DiForMet Project

Proyecto DiForMet – JCCM

General objective

The DiForMet Project, awarded to IGeA-UCLM, aims to analyse in detail the process of transformation of metallic mercury (Hg) in soils, as a basis for assessing in the most appropriate way the reduction of the risk posed by its presence in soils, by applying techniques aimed at immobilising the element. 

Partial objectives

1. To deepen the experimental study of metallic mercury transformations in soils, through a comprehensive experimental design that will allow the identification of the factors influencing the formation of possible/probable precursors of methylmercury and/or other labile species of the element.

2. Contribuir al conocimiento de las aportaciones microbiológicas a los procesos de transformación del mercurio: Análisis del impacto que dicho metal ejerce sobre las comunidades microbianas edáficas (previo a la adición de mercurio versus tras la adición de mercurio) en los siguientes aspectos:

   • The taxonomic composition and gene diversity of microbial communities. 
   • Gene expression. 
   • The functional behaviour of the microbial community in response to alterations in soil physicochemical composition. 
   • The effect on the response of the microbial community to different antimicrobials widely used in human clinical practice.
     
     

3. To evaluate the response of microbial communities to the presence of mercury, as well as their contribution to the generation or immobilisation of reactive species. This analysis will make it possible to establish a solid basis for designing mitigation strategies that reduce the mobility and toxicity of mercury in soils. 

4. Assessment of the possibility of applying the developed techniques to a real area affected by significant mercury contamination (Cerco Metalúrgico de Almadenejos, CMA).

Participating entities

• Minas de Almadén y Arrayanes S.A.: contributes its experience in studies on mercury in the study area.
• Research Support Service SAI-Microbiology of the San Pablo CEU University: contributes its experience in microbiological studies applied to the characterization of soil health.
• Researchers from the Department of Geosciences of the University of Florence (Italy): contribute their experience in the proposed methodological study.
  
  

The DiFoMet Project strengthens the leadership of IGeA-UCLM in research on the biogeochemical cycle of mercury and its environmental management, complementing research lines already consolidated in projects such as LIFE HERMES and reinforcing interdisciplinary and international collaboration around the restoration of contaminated soils. 

Featured publication related to the DiForMet project

Thermal desorption technique for mercury speciation in carbonate, siliciclastic and organic-rich soils

 

Source: https://doi.org/10.1016/j.chemosphere.2024.143349

Thermal desorption is a well-established technique for mercury (Hg) speciation in soils and sediments. However, the effects associated with different matrices have not yet been adequately assessed. In this study, thermal desorption was applied to Hg-free calcite mixed with a Hg standard, as well as to soils rich in carbonate and silicate minerals and organic matter. Hg⁰, HgCl₂, HgO, α-HgS, β-HgS and organomercury compounds were identified, highlighting that the soil matrix introduces notable differences in the decomposition temperatures of Hg compounds and suggesting that the mineralogical composition of the soil should be investigated before applying the thermal desorption technique.

The presence of Hg⁰ was also evaluated in detail, since, as previously observed, it can transform into Hg²⁺, which increases mercury mobility in the soil cover, with important consequences in contaminated soils located near active or decommissioned mines and/or industrial facilities (for example, chlor-alkali industries). For this purpose, experimental tests were carried out using carbonate-, silicate- and organic-rich soils doped with liquid Hg. It was observed that Hg⁰ tends to oxidize forming Hg⁺ and subsequently Hg²⁺ depending on the soil matrix and the reaction time. Notably, the oxidation rate proved to be relatively fast, since after 42 days the initial Hg⁰ content is reduced by half, following an exponential decay kinetics.

This implies that, in Hg⁰-contaminated areas, the fate of the generated Hg²⁺ may be: i) adsorption by organic matter and/or Fe–Mn–Al oxides, and/or ii) incorporation into shallow aquifers. This study represents a step forward in understanding the behaviour of Hg in contaminated soils of industrial and mining origin where liquid Hg is present in different soil matrices, and may provide useful indications for the design of remediation operations.