Publicación: Aproximación a los riesgos derivados de la presencia de residuos mineros en saladares del entorno del Mar Menor: dinámica de metales pesados y arsénico y su acumulación en plantas y moluscos
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Fecha
2009-06-19
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Antonio María Cervantes
Resumen
[SPA] El Mar Menor, localizado en el sureste de España, es una de las lagunas costeras
más grandes de Europa y del Mediterráneo. A pesar de las diversas figuras de protección medioambiental que obstenta, esta laguna y sus humedales asociados se encuentran afectados por diversas actividades antrópicas, entre las que destacan la
presencia de residuos mineros procedentes de la antigua zona minera de Cartagena-La
Unión, transportados y depositados durante los periodos de lluvias torrenciales a través
de las ramblas que drenan ese área. Como caso de estudio, el presente trabajo se centra en dos saladares, la Marina
del Carmolí y Lo Poyo, y en la línea de costa del Mar Menor asociada a ambos parajes.
[ENG] The present work focuses on two salt marshes, the Marina del Carmolí and Lo Poyo, and along the shoreline of the Mar Menor associated to both wetlands. Due to the activities that population develops in the area, which include harvesting of plants for feeding and adornment, sheepherding, capture of molluscs for eating, several recreational activities, and bathing, there may be some risks of toxicity and transfer of heavy metals and arsenic to the food chain. Thus, it was proposed a project with the following aims: (1) To carry out a first approximation to the risks of toxicity associated with the presence of heavy metals and arsenic in these environments, including their transfer to the food chain. (2) To study the biogeochemical processes associated with mobilization-immobilization of those toxic elements in the studied wetlands, under different flooding regimes either with or without rhizosphere. (3) To establish recommendations for use to preserve these ecosystems and reduce the risks associated with the presence of those contaminants. To achieve the first aim, the concentrations of heavy metals (cadmium, copper, manganese, lead, and zinc) and arsenic were determined in several rhizospheric and non-rhizospheric soil samples (total contents and the labile fraction extracted with 1 N hydrochloric acid) and in the most representative species of plants of both salt marshes, including those consumed by population and those used for sheepherding. Litter, roots, rhizomes, bulbs, green stems, ligneous stems, and leaves were separately analyzed. With the same objective, it was determined the accumulation of the same toxic elements in the sediments of the lagoon in sites adjacent to both salt marshes and in two species of marine molluscs collected that live in them and which are consumed by population: the carnivorous gastropod Hexaplex trunculus (commonly called 'seashell' or 'horn'), and a filter bivalve, the clam Tapes decussatus. Besides, it was determined the speciation of arsenic in H. trunculus because the different forms of this metalloid have very different toxicities. To achieve the second aim, it was performed a greenhouse experiment to study the influence of pH, flooding and rhizosphere on the mobilization of cited elements plus iron. For that, different pots were filled with mining wastes collected from two polluted areas: one acidic (from Lo Poyo salt marsh) and one basic (from the Marina del Carmolí salt marsh). For each mining waste, small specimens of Sarcocornia fruticosa and Phragmites australis were planted in the pots. Also, it was prepared pots without plant. Two different flooding regime were applied: (1) pots flooded three months and afterwards drying, and (2) pots flooded one month and another drying, alternately for six months. The water used to irrigate the pots was a mixture of water collected from two of the main surface watercourses of the zone. The Eh and pH were measured weekly with appropriate electrodes. Also the solution was extracted weekly from the pots using Rhizon type samplers. After acidifying the solution with two drops of concentrated sulphuric acid, dissolved organic carbon and dissolved As, Cd, Cu, Mn, Pb, Zn and Fe were measured. To achieve the third aim, the results and conclusions of the two previous points were integrated and combined. The results of field analyses indicated that the soils of the Marina del Carmolí and Lo Poyo salt marshes are strongly polluted by As, Cd, Mn, Pb, and Zn, but not for copper. Besides, the contents extracted with 1 N hydrochloric acid (a labile fraction) were high, which indicate that there is a risk of mobilization of those elements. Therefore, according to field and greenhouse data, it can be proposed some recommendations in order to minimize the risks due to metallic pollution. A possible strategy would be the continuous flooding of the polluted areas, together with the planting of the most appropriate species to perform a phytostabilization program. Based on the capacity to grow in the wettest soils and on their capability to accumulate toxic elements in roots, Arthrocnemum macrostachyum, Sarcocornia fruticosa, Juncus maritimus, Scirpus holoschoenus, and Phragmites australis, would be the most suitable species. The presence of vegetation also would prevent the erosion and the dragging of the mining wastes. Nevertheless, these practices should be accompanied with the addition of some kind of amendment to further immobilize the contaminants, as for example carbonates. After the addition of amendments it is necessary to follow a monitoring program in the areas in restoration in order to check that those actions are effective enough in short and long term.
[ENG] The present work focuses on two salt marshes, the Marina del Carmolí and Lo Poyo, and along the shoreline of the Mar Menor associated to both wetlands. Due to the activities that population develops in the area, which include harvesting of plants for feeding and adornment, sheepherding, capture of molluscs for eating, several recreational activities, and bathing, there may be some risks of toxicity and transfer of heavy metals and arsenic to the food chain. Thus, it was proposed a project with the following aims: (1) To carry out a first approximation to the risks of toxicity associated with the presence of heavy metals and arsenic in these environments, including their transfer to the food chain. (2) To study the biogeochemical processes associated with mobilization-immobilization of those toxic elements in the studied wetlands, under different flooding regimes either with or without rhizosphere. (3) To establish recommendations for use to preserve these ecosystems and reduce the risks associated with the presence of those contaminants. To achieve the first aim, the concentrations of heavy metals (cadmium, copper, manganese, lead, and zinc) and arsenic were determined in several rhizospheric and non-rhizospheric soil samples (total contents and the labile fraction extracted with 1 N hydrochloric acid) and in the most representative species of plants of both salt marshes, including those consumed by population and those used for sheepherding. Litter, roots, rhizomes, bulbs, green stems, ligneous stems, and leaves were separately analyzed. With the same objective, it was determined the accumulation of the same toxic elements in the sediments of the lagoon in sites adjacent to both salt marshes and in two species of marine molluscs collected that live in them and which are consumed by population: the carnivorous gastropod Hexaplex trunculus (commonly called 'seashell' or 'horn'), and a filter bivalve, the clam Tapes decussatus. Besides, it was determined the speciation of arsenic in H. trunculus because the different forms of this metalloid have very different toxicities. To achieve the second aim, it was performed a greenhouse experiment to study the influence of pH, flooding and rhizosphere on the mobilization of cited elements plus iron. For that, different pots were filled with mining wastes collected from two polluted areas: one acidic (from Lo Poyo salt marsh) and one basic (from the Marina del Carmolí salt marsh). For each mining waste, small specimens of Sarcocornia fruticosa and Phragmites australis were planted in the pots. Also, it was prepared pots without plant. Two different flooding regime were applied: (1) pots flooded three months and afterwards drying, and (2) pots flooded one month and another drying, alternately for six months. The water used to irrigate the pots was a mixture of water collected from two of the main surface watercourses of the zone. The Eh and pH were measured weekly with appropriate electrodes. Also the solution was extracted weekly from the pots using Rhizon type samplers. After acidifying the solution with two drops of concentrated sulphuric acid, dissolved organic carbon and dissolved As, Cd, Cu, Mn, Pb, Zn and Fe were measured. To achieve the third aim, the results and conclusions of the two previous points were integrated and combined. The results of field analyses indicated that the soils of the Marina del Carmolí and Lo Poyo salt marshes are strongly polluted by As, Cd, Mn, Pb, and Zn, but not for copper. Besides, the contents extracted with 1 N hydrochloric acid (a labile fraction) were high, which indicate that there is a risk of mobilization of those elements. Therefore, according to field and greenhouse data, it can be proposed some recommendations in order to minimize the risks due to metallic pollution. A possible strategy would be the continuous flooding of the polluted areas, together with the planting of the most appropriate species to perform a phytostabilization program. Based on the capacity to grow in the wettest soils and on their capability to accumulate toxic elements in roots, Arthrocnemum macrostachyum, Sarcocornia fruticosa, Juncus maritimus, Scirpus holoschoenus, and Phragmites australis, would be the most suitable species. The presence of vegetation also would prevent the erosion and the dragging of the mining wastes. Nevertheless, these practices should be accompanied with the addition of some kind of amendment to further immobilize the contaminants, as for example carbonates. After the addition of amendments it is necessary to follow a monitoring program in the areas in restoration in order to check that those actions are effective enough in short and long term.
Descripción
Palabras clave
Residuo minero, Mar Menor, Sedimento, Heavy metals, Molusco, Mollussc, Carmoli, Mining wate, Lo Poyo, Sediment
