| In this study,the research object is the typical farmland in the suburbs of Changsha,and collect soil samples and rice samples at the same point in the wild.The contents of Cu,Cr,Ni,As,Hg,Cd,and Pb as well as soil physical and chemical properties are analyzed to study the accumulation of heavy metals in the soil.The sources of heavy metal pollution and influence of pollution sources in soil are quantitative analyzed.Analyze the accumulation of heavy metals in different parts of rice,and use exposure measurement to assess the health risks of chemical non-carcinogenic factors and chemical carcinogenic factors of heavy metals in rice.It is of theoretical significance to study the pollution of soil heavy metals and the health risk assessment of rice by different pollutants.The main conclusions are as follows:(1)The content of heavy metals Cu and Cd exceeded the national secondary standard for soil environmental quality,and As,Hg,and Cr did not exceed the standards in the arable soil of typical farmland in the suburbs of Changsha.The heavy metal pollution in soil was mainly concentrated in the surface layer,and the content of Cu,Zn,Cd elements decreased significantly,Cr increased,and Pb did not change significantly.The correlation analysis showed that there was a highly significant positive correlation between soil organic matter,available potassium,alkaline dissolved nitrogen,Cd,Pb,and Zn,and there was a high possibility of homologous between soil nutrients and heavy metal elements.The bioavailability coefficient of elements was the highest in Cd and the lowest in Cr.In the degree of variation of the validity coefficient,Cr was the highest,Pb was the lowest,the spatial distribution of elemental concentration was not uniform,and Cd had the greatest harm to the soil.The accumulation rate of soil Pb was the largest,followed by As and Cd,and the accumulation rate of Cr and Hg were low.(2)In atmospheric deposition samples,the concentration of Pb was the highest(10.45 μg·L-1),and the concentration of Hg was the lowest(0.01 μg·L-1).The concentration of heavy metals in sedimentation changed greatly during the month,and the element concentrations all showed their maximum values in January and February,and the minimum values appeared in March and May.The sedimentation flux was significantly higher in the late spring,early summer and winter than in other seasons.Elemental concentration and precipitation became the main factors affecting the sedimentation flux.The seasonal variation of soil heavy metals in atmospheric deposition indicated that the deposition of atmospheric deposition to the surface layer would increase the content of soil heavy metals and the maximum value of Pb in the soil would increase seasonally.(3)Among the five sources of heavy metals,atmospheric deposition had the largest annual input flux of Cr,As,Cd,and Pb in the suburbs of Changsha,and the input of soil Hg was only smaller than irrigation water and straw return.Atmospheric deposition was one of the major sources of heavy metal pollution in soil.The input of organic fertilizers to soil Cr,As,Cd,and Pb was also high,and the impact on soil ranked second.The effects of irrigation water and straw on the accumulation of heavy metals in soil had their own priorities.Straw returning mainly affected Hg,Cr and As,and irrigation water mainly affected Hg,Ni and Pb in soil.Long-term irrigation could reduce the Cr content in soil.The influence degree of Cd sources in soil was ranked as atmospheric deposition,organic fertilizer,irrigation water,straw,soil parent material.(4)In addition to Cd in the study area,the remaining heavy metals in rice had different levels of excessive.phenomenon,among which,the average Cr and As content of the middle rice were the highest,exceeding the national standard 1.56 times and 8.47 times.It was worth noting that there was no excessive Cd in rice.The rice health risk assessment results showed that the rice samples collected in the study area were generally safe. |
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