Evaluation of tourism impact on soil metal accumulation through single and integrated indices

Recently, surface soils of remote or protected areas, that receive pollutants from the surroundings or in situ activities through dry and wet deposition, exceed the baseline content of heavy metals. In the last decades, the use of single and integrated indices is a powerful tool to process, analyze and convey information about metal accumulation degree for decision makers to better manage protected areas. Single indices provide information about only one metal, whereas the integrated ones give a holistic evaluation. The aim of the research was to assess the temporal trends of three single (Contamination Factor, Enrichment Factor and Geo-accumulation Index) and two integrated (Pollution Load Index, Nemerow index) indices in order to evaluate if the touristic impact caused soil metal (Cr, Cu, Ni and Pb) accumulation. In autumn 2016 and in spring 2016 and 2017, the surface soils (0–10 cm) were collected at eight sites inside the Vesuvius National Park (Southern Italy), characterized by intense tourism from spring to autumn. The metal concentrations were measured in the soils and used to calculate the indices. In addition, the Ecological Risk Factor was calculated and the phytotoxicological assays were performed. The findings showed that the surface soils of the Vesuvius National Park were polluted by Cr, Cu, Ni and Pb, according to both single and integrated indices. The touristic impact would seem to be the main cause of soil metal accumulation, as the highest values of the calculated indices were detected for samples collected at the end of the touristic season and the lowest at the beginning of the touristic season. Anyway, Cu and Pb would seem also to derive by ex situ anthropogenic sources, whereas Cr and Ni also by natural sources, such as spontaneous fires and substrate weathering. Finally, the soils showed phytotoxic effects and low ecological risks.