Input and output balance of heavy metals from an abandoned mining area in farmland soils
A small watershed of an abandoned pyrite mining area in the lower reaches of the Yangtze River was selected as the study area to explore the characteristics of heavy metals input and output fluxes in farmland soil of mining areas.We analyzed the spatial distribution characteristics of heavy metals(Cd,Pb,Cu,Zn,Cr)in soils by setting up monitoring fields to calculate the input and output fluxes of heavy metals in the soil of the study area and construct a content of heavy metals prediction model.The results showed that:Cd,Cu,Zn were the main heavy metal pollutant elements in the soil of the small watershed in the pyrite mining area,with 5.88%,33.99%,and 13.07%of the soil samples exceeding the risk screening values for soil pollution in agricultural land(GB 15618-2018),respectively.The proportions of Cd and Cr in rice grains exceeding the"National Food Safety Standard for Pollutant Limits in Food"(GB 2762-2017)were 36.00%and 13.33%,respectively.The spatial distribution of Cd,Cu,Zn in soil showed a trend of high content around the upstream mining pit and at the entrance of the downstream reservoir,and there was a significant positive correlation between them(P＜0.01),while the spatial distribution of Pb and Cr were different,and Cr showed a negative correlation trend with the other elements.According to monitoring field calculating,the total annual input fluxes of Cd,Cu,Pb,Zn,Cr in paddy soils were 15.62,86.63,292.92,325.89,90.30 g·hm-2·a-1,respectively,and the total annual output fluxes were 2.85,0.32,37.20,196.15,5.94 g·hm-2·a-1,respectively.Soil heavy metals exhibited a continuous accumulation characteristic.It was predicted that the content of Cd and Cu would significantly increase in the next 20 years while the content of Pb,Zn,Cr would decrease.In conclusion,strengthening water source management in upstream mining areas,advocating scientific irrigation in downstream farmland,and reducing the input of heavy metals such as Cd into irrigation water is crucial for the prevention and control of soil heavy metal pollution sources.
pyrite mining areaheavy metalspatial distributioninput and output fluxespredictive model
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