igeo) – developed by Müller, this index compares current concentrations with background values to determine pollution levels. Values are classified into seven categories, ranging from unpolluted to extremely polluted.
2. Contamination Factor (CF) – this index is the ratio of metal concentration in soil to the background concentration, indicating the degree of contamination.
3. Enrichment Factor (EF) – used to differentiate between anthropogenic and natural sources, calculated using a reference element such as Fe or Al.
4. Pollution Load Index (PLI) – provides a cumulative indication of overall pollution status across multiple metals.
5. Ecological Risk Index (RI) – developed by Hakanson, this index combines toxic response factors with contamination levels to quantify ecological risk posed by each heavy metal.
These indices offer a comprehensive view of the contamination status and help prioritize elements of greatest concern.
GIS-Based Spatial Analysis
GIS tools were applied to interpolate the spatial distribution of heavy metals across the park areas using kriging or inverse distance weighting (IDW) methods. This spatial analysis helps identify pollution hotspots and understand the influence of surrounding urban land use on soil contamination.
In addition, land use maps, traffic density data, and proximity to pollution sources (e.g., highways, industrial zones) were integrated to explore potential sources of contamination. Layered visualization through GIS enhances interpretation and supports urban planning decisions.
Results and Interpretation
The results revealed considerable variations in heavy metal concentrations across different parks, with some areas exceeding international soil quality guidelines, particularly for Pb, Cd, and As. The Igeo values indicated moderate to high pollution levels in parks adjacent to high-traffic roads and industrial areas. CF and EF values confirmed anthropogenic contributions, with significant enrichment for Cu, Zn, and Pb.
The ecological risk assessment highlighted Cd as the primary element posing considerable risk, followed by As and Pb. Some park locations fell into the "considerable risk" category according to the RI values, underscoring the need for targeted mitigation measures.
Spatial distribution maps generated by GIS clearly identified pollution hotspots and indicated a correlation between metal accumulation and nearby anthropogenic activities. Parks located in city centers or near transportation corridors showed higher contamination levels, emphasizing the importance of buffer zones and soil remediation interventions.
Environmental and Public Health Implications
Heavy metal accumulation in urban park soils not only degrades soil quality and ecological health but also poses direct and indirect risks to human health. Children are particularly vulnerable due to frequent contact with park soils through play. Chronic exposure to heavy metals can lead to neurological disorders, kidney damage, and developmental delays.
 
Therefore, understanding spatial patterns and ecological risks associated with heavy metal contamination in urban parks is critical for environmental risk management. The application of pollution indices and GIS supports evidence-based decision-making and enhances public awareness.
Recommendations
1. Regular Monitoring: Establish long-term monitoring programs in urban parks, especially in high-risk zones.
2. Remediation Strategies: Use phytoremediation or soil amendments to reduce bioavailability of heavy metals.
3. Urban Planning: Design green spaces with buffer zones and low-exposure zones for children.
4. Public Education: Raise awareness about contamination risks and promote safe park usage practices.
5. Policy Development: Implement regulations to limit urban emissions and manage land use near green spaces.
Conclusion
This study underscores the significance of combining pollution indices and GIS tools to assess heavy metal contamination in urban park soils. The findings reveal spatially heterogeneous contamination patterns and identify ecological and health risks, particularly in parks located in densely populated or industrialized zones. An integrated approach to monitoring, remediation, and urban design is essential for safeguarding environmental quality and ensuring the safe use of urban green spaces.

Keywords

Heavy metals
pollution index
urban park
soil
Shiraz

Subjects

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Quaternary Journal of Iran
Volume 10, 3 , 4
March 2025
Pages 430-446

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