Multi-devices field magnetic susceptibility: ‘3D’ spatialization of metallic contamination in soils and reverse correlation in carbonated context (Jebel Ressas, Tunisia)

Abstract

Soil contamination linked to abandoned lead–zinc mining wastes represents a serious environmental hazard of worldwide concern, raising the need for cost-effective tools to spatialize the contaminated area and assess the risks. In worldwide industrial environments, positive correlation between magnetic susceptibility and heavy metal soil contamination is often reported and used for fast preliminary site assessments. In this study, we report monitoring of an olive grove, situated below one of the abandoned tailings dump of the former Jebel Ressas Pb–Zn mining site (Tunisia), with three different commercial susceptibilimeters (Terraplus KT10, Bartington MS2D and Geonics EM38 induction device). Integration depths of above-mentioned susceptibilimeters vary from 3 to 150 cm. Similar broad-scale magnetic susceptibility maps for the three devices emphasize the effect of topography and runoff transfer as the main mechanisms for tailings material dispersion. Very low susceptibilities (~ 10 × 10–5 SI) characterize the contaminants magnetic signal, while uncontaminated soils susceptibilities are one order of magnitude higher (100–150 × 10–5 SI). This unique case of reverse correlation between magnetic susceptibilities and contamination (Pb, Zn, Cd) trace efficiently the degree of contamination and is substantiated by further mineralogical and magnetic properties analyses showing the predominance of iron amorphous oxyhydroxides in the dump, while (titano)maghemite is the main natural magnetic carriers in the uncontaminated soils in this specific carbonated context. The Geonics EM 38, with a proper calibration procedure, reveals a performant tool increasing the depth of investigation and when combined with shallower susceptibilimeter, opens perspectives for qualitative 3D spatialization of metallic contamination.