Font Size: a A A

Heavy Metal Enrichment Characteristics And Influencing Factors In Soil-rice System In High Geological Background Area Of Southwest Chin

Posted on:2023-05-05Degree:MasterType:Thesis
Country:ChinaCandidate:L WeiFull Text:PDF
GTID:2531306824497404Subject:Chemistry
Abstract/Summary:PDF Full Text Request
The southwest region has a large area of karst landforms,and heavy metals are generally enriched,which is the largest heavy metal geological high background area in China.Heavy metal pollution in southwest China originates from human causes and soil matrix causes,of which the soil matrix cause is closely related to the pollution risk of heavy metals.At present,there are relatively few systematic studies on the integration of soil and rice in the highbackground area of southwest geology,which leads to unclear ecological risks and control factors of heavy metal pollution in the soil in the region,which is not conducive to the rational use of land resources and the safe production of agricultural products.In order to identify the characteristics,presence morphology,bioavailability and control factors of heavy metal migration in the soil-rice system in the high background area of southwest geology,the soil and rice in the karst regions of Guizhou and Guangxi were selected as specific research objects for the coastal uprooting gradient,and the full characteristics of heavy metals in soil and rice organs,the forms of heavy metal deposition in soil,as well as the physical and chemical properties of p H and organic matter soils,were analyzed,and the heavy metal migration,enrichment characteristics and control factors of soil-rice system were explored by multivariate statistical analysis methods.Gain awareness of the following areas:1.The average values of heavy metals As,Cd,Cr,Cu,Ni,Pb,Sb and Zn in the study area were 23.23 mg/kg,0.87 mg/kg,88.50 mg/kg,50.45 mg/kg,38.63 mg/kg,28.76 mg/kg,6.45mg/kg,and 110.71 mg/kg,respectively,which were 2.1 times,9.0 times,1.6 times,2.5 times,1.7 times and 1.2 times the national soil background values,respectively.1.6 times.The phenomenon of heavy metals exceeding the standard in the soil is serious.The contents of six heavy metals except Pb and Sb exceeded the risk screening value of the Soil Environmental Quality Standard,and the exceeding rates were: Cd 50%,Cu 28.57%,As 21.43%,Ni 7.14%,Zn 7.14%,Cr 7.14%,of which there was a risk of heavy pollution of soil heavy metal Cd.2.The average values of As,Cd,Cr,Cu,Ni,Pb,Sb and Zn were 0.29 mg/kg,0.16 mg/kg,3.07 mg/kg,2.84 mg/kg,1.65 mg/kg,0.05 mg/kg,0.05 mg/kg,0.04 mg/kg and 24.64 mg/kg,respectively.According to the "GB 2762-2017 National Standard for Food Safety and Limits of Contaminants in Food",there were As,Cd and Cr exceeding the standards in the rice grains in the study area,and the excess rates were 7.14%,35.71% and 92.86%,respectively.Compared with the soil heavy metal excess rate,the excess rate of heavy metal As and Cd in rice grains is lower than the excess rate of soil heavy metal,indicating that the soil heavy metal content is high and the risk is large in Karst areas such as Guizhou and Guangxi,but the content in rice is low and the crop exceedance rate is relatively small.3.The enrichment capacity of rice on heavy metals is different,the enrichment effect on Zn and Cd is strong,and the enrichment effect on Cu,Ni,Cr,As,Sb and Pb is weak.The enrichment coefficients of heavy metals in various organs of rice are not the same,among which the root-stem transport coefficient of heavy metal Cd is the largest,the transport coefficient of heavy metals Zn and Cu in rice leaf-brown rice is the largest,and the transportation coefficient of the remaining heavy metals in rice stems and leaves is the largest.Only the heavy metal Cd in rice is at risk of heavy pollution,while other heavy metal pollution is less at risk.the rice soil is contaminated with heavy metals,but rice is not necessarily contaminated with heavy metals.4.Previous studies have shown that the content of heavy metals is affected by soil physical and chemical properties,but the p H and organic matter content of soil physical and chemical properties in the study area have little correlation with heavy metals in paddy soil.Heavy metals remain in the soil during weathering,and heavy metals Cd show significant correlation with Fe and Mn,indicating that Cd mainly exists in the oxide minerals of Fe and Mn.In this study,p H and organic matter had little effect on the enrichment of heavy metals in rice.5.On the whole,the heavy metals in the soil of the study area mainly exist in the form of iron manganese oxide bound state and residue state.Most of the heavy metals in the soil are fixed in the form of residue state and iron manganese oxide bound state,which reduces the bioavailability.However,Cd mainly exists in the form of water-soluble,exchangeable and carbonate bound state.The high content of bioavailable state is one of the reasons for the high over standard rate of Cd content in soil.6.The content of heavy metals is also different in different sampling areas.In terms of soil heavy metals,the average contents of Cd,Cr,Cu,Ni and Zn in the sampling area of Guizhou Province are higher than those in Guangxi.In terms of soil heavy metal forms,the average proportion of heavy metal forms in the sampling area of Guizhou Province is higher than that in Guangxi,but the content of heavy metals in rice organs is higher in the study area of Guangxi,the reason may be that different temperatures in the study area have a certain impact on the enrichment of heavy metals in rice.
Keywords/Search Tags:high geological background area, soil rice system, occurrence forms of heavy metals
PDF Full Text Request
Related items