Geochemical anomalies of heavy metals

The Geochemical Anomalies Map on a scale of 1:250,000 represents the surface enrichment (with regard to the contents determined by the XRF method) of Chromium, Copper, Nickel, Lead, Vanadium and Zinc in the approximately 780 soil sampling points of the Emilia-Romagna alluvial plain carried out for the Natural Background Map.

The assessment of the point contamination status in a soil is also ascertained by means of formulas comparing the metal concentrations detected in the surface area of the soil and the natural background value. The two formulas most commonly used in the literature, which are interchangeable, calculate:

• Geo-accumulation index (I geo) (Müller, 1979; Förstner & Müller. 1981), defined by:

Igeo = log2 Cn / (1,5*Bn) e

• Enrichment Factor (EF) (Rubio et al., 2000), defined by:

EF = (Bn – Cn) / Cn

where:

Cn = metal concentration at the site/sampling point at a depth of 20-30 cm

Bn = natural background content at the site/sampling point at 90-140 cm depth

In our case, the geo-accumulation index ‘Igeo’ was used in conjunction with a classification scheme, (Müller, 1981; Banat et al., 2005; Sainz & Ruiz, 2006), which distinguishes six classes of contamination based on different Index values.

These are therefore point maps from which a ‘general state of soil health’ can be deduced and which, together with the heavy metal background maps, identify the areas subject to the greatest pressure.