Potencialidades do Pinus pinaster e Cytisus multiflorus na fitoestabilização de escombreiras na mina de ouro de Santo António (Penedono) Potencialities of Pinus pinaster and Cytisus multiflorus on the phytostabilization of the Santo António (Penedono) gold mine dumps

Abstract

A mina de Santo António, localizada a cerca de 10 km ao norte de Penedono (Viseu), foi um importante centro mineiro, tendo-se aí principalmente explorado o ouro e outros elementos químicos, como o arsénio. Actualmente, todo o complexo mineiro está abandonado e bastante degradado. As escombreiras, cortadas por dois barrancos de grande dimensão, estão sujeitas a intensa erosão eólica e hídrica. Estas apresentam teores totais elevados para vários elementos, dos quais se destacam As, Pb, Cd e Au que atingem, respectivamente, 40 000, 653, 14 e 9,8 mg kg-1 . Estudou-se na área mineira, e em particular na envolvente das escombreiras, os solos e as plantas aí desenvolvidas (Pinus pinaster, Quercus pyrenaica, Castanea sativa, Cytisus multiflorus e uma gramínea do género Agrostis). As águas de drenagem da escombreira não vegetalizada apresentavam valores de pH de 2,58 e teores de As e Cd respectivamente de 160 e 0,05 mg/L. As águas recolhidas a jusante de escombreiras vegetalizadas com pinheiros e giestas, mostraram um decréscimo drástico de todos os elementos, em especial do As que ocorria com valores ambientalmente aceitáveis (The Santo António mine is located 10 km north of Penedono (Viseu, Portugal). This mine was in the first half of the twenty’s century an important gold and arsenic mining centre. Nowadays the mining complex is abandoned and presents high level of physical degradation. The waste dumps crossed by two large gullies are under strong water and wind erosion. The total concentrations of As, Pb, Cd e Au, in the dump material reached values as high as 40 000, 653, 14 and 9,8 mg kg-1, respectively. Soils and native plants as Pinus pinaster, Quercus pyrenaica, Castanea sativa, Cytisus multiflorus and gramineous plants (gen. Agrostis) from the mining area and the waste dumps surroundings were collect and analysed. The draining waters from a no vegetated dump presented a pH value of 2.58, and As and Cd concentrations of 160 and 0.05 mg/L, respectively. On the other hand, the draining waters from vegetated dumps with P. pinaster and C. multiflorus showed much lower levels for the concentrations of all analysed elements, particularly As that presented environmentally acceptable concentrations (<0,1 mg/L). Soil pH is between 2.9 and 5.3. Arsenic total and available concentrations in the soils surrounding the waste dumps were as high as 23900 and 220 mg kg-1, respectively. Aluminium and Cu concentrations in the available fractions were, respectively, 32.9 e 55.4 mg kg-1. However, Pb concentrations were quite low in the available fractions when compared with the total concentrations in the soils. Plants growing on the dump adjacent soils are metal tolerant without any visible symptoms of toxicity. P. pinaster, C. multiflorus and Agrostis gramineous plants showed higher levels for As, Al, and Pb in the aerial part when compared with other species. Nevertheless, these species show a good vegetative development and soil coverage, which minimises the wind and water erosion. For this reason, the phytostabilization of Santo António waste dumps can be undertaken by native plants as P. pinaster trees, C. multiflorus shrubs and gramineous plants (Agrostis), which absorb and translocate to the aerial part high levels of As, thus decreasing the amounts lixiviated.