Different land use types around megacities contribute contrasting heavy metal pollution and health risks in soil-leaf...

Variations in urban land use within megacities significantly influence heavy metal (HMs) accumulation and associated dietary health risks in soil-leafy vegetable systems. This study investigated ten seasonal leafy vegetables and their rhizosphere soils from three land-use types in Guangzhou, China: food-basket base (G0), industrial-adjacent (G1), and peri-urban sites (G2). Contamination and health risks were assessed using pollution indices and Monte Carlo simulation (MCS). Soils were primarily contaminated with cadmium (Cd) and copper (Cu), corresponding to mild pollution (P = 1.3) and slight ecological risk (RI = 50.4). Industrial-adjacent soils (G1) showed higher pollution and ecological risk (P = 1.9; RI = 67.2) than G0 and G2. In vegetables, chromium (Cr) was the dominant pollutant, with an exceedance rate of 49.5%, followed by nickel (Ni) (31.4%) and lead (Pb) (24.7%). Cd bioaccumulation factors ranged from 0.1 to 0.5, with lettuce showing the highest enrichment capacity. Deterministic assessment indicated that total target hazard quotient (TTHQ) exceeded 1.0 across all land-use types, while total target cancer risk (TTR) exceeded the acceptable threshold (10^-4) for both adults and children. Cr contributed 42.8-42.9% of non-carcinogenic risk, whereas Ni accounted for 51.2-51.3% of carcinogenic risk. MCS results further confirmed that adults faced higher probabilistic risks than children. Soil sand content, available phosphorus (AP), and soil Ni concentration were identified as key factors regulating HMs uptake by vegetables. These findings highlight substantial land-use-dependent risk variation and underscore the need for targeted soil management and crop selection strategies in rapidly urbanizing regions.