Transfer And Accumulation Of Heavy Metal Copper And Chromium In Soil-Plant System In Sewage Irrigation Area

In this paper,the migration and accumulation of Cu and Cr in soil-plant system in sewage irrigation area was investigated to provide scientific basis for remediation of soil contaminated by heavy metals.A sewage irrigation area in Jinzhong city,Shanxi Province as the research object,and retention of irrigation soil as the tested soil,locally grown corn as the selected plant,from the fall of 2016 to the fall of 2019,for four consecutive years of different magnetism(0~20 cm,20~40 cm,40~60 cm),different district(sewage irrigation system research division area from near to far to five area,The first area-The fifth area)content of Cu,Cr in various chemical forms of heavy metals in the soil,the study area of Cu,Cr content in each part of the corn and Soil-plant system Cu,Cr migration accumulation pattern was analyzed.The experimental results show that:(1)From the autumn of 2016 to the autumn of 2019,the heavy metal Cu in the soil adjacent to the sewage irrigation canal exceeded the standard for soil environmental quality and soil pollution risk control on agricultural land(Trial)(GB 15618-2018).The screening value of soil risk on agricultural land: Cu(100mg/kg),and the heavy metal Cr in the soil did not exceed the standard(250 mg/kg),with the increase of the distance from the sewage irrigation canal,the content of total Cu and Cr in the soil decreased,and the content of total Cu and Cr decreased year by year,the polluted soil was repaired to a certain extent.In the vertical direction,Cu and Cr are mainly concentrated in the surface layer(0~20 cm),and the content decreases with the increase of soil depth.(2)The contents of five forms of Cu elements in soil in different soil layers and different plots were as follows: The first area > The second area > The third area > The fourth area > The fifth area,while there was no obvious rule in the content of Cr.In the 0~20 cm soil layer,except for the iron-manganese oxide binding state,the content of Cu in other forms decreased with time.The contents of exchangeable Cr,carbonate binding Cr and residue Cr all decreased to different degrees,and the residue Cr content has been stable since 2017.Both Cu element and Cr element mainly exist in soil in organic binding state and residue state.In the 20~40 cm soil layer,the carbonate binding state of Cu element shows a downward trend with time,the residual Cu content has no obvious change,and the exchangeable state,iron-manganese oxide binding state and organic binding state of Cu element show an upward trend.The contents of the exchangeable state,carbonate binding state and residue state of Cr elements showed a decreasing trend with time,while the contents of the iron-manganese oxide binding state and organic binding state did not change significantly from 2017 to now.In the 40~60 cm soil layer,the exchangeable state of Cu element,the carbonate binding state and the iron-manganese oxide binding state all showed an upward trend,while the organic binding state and residue state showed no obvious change trend,and the contents of five forms of Cr element all decreased to different degrees.(3)According to the risk assessment of secondary phase and primary phase distribution ratio method(RSP),the pollution degree of Cu and Cr in the soil decreased as the distance between the soil layers from The first area to The fifth area increased.Cu element pollution in soil is serious,Cr element pollution is light.(4)The distribution of heavy metals Cu and Cr in each part of maize was as follows: root > stem >leaf > kernel.Cu content in different years of maize kernels were not more than the limited food standards(GB 2762-2012)(Cu≤10 mg/kg)or less,but the Cr content in the seeds were greater than 1 mg/kg and less than 20 mg/kg,more than the national food hygiene standard(GB 2762-2017),does not exceed the national feed hygiene standards(GB 13078-2017),as a result,sewage irrigation area can be used as feed of corn kernels.The enrichment ability of Cu and Cr in each part of maize was different,the root was the strongest,the stem and leaf was the second,and the seed was the weakest.The transfer coefficients of Cu and Cr in maize from large to small were: From root to stem and leaf > From stem and leaf to kernel > From root to kernel.(5)From 2016 to 2019,the content of Cu in maize roots,stems,leaves and kernels was significantly correlated with the content of Cu in soil and the content of Cu in available state(p<0.05,the same below).Cr element content in corn roots and soil Cr content,effective state of Cr content relevance is strong,the correlation coefficient is 0.7467,0.7360 respectively,Cr element content in the stem leaf and soil Cr content is strong correlation(r=0.6858),but weak correlation with soil effective state of Cr content(r=0.4680),the Cr element content in the seed and the soil Cr content and effective state soil Cr content relevance is weaker,the correlation coefficient is 0.2653,0.4410,respectively.