Atmospheric deposition as a substantial source of lead in wheat grain: Between-year variation and uptake-pathway...

Atmospheric deposition is a critical pathway for lead (Pb) entry into agroecosystems; however, the patterns of its between-year accumulation and the contributions of foliar and root uptake to Pb levels in crops remain unclear. In this study, we combined a two-year factorial field exposure with a foliar-exposure trial in wheat to elucidate these mechanisms. Pb concentrations in wheat varied in accordance with the interannual deposition flux of Pb, decreasing synchronously as the flux declined from the first to the second year, demonstrating that crop Pb levels tracked annual atmospheric inputs. Extending soil exposure to atmospheric deposition from one to two years did not increase Pb concentrations in soil solution or wheat tissues. This suggested that, under the conditions of this study, newly deposited Pb during the current growing season-rather than Pb previously deposited in the soil-may be the primary source of Pb in wheat, as its bioavailability decreased markedly with soil aging. Quantitative pathway partitioning further revealed a sustained high contribution from foliar uptake to grain Pb accumulation (24.7%-68.8%), highlighting aboveground exposure as the key target for intervention. Collectively, these findings challenge conventional soil-centric management frameworks and emphasize the importance of reducing atmospheric Pb deposition and regulating foliar uptake to ensure the safe production of crops.