Assessment of heavy metals in agricultural soils of the Durmah region, southwest Riyadh: Contamination levels, ecological risk, and source identification

This study assesses the levels, spatial distribution, ecological risk, and probable sources of heavy metals (HMs) in agricultural soils of the Durmah region in central Saudi Arabia. A total of 34 surface soil samples (<30 cm) were analyzed for Fe, Al, Mn, Zn, Ni, Cr, V, Cu, Pb, and Co using inductively coupled plasma–atomic emission spectrometry (ICP-AES). The mean concentrations (mg/kg ± SD) were 10778 ±2902, 5414 ± 2134, 168 ±59.13, 42.8 ±43.70, 15.4 ±5.50, 16.9 ±6.86, 14.9 ±5.62, 9.9 ±5.07, 3.54 ±1.36, and 3.33 ±1.91, respectively. These values are generally below global soil and crustal background levels. Enrichment factor (EF), contamination factor (CF), geoaccumulation index (Igeo), and risk index (RI) indicate deficient to minimal enrichment, low contamination, and insignificant ecological risk for most metals. Soil quality guidelines (SQGs) show that all samples fall below effects range low (ERL) for Cu, Pb, and Cr, whereas nine samples contain Ni and one sample contains Zn within the ERL–ERM range, a possible occurrence of adverse effects. Multivariate analyses reveal that Fe, Al, Mn, Ni, Cr, Pb, and V predominantly originate from lithogenic sources, associated with the weathering of the Triassic–Jurassic sedimentary formations. Conversely, localized enrichment of Zn, Cu, and Co may indicate minor anthropogenic inputs, which may be related to fertilizers and livestock feed. Overall, the Durmah region exhibits generally low ecological risk and deficient enrichment.