| In recent years,heavy metal contamination in farmland soil has become increasingly serious in China because of human activities such as sewage irrigation,metal smelting,and road traffic.A field survey was conducted to investigate characteristics of Cd,As,and Pb in soil and wheat grains.Health risks of Cd,As and Pb in wheat grain to local people were also evaluated.The farmland was influenced by smelter and sewage irrigation in the attitude and by road traffic in the horizon.In addition,field experiments were carried out in plots far from road and with relatively uniform Cd,As and Pb concentrations in soil.Effects of foliar modulators on the accumulation of Cd,As and Pb in wheat were studied by spraying Zn(0.2%ZnSO4),Mg(0.4%MgSO4)and Mn(0.2%MnSO4)separately and mixed,thus the foliar modulators were selected to reduce the accumulation of Cd,As and Pb in wheat grainsgrown in calcareous soils in north China.The results showed that,(1)Pollution status and distribution characteristics of Cd,As and Pb in farmland soils and wheat grains at field scaleFarmland soil in this areahas moderately pollution by Cd,As,and Pb.Cd,As,and Pb concentrations in soil samples all exceeded the risk screening values of farmland soil(GB 15618-2018),the exceeding rates were 100%,100%,and 36.7%respectively,while the exceeding rates of Cd and Pb concentrations in wheat grains were 76,7%and 13.3%respectively(GB 2762-2017).Cd,As,and Pb concentrations in soil collected at different distances from smelter and sewage river had no significant differences,while the median Cd and As concentrations in wheat grain of the closest group being 14.9%and 41.8%,respectively,higher than that of the highest group(P<0.05).In contrast,Pb concentrations in soil and wheat grains were mainly influenced by road traffic,with median Pb concentrations in soil and wheat grains of the closest group were 78.9%and 471%,respectively,higher than that of the highest group(P<0.05).Both Cd and As generated significant carcinogenic effects to local people through consumption of wheat(Ri>1×10-4).The cancer risk decreased in the order of Cd>As,and health risks for children caused by heavy metals were bigger than adults.However,Pb poses no health risks in this farmland.(2)Effects of foliar modulators on accumulation of Cd,As and Pb in wheatExcept Mg foliar treatment,which yield of wheat was 16.5%higher than that of CK(P<0.05),the wheat yield of other foliar modulators treatments showed no significant difference with that of CK.The concentrations of Cd,As,and Pb in different organs of wheat at the mature stage decreased in the oder of root,straw and grains.Except Mn foliar treatment,which significantly decreased the As concentration in wheat grains by 22.8%(P<0.05),metal concentrations in wheat grains of Zn,Mg and Mn foliar treatments showed no significant difference with that of CK.In addition,mixed foliar modulators were better for reducing Cd,As,and Pb concentrations in wheat grains than that of single foliar modulators,and all foliar modulators were better for reducing Pb concentrations in wheat grains than Cd and As.The Mg+Mn and Zn+Mg+Mn foliar treatments decreased the Cd,As,and Pb concentrations in wheat grains through inhibiting the transfer of Cd,As,and Pb from straw to grains.Mg+Mn foliar treatment decreased the Cd,As,and Pb concentrations in wheat grains by 18.0%,25.6%,and 41.1%(P<0.05),respectively,while the Zn+Mg+Mn foliar treatment decreased the Cd,As,and Pb concentrations in wheat grains by 19.0%,23.9%,51.3%(P<0.05).These results indicated that the accumulation of Cd,As and Pb in wheat grains can be effectively controlled by foliar application with Mg+Mn or Zn+Mg+Mn once at jointing stage,booting stage and early filling stage of wheat,respectively. |
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