Application of a plant bioassay for the evaluation of ecotoxicological risks of heavy metals in sediments affected by mining activities

Purpose. The objective of this work was to evaluate the effectiveness of a plant bioassay (Phytotoxkit®) for screening ecotoxicological risks in sediments affected by mining activities. Materials and methods A total of 42 sediment samples affected by mining activities were studied, including 39 sediment samples fromthe Sierra Minera, Spain, an area affected by old extraction procedures, and three sediments from an area affected by opencast mining. These three samples were then mixed with limestone filler at 10, 20 and 30 %, providing nine stabilised samples. The total and soluble metal(loid) content (As, Cd, Cu, Fe, Pb and Zn) was determined in all samples, and the Phytotoxkit® bioassay was applied to determine the ecotoxicological effect of this procedure. Results and discussion The stabilised material had a neutral pH and low soluble metal(loid) concentration, similar to that of samples in which a natural attenuation process had taken place because of mixing with surrounding carbonate-rich materials. An ecotoxicological survey identified the low toxicity levels of the stabilised samples

Trace element accumulation in plants from an aridic area affected by mining activities

Trace element contamination has been a serious problem in the vicinity of abandoned mine sites. In the studied area, mining activities have produced great amounts of wastes, characterized by high trace elements content, acidic pH and minerals from supergene alteration. Trace elements have been dispersed, both downstream and downslope from the mine mainly due, mainly, to surface run-off. Trace elements hydric mobilization usually takes place during the rainy season, an important pollution route in the studied area. A wide range of techniques have been proposed to remediate soils polluted by trace elements. Among them, phytoremediation-based technologies could provide a long-lasting solution. The aimof thisworkwas to determine trace element concentration in roots and leaves of five plant species (Limonium carthaginens, Arthrocnemum macrostachyum, Dittrichia viscosa, Glaucium flavum and Zygophyllum fabago) growing in soils polluted by mining activities in order to determine which part of the plants accumulate heavymetals to the greatest extent. Themetal concentrations in plants varied with plant species. Plant accumulation results showed that Z. fabago could act as an accumulator for Fe, and A. macrostachyum could accumulate in Fe, As and Mn. The other plant species collected from the mining sites were tolerant to trace element contamination

Geochemical and mineralogical characteristics of percolates and its evaporates from Technosols before and after limestone filler stabilisation

The chemistry of waters is recognized as a relevant monitoring tool when assessing the adverse effects of acid mine drainage. The weathering of sulphide minerals produces a great variety of efflorescences of soluble sulphate salts. These minerals play an important role for environmental pollution, since they can be either a sink or a source for acidity and trace elements. This communication deals with the leachability of potentially toxic elements (PTE) eluting from technosols formed from soils affected by mining activities and limestone filler. A total of three contaminated soils affected by opencast mining were selected and mixed with limestone filler at three percentages: 10 %, 20 % and 30 %, providing nine stabilised samples. These samples were stored in containers and moistened simulating rainfall. The percolates obtained were collected, and the PTEs content (As, Cd, Cu, Fe, Pb and Zn) was determined. Evaporation-precipitation experiments were carried out in these waters, and the mineralogical composition of efflorescences was evaluated. The study area is heavily polluted as a result of historical mining and processing activities, producing large amount of wastes, characterised by high trace elements content and acidic pH. The results obtained for the percolates after the rain episode showed that, before the stabilization approach, waters had an acidic pH, high electrical conductivity and high PTEs content. When these soils were mixed with 10, 20 and 30 % of limestone filler, the pH was neutral and the soluble trace element content strongly decreased, being under the detection limit when limestone percentage was 20 % and 30 %. The mineralogical composition of efflorescences before the stabilisation approach showed that predominant minerals were copiapite, followed by gypsum and bilinite. Other soluble sulphates were determined in lower percentage, such as hexahydrite, halotriquite or pickeringite. After the mixing with 10 % of limestone filler, the evaporates were mainly composed by gypsum and halite. Other minerals such as starkeyite (MgSO4·4(H2O), boyleite ((Zn,Mg)SO4·4H2O), tachyhidrite (CaMg2Cl6·12H2O) or bischofite (MgCl2) were quantified in low percentages. After mixing with 20 % and 30 % of limestone filler, main minerals were gypsum and halite, the presence of other phases being scarce. The addition of limestone filler to soils polluted by potentially toxic elements represents a useful and low impact strategy for reducing the soluble fractions of As, Cd, Cu, Fe, Pb and Zn. M.H.C. acknowledges the financial support of the Comunidad Autonóma de la Región de Murcia , Spain (Fundación Séneca, 19888/GERM/15

Trace elements contamination in an abandoned mining site in a semiarid zone

The distribution of trace elements throughout mining areas is an important issue because abandoned tailings can be a major source of environmental pollution. The aim of this study was to identify the trace element content, hydric dispersion ways and its reception areas in selected zones of the abandoned mining district of Sierra Minera Cartagena-La Unión. The results obtained allowed to establish points affected by primary, secondary and tertiary contamination, according to their proximity to contamination sources, as a function of its chemical and mineralogical composition. Applied GIS methodology allowed visualisation and confirmation of established conceptual model

Cost Optimisation for Minimizing the Visual Impact of Ornamental Stone Quarrying. A Case Study in Murcia Region

Quarrying of ornamental stone has adverse effects that are both visual and environmental. This paper aims to develop a methodology for minimising the costs associated with reducing the visual impact of ornamental stone quarrying. This study uses digital topographical maps of the study zone and a GPS and GIS application to calculate the extent of the area affected by quarrying activities for each altitude designated in the work plan and to calculate the extent of the potential visual impact. The results obtained applying the proposed methodology for the selected area suggested that the potential visual impact is minimal for an altitude of 520 metres, this being the optimal point for the observer. When altitude increases, the potential visual impact increases and the optimal point for the observer diminishes until the highest impact altitude (740 m) is readied. The optimal point that the exploitation should reach is that at which the values of the diagram generated by the (%) area of potential visual impact and area of exploitation (%) intersect. The methodology allows the optimal altitude to be determined for mining exploitations and helps assess the viability of a given exploitation from an environmental point of view

Monitoring salinization processes in soils by using a chemical degradation indicator

The main aim of this work is to progress in the study of desertification processes in Mediterranean regions in the framework of DESERTNET project by means of the execution of pilot studies and development of evaluation models. This paper shows the results of an investigation on the degradation processes of soils carried out in the Murcia Region (SE, Spain). Specifically, salinization problems in Murcia Region were evaluated by means of two chemical degradation indicators, salinization state and salinization rate. We define chemical degradation indicator as the representative value of an observed chemical phenomenon in soil which produce its degradation. Chemical degradation indicators were calculated in order to simplify the interpretation of all the complex processes involved in environmental monitoring. The results obtained showed that in some areas an increase in salinization processes is taking place. On the other hand, there are only a few points with high a risk of salinization, obtaining similar results in the two periods of time studied

Selenium content in soils from Murcia Region (SE, Spain)

The objective of this study was to determine the selenium content in soils from the Region of Murcia (SE, Spain) and to study the possible relationship between mineralogical composition, soil properties and selenium content. In addition, generic reference level (GRL) for selenium was determined according to Spanish legislation. For this study, 490 samples were selected in areas subjected to agricultural activity or abandoned agricultural soils with natural vegetation. Five different zones were established in order to study selenium variability. Four different mineralogical groups were established, based on significant relationship with the mineralogical composition, and each sample was included in one mineralogical group. The results showed that the concentration of selenium is correlated with the electrical conductivity, sulphate content and with the mineralogical composition, particularly positively with quartz and in a negative way with calcite percentage. In addition, selenium level was positively correlated with the phyllosilicate content. Established GRL for selenium varies with the mineralogical group, having a great transcendence from the legal and economic points of view

Weathering processes in waste materials from a mining area in a semiarid zone

Chemical and mineralogical characterization of waste materials present in an abandoned Pb, Zn–Ag mining site (SE, Spain) was carried out. In unaltered rocks, the mineralogy is characterized by plagioclase, pyroxene, magnetite, ilmenite, amphibole, biotite and quartz. Trace-element contents of these samples represent unaltered values. In mine-waste materials, pH ranged from acidic to slightly acidic and trace-element content was generally high, especially for Pb and Zn, although there were also substantial As concentrations. X-ray diffraction results suggested that these samples have a complex mineralogy, including alteration products. Surficial materials in the study area were affected by weathering processes, generating supergene assemblages, including Fe and Mn oxides and hydroxides, carbonates, hydrated sulfates and jarosite. Knowledge of the geochemical processes that took place in the past and whichare still taking place provide an important tool for assessing associated environmental problems in this area

Assessment of the mobility of metals in a mining-impacted coastal area (Spain, Western Mediterranean)

A study on metal mobilisation (Zn, Pb and As) from contaminated sediments in Portman Bay (SE Spain) was carried out. Thisarea has suffered a major impact from mining activity, as millions of tons of mine tailings have been dumped into the bay over a long period, gradually filling the bay. A three-step sequential extraction procedure, modified from the BCR (Community Bureau of Reference) method, as well as selective extractions (H2O, 0.1 N HNO3, citrate–dithionite and 1 M NH4OAc after H2O2 attack) were applied to selected samples in order to evaluate the potential mobility of fixed metals. Acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) were also determined. X-ray diffraction (XRD) and scanning electron microscopy coupled to with an energy-dispersion spectrometry (SEM-EDS) were applied to the characterization of both raw samples and the residues remaining after each extraction, providing additional information about the sediment phases carrying the metals studied. Metals associated with sediments showed different behaviour depending on the mineralogical phase they were bound to. Zn was the most labile metal, while Pb and As showed a lower mobility. The fraction of metals associated with jarosites presented a high stability under different physicochemical conditions, while metals associated with mineralogical phases that are undergoing supergenic alteration processes presented a high mobility. The results obtained may be useful to assess both the short and the long-term environmental impact of such disposal activities as well as supporting decisions for a future remediation of the zone

Use of limestone filler as a sorbent for the removal of As(V), Pb(II), Cu(II), Zn(II) and Cd(II) in contaminated sites

Many of the approaches used to treat soils contaminated by heavy metals are invasive, and do not restore the natural equilibrium of the environment [1]. For this reason, one of procedures used to stabilise heavy metal-contaminated soils in situ is to directly add amendments, which, while they may not totally eliminate toxic elements, help natural retention mechanisms, induce sorption and reduce mobility and bioavailability. In this respect, the use of calcareous materials may be an excellent, eco-friendly way for recovering this type of soils [2], and this communication reports studies made in our laboratory for such a purpose. The influence of different variables in the preparation of mixtures used to stabilize contaminated soils (soil pH, temperature and composition of the contaminated soil / limestone filler) was studied by means of a factorial experimental design. The main interaction effects of the factors obtained on different contaminated soils were used along with the results of the physicochemical and mineralogical characterization in the same data matrix to be analyzed by principal components analysis (PCA). To evaluate the optimal values of the variables, spectroscopic techniques were used to measure the level of leached metals (Pb, Cd, Cu, As, Zn and Fe). The environmental conditions were simulated and controlled by means of a climatic chamber to evaluate simultaneously the processes of geochemical alteration and passivation of the mixture. The results obtained showed that the corresponding factors of the experimental design may be an important source of information to show correlations on some of the most significant variables such as the concentration of metals and, in this way, optimize the use of the in situ stabilizer