| Biogas slurry returning to the field can improve soil physical and chemical properties,improve soil fertility and increase crop yield.However,in order to prevent disease and promote growth of livestock and poultry,Cu,Zn,Cr and other heavy metals are widely used as additives in livestock and poultry feed.However,trace heavy metals in feed cannot be completely metabolized,degraded and absorbed in animals,and about90% of heavy metals are discharged into feces,which leads to a large number of residual heavy metals in livestock and poultry feces and biogas slurry.Blind use of biogas slurry for crop irrigation may lead to the accumulation and pollution of heavy metals in farmland.Due to the characteristics of lotus root itself,after years of exploration,some areas directly use biogas slurry produced by pig farms to irrigate lotus root fields,realizing the utilization of biogas slurry resources,not only reduce the pollution of biogas slurry to the environment,but also improve the economic benefits brought by planting lotus root,which has the dual significance of ecological protection and economic improvement.However,due to the high content of heavy metals in biogas slurry,direct discharge into lotus root fields may cause the lotus root to inhale excessively rich heavy metals and enter the human body through the food chain,affecting human health.To study the influence of biogas slurry irrigation on soil and heavy metal pollution of lotus root,and to provide scientific basis for determining reasonable biogas slurry irrigation system and soil pollution prevention.In this study,11 lotus root and rhizosphere soil samples were collected from a pigraised biogas digester field in Jingdezhen,Jiangxi Province in early October 2021.The contents of Cr,Ni,Cu,Zn,As,Cd and Pb in the samples were analyzed and determined by ICP-MS.The soil heavy metals were extracted by BCR continuous extraction method.The soil-lotus root system was evaluated by enrichment factor,Nemerow index,potential ecological risk index and soil and agricultural product quality index.The carcinogenic and non-carcinogenic risks were evaluated by human health risk assessment,and the sources of heavy metals were analyzed by principal component analysis and APCS-MLR receptor model.The main conclusions are as follows:(1)The mean contents of Cd,Ni,Cu,Cr,Zn,As and Pb in soil were 0.16,25.12,24.09,53.65,71.89,11.15 and 24.74mg/kg,respectively.Were 1.60,1.32,1.16,1.12,1.07,1.04 and 0.77 times of the soil background value of Jiangxi Province,respectively.Except for Pb,the average contents of other elements were higher than the soil background value of Jiangxi Province.The heavy metals Cr,Ni,Cu,Zn and As are mainly in residue state,Cd is mainly in oxidizable state and acid soluble state,and Pb is mainly oxidizable state and reducible state.The average contents of Cr,Ni,Cu,Zn,As,Cd and Pb in lotus root were 2.55,0.93,2.76,9.02,0.036,0.0093 and 0.037mg/kg,respectively.The average content of Zn was the highest with a range of5.91～16.66mg/kg,followed by Cu.The contents of As,Cd and Pb ranged from 1.87 to4.18mg/kg,Cr ranged from 1.277 to 5.34mg/kg,Ni ranged from 0.58 to 1.89mg/kg,and the contents of As,Cd and Pb were relatively low.The range was 0.21～0.055,0.00029～0.0013 and 0.015～0.18mg/kg.(2)The average value of As in the soil of the study area reached the moderate enrichment level,and the average value of other 6 heavy metals were at the slight enrichment level.The potential and ecological risk index showed that Cd was the main ecological risk factor with moderate risk,and the other heavy metals were low risk.The whole study area presented moderate risk level.The evaluation results of risk evaluation by coding method showed that the ecological risk of bioavailability of soil heavy metal forms in this region was Cd>Zn>Cu>Ni>Pb>As>Cr,Cd presented medium risk,Ni,Cu,Zn and Pb were all at low risk,and Cr and As presented no risk.The ability of lotus root to absorb heavy metals from soil was in the order of Cu>Zn>Cr>Ni>Cd>As>Pb.The heavy metal composite quality index of soil-lotus root system showed that the soil-lotus root system was in a slightly polluted state on the whole.(3)In the human health risk assessment of soil heavy metals,the non-carcinogenic risk index(HQ)of seven heavy metals in the study area was all less than 1,indicating that the study area may not produce non-carcinogenic health risks to human beings;The carcinogenic risk of the three heavy metals in adults and children in the study area was Cr > As > Cd from large to small,and the carcinogenic risk index of the three heavy metals were all within the acceptable range.In the human health risk assessment of heavy metal in lotus root,the THQ value of Cr for children and adults is greater than 1,and the total target hazard coefficient(TTHQ)value for adults and children is greater than 1,which exceeds the limit standard,and there is a certain potential noncarcinogenic health risk for children,and the non-carcinogenic risk for children is greater than that for adults.(4)The results of principal component analysis showed that Ni,Cu,Zn,Cd and Pb were mainly derived from the application of organic fertilizer biogas slurry,As and Cd were mainly affected by natural sources,and Cr was mainly affected by atmospheric deposition.The results of APCS-MLR receptor model showed that most heavy metals(Ni,Cu,Zn,Cd and Pb)in soil came from agricultural biogas slurry irrigation,and their contribution rates were 43.04%,57.30%,63.03%,62.89%,54.88%,respectively.As and Cr mainly came from natural sources and atmospheric deposition.Their contribution rates were 53.83% and 43.46%. |
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