Sulfide mining wastes may lead to severe environmental and human health risks. This study aims to use geochemical and ecotoxicological indicators for the assessment of the ecological risks of potentially toxic elements (PTEs) in the San Quintín mining group to categorize wastes prior to mining restoration. Ecotoxicity was evaluated using crustacean (Dahpnia magna, Thamnocephalus platyurus) and algae (Raphidocelis subcapitata) bioassays. The geochemical and mineralogical results suggested that the mining residues underwent intense weathering processes, with active processes of acidity generation and metal mobility. Total PTEs concentrations indicated that the mining materials were extremely polluted, with Pb, Zn and Cd geoaccumulation index (Igeo) values higher than 5 in more than 90% of the samples. The pollution load index (PLI) showed average values of 18.1, which classifies them as very highly polluted. The toxicity tests showed a higher toxicity for plants than crustaceans, being the highest values of toxicity related to toxic elements (Pb, Cd and Zn), electrical conductivity and to pH. This paper presents for the first time the combination of indices in the categorization of mining waste prior to its restoration. The combination of them has made it possible to categorize the waste and adapt the restoration and remediation procedures.
<p>The exploitation of mineral resources is a fundamental activity for the development of societies, but the importance of the alterations caused to the environment has not been considered when carrying out these exploitations. In the case of metallic mining, sulphide oxidation and leaching of potentially toxic elements (PTEs) lead to soil and water pollution.</p> <p>Sierra Minera of Cartagena-La Uni&#243;n (SE, Spain) has historically been a major mining district. Technological development caused production to rise during the second half of the 20th century, leading to an increase in tailings dumps, producing one of the biggest ecological disaster on the Mediterranean coast.</p> <p>Sediments from Portman Bay were collected during the Pilot Project for its regeneration (2008). Samples have been analyzed in 12 cores of 10 meters deep, with one sample every meter. Two cores were selected and analyzed to a depth of 24 meters in order to reach the original bedding material and thus be able to make a 3D model of the extent of the contamination at depth.</p> <p>The total PTEs content was determined after an acid digestion. In addition, a characterization of the mineralogical composition has been carried out by XRD, both in powder samples and oriented aggregates for the determination of bulk and clay mineralogy respectively.</p> <p>The materials studied showed sandy texture, except collected close to the discharge point, as in the core located in the internal area of the Bay, where the texture is finer. The total PTEs content is high and follows the following order of concentration: Zn > Pb > As > Cu > Cd.</p> <p>The mineralogical results showed the presence of quartz, feldespars and phyllosilicates in most of the samples. The rest of the minerals present in the samples correspond to different phases of Fe as sulphides (pyrite), oxides (hematite and magnetite), oxyhydroxides (goethite), carbonates (siderite) and sulphates with different states of hydration, such as jarosite. Gypsum appears in most of the samples, regardless of their depth. The presence of jarosite is relevant in the surface samples of cores in the inner part of the bay, as well as in the first line of cores located near the dumping point. In the case of cores located further away from the coastline, the presence of this phase has been detected both at surface and at depth.</p> <p>Clay mineralogical data revealed that samples with mining residues contain greenalite, chlorite and mica-illite as main minerals, with minor amounts of minnesotaite, kaolinite and smectite. On the other hand, in the samples from the deeper zones corresponding to the bedding materials, the phyllosilicates found are mica-illite, kaolinite and chlorite in order of abundance.</p> <p>The statistical integration of the results has allowed the selection of quartz, pyrite, siderite and arsenic as representative variables for the 3D model. Taking into account that the current reclamation project in the bay includes mobilization of part of the waste to a mining cut, the use of these 3D models is very useful as a complement to the geochemical and mineralogical characterization.</p>
<p>San Quint&#237;n is one of the derelict mines in Alcudia Valley Mining District, where large amounts of mining wastes have been disseminated during the last two centuries. These dumps and tailings materials are an important source of contamination of heavy metals and metalloids in the area. Nowadays, the restoration project for the abandoned mining area is beginning to be drafted, including a risk assessment of the wastes before restoration works. In this work, we carried out toxicity studies of these polluted materials, including data about total and soluble contain of As, Cd, Pb, Zn and Fe, mineralogical composition, and some bioassays to determine the toxicity effect of the samples to crustaceans (<em>D. magna</em> and <em>T. platyurus</em>) and algae (<em>R. subcapitata</em>). The pollution load index (PLI) has been calculated for each sample based on the pollution index (PI). Multielemental data and the indices calculated show that most of the samples present extremely high values of potentially toxic elements, and high values of contamination respect the background levels: 444 mg kg<sup>-1</sup> Cd, 144,900 mg kg<sup>-1</sup> Pb, 47,700 mg kg<sup>-1</sup> Zn, 202,600 mg kg<sup>-1</sup> Fe and 549 mg kg<sup>-1</sup> As. The bioassays suggest a relationship with pH, conductivity and grainsize. The EC<sub>50</sub> values were 458.7 to <2 of toxic units (TU) for <em>D. Magna</em> whereas for <em>T. Platyurus</em> the results oscillated between 2500 to <2. On the other hand, for algae organisms were 2083.3 to <2 TU. The studies carried out reveal the large accumulation of potentially toxic elements in mining waste and the risk they may pose to the associated ecosystems that develop in the area, as well as to human health.</p>
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