Cross-regional assessment of heavy metal contamination and Cd exceedance risk in specialty vegetable-producing soils across China.

Soil heavy metal contamination in specialty vegetable-producing areas has received increasing attention, yet cross-regional evidence under a unified framework remains limited. Here, 348 soil samples were collected from seven vegetable production systems across six agricultural regions of China to characterize the distribution of As, Cd, Cr, Hg, and Pb, assess contamination and ecological risk, and identify key factors associated with Cd exceedance. Heavy metal contamination showed pronounced spatial heterogeneity across both agricultural regions and vegetable production systems. Cd had the highest exceedance rate (12.93%), followed by Cr (4.30%), As (2.59%), Pb (0.57%), and Hg (0.00%), and consistently emerged as the dominant contaminant across the geoaccumulation, contamination, and exceedance assessments. The mean potential ecological risk index (RI) was 173.04, indicating a moderate overall ecological risk, with Hg and Cd contributing most to the composite risk. Correlation and ordination analyses identified TN, OM, TP, and pH as key soil properties associated with heavy metal distribution. XGBoost showed the best performance for Cd exceedance screening, and SHAP analysis identified OM and pH as the most influential predictors. High Cd exceedance probability was concentrated mainly in Southwest China, with additional hotspots in parts of Central-South China. These findings demonstrate marked regional and production-system differentiation in heavy metal contamination of specialty vegetable-producing soils and support prioritizing Cd in risk screening and monitoring.