| It has been proved that the effects of heavy metals on regional ecological environment and health of population are more pronounced in red soil areas in south China,the content characteristics and risk assessment of heavy metals in Yunnan red soil area were still lack systematic study.In this study,130 sites were set up in the red soil area of the high heavy metal background in Yunnan Province,sampling 0-20 cm soil samples and corresponding crop samples respectively.Crop edible part Pb,Cd content,total and available heavy metal concentration in soils and soil moisture content,pH,organic matter and CEC were determined.The results were used to analyze the pollution status and ecological risk of the farmland,analyzing and comparing the difference of the heavy metal contamination of crops and their ability of beneficiation.Correlation analysis was conducted to determine how the heavy metals in soils and crops were related to SOM,moisture content,CEC and pH,Single gene index method and Geoaccumulation index was used to evalutate heavy metals pollution in soil and crops,and health risks were analyzed.The key research findings are as follows:1.The distribution of heavy metal content in various regions:Cd pollution exists widely in relative comparison,and Pb pollution is more serious.The Pb,Cd concentrations in the soil of Huize and Gejiu were relatively high,which was well beyond the second level criterion of Standard of Soil Environment.2.The effective states of Pb and Cd in the study area was positively correlated with the total amount of Pb and Cd,notable negatively correlation between CEC and available Pb and Cd were achieved.The available Pb and Cd have negative correlation with pH,but the correlation is not obvious,and the correlation with organic matter is not significant.The bioactivity coefficient of Pb,Cd in southern Yunnan is high.3.The order of Pb content in crops from big to small is:potato>pepper>lettuce>ginger>corn>wheat>broad beans,the average content of Pb in potato,pepper and lettuce is 0.89,0.59 and 0.50mg·kg-1respectively,which was 4.43-fold,2.97-fold and1.67-fold grater than the national hierarchical standard of heavy metal to appraise crops and vegetables,respectively.The TF trend in Pb in total crops and vegetables was in the descending order of lettuce>potato>ginger>pepper>weat>maize>broad beans.The order of Cd content in crops from big to small is:lettuce>pepper>potato>ginger>corn>broad bean>wheat,the average content of Cd in lettuce,pepper and potato was 0.92mg·kg-1,0.62mg·kg-1and 0.25 mg·kg-1,which was4.6-fold,6.2-fold and2.5-fold grater than the national hierarchical standard of heavy metal to appraise crops and vegetables.The TF trend in Cd in total crops and vegetables was in the descending order of lettuce>ginger>pepper>potato>maize>weat>broad beans.The Pb and Cd concentration coefficients of lettuce were significantly different from those of other crops.The Pb concentration of crops was significantly positively correlated with organic matter.4.The single gene index method,the Geoaccumulation index method and health risk assessment was used to evaluate heavy metal pollution in this study.Among the soil samples,corresponding to 31.50%and 82.31%were above the Pb,Cd national standards,respectively,when evaluated with single factor index method.The results show that Pb pollution is the most common in northeast Yunnan province,8.57%and2.86%of the samples of Pb and Cd are extremely polluted,followed by the southern Yunnan province,7.27%of the samples Pb and Cd are extremely polluted.The results of health risk assessment showed that children were at higher risk than adults.The pollution level of Cd is greater than Pb.Compared with the health risk assessment based on the total content of heavy metals,the soil health risk assessment was lower than that of the available heavy metal concentrations.The results of soil heavy metal health risk assessment showed that that intake of Pb,Cd through consumption of soil does pose a significant potential health hazard in JS,XC,KS,ZH.The THQ value of heavy metal through soil was less than 1 in southeast Yunnan and southwest Yunnan,indicating that intake of heavy metal through consumption of soil does not pose a significant potential health hazard in these areas.In addition,Pb has a much higher exposure risk than Cd.The HI were used to assess the human health risks associated with heavy metal contamination of selected crops in the study area.The HI value of Pb through potato was than 1,indicating that intake of Pb through consumption of potato does pose a significant potential health hazard.The HI value of Cd through all crops was than 1,indicating that intake of Cd through consumption of potato does pose a significant potential health hazard.5.In this study,the safety threshold of Pb and Cd in three crops was obtained and compared with the second level criterion of Standard of Soil Environment?GB15618-1995?.The results showed that the Pb threshold value of the three crops was well below the limit,and the Cd threshold was much higher than the limit. |
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