| At present,the research of soil heavy metal pollution in China mainly focuses on the pollution problem caused by human activities,and there are still some deficiencies in the more hidden and difficult to find pollution problem caused by excessive soil background value.Therefore,through the comparative study of heavy metal cadmium(Cd)pollution characteristics and influencing factors in soil and rice under different main pollution causes,it can provide the basis for the regional development of differentiated prevention and control standards according to different pollution causes and enrichment rules,and ensure the soil environmental quality and rice production safety.In the paper,based on the geochemical survey data and field survey data of soil and rice samples collected in the north of A District,Zhuhai City,Pearl River Delta and B town,Yixing City,Yangtze River Delta,the single factor index method,improved geological accumulation index method,bioaccumulation coefficient and geostatistical analysis were used to analyze the distribution of Cd in farmland soil and rice.The results showed that the pollution exceeded the standard and the spatial distribution characteristics were analyzed and studied;at the same time,combined with the potential ecological risk and human health risk assessment model,the risk and exposure caused by Cd in the two study areas were compared and analyzed,and the corresponding risk areas were divided.The conclusions are as follows:(1)In the two study areas,there is not a simple linear relationship between soil Cd exceeding standard and rice Cd exceeding standard.The exceeding standard rate of soil Cd in the north of A is much higher than that in B,but the exceeding standard rate of rice Cd in B is higher than that in the north of A,which is related to the differences of pollution sources and causes of soil Cd in the two study areas;at the same time,the soil Cd in the two study areas has reached the maximum level.The results showed that there was a high level of variation,which was affected by different degrees of human activities.(2)The correlation coefficient between Cd content in rice seeds and p H was the most obvious in the two study areas,and it was closely related to other soil physical and chemical indexes(such as CEC and OM),but showed opposite correlation in different study areas;there was a certain difference in the spatial distribution of soil rice in the two study areas,but the parent materials of soil formation in the superimposed high value area were River and clastic sediments Lord.(3)The results show that the potential ecological risk of B is higher than that of the A north.In the later period of B,there were more pollution caused by human activities,and the total content of Cd in soil was higher.There is a certain degree of noncarcinogenic risk of Cd to different groups of human body in the two study areas,and the noncarcinogenic risk of children and adults in the way of manual intake exceeds the limit value of 1.According to the target hazard coefficient,the proportion of risk area in town B is close to 1/3,and the risk is more serious than that in the north of A.Under the influence of different main pollution caused by natural and human activities,multiple indicators of Cd in soil and rice have different performance.At the same time,the regional risk and human exposure risk of Cd are also quite different.Therefore,different schemes should be adopted for the pollution control and risk management of agricultural system with excessive Cd under different causes. |
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