Quantitative analysis of lead sources in wheat tissue and grain under different lead atmospheric deposition areas

Due to rapid growth of industrialization and human activities, such as mining and smelting, lead (Pb) has become a major environmental contaminant. As Pb can pose risks to human health, preventing Pb pollution in wheat is important for food safety, requiring accurate verification of pollution sources. Pb concentrations and isotope ratio levels in soil, in the atmosphere, and wheat tissue (root, stem, leaf, grain) in an area of high-Pb deposition (in the vicinity of a Pb smelter in Jiyuan city) and an area of low deposition (the northwest suburb of Zhengzhou city) were examined. The Pb isotope ratio and the binary mixed model were used to quantify the contribution of soil and atmospheric deposition to Pb content in wheat tissues. Results show that Pb content in soil, atmospheric deposition, and wheat in the high deposition area were significantly higher than those in the low deposition area. Pb content in soil, atmospheric deposition, wheat roots, stems, leaves, and grains in the high-deposition area were 355.32 ± 14.78, 5477.90 ± 187.85, 158.72 ± 9.56, 21.36 ± 1.72, 26.49 ± 1.96, and 0.94 ± 0.02 mg kg^-1, respectively. Pb content in the low-deposition area were 6.10 ± 0.75, 78.50 ± 4.35, 2.47 ± 0.23, 1.03 ± 0.07, 2.11 ± 0.13, and 0.08 ± 0.01 mg kg^-1, respectively. The Pb isotope ratio recorded obvious differences between soil and atmospheric deposition in the two areas. Combined with the significant correlation between Pb isotopes in various tissues of wheat and environmental media, and analysis of the isotopic composition characteristics of wheat and environmental media, in the high-deposition area, the contribution rate of atmospheric deposition in wheat roots, stems, leaves, and grains was 14%, 66%, 84%, and 77%, respectively. And the soil contribution rate was 86%, 34%, 16%, 23%, respectively. In the low-deposition area, the contribution rate of atmospheric deposition in wheat roots, stems, leaves, and grains was 49%, 73%, 93%, and 83%, respectively. And the soil contribution rates were 51%, 27%, 7%, and 17%, respectively. In the low-Pb deposition area, the contribution rate of atmospheric deposition in wheat was higher than that in the high-deposition area. Atmospheric deposition was the main source of Pb in grains, leaves, and stems of wheat in different depositional areas. Pb in wheat roots mainly derives from soil, and the Pb contribution rate of soil to wheat roots in the high-deposition area was significantly higher than that in the low-deposition area.