(2020) Trace metal Legacy in Mountain Environments: a view from the Pyrenees mountains

The mineral reserves of mountain environments have been exploited since the beginning of metallurgy and legacy contamination from activities such as mining persist to this day. This is particularly the case in the soils of the European mountains where potential harmful trace elements (such as Pb, Sb, As, and Hg) of anthropogenic origin have accumulated since Antiquity. The French Pyrenees are no exception to this, as many mine sites in the region date back to the Bronze Age, resulting in landscape alternations and anthropogenic environmental impacts on a millennial scale. The mountain critical zone is sensitive both to human-induced environmental changes (e.g., agriculture, mining, clear-cutting) as well as to climate-induced rapid environmental fluctuations. The legacy of trace metal contamination in other environments has been documented at individual sites in Europe and around the world, however, the fate of such legacy metals over time, in particular within mountainous regions, is poorly understood. This is despite the fact that a large proportion of metals was deposited and stored before 1800 CE in these areas. Using a case study from the Central French Pyrenees as a specific example, we here show that legacy metal (e.g., Pb) contamination in mountain environments is still persistent and a potential threat to mountain ecosystem health. We emphasize methods that aim to understand, in an interdisciplinary and coordinated way, the fate of legacy metals in the Central Pyrenees and beyond. We highlight the importance of research in the mountain critical zone for the whole of Europe, as mountains are the source of water and provide regional economic and socio-ecological resources. The goal of this chapter is, therefore, to draw attention to and provide fellow researchers with, the background information and methodologies needed to address the problem of legacy metal accumulation, transport, storage, remobilization, and redeposition in mountain watersheds, as well as potential subsequent environmental impacts downstream.