Effect of Continuous Application of Municipal Standardized Sewage Sludge on the Risk of Heavy Metal Pollution in Apples and Orchard Soil
To investigate the impact of continuous application of municipal sludge on the risk of heavy metal contamination in apples and orchard soil,a field experiment was conducted with four treatments:conventional fertilization(T1),moderate sludge application(T2),high sludge application(T3)and low sludge application(T4).The study analyzed the risk of heavy metal contamination in apples and soil under different sludge application rates and durations.The results indicated that the concentrations of Cd,Cr,Pb,Hg,and As in apples did not exceed the regulatory limits.After three years of sludge application,the single-factor pollution indexes for heavy metals in the soil were below the warning thresholds by 71.98％to 75.98％,66.57％to 69.90％,92.32％to 94.01％,78.59％to 90.40％,and 17.22％to 23.29％,respectively.The Nemerow comprehensive pollution index and potential ecological risk index were also below the warming thresholds by 9.51％to 16.08％and 82.50％to 86.75％,respectively.Following three years of sludge application,the single-factor pollution index for Hg and As increased by 29.52 times and 83.14％compared to background levels.The potential ecological risk index for treatments T2 to T4 increased by 78.38％,95.69％and 48.18％respectively,compared to background values.The potential ecological risk contribution rate of Hg increased from 11.00％—17.02％to 19.32％—33.70％,while As increased from 21.55％—24.61％to 31.54％—39.17％.Based on the calculations for Cd and Hg,the safe application duration for sludge was relatively shorter,ranging from 32.30 to 116.31 years and from 36.07 to 129.91 years,respectively.In summary,after the continuous application of sewage sludge for three years,both apple fruit and soil remained in an uncontaminated state.However,with the increasing of sludge application duration,the single-factor pollution index for Hg and As,comprehensive pollution index and potential ecological risks all increased,with Hg and As being the primary contributing factors.Based on the safe application duration of sludge,Cd and Hg emerged as the most significant limiting elements.The rational utilization of sludge does not lead to heavy metal contamination in the soil.
AppleOrchard soilMunicipal standardized sewage sludgeRisk of heavy metal pollution
万方数据
维普
