Evaluating Tree Leaves for Cadmium Biomonitoring in an Industrial–Agricultural Area: A Multi-Species Comparison with Atmospheric Deposition

Atmospheric deposition transfers heavy metals to farmland, but plant matrices differ in how they record these inputs. This study evaluated leaf tissue and leaf-surface dust as biomonitors in an industrial–agricultural area in Jinhua, Zhejiang, China, selected for its adjacent farmland, industrial facilities, and transport routes. Cd, Cr, Pb, As, and Hg were measured in 74 topsoil samples. Cd was measured in atmospheric-deposition samples and in leaf tissue and surface dust from four tree species at 15 paired sites during autumn–winter and spring–summer. The geoaccumulation index (Igeo), spatial analysis, correlations, a downwind transect, and random forest models based on candidate-source distances were used. Cd showed the most widespread soil enrichment (mean Igeo = 1.25; 97.3% of samples in classes 1–4). Mean Cd in atmospheric-deposition samples decreased from 6.27 mg kg−1 in autumn–winter to 3.01 mg kg−1 in spring–summer, whereas Juniperus chinensis leaf-tissue Cd increased from 0.25 to 0.35 mg kg−1. J. chinensis leaf-tissue Cd was spatially correlated with Cd in atmospheric-deposition samples in both periods (r = 0.77 and 0.53), and exploratory random forest rankings shared leading distance predictors with those for atmospheric-deposition samples. After adjustment for soil Cd, the correlations were 0.545 (p = 0.044) and 0.496 (p = 0.071). These findings support further evaluation of J. chinensis for preliminary spatial screening and prioritization of direct monitoring. Root uptake, resuspended soil dust, unmeasured leaf traits, and the small sample size limit inference; the associations do not establish uptake pathways or identify individual sources.