| Baiyin region is a major base for non-ferrous metal mining and smelting in China. Long history of mining and excessive industrial and agricultural activities have made the farmland soil seriously polluted, among which heavy metal pollution is the worsest. Soil heavy metal may accumulated in crop plant through soil-plant system and enter human body via food chain, causing great harm to human body. Although soil remediation steps have been carrying out, soil pollution is still serious. As a main food crop, spring wheat is widely grown in local. However, it is still unclear, under the condition of environment polluted, how is the accumulation of heavy metal in spring wheat (Triticum aestivum), neither of the potential risk to local inhabitants posing by long-time intake of polluted wheat grain. Therefore, it is of great significance for crop safe production in local and reducing the health risk to study the accumulation of heavy metal by wheat from soil and its influencing factors.In present study, farmland along Dongdagou was chosen as the study area. Soil properties (rapid available nitrogen and phosphorus, soil pH) and Cu, Zn, Pb and Cd in wheat plant (root, stem, leaf, husk and grain) collected from different sites were determined to investigate the effect of spring wheat to enrich heavy metal and its influencing factors; heavy metal in wheat plant of different development stages (trefoil stage, tillering stage, jointing stage, heading stage, flowering stage, filling stage and mature stage) were also determined to clearify the relationship between time and heavy metal in wheat plant. Finally, different planting densities were designed to investigate the feasibility of whether increasing planting density can reduce the amount of heavy metal accumulated in wheat plant and the health risk to human via intake of wheat grain. Results were as following:1. Soils of Dongdagou farmland were seriously polluted by Cu, Zn and Cd, whose concentrations were far beyond the environmental quality standard for soils of China (100 mg kg-1, 300 mg kg-1 and 1 mg kg-1 for Cu, Zn and Cd, respectively). Pb concentration surpassed the limit of China (300 mg kg-1) in soil of upstream Dongdagou, while under that in downstream. Heavy metal in wheat tissues were significantly positively correlated with soil rapid available nitrogen (p < 0.05), while no significant relationship was found with soil available phosphorus (p> 0.05). Moreover, exchangeable and carbonates fractions of heavy metal in soil also attributed to the concentrations of heavy metal in wheat tissues.2. Heavy metal concentrations in wheat plant peaked at trefoil stage and tillering stage, then decreased with increasing time. The amount of heavy metal accumulated in wheat increased with time. The concentrations of four metals varied in different parts of wheat, for Cu:root> husk> leaf> stem> grain, Zn:root> grain> leaf> husk> stem, Cd:root> leaf> stem> husk> grain and Pb:root> leaf> husk> grain> stem.3. With increasing planting density, Cd and Pb concentrations in wheat plant decreased significantly, the health risk also decreased. But the decline of production was small, indicating that increasing planting density can be a safer way for production.4. With increasing planting density, the amount of heavy metal extracted by wheat reduced, especially at the highest planting density (p< 0.05), indicating that planting density of plant or crop is one of the key factors affecting the removal effect in situ phytoremediation of soil.In all, soils in farmland along Dongdagou were seriously polluted by heavy metal. Wheat grown on the soils contained high concentrations of heavy metal and the concentrations were mainly positively correlated with soil rapid available nitrogen, exchangeable and carbonates fractions (p< 0.05). The ability of wheat tissues to enrich heavy metal were different, but decreased with development stage and increasing planting density. Heavy metal in wheat grain posed potential health risk to local inhabitants, but the risk can be lowered with the way of increasing planting density and without significant decrease of wheat production. In conclusion, present study is with great reference significance for safe prodution of spring wheat in local and reducing health risk of local inhabitants. |
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