Recent and historical pollution legacy in high altitude Lake Marboré (Central Pyrenees): A record of mining and smelting since pre-Roman times in the Iberian Peninsula.

We have analyzed potential harmful trace elements (PHTE; Pb, Hg, Zn, As and Cu) on sediment cores retrieved from lake Marboré (LM) (2612 m a.s.l, 42°41'N; 0° 2'E). PHTE variability allowed us to reconstruct the timing and magnitude of trace metal pollutants fluxes over the last 3000 years in the Central Pyrenees. A statistical treatment of the dataset (PCA) enabled us to discern the depositional processes of PHTE, that reach the lake via direct atmospheric deposition. Indeed, the location of LM above the atmospheric boundary layer makes this lake an exceptional site to record the long-range transport of atmospheric pollutants in the free troposphere. Air masses back-trajectories analyses enabled us to understand the transport pathways of atmospheric pollutants while lead isotopic analyses contributed to evaluate the source areas of metal pollution in SW Europe during the Late Holocene. PHTE variability, shows a clear agreement with the main exploitation phases of metal resources in Southern Europe during the Pre-Industrial Period. We observed an abrupt lead enrichment from 20 to 375 yrs CE mostly associated to silver and lead mining and smelting practices in Southern Iberia during the Roman Empire. This geochemical data suggests that regional atmospheric metal pollution during the Roman times rivalled the Industrial Period. PHTE also increased during the High and Late Middle Ages (10-15th centuries) associated to a reactivation of mining and metallurgy activities in high altitude Pyrenean mining sites during climate amelioration phases. Atmospheric mercury deposition in the Lake Marboré record mostly reflects global emissions, particularly from Almadén mines (central Spain) and slightly fluctuates during the last three millennia with a significant increase during the last five centuries. Our findings reveal a strong mining-related pollution legacy in alpine lakes and watersheds that needs to be considered in management plans for mountain ecosystems as global warming and human pressure effects may contribute to their future degradation.

Modeling of geochemical processes related to uranium mobilization in the groundwater of a uranium mine.

This paper describes the processes leading to uranium distribution in the groundwater of five boreholes near a restored uranium mine (dug in granite), and the environmental impact of restoration work in the discharge area. The groundwater uranium content varied from <1 microg/L in reduced water far from the area of influence of the uranium ore-containing dyke, to 104 microg/L in a borehole hydraulically connected to the mine. These values, however, fail to reflect a chemical equilibrium between the water and the pure mineral phases. A model for the mobilization of uranium in this groundwater is therefore proposed. This involves the percolation of oxidized waters through the fractured granite, leading to the oxidation of pyrite and arsenopyrite and the precipitation of iron oxyhydroxides. This in turn leads to the dissolution of the primary pitchblende and, subsequently, the release of U(VI) species to the groundwater. These U(VI) species are retained by iron hydroxides. Secondary uranium species are eventually formed as reducing conditions are re-established due to water-rock interactions.

The impact of the Aznalcóllar mine tailing spill on groundwater.

As a consequence of a mine tailing dam collapse on the 25th April 1998, more than 4000 ha of the Guadiamar riverflat and farmlands were flooded by 4 hm3 of sulphide slurry. A number of open wells (12 of the 47 analyzed) were also flooded and the water was contaminated. Before the spill, the groundwater in the aquifers was of calcium-carbonate and calcium-sulphate type, with moderate mineralisation and near neutral pH. With the exception of some of the wells close to the mine, this groundwater had a low concentration of the metals associated with the Aznalcóllar mine. After the flood the following metals had anomalous concentrations in well water: Zn, Mn, Pb, Co, Cd and Tl. Of these, Zn seems to be the best tracer of the contamination, owing to its high concentrations. During the 5 months following the spill, water from the unflooded wells did not show an increase in metal concentration. Apart from some exceptions in August, the metal concentration in the affected wells showed a progressive decrease reaching levels closer to those in the wells free from contamination. Nevertheless, in the following dry seasons the draw-down of the water level may lead to exposure and weathering of sulphides in the wells, which could cause an increase in pollution. Therefore, thorough cleaning of all highly contaminated wells is strongly recommended.