Potentially Toxic Elements’ Contamination of Soils Affected by Mining Activities in the Portuguese Sector of the Iberian Pyrite Belt and Optional Remediation Actions: A Review

Abstract

Both sectors of the Iberian Pyrite Belt, Portuguese and Spanish, have been exploited since ancient times, but more intensively during and after the second half of the 19th century. Large volumes of polymetallic sulfide ore were extracted in open pits or in underground works, processed without environmental concerns, and the generated waste rocks and tailings were simply deposited in the area. Many of these mining sites were abandoned for years under the action of erosive agents, leading to the spread of trace elements and the contamination of soils, waters and sediments. Some of these mine sites have been submitted to rehabilitation actions, mostly using constructive techniques to dig and contain the contaminated tailings and other waste materials, but the remaining soil still needs to be treated with the best available techniques to recover its ecosystem functions. Besides the degraded physical structure and poor nutritional status of these soils, they have common characteristics, as a consequence of the pyrite oxidation and acid drainage produced, such as a high concentration of trace elements and low pH, which must be considered in the remediation plans. This manuscript aims to review the results from studies which have already covered these topics in the Iberian Pyrite Belt, especially in its Portuguese sector, considering: (i) soils’ physicochemical characteristics; (ii) potentially toxic trace elements’ concentration; and (iii) sustainable remediation technologies to cope with this type of soil contamination. Phytostabilization, after the amelioration of the soil’s properties with organic and inorganic amendments, was investigated at the lab and field scale by several authors, and their results were also considered.

The “Infernaccio” Gorges: Microbial Diversity of Black Deposits and Isolation of Manganese-Solubilizing Bacteria

“…These minerals are extracted through invasive processes, such as acid drainage or the creation of massive mines. Waste products are generated during these processes, leading to environmental pollution (air, soil, and water) and severe risks to humans [ 49 ].…”

Low Abundant Bacteria Reflect Soil Specificity—Analysis of Bacterial Communities from Archaeological Investigation of Pre-Industrial Saline Ash Deposits of Bad Dürrenberg (Germany)

“…The use of various agrochemicals in crop production as well as the release of industrial and domestic influences the soil conditions and thus microbial populations. In particular, mining and metallurgy are responsible for massive changes and damage to soils due to acidification and release of toxic metal ions [3][4][5][6].…”

“…Thus, these soils influenced by early human activity could be considered as interesting sampling places for the search of new bacterial strains or consortia with promising tolerance and metabolic traits. The special effect of early metal mining and metallurgy on soil conditions have become a topic for microbiological investigations since some years, as seen in [5,6,9,13,14]. In contrast, other ancient mining activities such as coal and salt mining have received less attention.…”

Three Soil Bacterial Communities from an Archaeological Excavation Site of an Ancient Coal Mine near Bennstedt (Germany) Characterized by 16S r-RNA Sequencing

“…Potash mines release large amounts of salt, causing high levels of salinity in the soil surrounding the mines-especially in valley areas-as well as in the rivers of the concerned regions. However, despite the negative impacts of human engineering activities on microorganisms, such as through mining [11][12][13][14], soil fertility, and ecological robustness [15][16][17], technical environments can also contribute to the microbial diversity of microbiological populations. There are many cases of researchers reporting the discovery of new bacteria, for example, in special technical environments.…”