Accumulation and Transport Characteristics of Cd, Pb, Zn, and As in Different Maize Varieties

Abstract

The enrichment and translocation characteristics of Cd, Pb, Zn, and As by various parts of maize plants were investigated using field experiments in 22 maize varieties simultaneously under uncontaminated, low, middle, and serious heavy metal Cd, Pb, Zn, and As complex-contaminated farmland soil conditions. The relationship between the uptake of Cd, Pb, Zn, and As by maize plants and the morphological content of heavy metals in the soil was also discussed through principal component analysis and correlation analysis of the concentrations of eight heavy metals, including Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn. The results showed that:① the distribution pattern of Cd and Zn contents in different parts of the maize plant was as follows:upper stalk>lower stalk>root>seed, the distribution pattern of Pb was As follows:root>lower stalk>upper stalk>seed, and the As distribution pattern was:root>upper stalk>lower stalk>seed. The different distribution patterns were closely related to the accumulation characteristics of the crop itself and the environmental activity of Cd, Pb, Zn, and As in the soil of the study area. ② There were significant differences in Cd and Pb accumulation among 22 maize cultivars due to their genetic background (P<0.05), which showed four trends:Cd and Pb compound high-accumulation varieties, single Cd or Pb low-accumulation varieties (low Cd and high Pb, low Pb and high Cd), and Cd and Pb compound low-accumulation varieties. Among them, the content of Cd in the grain of the three varieties exceeded the national food safety standard, and the content of Cd in the stem and leaf of 14 varieties exceeded the national food health standard. The Pb content in stems, leaves, and grains of all cultivars did not exceed the standard, but the Pb content in grains of some cultivars was close to the limit and had the risk of exceeding the standard. The content of As in the stem, leaf, and grain of different maize varieties was much lower than the standard limit value, showing a stable low-accumulation characteristic. The content of Zn in the stem and leaf of different maize varieties increased with the increase in the content of Zn in soil, but the content of Zn in grain remained within the threshold of normal plant growth. ③ Cd, Pb, Zn, and As in maize plants in the study area had a certain homology and were mainly affected by the excessive levels of Cd, Pb, Zn, and As pollutants in the soil. This showed that anthropogenic sources were brought about by mine extraction and tailings stockpiles, whereas Cu elements in maize plants were affected by certain anthropogenic pollution sources, though to a limited extent. Hg, Ni, and Cr in maize plants had a certain homology; this showed the natural source of soil parent material and weathering product accumulation. ④ The contents of Cd, Pb, Zn, and As elements in various parts of the corn plant, as well as the contents of Cr and Ni elements all had a very significant positive correlation (P<0.01). The transport mechanisms of Cd, Pb, Zn, and As elements in the plant may have a common. However, there was a synergistic effect in the migration from the root of the corn to the upper part of the ground, and the same was true for the elements of Cr and Ni. The elements of Hg and Cd, Pb, Zn, and As in the corn stems and leaves and Hg and Cd, Hg, As, Pb, Cr, Ni, and Zn in grains all showed certain antagonistic effects. ⑤ The comparison method simultaneously satisfied the following requirements:the contents of Cd, Pb, and As in stems and leaves did not exceed the national food hygiene standards, and the contents of Cd, Pb, and As in the grains did not exceed the national food safety standards. The cluster analysis of Cd, Pb, and As in grains was a low-accumulation group, and the enrichment and transport coefficients of Cd, Pb, and As in the stems and leaves and grains were low as the optimal conditions. C18 (Xianyu 335) could be selected as the optimal maize variety with low accumulation of Cd, Pb, and As and normal Zn content in grain, which is suitable for promoting and applying in the heavy metal complex-polluted farmland around industrial and mining enterprises in north China.