The Distribution Characteristics And Assessment Of Heavy Metals In Rice From The Floodplain Of Le’an River

The quality of the crops grown on the basis of the heavy metal-polluted cultivated land will be directly affected by the pollution.It will cause larger harm to human health through consumption of the food crops.This article is intended to clarify the distribution characteristics of heavy metals under the influence of polluted river water from the typical section of rice soil Le’an River floodplain,evaluate the level of heavy metal pollution in cultivated soil and rice,illustrate the amount of heavy metal in rice and the regulation of accumulated spatio-temporal variation and the antioxidation reaction of rice against the heavy metal’s combined stress.According to actual field condition,21 Soil samples and rice samples were selected and collected separately in different spatio-temporal situation(3 main rice growing periods and 11 typical monitoring unit of the Le’an River floodplain).The main conclusions based on the experimental analysis and the use of evaluation index is as follows:The heavy metal elements Cu,Zn,Pb,Cd,Cr and As are extracted using electric heating plate method.The content of the elements in the samples are detected by ICP-MS.According to the measured data,the average contents of six heavy metals all exceed the Jiangxi Soil Standard.But if based on the national secondary standard,the average content of As、Cu、Cd exceed the standard and the average content of Cr、Zn、Pb is under standard.It shows that the pollution of As,Cu,Cd is more serious.According to analysis of the spatial distribution characteristics that showed by spatial interpolation method in Arcgis software,the content of heavy metals are higher in Mingkou、Lankeng and Shanglian villages.From view of partitons,the 6 kinds of heavy metal concentration in B and D areas is higher than A and C areas.But the content of heavy metals is close to the value of Jiangxi soil standard where reservoir water is used to irrigating,thus it shows that there is a significant impact of heavy metal pollution on soil by sewage irrigation.Through the cluster analysis method of source of 6 elements is relatively single,mainly from the polluted river water for irrigation,all samples are classified into four categories,echoing the spatial distribution characteristics of heavy metals.On the basis of the analysis of total heavy metals,This paper evaluates the degree of farmland soil heavy metal pollution with single factor index method 、pollution load index method and potential ecological risk index method.It finds that the whole area is heavy polluted.The main pollution elements are Cd,Cu and As.The RI’s value of each partition was calculated by the comprehensive potential ecological risk index.The results show that D is in very strong risk,A and B areas are in intensity of risk,only C area is in mild risk.Based on the determination of 6 kinds of heavy metals in different growth stages and different parts of rice,focusing on major pollution elements Cd、Cu、As in the main growing period of ricein different position,the results show that the content of the above three elements in leaves and stems of rice the trend of "first decreased and then increased".The maximum appeared at tillering stage.From the high,medium and low three levels of concentration,the heavy metal content increased with the increase of concentration,high value > median >CK.Combined with the heavy metal content in the soil of the former analysis,it is shows that the heavy metal content in rice growing site is positively correlated with the amount of heavy metals in soil.The average size of heavy metal enrichment factors in paddy was Zn>Cd>Cu>Cr>Pb>As,which showed that Zn and Cd is more likely to be enriched in rice than the other elements.Through using the method of single factor pollution index and heavy metal total HI index to assess the health risk of rice.It shows that the standard is exceeded at more than half of the study areas and the sequence of the degree of pollution is As>Pb>Cr>Cu>Cd>Zn.According to the assessment of the risk of rice’s health,it shows that there is a bigger health risk to human who have eating polluted rice,much more,chronic toxicity effects on people who have polluted rice from Mingkou,Lankeng,Shang lian Village.The results showed that the chlorophyll content was increased by low stimulation,and also showed that the photosynthetic performance of rice leaves was increased.But beyond a certain threshold,the content of chlorophyll decreased.In the growth period,the change trend of the chlorophyll content of rice leaves showed "first increased and then decreased",and the average size of rice was ranked as heading period > mature stage > tillering stage.The chlorophyll content in rice leaves are negatively correlated with the content of the six heavy metals in the soil.Through the determination of various points at mature stage of rice root and leaf SOD,POD,CAT,GSH and MDA five enzyme content.The content of SOD,POD,CAT and GSH in these antioxidant content increased with the increase of heavy metal content of sample,showing a trend of “first increased and then decreased”.The changes of the content of different enzyme critical values are different.The change trend of oxidative metabolites(MDA)was the opposite,showing the trend of "first decreased and then increased".The IBR index method was used to evaluate the pressure of heavy metal pollution on the biomarkers.The result shows that the sort of the four areas from high to low is: D>B>A>C.The area C is clean,the area A is be polluted,and D and B areas are most polluted in these regions.The results of the resonse of the biomarkers indicated that the heavy metal pollution in the study area has a significant risk of physiological stress on rice.