Spatial distribution and risk assessment of heavy metals in the farmland along mineral product transportation routes in Zhejiang,China

Various metal pollutants transported from certain sources may considerably contaminate the soil environment. It was reported that transportation related metal pollution was closely associated with the distance, the freight volume and traffic emissions. However, the effect of topography on the heavy metal distribution in the soils along transportation routes has received little attention. In the present investigation, arable soils along two selected transportation routes for mineral products were studied to characterize the topographic impacts on their level of metal pollution. Soil samples were collected within a 5‐m radius following ‘S’ sampling procedure using spatial autocorrelation analysis. The descriptive statistics showed that most of the heavy metal (Pb, Zn, Cu and Cd) concentrations exceeded the background value of Zhejiang Province and contents of most metals in Area B, within a plain, were generally higher than in Area A, a valley within a hilly region. LISA maps showed that all heavy metals did not have similar spatial autocorrelation in Area B. The spatial distribution maps in Area A showed that distribution of most of the contaminants Zn, Cu, Cd and Pb had a similar spatial structure and were located along a transportation route. In Area A within valley topography, metal concentrations in soils were found generally to decrease with increasing distance from the road. However, this was not valid for Area B on the plain, where the metals concentrated in the soils could be derived from multiple sources, particularly emissions from nearby local industry.