The Cartagena-La Unión mining district (SE Spain): a review of environmental problems and emerging phytoremediation solutions after fifteen years research.

After mining in the Cartagena-La Unión Mining District (SE Spain) was discontinued in 1992, various studies have shown that large amounts of toxic metals continue to be transferred with the spread of unstabilized mining wastes to the nearby ecosystems. Local creeks seem to be important pathways carrying eroded materials from the headwaters to the nearby coastal areas of the Mediterranean Sea. Studies have shown the presence of high metal concentrations in the sediments of riverbeds and in river mouths and adjacent coastal marshes (e.g. 500 mg kg(-1) As; 12 000 mg kg(-1) Pb). Also, some nearby agricultural areas are affected (up to 10 mg kg(-1) Pb in lettuce leaves). Metal transfer into biota has been demonstrated in creek sediments in relation to benthic organisms (up to 222 mg kg(-1) Pb in molluscs). The mining wastes in the area are spontaneously colonized by native plant species. On the tailings, most of the plant species are grasses (e.g. Lygeum spartum, Piptatherum miliaceum); in polluted salt marshes, halophytic species dominate (e.g. Arthrocnemum macrostachyum). Metal uptake by plants is in general low (10 mg kg(-1) for Cu; <200 mg kg(-1) Pb; <500 mg kg(-1) Zn). Preliminary tests have shown the suitability of amendments (e.g. lime, fertilizer, pig manure) to improve the establishment of certain vegetation on the tailings. Phytostabilization appears to be a promising technology to decrease erosion in the tailings. However, tailings must be individually analysed in order to determine their geostructural stability, as in addition, mechanical stabilization will be needed in some cases to prevent collapse.