Biogeochemical prospecting of metallic critical raw materials: soil to plant transfer in SW Ciudad Real Province, Spain.

The soil-plant transfer of trace elements is a complex system in which many factors are involved such as the availability and bioavailability of elements in the soil, climate, pedological parameters, and the essential or toxic character of the elements. The present study proposes the evaluation of the use of multielement contents in vascular plants for prospecting ore deposits of trace elements of strategic interest for Europe. To accomplish this general goal, a study of the soil-plant transfer of major and trace elements using Quercus ilex as a study plant has been developed in the context of two geological domains with very different characteristics in geological terms and in the presence of ore deposits: the Almadén syncline for Hg and the Guadalmez syncline for Sb. The results have made it possible to differentiate geological domains not only in terms of individual elements, but also as a combination of major and trace elements using Factor Analysis. The bioconcentration factors have demonstrated the uptake of macronutrients and micronutrients in very high concentrations but these were barely dependent, or even independent of the concentrations in the soil, in addition to high values of this factor for Sb. The Factor Analysis allowed for the differentiation of geogenic elements from other linked to stibnite ore deposits (Sb, S, and Cu). This element (Sb) can be uptake by Quercus ilex via the root and from there translocating it to the leaves, showing a direct relation between concentrations in soil and plants. This finding opens the possibility of using Quercus ilex leaves for biogeochemical prospecting of geological domains or lithological types of interest to prospect for Sb deposits.

Trace elements in farmland soils and crops, and probabilistic health risk assessment in areas influenced by mining activity in Ecuador.

Consumption of food grown in contaminated soils may be a significant human exposure pathway to pollutants, including toxic elements. This study aimed to investigate the pollution level of trace elements in farmland soil and crops collected in orchards from Ponce Enriquez, one of the Ecuador's most important gold mining areas. The concentration of arsenic (As), cadmium (Cd), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) was analyzed in soil and crop samples (celery, chives, corn, herbs, lettuce, turnips, green beans, cassava, and carrots). In addition, a probabilistic human health risk assessment, in terms of hazard quotients (HQ) and cancer risk (CR), was conducted to assess the potential risk related to local crop ingestion. The contents of As, Cr, Cu, and Ni in soils exceeded the Ecuadorian quality guidelines for agricultural soils. The trace elements concentration in local crops was higher than the maximum permissible levels set by the Food and Agriculture Organization of the United Nations (FAO). The HQ and CR of local crop ingestion were several orders higher than the safe exposure threshold, mainly for lettuce, chives, and turnips. Our results revealed that inhabitants of the study area are exposed to developing carcinogenic and non-carcinogenic effects due to long-term food consumption with high trace elements. This study sheds light on the need to assess further the quality of agricultural soils and crops grown in mining areas with signs of contamination to guarantee consumer food safety.

An approach for evaluating the bioavailability and risk assessment of potentially toxic elements using edible and inedible plants-the Remance (Panama) mining area as a model.

Mining affects the environment, particularly through the persistence of accumulation of tailings materials; this is aggravated under tropical climatic conditions, which favours the release of potentially toxic elements (PTEs) bioavailable to the local flora and fauna and supposing a risk to human health. The Remance gold mine (Panamá), exploited intermittently for more than 100 years, and has remained derelict for over 20 years. Within the area live farmers who carry out subsistence agriculture and livestock activities. The objective of this study has been to study the transference of PTEs in the local agricultural soil-plants system, with the goal of identifying their bioavailability to perform a human risk assessment. The results obtained of the Bioaccumulation coefficient in local plants show very weak to strong absorption of As (< 0.001-1.50), Hg (< 0.001-2.38), Sb (0.01-7.83), Cu (0.02-2.89), and Zn (0.06-5.32). In the case of Cu in grass (18.3 mg kg-1) and plants (16.9 mg kg-1) the concentrations exceed the maximum authorised value in animal nutrition for ruminants (10 mg kg-1). The risk to human health for edible plants exceeds the non-carcinogenic risk for rice, corn, cassava, and tea leaves for Sb (HQ 19.450, 18.304, 6.075, 1.830, respectively), the carcinogenic risk for Cu (CR = 2.3 × 10-3, 7.7 × 10 -4, 1.1 × 10-3, 1.0 × 10-3, respectively), and the carcinogenic risk for As in rice, corn and tea leaves (CR = 8 × 10-5, 3 × 10-5, 3 × 10-5, respectively). Urgent measures are needed to alleviate these effects.

Evaluation of antimony availability in a mining context: Impact for the environment, and for mineral exploration and exploitation.

This work aims to establish Sb mobility, its transfer to biota and its effect on soil health in a semi-arid climate. The results show the presence of stibnite (Sb2S3) as the main primary Sb compound, bindhemite (Pb2Sb2O6(O,OH)), and minor proportions of stibiconite (Sb3+(Sb5+)2O6(OH)) as oxidised Sb species. This research also observes very high total Sb contents in mining materials (max: 20,000 mg kg-1) and soils (400-3000 mg kg-1), with physical dispersion around mining materials restricted to 450 m. The soil-to-plant transfer is very low, (bioaccumulation factor: 0.0002-0.1520). Most Sb remains in a residual fraction (99.9%), a very low fraction is bound to Fe and Mn oxy-hydroxides or organic matter, and a negligible proportion of Sb is leachable. The higher Sb mobility rates has been found under oxidising conditions with a long contact time between solids and water. The main factors that explain the poor Sb mobility and dispersion in the mining area are the low annual rainfall rates that slow down the Sb mobilisation process and the scarce formation of oxidised Sb compounds. All these data suggest poor Sb (III) formation and a low toxicological risk in the area associated with past mining activities. The low mobility of Sb suggests advantages for future sustainable mining of such ore deposits in a semi-arid climate and is also indicative of the limitations of geochemical exploration in the search for new Sb deposits.

Environmental challenges related to cyanidation in Central American gold mining; the Remance mine (Panama).

Mine tailings are a potential source of environmental pollution because they typically contain potentially toxic elements (PTEs) and the residue of chemical compounds used during extraction processes. The Remance gold mine (NW Panama) is a decommissioned mine with mining activity records dating from the 1800s and several periods of abandonment. Very little remediation work has been performed, and waste is exposed to climatic conditions. This study aimed to evaluate the PTEs and cyanide contents in mine waste after mining operations ceased some 20 years ago, and to evaluate the degree of pollution and the environmental risks they pose with the use of the Pollution Load Index (PLI) and the Ecological Risk Index (RI). Although the total cyanide (T-CN) concentration (1.4-1.9 mg kg-1) found in most of the study area falls within the limits of gold mining tailing values for American sites (1.5-23 mg kg-1), it is worth noting that the values of the tailings of the last used mining operation exceed it (25.2-518 mg kg-1) and persist at the site. The PLI and RI suggest that the tailings from the mine and mine gallery sediments represent a source of pollution for soils and surrounding areas given their high content of PTEs (As, Cu, Sb, Hg) and T-CN, which pose serious ecological risks for biota. Therefore, it is necessary to draw up a remediation plan for this area.

Ecological and Health Risk Assessments of an Abandoned Gold Mine (Remance, Panama): Complex Scenarios Need a Combination of Indices.

The derelict Remance gold mine is a possible source of pollution with potentially toxic elements (PTEs). In the study area, diverse mine waste has been left behind and exposed to weather conditions, and poses risks for soil, plants and water bodies, and also for the health of local inhabitants. This study sought to perform an ecological and health risk assessment of derelict gold mining areas with incomplete remediation, including: (i) characterizing the geochemical distribution of PTEs; (ii) assessing ecological risk by estimating the pollution load index (PLI) and potential ecological risk index (RI); (iii) assessing soil health by dehydrogenase activity; and iv) establishing non-carcinogenic (HI) and carcinogenic risks (CR) for local inhabitants. Soil health seems to depend on not only PTE concentrations, but also on organic matter (OM). Both indexes (PLI and RI) ranged from high to extreme near mining and waste accumulation sites. As indicated by both the HI and CR results, the mining area poses a health risk for local inhabitants and particularly for children. For this reason, it will be necessary to set up environmental management programs in the areas that are most affected (tailings and surrounding areas) and accordingly establish the best remediation strategies to minimize risks for the local population.