A Research On The Spatial Variation Of Heavy Metal In The Farmland In The Liangqing Area Section Of Highway G325 In Nanning City

The pollution of farmland soil mainly caused by various poisonous and harmful substances which generated by transportation vehicles in the manner of atmospheric disposition.Heavy metal pollution is a kind of irreversible environmental pollution.And once there is heavy metal pollution in highway soil and crops system, the ecological environment will be impacted and then do harm to human health through the food chain. Therefore it is of great importance to enhance the monitoring on the heavy metal pollution in farmland soil along the highways in order to protect the ecological system of soil, crops safety and human health.The Liangqing Area section of Highway G325 in Nanning City is the ending section of the whole Highway G325. It goes through the four main towns in Liangqing Area which include Liangqing town, Nama town, Datang town and Nanxiao town from the north to the south. This section of Highway G325 is 73 kilometers long and 9 meters wide with two driveways. It is also a vital highway connecting Nanning City to the provinces and cities around.Based on above conditions, this paper, taking the Liangqing Area section of Highway G325 in Nanning City as the object of study, and Liangqing town, Nama town, Datang town and Nanxiao town as four sampling sites, collects some soil and rice samples close to the trunk roads. By measuring the heavy metal elements in soil and crops, this paper studies and analyzes transportation pollution’s impact on the physical and chemical characteristics of the soil around the highways and the heavy metal elements inside. The findings is as below.For the Liangqing Area section of Highway G325, the heavy metal in the soil and the rice first increases and then decreases horizontally as the distance gets longer.The peak values are mainly in the range from 20 to 50 meters from the highway and are greatly impacted by the heavy metal in the range from 5 to 50 meters.As, Cd, Cr, Cu and Pb are the 5 kinds of heavy metal elements which have been detected in the farmland soil in Liangqing Area. According to the detection results in the four towns, As, Cd, and Pb are more than the reference value of the local soil. This means that the soil and the rice in the farmland within 200 meters from the highway have been impacted and all of the four sampling sites suffer from the accumulation of heavy metal.By comparing the heavy metal in different parts of the rice in the four sampling sites, this paper found out that Cu is the most followed by Cr and Pb. For the five kinds of heavy metal elements except for Cd, the root of the rice contains the most heavy metal followed by the leaves and the stem. But for Cd, the sequence is the root,the stem and the leaves. In general, Liangqing town and Nama town have more heavy metal elements than other two towns with the minimum value being around 2mg/kg.The analysis on the correlation between the heavy metal elements in the rice and that in the very soil shows that there is significant correlation between As in the rice as well as Cr in the soil, Cu in the rice as well as Cu and Cd in the soil, Pb in the rice as well as Cr in the soil, Ph in the soil as well as As, Cr, Cd and Pb in the rice.The analysis on the correlation among the heavy metal elements in the soil indicates that the element groups in which the elements are highly correlated with each other include Cd and Pb, Cu and Pb,Cr and Cu. And Cu and Pb are elements which are extremely correlated with each other. Therefore there comes a primary conclusion that all the elements from the above element groups probably come from the same source of pollution(they are highly homologous). As and Cr are not closed with other elements which shows that they come from special sources and the sources are probably external ones.According to the analysis on the correlation between the heavy metal elements in the soil and the physical and chemical characteristics of the soil, there is significant correlation between Cu and Pb as well as the soil’s PH value. And there is no significant correlation between the soil’s PH value and the other three elements. As and Cr are greatly correlated with the soil’s organic matter, but Cd and Cu and Pb aren’t.