Geo-statistical and multivariate analyses of potentially toxic elements' distribution in the soil of Hainan Island (China): A comparison between the topsoil and subsoil at a regional scale

Geo-statistical and multivariate analyses are effective methods to determine the source and influence factors of potentially toxic elements (PTEs) in the soil. Hainan Island, belonging to tropical marine monsoon climate, is a typically individual island with slight industrial activities. In order to study the impact factors on PTEs distribution in the soil at a regional scale, such as impact of lithology, pedogenesis and anthropogenic activities, Hainan Island is an optimal place. For comparison, the topsoil and the corresponding subsoil were sampled and eight PTEs were analyzed respectively. The concentrations of PTEs were counted, such as minimum, maximum, median and mean values. Based on it, the background values and concentration enrichment factors of PTEs were also calculated or illustrated. Exception to Cd and Hg, the concentration of other PTEs in the topsoil were lower than those in the subsoil for all lithological areas since the strong leaching under special climate. By using geostatistical and multivariate analyses, such as Pearson correlation analysis, principal component analysis, variography and robust biplot analyses, the dominant impact factors are determined for PTEs both in the topsoil and subsoil. Thus, the spatial distribution of PTEs is well explained at a regional scale. Generally, PTEs in the soil represent the components of soil parent materials associated with lithological rocks. Nevertheless, Co, Cr, Cu and Sc elements were dominantly inherited from soil parent materials while Cd, Hg and Pb were greatly superposed by exogenous inputs. On the other hand, elements of As and Zn might be greatly influenced by pedogenesis and weathering process. So, geo-statistical and multivariate analyses are effective methods to discuss the sources or impact factors for PTEs in the soil, and also the comparison between the topsoil and the subsoil provides an opportunity to illuminate the main impact factors on PTEs at a regional scale, including parent materials, weathering process and anthropogenic inputs.