Assessment of Indexes for Heavy Metal Contamination in Remote Areas: A Case Study in a Pyrenean Forest, Navarra, Spain.

The objective of the present work was to verify and compare the performance of different geochemical indices employed to identify the anthropogenic origin of selected heavy metals and other trace elements in soils. To that end, two background values, the upper continental crust and the metal content in the bed rock, were used and obtained from a forested basin of the western Pyrenees. The enrichment factor (EF), geo-accumulation index (I), and contamination factor (C) were finally evaluated for their ability to determine anthropogenic contamination: Results indicate that an in-depth knowledge of the bed rock geochemistry and the geological background content is essential to distinguish between the natural variability of soils and any anthropogenic contribution of heavy metals. Although both EF and C show a similar ability to detect soil contamination, the latter is proposed as a more appropriate and sensitive marker given its ability for finding episodically elevated contamination levels.