A Source-Oriented Ecological and Health Risk Assessment of Soil Heavy Metals in a Small Watershed of Henan Province, China: A Coupled PMF-RI/PMF-HRA Approach

The quantitative identification of heavy metal sources is essential to clarify their relationships with ecological and health risks. This study focused on the Manghe Watershed in Jiyuan City, Henan Province, China, integrating the Positive Matrix Factorization (PMF) model, ecological risk index (RI), and health risk assessment (HRA) to construct a coupled PMF-RI/PMF-HRA framework to quantify source-specific risk contributions and propose targeted mitigation strategies. Key findings included: (1) Among the 121 surface soil samples, Cr and Ni showed natural background levels, while Cd, Pb, Hg, Zn, As, and Cu exceeded regional backgrounds by 1.63–33.65 times with anthropogenic-driven spatial heterogeneity. (2) The PMF identified four sources: natural–agriculture mixed (42.65%), the main contributor to Cr, Ni, As, and Cu; industrial activity (24.99%), the primary source of Cd and Zn; traffic–agriculture mixed (20.99%), primarily emitting Pb and As; and coal combustion (11.36%), dominating Hg emissions. (3) Ecological and health risks were governed by heavy metal toxicity and exposure pathways rather than mere concentration levels. Specifically, industrial sources (Cd, Zn) should be prioritized for ecological risk control, whereas natural–agricultural mixed sources (As, Pb, Cr) should be prioritized for health risk control. Oral ingestion was the dominant exposure pathway for both non-carcinogenic risk and carcinogenic risk in children, with the natural–agricultural mixed source contributing the most to this pathway. (4) The total carcinogenic risk (TCR) for children was 1.17 × 10−4, which exceeds the commonly accepted unacceptable threshold of 1 × 10−4, indicating a potential carcinogenic concern. (5) The PMF-RI and PMF-HRA frameworks quantitatively proved that the main sources of ecological risks and health risks may be completely different, and this phenomenon was jointly regulated by the toxicity response coefficient and exposure pathways. A “source–risk-pathway” quantitative attribution was achieved and provides clear support for targeted interventions, emphasizing source control for industrial emissions (Cd-Zn), traffic–agriculture inputs (Pb-As), and coal-derived Hg, alongside optimized agricultural practices.