| Soil,the cornerstone of human survival and development,is an important material basis for food security production.However,human activities such as mining,smelting,transportation,agricultural production activities have led to soil heavy metal pollution.The national soil pollution survey bulletin in 2014 showed that the total exceeding rate of heavy metals in soil was 16.1%,and the exceeding rate of heavy metals in cultivated land was 19.4%.The overall situation of soil environment was not optimistic.Based on the analysis of the contents,spatial distribution and ecological risk of heavy metals Cr,Ni,Cu,Zn,Cd and Pb in soil and wheat grains at the plot scale,this paper took a wheat field with sewage irrigation in Xinxiang County,Henan Province as the research object,and we investigated the content characteristics,loading factors and correlation of heavy metals in soil aggregates with different particle sizes,and then the effect of different immobilizating materials on remediation of heavy metal contaminated soil was explored.The main research contents and results are as follows:（1）Soil p H in the study area ranged from 7.38-9.07 with a coefficient of variation of 3%,which was a weak variation.Organic matter content ranged from 11.04 to 42.99 g·kg-1,cation exchange capacity from 5.80 to 14.81 cmol·kg-1,electrical conductivity from 124.77 to 394.70μS·cm-1,and coefficient of variation were 17%,15%and 24%,respectively,indicating low variation.From the spatial distribution of soil physical and chemical properties,the p H value in the central region of the study area was the highest,the p H value in the west was slightly lower,and the p H value in the north,east and south was the lowest.The soil organic matter content was the highest in the northeastern region,and the content was low in the central and southern regions.The content of cation exchange capacity in the north was the highest,and the content gradually decreased from north to south.The soil electrical conductivity in the study area was generally higher in the eastern region and lower in the western region.The content of heavy metals in soil aggregates with different particle sizes was different,but only the content of Cd in soil aggregates with different particle sizes was significant,and the overall performance was 0.5-0.25 mm>1-0.5 mm>5-2 mm>2-1 mm>（<0.25 mm）>8-5 mm.The mass loading factors of heavy metals in different particle sizes were 5-2 mm>8-5 mm>2-1 mm>（<0.25 mm）>1-0.5 mm>0.5-0.25 mm.According to the content of available metals in soil aggregates,the content of Cr and Zn was the highest in<0.25 mm aggregates,and the content of Ni,Cu,Cd and Pb was the highest in 0.5-0.25 mm aggregates.The total content of heavy metals in each particle size of aggregates was significantly positively correlated with the available state（P<0.05）.（2）The contents of Cr,Ni,Cu,Zn,Cd and Pb in soil were 319.60,21.76,6.40,35.52,0.95 and24.35 mg kg-1,respectively,the contents of Cr,Cd and Pb in all sites exceeded the background value of soil heavy metal content in Henan Province.The contents of Ni and Zn in some sites exceeded the background value of soil heavy metal content in Henan Province,and the exceeding rates were 12.38%and 2.97%,respectively.The content of Cu did not exceed the background value of soil heavy metal content in Henan Province.According to GB 15618-2018 Soil pollution risk control standard of agricultural land for soil environmental quality,Cd content in soil exceeded the standard screening value,Cr content partially exceeded the standard screening value,and the exceeding rate was 98%,but the contents of Ni,Cu,Zn and Pb did not exceed the standard screening value.From the distribution characteristics of soil heavy metal profile,the content of soil heavy metal decreased with the increase of vertical depth.Cr,Ni,Cu and Pb in the study area mainly existed in the form of residual state.The exchangeable fraction of Cr was less than 0.01%,and the exchangeable fraction of Ni,Cu,Zn,Cd,and Pb was 0.23%,1.32%,0.71%,14.19%,and 0.02%,respectively.From the perspective of spatial distribution,Cr content was the highest in the southern riverside region of the study area,and gradually decreased from south to north.In the west and northeast directions,Cr content was slightly lower than that in the south,and the content in the central region was lower.The highest content in the south was 2 to 3 times that in the central region;The content of Ni is the highest in the south,and lower in the central region than in the south,and lower in the east and west directions;The Cu content is mainly higher in the northeast and southwest direction,but lower in other regions;The higher Zn content was mainly distributed in small sided shape,and it was distributed in the middle,north,south and southwest of the study area;The content of Cd was higher in the south,east and central and northern regions,but lower in other regions;The content of Pb is higher in the central east and central north of the study area,lower in the southeast and lower in other areas;The source of heavy metal pollution in this area may be due to sewage irrigation,atmospheric deposition and organic fertilizer application.From the point of view of several ecological risk assessment methods,Cd pollution in farmland soil in the region was serious.（3）Some samples of Cr,Ni,Cd and Pb exceeded the food safety standards（GB 2762-2017）.From the perspective of bioaccumulation coefficient,Cr showed extremely weak uptake,while Ni,Cu,Zn,Cd and Pb showed medium uptake.The average bioaccumulation coefficient of heavy metals in wheat grain samples was in the order of Zn>Cu>Cd>Ni>Pb>Cr.From the spatial distribution of heavy metals in wheat grain,Cr content is higher in the central region,and lower in the southern region;Ni content is higher in the central and southern regions and lower in the northeastern and western regions;Cu content is higher in the central and western regions.Low content in the eastern region;Zn content is higher in the southern region and lower in other regions;The content of Cd was the highest in the southern region,followed by the northern region,and the content was low in other regions.The Pb content in the western and eastern small areas is low,high in other areas.From the correlation analysis of heavy metal content in wheat grain and soil physical and chemical properties,there was no significant correlation between Cr and Ni in wheat grain and soil physical and chemical properties.Cu was significantly correlated with soil p H,organic matter and electrical conductivity,and the correlation coefficients were 0.31,-0.17 and-0.17,respectively.Zn was significantly negatively correlated with conductivity,and the correlation coefficient was-0.14;Cd and Pb were significantly positively correlated with cation exchange capacity（r=0.15）.According to the target hazard quotient,Cu and Zn in some samples of wheat grains have certain health risks for children,and Cr,Cd and Pb in some samples also have certain health risks for adults and children.Compared with Cu and Zn,the health risks are more serious,and the proportion of THQ>1 is more.In this study,the THQ and TTHQ risk values of several heavy metals are all children>adults.（4）The pot experiment was conducted to study the effects of sepiolite（HP）,sawdust charcoal（MX）and their combination（HM）on the physical and chemical properties of heavy metal contaminated soil,the effective state of heavy metals and the content of heavy metals in wheat.The results showed that the soil physical and chemical properties were significantly improved after the application of sepiolite and sawdust charcoal,and the p H,soil organic matter and electrical conductivity of other treatments were significantly improved compared with CK,Under MX treatment,soil organic matter increased by 19.26%,while the electrical conductivity increased by32.7%under HMⅠtreatment.The available content of Cr,Ni,Cu,Zn,Cd and Pb in soil decreased to a certain extent.The content of Cr,Ni,Cu,Zn and Pb decreased most in MX treatment,and the content of Cd decreased most significantly in HPⅠtreatment.Compared with CK,wheat seedling biomass under HPⅠ,HPⅡ,MX,HMⅠand HMⅡtreatments were significantly increased by 32.19%,54.08%,56.05%,52.12%and 46.57%,respectively,and MX was the most significant increase.Overall,the application of sepiolite and sawdust charcoal significantly inhibited the content of heavy metals in wheat root parts,among them,the contents of Cr,Ni and Pb in HMⅡtreatment decreased by 39.78%,52.83%and 46.62%,respectively,compared with CK,however,Cd content in HMⅠtreatment decreased the most significantly,reaching 41.3%.The contents of Cr,Ni,Cd and Pb in the shoot of wheat were significantly decreased in all passivation treatments,the Cr content was decreased by 74.17%in HMⅠtreatment,the contents of Ni and Cd were decreased by 66.57%and 20.69%in MX treatment,respectively,while the contents of Pb were decreased by 43.16%in HMⅡtreatment.The results show that different passivating materials have strong remediation potential for heavy metal contaminated soil. |
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