Study On The Effects Of Typical Heavy Metal Polluted Farmland Over Crops In Gejiu

In recent years,with the rapid development of China’s industry and the rapid expansion of cities,the area of land pollution has increased sharply.Among them,the problem of heavy metal pollution in soil is particularly prominent,which has become a major problem endangering the quality of soil environment and food security in China.Based on the previous literature review and field investigation,this study selected the cultivated land around Datun Town,Gejiu City,Yunnan Province,as the research object,and studied the impact of typical heavy metal contaminated cultivated land on crops.Based on the single factor index,Nemero index,potential ecological hazard index and human health wind assessment,the status of heavy metal pollution in soil-crop system and the health of local residents were evaluated.The mechanism of heavy metal migration and transformation in soil-crop system was explored by correlation analysis and multiple linear regression.The main conclusions are as follows:1.According to the single pollution index of heavy metals in soil,the pollution of Pb,Cd and As is more serious in the study area,and the situation of Zn is relatively optimistic.The comprehensive index P of heavy metals in 54 sites of soil survey is higher than 3,which belongs to heavy pollution.Because Cd and As contributed more to soil pollution in the study area,the accumulation of heavy metals in soil was very high,which showed strong ecological hazards.2.Compared with national food safety standards,the exceeding rates of Pb,Cd and As in rice were 35.0%,55.0% and 100.0%,respectively;those in maize were 12.5%,0.0% and 0.0% respectively;those in bitter cabbage were 100%,60.0% and 100% respectively;and those in Millet cabbage were 100%.Zn did not exceed the standard.Vegetables generally have higher uptake capacity of heavy metals,especially Cd,than cereals.3.The relationship between total and available heavy metals in soil and pH,cation exchange capacity was analyzed.The results showed that except As,theavailable states of three heavy metals,Pb,Cd and Zn,increased with the increase of total amount,and showed a very significant positive correlation(P <0.01);the available states of all heavy metals in soil decreased with the increase of pH;the cation exchange capacity of soil was negatively correlated with the proportion of available Zn and As,and positively correlated with the proportion of available Pb and Cd.4.Analysis of factors affecting heavy metals uptake by rice indicated that exchangeable As and Fe-Mn As,exchangeable Pb and organic Pb,Fe-Mn Cd and exchangeable Zn were easy to be absorbed and utilized by rice.If these forms could be controlled,the sources of heavy metals uptake by rice would be greatly reduced.In addition to the negative correlation between Zn and CEC in rice,Pb,Cd and As were related to CEC in soil.There was a positive correlation.It indicated that the adsorption state of heavy metals in soil also showed bioavailability for rice.Only Fe-Mn oxide bound Cd was positively correlated with pH in the bioavailable form of heavy metals in paddy soils.5.The daily intake of Cd by local residents exceeded the provisional daily intake standard PTDI,reaching 157.1% of PTDI.The elements of Pb,Zn and As did not exceed the standard.USEPA risk model was used to assess the health risks of local adults and children eating local rice and vegetables.It shows that the carcinogenic and non-carcinogenic risk factors HI of rice and vegetables intake by residents are far beyond the upper limits of USEPA and ICRP,and the non-carcinogenic risk of children is higher than that of adults,which should be paid attention to.At the same time,Cd has the highest carcinogenic risk,which indicates that Cd is the primary pollutant leading to human carcinogenic risk in the study area.