Classification Of Cd Pollution Degree In Soil For Safety Of Potatoes Planting

Taking soil of potato producing area in Weining county as the research object,we classified Cd of pollution degree,carrying out field samples and pot experiment,combined with single factor index method?Nemero comprehensive pollution index method and potential ecological hazard index method based on Guizhou Province soil background value and agricultural soil pollution risk control standard(GB15618-2018).We analyzed the accumulation characteristics of heavy metals in soil and potatoes.The contents of Cd?Pb?Cr?Hg?As?Cu and Zn of heavy metals in soil and potato were evaluated at risk,and the spatial variation trend of heavy metals in soil was analyzed by ArcGIS.Heavy metal of Cd for potato safety based on filed and potted experiment with content-effect as the core,the safety threshold of soil Cd based on potato quality and safety was obtained,and then the contamination degree of potato producing soil was classified according to the safety threshold and GB15618-2018.The results showed:(1)The analysis of soil heavy metal content showed that the average content of different heavy metals Cd?Pb?Cr?Hg?As?Cu?Zn were 2.21?62.26?131.98?0.13?14.68?101.56?186.77 mg/kg,respectively,which exceeded the soil background value of Guizhou Province.Compared with GB15618-2018,the Cd?Cu and Zn exceeded the screening value,and were 7.37?2.03?3.11 times of the screening value,respectively,and the other elements were below the screening value.The spatial distribution of Cd content in potato soil decreased gradually from southeast to northwest.(2)With reference to soil background value and soil pollution risk control standard of agricultural land in Guizhou Province,Nemero comprehensive pollution index evaluation method shows that soil is polluted to varying degrees,and its main pollution factor is Cd.The comprehensive pollution index was 2.81 and 4.97 respectively,the degree of pollution was moderate pollution and severe pollution.Combined with two evaluation criteria,the potential ecological risk index method showed that the soil heavy metals were all moderate hazard level,and the single potential ecological hazard index is Cd.(3)Fractionation of Cd for Soil in potato producing areas was mainly reductive state,accounting for 42.64%of the total,followed by residual and exchangeable forms,accounting for28.49%and 22.62%of the total,respectively.The lowest average content is oxidizable which the porportion was 6.25%.The available state make up 65.26%,It showed that its bioavailability was stronger.(4)The average content of Cd?Pb?Cr?Hg?As?Cu and Zn in potato was 0.095?0.205?0.124?0.004?0.014?0.952?4.172 mg/kg,respectively.The average value of total hazard index was 0.744,TTHQ<1which indicated that the level of heavy metals in the potatoes do not represent any toxicological risk to human.(5)The safety threshold of Cd in potato soil:According to the national standars for limited0.10mg/kg of Cd in food GB2726-2012,the safety threshold of Cd in soil among pH?5.5?5.5<pH?6.5?6.5<pH?7.5?pH>7.5 were 0.68?2.59?4.82?12.52 mg/kg,respectively.The safety threshold of Cd in pot experiment was 1.50mg/kg and 0.12mg/kg.(6)Based on the safety threshold,the soil pollution degree of potato producing area was classified:The soil environment quality is preliminarily evaluated.According to GB15618-2018,2.07%of the soil pollution risk control standards belong to the priority protection category,66.84%of the samples belong to the category of safe use,31.09%of the samples belong to the strictly controlled category;Reference to safety threshold,belonging to the priority protection class and the safe utilization,and the strict control is 17.10%?58.55%?24.35%.Results of the evaluation of single-factor pollution index.Based on the screening value,the proportion of the Cd element P_i?0.7 was 1.55%,the proportion of 0.7<P_i?1 was 1.04%;the proportion of 1<P_i?2was 16.06%;the proportion of 2<P_i?3 was 12.44%;the proportion of P_i>3 was 68.91%.Based on safety threshold,the proportion of Cd element P_i?0.7 was 62.18%;the proportion of 0.7<P_i?1 was 10.88%and the proportion of 1<P_i?2 was15.54%the proportion of 2<P_i?3 was 6.22%;the proportion of P_i>3 was 5.18%.The comprehensive pollution index.Referring to the screening value,63.73%of the soil samples were severe pollution,21.76%were moderate pollution,13.47%were mild,and 1.04%were in the cordon and there was no safety level.Based on the safety threshold,accounting for 23.83%of the total samples,reached severe pollution,24.35%to moderate pollution,39.38%to slightly pollution,9.85%to warning level,and 2.59%were safety level.