Efrén Garcia-Ordiales

Heavy metal contamination in sediments of an artificial reservoir impacted by long-term mining activity in the Almadén mercury district (Spain)

Sediments from the Castilseras reservoir, located downstream on the Valdeazogues River in the Almadén mercury district, were collected to assess the potential contamination status related to metals(oids) associated with river sediment inputs from several decommissioned mines. Metals(oids) concentrations in the reservoir sediments were investigated using different physical and chemical techniques. The results were analyzed by principal component analysis (PCA) to explain the correlations between the sets of variables. The degree of contamination was evaluated using the enrichment factor (EF) and the geoaccumulation index (Igeo). PCA revealed that the silty fraction is the main metals(oids) carrier in the sediments. Among the potentially harmful elements, there is a group (Al, Cr, Cu, Fe, Mn, Ni, and Zn) that cannot be strictly correlated to the mining activity since their concentrations depend on the lithological and edaphological characteristics of the materials. In contrast, As, Co, Hg, Pb, and S showed significant enrichment and contamination, thus suggesting relevant contributions from the decommissioned mines through fluvial sediment inputs. As far as Hg and S are concerned, the high enrichment levels pose a question concerning the potential environmental risk of transfer of the organic forms of Hg (mainly methylmercury) from the bottom sediments to the aquatic food chain.

Stream bottom sediments as a means to assess metal contamination in the historic mining district of Almadén (Spain)

Located in the southern half of Spain, Almadén is the world’s largest Hg district and mercury has been mined there for over 2000 years. Its slag heaps and old metallurgy plants represent a risk to watercourses that flow through the district and receive the run-off from the mines. This study collected sediment samples along the length of the main watercourses in the mining district. High levels of heavy metals were detected, with Hg levels varying between 1.77 and 255.88 mg kg−1, Pb levels between 20.59 and 131.07 mg kg−1 and Zn levels between 59.06 and 131.07 mg kg−1. The dispersion of these heavy metals in rivers as a result of mining activities has caused sediment quality degradation. As such, when measured using reference indexes such as the SeQI and the EF, sediment quality for the entire district is practically poor, due to anthropogenic contributions, with the concomitant threat to the surrounding environment.

Occurrence and speciation of arsenic and mercury in estuarine sediments affected by mining activities (Asturias, northern Spain)

Sediments contaminated by Hg and As from two historical mining areas have been deposited in the Nalón estuary (Asturias, northern Spain) since 1850. Total mercury (Hgtotal) concentrations in the sediments range from 0.20 μg g-1 to 1.33 μg g-1, most of it in the form of sulphides. Concentrations of methylmercury (303.20-865.40 pg g-1) are up to two orders of magnitude lower than the concentration of Hgtotal. Total As concentration (Astotal) is enriched compared to the background level for the area. The relative abundance of As(V) on As(III) in the sediments ranges from 97.6% to 100%, whereas inorganic Hg accounts for more than 99% of the total Hg. The occurrence of the most toxic species, inorganic As(III) and organic methylmercury, seem to be related to redox conditions together with the amounts of sulphur which act as natural barriers which inhibit the biological and chemical speciation processes. Despite the high amounts of Hg and As present in the sediments, their transference to the water column appear to be limited thus converting sediments in an effective sink of both elements. Special attention should be paid to potential variations of the environmental conditions which might increase the element mobility and exchange between sediments and the water column.

Trace metal pollution in freshwater sediments of the world’s largest mercury mining district: sources, spatial distribution, and environmental implications

PurposeThe Almadén mining district has suffered long-term extraction activity, and this has left significant areas of decommissioned mining liabilities. Nowadays, the uncontrolled runoff and related erosion and transport of trace metal-enriched soils and sediments affect the whole freshwater ecosystem. The goal of this study was to distinguish geogenic from mining-related sources of trace metals in freshwater sediments, to understand their dispersion in the watershed, and, finally, to evaluate the potential environmental implications for future corrective plans.Materials and methodsFreshwater surface sediment samples were collected from ten points along the main streams of the watershed (nine inside the mining district and one control point outside the district). Sediments were air dried and analyzed by different standard methods for pH, total major and trace element concentrations, total organic carbon, and grain size. In addition to the determination of the enrichment factor, a multi-statistical approach was applied involving discriminant analysis, Student’s t test, and Mann-Whitney U analysis.Results and discussionSediments inside the district contained high levels of major and trace elements with respect to the control point. The predominance of fine fractions in these sediment samples appears to be one of the most important factors that affects trace metal concentrations. Among the trace elements, not only Hg but also As, Pb, and Zn are discriminative geochemical markers, thus allowing the identification of the different mining sources and their individual or combined impact throughout the district. Furthermore, the high enrichment factors obtained for As, Hg, Pb, and Zn with respect to the local background values highlight the persistent and severe impact from the decommissioned mines on the freshwater surficial sediments and their potential geoavailable risk for aquatic organisms.ConclusionsThe geochemistry of freshwater sediments alone demonstrates that different contamination sources are recognizable within the mining district and these can be related to the specific decommissioned mines. In addition, the discrete sources can be clearly distinguished on the basis of the statistical analysis of the geochemical data. Despite the closure of the mines, stream sediments are still the main repository of trace metals within the district, and they are therefore a potential threat to the freshwater ecosystem.

Geochemical distribution of major and trace elements in agricultural soils of Castilla-La Mancha (central Spain): finding criteria for baselines and delimiting regional anomalies

Castilla-La Mancha (central Spain) is a region characterized by significant agricultural production aimed at high-quality food products such as wine and olive oil. The quality of agricultural products depends directly on the soil quality. Soil geochemistry, including dispersion maps and the recognition of baselines and anomalies of various origins, is the most important tool to assess soil quality. With this objective, 200 soil samples were taken from agricultural areas distributed among the different geological domains present in the region. Analysis of these samples included evaluation of edaphological parameters (reactivity, electrical conductivity, organic matter content) and the geochemistry of major and trace elements by X-ray fluorescence. The dataset obtained was statistically analyzed for major elements and, in the case of trace elements, was normalized with respect to Al and analyzed using the relative cumulative frequency (RCF) distribution method. Furthermore, the geographic distribution of analytical data was characterized and analyzed using the kriging technique, with a correspondence found between major and trace elements in the different geologic domains of the region as well as with the most important mining areas. The results show an influence of the clay fraction present in the soil, which acts as a repository for trace elements. On the basis of the results, of the possible elements related with clay that could be used for normalization, Al was selected as the most suitable, followed by Fe, Mn, and Ti. Reference values estimated using this methodology were lower than those estimated in previous studies.

Seasonal and spatial distribution of mercury in stream sediments from Almadén mining district

The spatial and temporal distributions of Hg in different fractions of sediment samples from the Valdeazogues River (Almadén) were investigated. Almadén is widely known as the worlds largest Hg mining district. A total of nine sites during six time periods were monitored using a BCR (Community Bureau of Reference) sequential extraction procedure. The results showed that Hg is mainly present as residual cinnabar but there is another important organic fraction in which Hg is primarily incorporated. Higher proportions of Hg in the residual fraction were found in wet seasons, while the opposite is true in the organic fraction. The exchangeable/carbonate and Fe-Mn oxide phases are the minor Hg fractions, and they were found less susceptible to seasonal changes. The potential risk for the aquatic medium was evaluated based on the proportions of non-residual (exchangeable/carbonate + Fe-Mn oxides + organic) fractions. The high proportions of Hg potentially (bio)available, together with the Hg total concentrations, indicated an important risk, especially in areas close to the mines. Although the risk is important in all seasons, it is particularly noticeable during dry periods due to the increase in the organic fraction, which may favor potential transference from the sediments to the environment due to the physic-chemical river conditions.

Incidence of the Almadén historical mining district on the hydrochemical characteristics of Valdeazogues Basin (Spain)

The distribution of dissolved potentially harmful elements (PHEs), major ions and physico-chemical parameters in the Valdeazogues river basin was studied during 9 surveys, carried out between 2010 and 2013. The observed physico-chemical parameters depend on the season, the major ions depend of the nature of the lithological materials and the PHEs depend of the characteristics of the mine inputs. The Principal Component Analysis performed on the analysed dataset, distinguished the sources of contaminants introduced into waters and that nowadays mine runoffs play a role higher than the played by the natural inputs.