Foliar Uptake Exceeds Soil Contamination: Dominant Contribution of Bioavailable Atmospheric Trace Metals to Crop Accumulation.

Abstract

Atmospheric deposition is a major source of trace metals (Cd, Cu, Pb, Zn, and As) to crops, yet the relative contributions of exposure pathways and soil metal pools are unclear. Using a two-year open-top chamber (OTC) field study and greenhouse experiments, combined with synchrotron radiation microscopic X-ray fluorescence (SR-μXRF) and diffusive gradients in thin films (DGT), we assessed the impacts of wet/dry deposition and soil type on rice and pak choi. Newly deposited metals showed high bioavailability and increased soil bioavailable pools. Foliar exposure contributed 22-77% to metal accumulation in edible tissues than root uptake, regardless of soil contamination. Rice nodes act as redistribution hubs, transporting foliar-acquired metals upward while limiting downward movement. SR-μXRF revealed distinct within-node metal distribution patterns between exposure pathways. These findings establish foliar uptake as a dominant and quantitatively significant entry route for trace metals, highlighting the necessity of selecting low-accumulation crops to reduce foliar exposure to safeguard food safety.