Spatial heterogeneity, source contributions, and hazard mapping of potentially hazardous elements in irrigated soils of the Yellow River Basin, Northwest China

Abstract

Potentially hazardous element (PHE) contamination threatens agroecosystem sustainability and food security, particularly in irrigated regions. The Yellow River Basin in Northwest China is a critical agricultural zone where intensive irrigation and fertilizer use may accelerate soil contamination. A total of 487 topsoil samples were collected under a stratified random design. Concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were analyzed with strict quality assurance protocols. Spatial heterogeneity was quantified using the Optimal Parameters-based Geographical Detector (OPGD) model, while source apportionment was performed through Positive Matrix Factorization (PMF). Marked spatial variability was observed, with coefficients of variation exceeding 50% for As, Pb, and Cd. Hotspots were concentrated in northern and central irrigation zones. Total nitrogen showed the strongest statistical association with PHE distribution (Q = 0.796), followed by soil texture. PMF analysis identified agriculture-related inputs (Cd), industrial emissions (Zn, Cu), geogenic background (Cr, Ni), and traffic residues (Pb) as major contributors. Although most concentrations remained below national screening thresholds (GB 15618-2018), cadmium slightly exceeded the threshold (mean = 0.32 mg·kg⁻¹ vs. 0.30 mg·kg⁻¹), with localized enrichment hotspots for Cd, Pb, and Zn. Hazard mapping delineated high-risk zones in the eastern and southern districts, underscoring the importance of targeted management. These findings highlight nutrient status and agricultural practices as key drivers of PHE accumulation, providing insights for cadmium control and sustainable fertilization strategies in irrigated agroecosystems.