| In recent years,the arable land area polluted by heavy metals has kept growing in our country,and caused many food safety incidents.The health risk resulting from heavy metal pollution of paddy field as a primary farming land,does be remarkable.These have affected not only the yield and quality of rice,but also all of the ecosystem in farmland,and even the health of animals and humans through the food chain.The problem of paddy field heavy metal pollution is developing gradually at present.Thus,the task how to research and control the pollution has been becoming so urgent.Herein,eight common heavy metals(As,Cd,Cr,Cu,Hg,Ni,Pb,Zn)relating to humans closely in Jiang'an County were selected in the study.The contents of these heavy metals in rice and soil at different positions were detected.According to related background values and national standards,the index of heavy metals,including soil environmental quality,rice safe quality and pollution degree,were evaluated.Meanwhile,the content relationship of heavy metal between soil and rice was also studied,as well as the effect of pH and organic compounds on the absorption capacity of heavy metals.Finally,some suggestions on metal prevention were proposed.The main results are as follows:1.Based on standard ? of the national environment standard quality for soils,the pollution of Cd is most serious in this region,in which the proportion is up to 77.1%.According to the results of Nemerow integrated evaluation,one-third samples have potential ecological risk.Compared with background value,the degree of potential ecological risk from the heavy metals is low,with a risk index of 134.59,indicating a safe state.The single coefficients are in the order of Hg>Cd>As>Pb>Cu>Ni>Cr>Zn.Distribution laws of potential ecological risk from heavy metals are North>Middle>South,Traffic trunk>Farming area>industry concentrating area>Nature reserve,and Flat>Floodplain>Hill.2.Zn is highest in the metal contents of rice from the region,while Hg is lowest.According to national standards of food safety,except Cd and Cr in a few samples,the remaining samples meet the standards.The results of Nemerow integrated evaluation show that 8.6%of rice is polluted by heavy metals.Compared to the background value,the heavy metal pollution on rice is serious,while the pollution index of Ni is 23.09,the pollution of Cd is negligible,and the pollution indexes of other six elements are between the two indexes.Moreover,the pollution is most serious in central regions of industrial zone and the southern regions of nature reserve.3.The correlation of total heavy metals between soil and rice is weak,with the correlation coefficient of As being the highest,as 0.202.The enrichment coefficient of rice is in the range of 0.002?0.231,and the order is Zn,Hg,Ni,Cd,Cu,As,Cr,Pb,from high to low.According to the results of multiple linear regression,the enrichment coefficient is correlated to pH positively,and correlated to organic matter negatively.What's more,the absorption capacity of heavy metals in rice is affected by pH in the following order Ni,As,Zn,Cd,Hg,Cu,Cr,Pb,from high to low. |
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