From environment to human: systematic assessment of heavy metal contamination and exposure in a typical karst agricultural area.

Karst agroecosystems are highly vulnerable to heavy metal contamination, yet integrated assessments linking environmental pollution to human exposure remain limited. This study investigated soils, surface water, and food crops in a karst agricultural town of Southwest China and used hair and nail biomonitoring to examine potential linkages between environmental contamination, food exposure, and human metal accumulation. Cultivated soils showed pronounced enrichment of Cd, Pb, and Zn, with Cd driving severe pollution (Pi > 10; Pn > 1), whereas surface water met Class I standards. Agricultural products frequently exceeded food safety limits for Cd and Cr, and Cd exhibited the highest bioaccumulation potential. Positive Matrix Factorization resolved four major factors, with elemental loading patterns suggesting contributions potentially associated with mining/industrial/traffic activities, lithogenic sources, and agricultural inputs. Monte Carlo health risk assessment indicated substantial potential health concerns, with children facing higher non-carcinogenic risks (HI = 4.55) and both adults and children showing unacceptable carcinogenic risks (TCR = 1.71 × 10-3 and 1.42 × 10-3, respectively), with Ni and Cd contributing substantially to the estimated risks. Biomonitoring revealed distinct age-specific accumulation patterns, with children showing higher levels of Zn, Cr, and Ni and adults of Pb, Cd, Cu, and As, further supported by multivariate analysis. Overall, the findings suggest that geological background and anthropogenic activities may collectively contribute to metal occurrence and exposure in this karst agroecosystem, and highlight Cd and Ni as priority elements for risk control in vulnerable karst regions.