Heavy metal contamination in Saudi Arabian soil and water: Regional distribution

Arid and semi-arid environments are highly vulnerable to potentially toxic element accumulation because low rainfall, high evaporation, dust transport, episodic runoff, irrigation return flow and groundwater salinity can concentrate metals in soil and water. Saudi Arabia provides a distinctive national case because rapid urbanization, agriculture, cement production, wastewater reuse, coastal development and petroleum-related activities occur across contrasting geological provinces. This review critically synthesizes published evidence on heavy-metal and trace-element concentrations in Saudi Arabian soil, sediment, groundwater, surface water, irrigation water, seawater and wastewater-influenced systems. The review follows a structured critical-review approach: peer-reviewed studies were screened for location, matrix, analytical method, concentration data, quality assurance/quality control information, guideline comparison and reported pollution or risk indices. The evidence shows strong spatial heterogeneity. Central-region datasets dominate the literature, whereas northern agricultural areas, western Red Sea coastal-industrial sites, southern wadis and landfill-affected areas, and eastern oil-related and coastal settings remain important but unevenly represented. Reported hotspots include Cd up to approximately 22 mg/kg in industrial soil, elevated Zn in Riyadh playground soils, As up to approximately 0.18 mg/L in well water and Fe up to approximately 1.45 mg/L in well water. Priority elements are As, Cd, Pb, Cr, Ni, Cu, Zn, Fe and Mn. Their interpretation requires matrix-specific guideline comparison, geogenic background assessment, and land-use context. The review identifies carbonate-evaporite aquifers, Arabian Shield-derived sediments, wadi transport, irrigation return flow, industrial emissions, wastewater inputs and petroleum-related activities as interacting controls. Hydrogeophysical and hydrochemical analysis is emphasized as complementary evidence for aquifer-pathway interpretation. A harmonized national monitoring framework that uses standardized sampling, complete quality assurance/quality control (QA/QC) reporting, geographic information system (GIS) mapping, bioavailability assessment, and ecological and human health risk indices is recommended.