Distribution Characteristics And Pollution Risk Assessment Of Heavy Metals In Soil-Wheat System Of Yellow River Irrigation District In Lubei Plain

It is important to explore the distribution of heavy metals in soils and crops and to assess the pollution risks of soils and crops.It is of great benefit to improving the quality of agricultural products and promoting food security.It also has very important theoretical guiding significance for the development of agriculture and environmental protection.Therefore,this study selected wheat plantations in 12 typical Yellow River irrigation areas in the Lubei Plain as sampling points.The total amount of heavy metals Cu,Zn,Cd,Cr,Ni and Pb in the soil was determined.The contents of heavy metals Cu,Zn,Cd,Cr,Ni and Pb in roots,stems,leaves and grains of wheat were determined.The distribution characteristics and influencing factors of heavy metals in soil and wheat in the study area were studied,combined with the physical and chemical properties of the soil.The pollution risk,ecological risk and health risk of heavy metals in the study area were evaluated.The conclusions obtained are as follows:?1?Heavy metals Cu,Zn,Cd,Cr,Ni and Pb in different soil layers of the study area have accumulated to different extents.The average content of the agricultural land is not higher than the standard value of agricultural land in China,but higher than the soil background value of the Lubei Plain.In particular,the content of Cd is higher than the background value of up to 3 times,and the accumulation is most obvious.By comparing the heavy metal content of different soil layers,it was found that the content of heavy metals decreased with the deepening of the soil layer.?2?It was found by correlation analysis that except for the significant correlation between Cu and irrigation years?p<0.05?,the other heavy metals were not significantly correlated with irrigation years;Cd,Ni and Pb were significantly positively correlated with soil pH and silt content?p<0.05?.There was a significant negative correlation with the sand content?p<0.05?.It was found by correlation analysis that Cd,Ni and Pb have homology,and Zn has homology with Ni and Pb.Other heavy metal elements are less likely to have homology and may come from different sources of pollution.Principal component analysis and cluster analysis further concluded that the heavy metal factor 1 in the soil affected by the study area is derived from the use of chemical fertilizers,external factors such as road traffic,mainly Cd,Ni and Pb.Factor 2 is mainly derived from the parent material,including Zn,Cr and Cu.?3?By analyzing the proportion of metal chemical forms,the residue state is the highest.The content of oxidizable and reducible states is second.The lowest content is the HOAc dissolved state.The residual state of Zn,Cd and Ni is significantly affected by the total amount,and the correlation between the chemical forms of heavy metals is not significant.The effective state content of Cu,Zn,Cd,Cr,Ni and Pb in the study area exceeds their corresponding international standard values.Soil pH,CaCO₃,total organic carbon,caustic nitrogen and total nitrogen have a greater effect on the effective content of soil heavy metals in the two soil layers.The effect of irrigation years on it is small.?4?The absorption and enrichment of heavy metals in different parts of wheat are different.The enrichment factors of Cu,Cd and Ni are larger in wheat roots and leaves,indicating that the roots and leaves of wheat have stronger absorption and enrichment ability for these three elements.Except for Zn and Cr,the other four heavy metals showed a very significant correlation between the roots,stems and leaves of wheat plants.There was no significant correlation between the heavy metal content in all parts of wheat plants and the total soil content,indicating that the increase of total heavy metals in soil could not directly increase the bioavailability of heavy metals,and increased the absorption of heavy metals by wheat plants.?5?The accumulation index of heavy metals Cd and Ni in the two soil layers of the study area is the largest,and the over-standard rate is also the highest.The single factor pollution index evaluation found that the main pollutant in the soil of the study area was Cd.The accumulation index of Cu in wheat grains has been higher than the warning line and began to be contaminated by Cu.The Nemero comprehensive pollution index evaluation found that the soil in the study area is a mild pollution level.The pollution index of wheat kernels is higher than the warning line but at a clean level,there is a risk of mild pollution.The TCLP method found that there was no ecological risk of heavy metal pollution in the soil.The order of health risk?non-carcinogenic risk?caused by heavy metals in wheat is Cu>Zn>Pb.The health risk values?HI?of adults and children are greater than 1,explaining that heavy metals in wheat in the study area are likely to have an impact on human health.The health risk index for adults and children of Cd,Cr and Ni is higher than the maximum(1×10^-4)acceptable risk level recommended by USEPA,which may present a risk of cancer.