A review on integrated assessment of heavy metal contamination in urban soils and groundwater

Heavy metal pollution in soils and groundwater has significantly increased due to rapid urbanization and industrialization in recent years, posing serious threats to ecosystem sustainability, food security and human health. Heavy metals are dangerous pollutants because they are persistent, non-biodegradable and capable of bioaccumulation, unlike organic pollutants. Anthropogenic activities such as the dumping of solid waste, car emissions, wastewater irrigation and industrial effluents are the primary contributors. Lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg) and chromium (Cr) are among the metals with the most diverse mobility and toxicity profiles in the environment. Although groundwater is contaminated via various sources such as leaching, landfill infiltration and hydrogeological transport, urban soils serve as the primary reservoirs, facilitating pollution through runoff and deposition. To understand this various assessment methods are adopted. Assessment methods range from simple geochemical analysis and traditional sampling to more complex methods like machine learning,remote sensing (RS), geographic information systems (GIS) and predictive modelling. Socioeconomic vulnerabilities and multi-pathway exposures are proving to be important factors in risk assessment models for human and ecological health. Remedial initiatives include both conventional approaches and eco-friendly strategies such as phytoremediation, bioremediation and artificial wetlands. This study identifies key gaps and future directions, including the use of digital technology, pollutant speciation, long-term monitoring and collaborative governance. A combined, preventative and context-specific strategy is needed for the maintenance of public health, urban ecosystems and sustainable urban resilience. This paper focuses on the state-of-the-art in the field and highlights the sources, pathways, environmental behaviour and remediation methods of heavy metals in urban soils and groundwater.