| The safe and effective use of lightly polluted farmland in heavy metals is essential for soil health and production safety.In this study,the soil of farmland around a lead-zinc mining area in Shaanxi Province was selected as the source of heavy metal pollution.A total of 228crop samples and their corresponding rhizosphere soils,including 14 herbaceous plants,18vegetables,and 20 food crops were collected for the screening of heavy metal low accumulation crops.The seedling stage test was to screen super-enriched plants and intermixed species,including 12 super-enriched varieties and 4 planting modes.Taking the polluting elements Cd,Pb and Zn as the research objects,the heavy metal content of crop and soil samples were determined by atomic absorption method,and the soil pollution level was comprehensively evaluated by the single-factor pollution index method and Nemerro comprehensive pollution index method.According to the results of clustering and correlation analysis,the cumulative content,enrichment coefficient and transport coefficient of heavy metals in the aboveground and underground parts of different crops were compared,and the health risks caused by heavy metals ingested by vegetables or cereals were evaluated,and the following main results and conclusions were obtained:（1）The comprehensive pollution index of each heavy metal element is 2.88,which belongs to medium and mild compound pollution farmland.The excess rate of Cd was detected in the edible parts of all crops was 58%,and Pb was not detected in the edible parts of vegetable and food crops.Through the control optimization method,the field experiment screened out pepper,bitter melon and pod vegetables,dogtail and purslane vegetables with low accumulation of heavy metals and herbs,respectively,and the enrichment coefficients of edible parts of vegetables were sorted as follows:leafy vegetables>rhizomes>melons and fruits>nightshade fruits>pods;Yujiao No.5（wheat）,Pingdecun No.1（wheat）,peanut four red（peanut）,M02Q2016（soybean）and Shaanxi Dan 650（maize）were selected as the preferred crops planted in mildly contaminated soil in Cd and Pb with Zn content at normal levels.The enrichment capacity of the edible part of legumes is low(content less than 0.1mg·kg-1),and the Cd content of edible parts of grasses（corn,millet,chyme）exceeds the national grain safety standard value(0.1 mg·kg-1)by 18～20 times.The tissue enrichment coefficients of grain crops were as follows:leaf>root>stem>shell>seed,leaf>stem>root>seed.The transport coefficients were as follows:leaf>shell>stem>seed,leaf>stem>shell>seed.（2）The seedling stage experiments screened out the varieties of amaranth with strong enrichment ability of metal Cd,Pb and Zn,and sunflower was a super-enriched crop.Compared with mixed seeds,the interplanting mode of sunflower and wheat（spacing 15 cm）was selected,which could effectively improve the photosynthetic utilization rate of plants and reduce the transport of heavy metals to the aerial part of wheat.（3）The correlation of single elements in the soil-crop system was as follows:Zn in rhizosphere soil and Zn in edible parts showed synergistic effects;Cd and Pb showed a negative correlation in rhizosphere soil and grain,showing antagonistic effects.（4）The health risk assessment results brought by long-term consumption of vegetables and food crops for residents are:children>adults,combined with the planting of crops in the field.In order to achieve the purpose of remediating contaminated soil while safe production,this study analyzed the differences in the ability of different crops,different crop varieties and different crop organs to transport and enrich heavy metals.The agronomic measures of low-accumulation heavy metal varieties and super-enriched plants and interspecies combined restoration suitable for medium and mild heavy metal polluted farmland were screened,which provided new methods and ideas for joint restoration for agricultural production and helped to accelerate the remediation process of heavy metal contaminated soil. |
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