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

Abstract

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. IntroductionDecommissioned mercury mines represent a significant source of mercury (Hg) and also occasionally of other heavy metals in the environment as a result of the dumping of waste material originating from mines and metallurgy plants with a high concentration of Hg [1][2][3][4][5]. The metallurgical processing of Hg in mining districts has left a legacy of major mining liabilities as a result of the inefficient calcination of the mineral cinnabar. As this is an incomplete process, other types of soluble and insoluble compounds not originally present at the site, such as metacinnabar or mercury salts, are formed during the processing [6,7].The run-offs originating from the mining liabilities have an adverse effect on the ecosystems of the areas surrounding the mercury mines [8][9][10][11]. Stream-bed sediments and bodies of water located downstream from the mercury mines are characterised by significant levels of Hg and heavy metals, which can persist for decades after mining activities cease [5,7,12].The mining district of Almadén, located in south-central Spain, is the world's largest geochemical mercury anomaly, and it has produced one-third of total global production of this element [13]. The district includes a series of deposits with a range of structures and textures that share a relatively simple paragenesis whose dominant mineral is cinnabar, with pyrite present in lesser quantities. The most important mineralisation type, found in the mines of Almadén and El Entredicho, consists of stratabound cinnabar disseminations in Criadero Quartzite (Lower Silurian) [13]. Other type of mineralisation present in the area is composed of cinnabar filling veins and replacements of volcanic rocks that cannot be associated with specific stratigraphic layers [14,15]. Throughout its history, the district has been the site of various mines and metallurgy facilities. In terms of mines, Almadén is by far the largest and it has been the one most heavily mined, followed by El Entredicho, Las Cuevas and Nueva Concepción. In terms of metallurgy plants, some of them exist along the district, but two are the...

Sequential extraction procedure as a tool to investigate PTHE geochemistry and potential geoavailability of dam sediments (Almadén mining district, Spain)

“…However, in the same reservoir, under alkaline values of local waters (Berzas Nevado et al, 2003), the Mn 2+ adsorbed on the surface of the sediments can interact with CO 3 2− present in the water column to form rhodochrosite (Garcia-Ordiales, 2016), which is easily leached and may be available to aquatic life. Conversely, the lowest recovery percentages in the F1 were obtained for Co, Cr and Ni, whose median values for total contents (21, 59 and 43 mg kg −1 , respectively) are consistent with the local geochemical background values (García-Ordiales et al, 2014). This fact can be explained by the presence of ultramafic rocks outcropping in several parts of the district (Higueras, 1995).…”

“…The results obtained from the Cd index ( Fig. 4a), which was calculated with respect to the regional geochemical background (García-Ordiales et al, 2014), reveals a homogeneous degradation of the sediment quality for most of the sampling points. This situation is significantly more adverse in Cs6 (21.0) and Cs9 (20.0).…”

“…However, the extent of contamination is not strictly limited to the vicinity of mines; contaminated material may be physically remobilized during floods, thus dispersing contaminants over hundreds of kilometers from historical mine sites. The environmental quality of the Valdeazogues River has been negatively affected by run-off waters from the mined areas (Berzas Nevado et al, 2003;García-Ordiales et al, 2014).…”

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

“…This point is also coincident with the greatest depth of the reservoir, and it suggests that the local physico-chemical conditions in the aquatic environment associated with depth may play an important role in favoring the production of organic Hg species in sediments. In the Almadén district, Hg is commonly present in sediments from freshwater courses (Berzas Nevado et al 2003;García-Ordiales et al 2014), either as cinnabar or as hydroxides (Esbrí et al 2010). In the form of cinnabar, Hg is usually associated with fine sediments because of its high chemical stability but, due to the large number of abandoned mining operations in Almadén, cinnabar particles can be associated with other grain-size fractions such as sandy particles -19.20-38.50 67.20-102.80 Alqueva reservoir, Portugal (Palma et al 2014) Units: major elements Al and Fe expressed in % weight; trace elements expressed in μg g −1 depending on the distance from the source (García-Ordiales et al 2014).…”

Hydrochemistry of Ground Waters from Urban Wells in Almadén (Central Spain): Water Quality Around the World’s Largest Mercury Mining-Metallurgical Complex

“…In this respect, the 83 % of the wells exceed the US EPA the recommendation of 10 mg L −1 (US EPA 2011), and 50 % of the wells surpass the EUC reference (EUC 1998) and the Spanish regulation (BOE 2003) of 50 mg L −1 . As noted above, most of the samples with high concentrations are located in the town or close to the urban area where the main source of nitrate may be related to domestic wastes (water and solid wastes, e.g., Wakida and Lerner 2005), product of leaking sewers like those described by Garcia-Ordiales (2014) in the Azogado stream near to well 21 of his work, or in ours in well 1. A Cl − (and also of Na + ) significant presence in groundwater in urban wells (Fig.…”