Residual pollution and vegetation distribution in amended soils 20 years after a pyrite mine tailings spill...

The present work assesses the residual pollution in the Guadiamar Green Corridor (SW, Spain) after a long-term aging process (18 years) since the accident of the Aznalcóllar pyrite mine. We have focused on the study of trace elements (Cu, Zn, Cd, As and Pb) in soils, their fractionation and the transference to the surrounding vegetation. The residual polluted areas are characterized by scattered plots with absence of vegetation, presenting high concentrations of trace elements, acidic pH and low organic carbon content. Surrounding these polluted plots, two vegetation gradient belts are clearly identified by changes in plant cover and richness. The inhibition of plant growth in the bare soils is related to the highest mobility of soluble and exchangeable Cu, Zn and Cd forms, which significantly decrease with the distance to the polluted plots. Plant richness and cover show differences between belts; bioaccumulation of trace elements in plants also differs, with a preferential accumulation in roots. Despite the low bioavailability of As and Pb in soils, bioaccumulation factors in plants for these elements are significantly higher in belt 1 in relation to belt 2. High Cu and Cd potential toxic concentrations in aerial parts of vegetation are found, posing a risk for livestock and a potential entrance to the food-chain. On the other hand, Lamarckia aurea (L.) Moench (in belt1) and Trifolium campestre Schreb. (in belt2) were the most dominant species in severely polluted soils. Elevated concentrations of trace elements in the vegetation growing in the area indicate plant adaptation mechanisms to live in these severely polluted soils, which can be used as a good bioindicator of pollution in similar polluted areas.