| Agronomic crops grown on the reclaimed metal-mined wastelands are a noticeable pathway for toxic pollutants entering the human food chain. Agricultural rehabilitation of mine spoils in China is pretty common and its effect has been largely overlooked. Extensive sampling of the edible crops and associated soils have been conducted for the three typical manganese reclaimed minelands (Bayi, Lipu and Pingle) in Guangxi. Heavy metal contamination of crops was assessed against China Food Safety Standards and assessment of nutrient elements and heavy metals of the reclaimed minesoils were determined. The restoration measures of manganese mine wasteland were proposed in this study. The major results were as follows:(1)The pH and EC of the three reclaimed Mn minesoils basically met the grown needs of crops. The organic matter of Bayi and Lipu, and TN of Lipu minesoils fell into"good"class. The TP of Lipu and Pingle minesoils also satisfied the growth demand of crops. However, the organic matter and TN were in a low level and could be a limiting factor for plant growth. The TOM and TN of the three minesoils were significantly lower than those of the control site.(2)The total concentrations of Mn, Pb, Zn, Cr, Cu and Cd in the three reclaimed Mn minesoils were characterized by high level of various heavy metals, all of which exceeded the relevant soil background values for Guangxi. The highest concentrations of total Mn and Zn were 18558.9 and 227.49 mg·kg-1 in Pingle mineland, respectively. The highest concentrations of total Pb and Cr were 252.72 and 200.02 mg·kg-1 in Lipu mineland, and the peak levels of total Cd and Cu were 28.21 and 41.47 mg·kg-1 in Bayi mineland respectively.(3)The extracted Mn, Pb, Zn, Cr, Cu and Cd concentrations of the three reclaimed Mn minesoils with 0.1M HCI were all less than 8%. But the extracted concentrations of Mn and Cd still exceeded the relevant soil background values for Guangxi and China Soil Quality Standard (class II). The largest values of extracted Mn and Cu were 449.1 and 4.38 mg·kg-1 in Pingle mineland, respectively. The highest concentrations of extracted Pb and Zn were 6.10 and 8.24 mg·kg-1 in Lipu mineland. The highest concentrations of extracted Cr and Cd were 3.63 and 1.19 mg·kg-1 in Bayi mineland respectively.(4)Pearson correlation analysis of soil heavy metal concentrations showed: A significantly positive correlation (P<0.01) existed between the total Mn and its extracted concentrations, and between total Cd with its extracted concentrations in Bayi mineland. A significantly positive correlation existed between the total Mn and total Zn concentrations in Bayi mineland. And the significantly positive correlation existed among the extracted Mn, extracted Zn, and extracted Cd concentrations in Bayi mineland. The significantly positive correlation existed between the total Cd and total Cu concentrations, and between the extracted Zn and extracted Cu concentrations in Lipu mineland. The significantly positive correlation existed between the total Mn and total Cu concentrations, and between the total Zn and total Cd concentrations in Pingle mineland. And the significantly positive correlation existed among the extracted Mn, extracted Zn, and extracted Cd concentrations in Pingle mineland.(5)Pollution index and potential ecological risk index of Pb, Cr, Zn, Cu and Cd assessment indicated heavy pollution or high potential ecological risk of Cd and Mn were found and different level pollution of Pb, Cr or Zn existed in the three reclaimed Mn minelands. The main pollutant was Cd in the three Mn minesoils. Composite pollution index showed all the reclaimed Mn minelands were heavily polluted with heavy metals.(6)In the three minelands, the heavy metal ranges in the edible crops were Mn 0.39-402.27 mg·kg-1 , Pb 0.23-21.71 mg·kg-1 , Cr undetectable to 16.31 mg·kg-1 , Zn 0.59-39.56 mg·kg-1,Cu undetectable to 7.35 mg·kg-1,and Cd undetectable to 2.90 mg·kg-1 respectively. The highest content of heavy metals in the edible crops were Mn 44.04 mg·kg-1, Pb 5.45 mg·kg-1, Cr 2.41 mg·kg-1, Cu 2.37 mg·kg-1, Cd 0.75mg·kg-1. The contents of Mn, Zn, Pb, Cr, Cu and Cd in beans were almost highest among all other categories of the agronomic crops in the three Mn minelands.(7)Simple pollution index (Pi) assessment indicated no Zn and Cu pollution among the edible crops, but heavy pollution existed for Pb, Cd and Cr found in the three minesoil. The pollution rates of Pb, Cr and Cd in agronomic crops were 98.4%, 88.9% and 63.5%, respectively. Composite pollution index (Nemerow index, PN) indicated all crops were polluted by heavy metals with heavy grade being more than 76%.(8)Crops tended to have a low heavy metal accumulation (as indicated by Biological Accumulation Coefficient, BAC<0.4) in edible parts of the three minesoil, while the BAC of Mn and Zn in the leaf of tea and the BAC of Cd in the peanut, Cassava and sugarcane were all higher than 1. Both of the highest BAC in Lipu and Pingle minelands were Cd (0.37 and 0.21) and the lowest were Mn (0.04 and 0.01). And the highest BAC in Bayi mineland was Zn (0.27) and the lowest was Cr (0.04).(9)These findings reflected direct growth of edible crops on the Mn mine wastelands may risk human health. To avoid or reduce the risk, soil amendment, bio-remediation and tracing monitoring of toxic metals are needed and the cost is very high. In fact, restoration of minelands can have much more diverse functions such as nursery, forestry, biodiversity conservation, checking soil and wind erosion, recreation and tourism, or just beautifying the damaged landscape.
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