Potentially toxic elements in irrigation-well groundwater: occurrence, spatial heterogeneity, and controlling processes (Al-Jilah, Saudi Arabia)

Groundwater sustains arid agroecosystems, but repeated irrigation and soil–water interactions can mobilize potentially toxic elements (PTEs) and enhance their transfer to shallow aquifers through percolation and irrigation return flow. This study determined As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn in 30 groundwater wells from the Al-Jilah agricultural area (west of Riyadh, Saudi Arabia) using ICP-MS. Concentrations (µg/L) were: Cr 0.02–17.6, Cu 0.01–30.0, Zn 0.35–3430, Fe 0.48–63.4, Ni 0.14–26.2, As 0.02–0.14, Ba 5.03–40.3, Mn 0.01–10.9, Cd 0.0017–0.5080, and Pb 0.0015–0.0709. All measured PTEs were below WHO and national drinking-water limits, except Zn, which exceeded the WHO aesthetic guideline (3,000 µg/L) at one well. Spatial interpolation identified localized enrichment zones in the northeastern and southeastern sectors, associated with heterogeneous recharge, irrigation return flow, and lithologic controls. Pollution indices (HPI, MI, and Nemerow) indicated generally low cumulative metal loading, with 26 of 30 samples having MI < 1. Human-health risk assessment (CDI, HQ, HI, and LCR) indicated no non-carcinogenic risk and carcinogenic risk within acceptable limits. Multivariate analyses (correlation analysis and PCA) suggested mixed geogenic and agricultural sources, supporting targeted monitoring and improved irrigation/agrochemical management.