Arsenic in Soils Affected by Mining: Microscopic Studies vs. Sequential Chemical Extraction.

Jessica Álvarez-Quintana,Rodrigo Álvarez,Almudena Ordóñez

doi:10.3390/ijerph17228426

Abstract

Soil samples from three inactive mines, corresponding to different Arsenic-bearing mineralization types, were collected and studied. The aim was to determine the influence of mine wastes mineralogy/geochemistry and texture in As mobility and to compare results from sequential chemical extraction and microscopic techniques (optical and electron) at a grain scale. Arsenic in soils is found mainly associated to the residual fraction, indicating that mechanical As dispersion is mainly responsible for As soil pollution. The use of objective microscopic techniques (i.e., Scanning Electron Microscopy-Energy Dispersive Spectroscopy -SEM-EDS-, High Resolution Transmission Electron Microscopy -HR-TEM) has pointed out that the selected sequential extraction method overestimates the role of Mn amorphous oxy-hydroxides and organic matter in As retention while underestimating the mechanism of As adsorption onto clay particle surfaces.

Highlights

There is a large amount of scientific literature available that addresses the environmental aspects of mining waste
Concerning soil pollution, during the last decade of the 20th century, some generalist and multidisciplinary studies were published; these early investigations focused on the determination and spatial distribution of total concentrations of the elements of concern in each case
An excellent critical summary of sequential extraction procedures can be consulted in the work of Zimmerman and Weindorf [5]

Summary

Introduction

There is a large amount of scientific literature available that addresses the environmental aspects of mining waste. A significant advance in the approach, from a practical point of view, of polluted soil investigations, is constituted by the risk assessment methodologies proposed by the US Environmental Protection Agency at the end of the century These protocols constitute a turning point from which more attention has been paid to the chemical forms in which the contaminants are present in the soil, highlighting that only the bioavailable fraction should be considered when calculating risk indexes. The so-called “sequential extraction procedures” have been commonly considered by the scientific community as a useful tool to assess both the chemical speciation/mobility and the bioavailability of metals/metalloids from their association with certain solid phases. An excellent critical summary of sequential extraction procedures can be consulted in the work of Zimmerman and Weindorf [5]

Methods

Results

Conclusion