Research Of Characteristic On Heavy Metal Concentrations And Distribution Of Roadside Soil And Grass Around Kathmandu, Nepal

Traffic activities in roadways are a major resource of the heavy metal contamination in roadside soils. In this research, a Multivariate Analysis of Variance (MANOVA) is conducted to investigate the distributions and concentrations of heavy metals (Cu, Zn, Cd, and Pb) in three types of roadside soils and farmland grass in the Kathmandu region, Nepal. Totally,342samples of rural mountainous farmland topsoil,120samples of suburban farmland topsoil,161samples of urban roadside topsoil, and60samples of farmland grass were collected under the experiment design. It is found that in the study areas, the concentrations of heavy metals in the rural farmland topsoil are generally lower than those in the suburban farmland topsoil and urban roadside topsoil, except for Cd. The factors have different effects on the heavy metals'accumulation process in the soil and grass. For example, tree has a significant protection effect on roadside soils and grasses from the heavy metal contaminations. Terrain displays different trends for different heavy metals'concentrations and distributions. However, in this study it was not found that the heavy-metal concentrations in the soil and grass are consistently decreasing with the increment of roadside distance. The analysis of heavy metal transfer factor indicates that the intake capabilities of heavy metals from soil to grass is in the order of Zn> Cu> Pb. When assessing the risk index of heavy metals pollution, on average there is no serious pollution owing to traffic emission in the study area. In order to prevent local pollution, people need to notice the locations with maximum values of metals' contents. The most significant finding in this study is that the trees growing linearly along the roadways can play a protective role in reducing the heavy metals' concentrations in the roadside farmland soils and grasses. What's more, as the soil's heavy-metal concentrations increase, the capability of heavy-metal transfer to the grass decreases, and this relationship can be characterized by an exponential regression model. The results would be useful for understanding how the heavy-metal accumulation in farmland roadside soil and grass owning to traffic activities, which is helpful in making policies for avoiding heavy-metal contaminants in agricultural areas.