Short communicationAssessment of metal(loid)s availability and their uptake by Pinus halepensis in a Mediterranean forest impacted by abandoned tailings
Introduction
Mining contamination is considered a critical issue in many sites worldwide due to its negative effects on environment (Conesa and Schulin, 2010). Mine tailings are known to produce most of the environmental impacts in former mining sites due to the spread of metal(loid)s enriched particles from their bare surfaces by via wind, water run-off and/or leaching. In some cases, mining contamination may reach regional scales affecting urban areas, agricultural lands or ecological protected sites (García-Lorenzo et al., 2012). This may increase the risk of transferring pollutants into food chain. For this reason, it is necessary to keep the environmental risks of these areas under a safety level and to perform a periodic monitoring of the geochemistry of the pollutants, not only at the tailing sites but also at their surroundings. Soil parameters such as pH, Eh, organic compounds, mineralogy or electrical conductivity have been shown to play an important role in the metal(loid) spetiation and therefore, at their uptake by biota (María-Cervantes et al., 2010).
Phytostabilisation (using plants to immobilise metal(loid)s) have been proposed as a feasible tool to effect the surface stabilisation of mine tailings under semiarid climate (Mendez and Maier, 2008). For this purpose, suitable plant species must show good adaptation to drought, metal(loid)s soil concentrations, salinity or low metal(loid) accumulation into shoots. In order to meet these requirements, the employment of indigenous plant species seems a good alternative (Rufo and De la Fuente, 2010). The former Cartagena-La Union Mining District (Supplementary material, Fig. SM1) located at Southern Spain has been widely researched for dynamics of metal(loid) contamination (Martínez-Sánchez et al., 2008) and emerging soil remediation low cost technologies, including phytostabilisation (Conesa and Schulin, 2010). Research on plant candidates for the in situ phytostabilisation has proposed the use of grasses (e.g. Lygeum spartum L., Piptatherum miliaceum (L.) Cosson), halophyte (e.g. Arthrocnemum macrostachyum (Moric.) Moris), weed (e.g. Zygophyllum fabago L.) or shrubs (e.g. Dittrichia viscosa (L.) Greuter) (Conesa et al., 2011, Martínez-Sánchez et al., 2012). According to Jefferson (2004) the main goal of a restoration project should be to recreate sustainable plant communities which reflect the diversity and composition of the surrounding natural plant communities. For this reason, the additional employment of tree species to the already listed plants would provide a better ecological-landscape assembling. For instance, Pinus halepensis Miller is a woody plant species which has been widely employed on the restoration of degraded semiarid ecosystems in the Mediterranean area (Fuentes et al., 2007). In addition, pine tree species have been proposed to be used as bioindicators of metal(loid) availability in polluted sites (Sun et al., 2009).
The aim of this study was to determine the influence of soil parameters on metal availability in a Mediterranean forest affected by mining contamination and the potential employment of P. halepensis for monitoring metal pollution and phytostabilising mining polluted sites under semiarid climates.
Section snippets
Materials and methods
Sampling was conducted at a tailing disposal area located at the Cartagena-La Union Mining District. Five tailings, where P. halepensis grew spontaneously, were selected (T1–T5). In addition, the spread of contamination into the surrounding areas (Supplementary material, Fig. SM2) was evaluated by performing a sampling at the tailings’ surroundings (F0), 100 m far from tailings (F1), up to 1 km (F2), and up to 3 km (F3). Tailing samples (T1–T5) were waste materials, F0 and F1 were soils developed
Soil parameters and metal(loid) concentrations
Soil properties are shown in Fig. 1. The pH of all the samples was in the range of neutral-slightly alkaline soils (pH 7–8). The soil samples from forest zones showed lower electrical conductivity values (∼0.3 dS m−1) than the tailing ones (0.9–2.8 dS m−1). Organic carbon (OC) total nitrogen (TN), and dissolved organic carbon (DOC) values for tailing samples were about the half of those obtained at forest samples. Tailing samples had sand percentages close to 80%, while F-samples were below 70% for
Metal(loid) content in the studied soils and influence of soil parameters on metal(loid) availability
According to the Spanish guidelines for soil contamination, the thresholds to determine whether a soil is polluted or not must be established regionally, based on the site-specific geochemical backgrounds. A comprehensive report of the geochemical backgrounds of Murcia Region performed by Martínez-Sánchez and Pérez-Sirvent (2007) showed that the soils from the nearby Cartagena plain had a geochemical basis of 12.6 mg kg−1 Cu, 9 mg kg−1 Pb and 41 mg kg−1 Zn. The same authors affirmed that the
Conclusions
The risk assessment of potential land uses (agricultural or forest) of areas surrounding the studied tailings should take into account the high metal(loid)s concentrations which contain. The alkaline pH and some carbonate minerals of the surrounding soils may keep low the metal(loid) available concentrations and therefore, decrease the risk of pollutants leaching. CaCl2-extractable As and metal concentrations did not correlate with the corresponding concentrations in pine needles indicating
Acknowledgements
Financial support for this research was provided by the Ministerio de Economía y Competitividad of Spain and FEDER (Project CTM2011-23958) and Fundacion Séneca de la Comunidad Autónoma de la Región de Murcia (Project 15296/PI/10). Dr. Héctor M. Conesa thanks the Spanish Ministerio de Economía y Competitividad and UPCT for funding through the “Ramon y Cajal” programme (Ref. RYC-2010-05665). We thank SAIT (Luis Alberto Alcolea, Ana Vanessa Caparrós, Magdalena Vázquez, Vicente Muñoz y Ana Belén
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