Spatial Distribution and Potential Ecological Risk Assessment of Heavy Metals in Roadside Soils on Different Operated Times along the Lianyungang-Horgas Highway

Wanliu and Xiaowangzhuang transects which operated in 1994 and 2001 respectively along Zhengzhou-Shangqiu section on Lianyungang-Horgas highway were chosen to investigate heavy metal (Cd, Cu, Pb, Zn, Ni, and Cr) pollution and potential ecological risks of roadside soils. Concentrations of soil heavy metals on Wanliu transect were higher than that on Xiaowangzhuang transect. The content of soil heavy metals increases with the distance away from highway, reaching a maximum value, and then decreases gradually. Potential ecological risks of the soil metals are at moderate level on Wanliu transect, while slight level on the other transect. Concentrations of most soil heavy metals and their potential ecological risks present skewness distribution with the distance form highway roadbed. The highest risk indexes (RI) for different metals on Wanliu transect are among 50 similar to 100 m from highway roadbed, farther than that on Xiaowangzhuang transect at 35 m. Most of the soil samples on northern side of the highway show higher metal concentrations and potential ecological risks than that on southern side. The total risk index was contributed by the heavy metal of Cd (averagely 61.39%), which is the main factor of potential ecological risks. The grade standards for different ecological risk levels must be modified according to types and amount of pollutants studied and their toxic-response factors.