| The rapid development of industrial operation(IOS)is one of the main reasons for soil pollution of heavy metals in vegetable fields.Some studies have found that heavy metals exceed the standard in soils and vegetable edible parts of vegetable fields polluted by industrial operation.Secondly,the heavy use of organic fertilizer(OFS)will also bring hidden heavy metal dangers to the safe production of vegetables.The transfer of heavy metals in the soil-vegetable system is affected by factors such as the type and fractionation of heavy metals in soils.Due to its own fraction and environment,heavy metals from different pollution sources may have different pollution levels.Therefore,this research selected vegetable fields polluted by IOS and OFS as objects,through field experiments to study the content,fractionation,bioavailability of heavy metals in soils contaminated by IOS and OFS and the accumulation of heavy metals by vegetables,evaluated its transferability in the soil-vegetable system.This study provided a scientific theoretical basis for the risk assessment of heavy metal pollution in vegetable production.The results are as follows:(1)This study selected vegetable fields polluted by lead-zinc mine,steel plant,smelter,and copper mine in the Yangtze River Delta(YRD),collected 12 kinds of leafy vegetables,such as Brassica Chinensis L,Cilantro,Lettuce,Spinach,Garlic bolt,Celery,Chinese kale,Lactuca Sativa Linn,Water spinach,Amaranthus tricolor L,Gynura cusimbua,Water spinach and Chives and corresponding rhizosphere soils.The result showed that the range of Cd,Pb,Cu,Zn contents(mg·kg-1)of vegetable fields contaminated by IOS were 0.327～5.681,16.15～908.32,34.35～121.37 and 100.19～1047.40,compared with the soil risk value(GB 15618-2018),the Cd content in all the vegetable fields reached 1.28～8.27 times of the soil risk value,the Pb content in fields contaminated by lead-zinc mines and copper mines reached 1.72～4.13 times,the Zn content in fields contaminated by lead-zinc mine and smelter reached 1.72～4.13 times.The contents of Cd,Pb,Cu,Zn(fresh weight,mg·kg-1)in the edible part of vegetables were 0.026～0.662,0.064～1.110.0.271～2.338,and 1.081～19.443,respectively.Except for the smelter,the Cd contents in the edible parts of vegetables in the other areas were 1.18～1.68 times of the food hygiene standard(GB2762-2017).Except for the steel factory,the Pb contents were 1.53～2.05 times of the same standard.(2)According to the results of the continuous extraction of seven steps,the residual fractionation(F7)of Cd,Pb,Cu,and Zn in soils contaminated by IOS was 11.59%～57.09%,14.58%～52.76%,2.32%～63.47%and 25.08%～77.87%,respectively.Secondly,the exchangeable(F2),carbonate bound(F3)and Fe-Mn oxides(F5)fractionation of Cd in soils contaminated by IOS were 6.24%～34.17%,2.56%～38.73%and 7.32%～33.92%.The humic acid bound(F4)and F5 of Pb,Cu,and Zn can reach 11.05%～39.18%and 19.87%～60.88%,9.66%～17.57%and 11.07%～39.88%,1.05%～14.89%and 15.38%～37.05%.The bioavailability of Cd and Pb in soil contaminated by IOS was very high,and the effective fractionation(F1+F2+F3)accounted for 10.72%～59.84%and 2.51%～27.73%.(3)At the same time,we selected large-scale vegetable bases that used chicken manure and pig manure in the YRD,collected 12 kinds of leafy vegetables,such as Brassica Chinensis L,Cilantro,Lettuce,Spinach,Garlic bolt,Celery,Chinese kale,Lactuca Saliva Linn,Sonchus oleraceus L,Crown daisy,Indian lettuce and Chives and corresponding rhizosphere soils.We found that the range of Cd,Pb,Cu,Zn contents(mg·kg-1)of vegetable fields contaminated by OFS were 0.328～1.341,12.94～64.45,31.71～100.02 and 107.67～322.42,compared with the soil risk value,the over-standard rates of Cd,Cu,and Zn in soils contaminated by OFS were 100%,18.52%,and 25.93%,respectively.Compared with the food hygiene standard,the over-standard rates of Cd,Pb,and Zn in the edible part of vegetables were 3.70%,29.63%,and 7.41%.(4)The F7 and F4 of Cd,Pb,Cu,and Zn in soils contaminated by OFS was 14.96%～48.36%,5.33%～46.77%,19.80%～52.27%,22.94%～63.78%and 19.09%～41.99%,14.68%～31.47%,21.44%～41.48%,9.98%～31.85%.Secondly,the F5 of the four heavy metals accounts for a relatively high proportion,reaching 8.40%～35.14%,20.41%～59.99%,13.19%～32.94%,and 10.93%～23.42%.The bioavailability of Cd and Zn in soil contaminated by OFS was very high,and the effective fractionation accounted for 3.95%～37.34%and 4.65%～28.51%.(5)The average contents of Cd,Pb,Cu,and Zn in IOS-contaminated soils were 2.01,8.25.1.31,and 1.70 times of the same contents in OFS-contaminated soils.The contents of Cd and Pb in the IOS-contaminated edible part of vegetables were 6.08 and 1.70 times of the same contents in the OFS-contaminated edible part of vegetables,while the contents of Cu and Zn in the OFS-contaminated vegetables were 1.59 and 1.26 times of the same contents in the IOS-contaminated vegetables.The average ratio of F2 and F3 of Cd and Pb in IOS-contaminated soils was 3.18,1.36,and 2.49,1.20 times of the same fractionation in OFS-contaminated soils.The F2 fractionation of Cu in OFS-contaminated soils was 2.76～5.25 times of the same fractionation in IOScontaminated soils.The F2 fractionation of Zn in IOS-contaminated soils was 1.27～1.94 times of the same fractionation in OFS-contaminated soils.The F4 fractionations of Cd,Cu,and Zn in OFS-contaminated soils were 2.38,2.15,and 2.78 times of the same fractionation in IOS-contaminated soils.The F6 fractionations of Cd,Pb,Cu,and Zn in OFS-contaminated soils were 1.72,2.71,1.37,and 2.09 times of the same fractionation in IOS-contaminated soils.Cd had a high and medium mobility risk,Pb had medium and low mobility risks,Cu both had the low mobility risks,and Zn had the low and medium mobility risks in IOS and OFS-contaminated soils,respectively.The IOS and OFS-contaminated soils all had a medium potential adverse effect.But,the mRAC value was significantly higher in IOS-contaminated soils than that in OFScontaminated soils.(6)The transfer factor(TF)was used to measure the ability of heavy metals in the soil-vegetable system to be absorbed by vegetables.The TFtotai and TFavail were calculated with reference to the total heavy metal content and effective state content of the soils,respectively.The mean values of Cd-TFtotai and TFavail in IOS-contaminated systems were 390.89%and 191.16%higher than those in OFS-contaminated systems.But the TFtotai and TFavail of Cu and Zn in OFS-contaminated systems were 132.25%,104.83%,and 59.88%,74.54%higher than those of IOS-contaminated systems,respectively.In the soil-vegetable system,the Cd of IOS had a stronger transferability,while the Cu and Zn of OFS had a stronger transferability.The Cd content in the edible part was extremely significantly correlated with the soil bioavailable content of Cd both in IOS and OFS-contaminated soil-vegetable system,but Cu and Zn contents in the edible part were significantly correlated with the soil bioavailable content of Cu and Zn in OFS-contaminated soil-vegetable system.In order to ensure the safety of leafy vegetables,it is recommended to plant Cilantro and Spinach in IOS-contaminated soil or Cilantro,Spinach,Celery,Crown daisy and Indian lettuce in LMS-contaminated soil. |
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