UMBRELLA: Using MicroBes for the REgulation of heavy metaL mobiLity at ecosystem and landscape scAle

Abstract

This special issue focuses on metal-contaminated areas resulting from mining activities. These sites are characterized by low nutrient availability, poor soil quality, and low pH, in addition to high metal loads. The contamination at former mining sites most often is associated with acid mine drainage leading to the dispersal of metals. The resulting areas are compromised with respect to both use of land for, e.g., agronomy and forestry, and groundwater, the main source of drinking water, restricting future use. In addition, the contamination can spread, if not attended to, contaminating additional, previously non-contaminated ecosystems. Government regulations for effective management of contaminated sites exist worldover, and reclamation of acid mine drainage-influenced areas attracts growing interest. Remediation actions are necessary, which, in addition to geo-engineering strategies, increasingly include monitored natural attenuation and bioremediation. This needs to be based on a detailed understanding of processes in bio-geo interactions at metal-contaminated sites, which is addressed here to provide an integrated approach summarized in a scheme for useful application of each of these remediation actions shown in this special issue at a generalized former mining site. The proposed applications help to minimize the risk to human health and environmental impact and are cost-efficient. Soil is the basis of terrestrial life and has a major impact on human life through its use for agriculture, forestry, or general land use. In addition, it remains the largest terrestrial ecosystem that is shaped by high numbers of microorganisms and plant roots. The metabolic activities of both microorganisms and plants sustain pedogenesis which, however, differs with respect not only to base rock material and climatic conditions, but also to, e.g., pollution. Root exudates as well as microbiological acidification and release of chelating agents take part in heavy metal mobilization and immobilization processes, which are of high impact at metal-rich sites. The ecotoxicologically relevant heavy metal concentrations are dependent on interaction with soil particles and microbial surfaces; hence, inoculation strategies may improve future land use. Mobilization and distribution pathways for metals from source, where geo-engineering techniques may be deployed, to sink need to be re-evaluated. Nature has evolved ecosystems able to cope with high metal loads, and by learning from the evolutionary and biological processes, it may be feasible to adopt additional strategies for bioremediation. During natural attenuation, new minerals can be formed. This might lead to supergenic ore formation and hence provides means to even use these metals without disturbing new, natural sites. In this special issue, we will discuss all mentioned mobilization and immobilization mechanisms to contribute to a general understanding of bioremediation potentials. Thus, we may draw on the potential of natural attenuation instead of premature application of high-cost geo-engineering, depending on sitespecific parameters. This concept will allow for the reduction of the costs of an estimated 38 billion Euro per year incurred by society at large for soil destruction and environmental degradation. The formation of acid mine drainage (AMD) or also of acid rock drainage (ARD) is a process related to unearthing metal ores, many of which are sulfidic ores. Similar processes leading to AMD apply to coal mining, since coal also contains sulfur in pyrite and marcasite as well as organically bound sulfur. The anoxic environment in the mine does provide Responsible editor: Philippe Garrigues