| As a by-product of wet-process phosphoric acid production,phosphogypsum will generally bring 4.5-5t of phosphogypsum for every 1t of phosphoric acid（in P2O5）produced,and the current stockpile is harmful to the surrounding groundwater,surface water,soil,vegetation,and agriculture.To further understand whether heavy metals in phosphogypsum pollute the surrounding environment and the environmental risk,this study chose the phosphogypsum dumpsite of Wengfu Group in Machangping,Fuquan City,as the research object to study the pollution characteristics of heavy metals in groundwater,surface water,soil and plants around the dumpsite and to assess the environmental risk,and the following main conclusions were obtained.（1）The main characteristic pollutants of phosphogypsum leachate were F-,SO42-and TP,with contents of 2775 mg/L,4546 mg/L and 5962 mg/L,respectively,and the contents of heavy metals Cr,Cu,Zn,As,Cd,Pb,and Mn were 6.58 mg/L,1.32 mg/L,12.08 mg/L,17.59 mg/L,0.04 mg/L,0.17 mg/L,and 43.2 mg/L,with Mn and Zn polluting the most seriously.（2）Except for individual high values of Mn elements in surface water and groundwater around phosphogypsum dumps,the content of other heavy metal elements,such as Cr,Cu,Zn,As,Cd,and Pb,is lower than the limit value of Class III in Surface Water Environmental Quality Standard（GB3838-2002）and Groundwater Environmental Quality Standard（GB/T14848-2017）.The main sources of heavy metals in the water bodies of the study area were determined by principal component analysis as follows:industrial sources and natural sources contributed the most with 27.29%,followed by phosphogypsum dumps with 21.93%,agricultural sources with 13.17%,human activities with 10.28%,and domestic sources and others with 8.59%.（3）The content of heavy metals in the soil around the phosphogypsum dumps gradually decreases with the distance from the dumps,and within 100 m downwind of the dominant wind（Dutian）direction of the year-round,the contents of Cr,Cu,Zn,As,Cd and Pb reach 107.10 mg/kg,52.76 mg/kg,102.13 mg/kg,26.14 mg/kg,1.18 mg/kg,58.94 mg/kg,which were generally higher than the rest of the regions.Among them,heavy metal Cd contamination is the most serious,with an average content of 1.01mg/kg,1.11 mg/kg,0.95 mg/kg and 1.20 mg/kg in the direction of Baiji,Yanghuachong,Dutian and Bailang,which all exceed the background value of Cd soil in Guizhou province（0.66mg/kg）and the Soil Environmental Quality-Soil Contamination Risk Control Standards for Agricultural Land"（GB15168-2018）in the Cd risk screening value.The main sources of heavy metals in the soil of the study area were determined by principal component analysis as follows:industrial sources and human activities contribute the most with 40.04%;followed by natural sources with 14.99%;then phosphogypsum dumps with 11.47%;and finally,agricultural sources with 9.90%.（4）The heavy metals（Cr,Cu,Zn,As,Cd,Pb,etc.）in the soils of the study area were mainly in the residue state,accounting for 40.16-87.11%of the total.Among them,the exchangeable state of Cd accounted for 8.19-11.07%of the total and had higher activity than other heavy metals;the sum of the reducible and oxidizable states of Pb accounted for more than half of the total and had higher potential for release when environmental changes occurred.Analysis of the bioeffectiveness of heavy metals in the soils of the study area revealed that Cd had the highest easy availability of 9.25%and Pb had the highest potential and available availability of 56.17%and 57.42%,respectively.（5）The analysis on phosphogypsum stack corn samples found that the average contents of heavy metals Cr,Cu,Zn,As,Cd and Pb were 0.10 mg/kg,1.81 mg/kg,10.42mg/kg,0.007 mg/kg,0.036 mg/kg and 0.0004 mg/kg,which did not exceed the national food safety standard（GB2762-2017）.（6）Based on the WQI water quality evaluation results,the average WQI values of surface water and groundwater around the phosphogypsum dump are 44.71 and 58.26,respectively,and the water quality conditions are excellent and good.Meanwhile,the analysis of TP and fluoride content of water bodies around phosphogypsum dumps at different times found that the water quality around phosphogypsum dumps over time was improving and gradually complied with surface water and groundwater class III standards,indicating that the pollution treatment of phosphogypsum dumps gradually achieved results.The evaluation results of geological accumulation index method show that the whole study area is mainly light pollution of Cd and light pollution of Cu in some areas,and Cr,Zn,As,and Pb show no pollution as a whole.The evaluation results of Nemero comprehensive pollution index method show that the pollution index range of the whole study area is 1.02-3.99,with an average value of 1.50,which belongs to mild pollution.The evaluation results of potential ecological risk index method show that the potential ecological risk index RI of the whole study area is less than 110,which belongs to mild ecological risk. |
