Study On Safety Threshold Of Typical Heavy Metals In Reclaimed Agricultural Soil From Inefficient Industrial Land

Since the reform and opening up,China's urbanization process has been speeding up and a series of land problems have appeared.In the face of declining arable land and land constraints,it has become an inevitable choice for inefficient industrial land reclaimed agricultural.Much inefficient industrial land may be polluted to some extent,by simple ecological restoration and agricultural processing,still can meet the demand of agricultural soil,has a great potential for agricultural use.However,there are some indicators in the existing soil standards that may be "overly strict" in the field of reclamation,and some indicators are "too loose".Accumulation of heavy metals of the discrepancy between different crops,scientific and reasonable safety threshold value of soil heavy metal for inefficient industrial land reclamation of agricultural crops,so as to effectively guarantee the quality and safety of agricultural products.In this study the five kinds of common crops,green pepper(CapsicumannuumL),cucumber(CucumissativusL),cowpea(Vignaunguiculata),spinach(SpinaciaoleraceaL)and rice(Oryza sativa)as the selected crops,adding Cd,Pb,Ni,Mn,Cr and Hg to the original soil of an inefficient industrial site as experimental soil.By potted plant experiment study the effects of heavy metal on the crop biomass,absorptioncharacteristics in crops,and the correlation between soil heavy metal content and heavy metal in crops.According to GB2762-2017 "food contaminants in limited value" regulation and Tanget hazand quotients(THQ)calculated contamination in food limited value,calculated the safety threshold of different crops planted in different heavy metal polluted soil,as guide for inefficient industrial land reclamation agricultural security classificationThe results were as follows:(1)Low concentration Cd,Pb,Ni and Mn promote crop growth,while high concentrations inhibit the growth of crops.Cr,Hg influence on crop biomass showed no obvious regularity.Ni as the nutrient element of crops,can promote the growth of crops more than other heavy metals.The effects of the same heavy metals on the biomass of different crops under the same concentration were different.(2)The amount of heavy metals in edible parts of crops increased with the increase of soil heavy metal content,and different crops had different accumulation capacity of different heavy metals.In this experiment,different kinds of crops in the same experiment condition,showed different capacities of heavy metal enrichment.The capacities of Cd enrichment ranking as: spinach>rice>green pepper>cucumber>cowpea,the capacities of Pb enrichment ranking as: rice> cucumber>spinach>green pepper>cowpea,the capacities of Ni enrichment ranking as: cowpea>rice>spinach>green pepper>cucumber,the capacities of Mn enrichment ranking as: spinach>cucumber>green pepper>cowpea,the capacities of Cr enrichment ranking as: rice>spinach>cowpea>green pepper,the capacities of Hg enrichment ranking as: rice>spinach>cowpea>green pepper.(3)The absorption of heavy metal in different parts of crops was different.Similarly,the distribution characteristics of heavy metal in same organs of different species crops were not the same.The Cd concentration in different parts of green pepper ranked from highest to lowest is: stem and leaf>root>edible part,cowpea ranked from highest to lowest is: root> stem and leaf>edible part,spinach ranked from highest to lowest is: stem and leaf>root,rice ranked from highest to lowest is: root >stem and leaf>edible part.The Pb concentration in different parts of green pepper,cucumber,cowpea and rice ranked from highest to lowest is: root> stem and leaf>edible part,spinach ranked from highest to lowest is: stem and leaf>root.The Ni concentration in different parts of green pepper,cucumber,cowpea and rice ranked from highest to lowest is: root> stem and leaf>edible.The Mn concentration in different parts of green pepper,and cucumber ranked from highest to lowest is: stem and leaf>root>edible,cowpea ranked from highest to lowest is: root>stem and leaf>edible part,spinach ranked from highest to lowest is: stem and leaf>root.The Cr concentration in different parts of cowpea ranked from highest to lowest is stem and leaf>root,the Cr concentration in different parts of spinach varied not regularity,ranking as stem and leaf>root at low levels,root>stem and leaf at high levels,rice ranked from highest to lowest is root>stem and leaf>edible part.The Hg concentration in different parts of green pepper,cucumber,cowpea,spinach and rice ranked from highest to lowest is: root>stem and leaf.(4)The translocation factors of each part of the crops in the soil with heavy metals pollution is shown as root-stem and leaf translocation factors>root-edible translocation factors.Different crops have different enrichment coefficients,Cd enrichment coefficient in different crops is spinach>rice>green pepper>cucumber>cowpea,Pb enrichment coefficient in different crops is spinach>rice>green pepper?cucumber>cowpea,Ni enrichment coefficient in different crops is cowpea>rice>cucumber>green pepper,Mn enrichment coefficient in different crops is spinach>cowpea>cucumber>green pepper,Cr enrichment coefficient in different crops is green pepper>cucumber>rice>spinach,Hg enrichment coefficient in different is rice>spinach>green pepper>cowpea.(5)The Cd,Pb,Ni,Mn and Cr concentration in the ediable parts of crops had a significiant correlation with total Cd,Pb,Ni,Mn and Cr content in the corresponding concentration soil,the contents of Hg in ediable parts of crops had no significant correlation with the contents of total Hg in soil.(6)According to pot experiment,the safety threshold of soil heavy metal in different crops was different.In Cd pollution treatment soil,green pepper 1.04 mg/kg,cucumber 4.2 mg/kg,cowpea 7.46 mg/kg,spinach 0.2 mg/kg,rice 0.59 mg/kg.In Pb pollution treatment soil,green pepper 3600 mg/kg,cucumber 402 mg/kg,cowpea 3778 mg/kg,spinach 3178 mg/kg,rice 571 mg/kg.In Ni pollution treatment soil,green pepper 477 mg/kg,cucumber 573 mg/kg,cowpea 215 mg/kg,spinach 608 mg/kg,rice 331 mg/kg.In Mn Pollution treatment soil,green pepper 3618 mg/kg,cucumber 3147 mg/kg,cowpea 2607 mg/kg,spinach 992 mg/kg.In Cr pollution treatment soil,green pepper 900 mg/kg,cowpea 2440 mg/kg,spinach 1250 mg/kg,rice 3283 mg/kg.In Hg pollution treatment soil,green pepper 3.0 mg/kg,spinach 2.0 mg/kg,rice 1.0 mg/kg.