This study is focused on one of the most important spills that ever happened in Europe, the Aznalcóllar’s mine spill. The extensive application of phytostabilization in the area led to the implementation of the Guadiamar Green Corridor (GGC). Soil physicochemical properties were analyzed and the total concentration of Pb, As, Zn and Cu was measured by X-ray fluorescence (XRF); bioassay using Lactuca sativa L. was applied to assess potential toxicity. Two decades after the accident, some soils affected by residual contamination continue to appear in the area. According to regulatory levels, Pb and As concentrations are exceeded in around 13%and 70%, respectively, in the uppermost part of the soils (first 10 cm). The change in soil properties after bioremediation treatment positively promoted the reduction in the potential mobility of pollutants by the increase in pH, CaCO3 content and organic carbon. Anyway, the bioassay with Lactuca sativa, indicated that around 25% of the soils showed toxicity by the reduction of the root elongation in relation to the control samples. Our results indicate that monitoring of the GGC is still needed, together with the application of soil recovery measures to reduce the potential toxicity in some sectors of the affected area.
This study evaluated the effectiveness of remediation treatments in the long-term (20 years) for one of the largest mine spills in the world, the Aznalcóllar accident. Soil recovery was carried out through the application of various rates of organic (compost and manure) and inorganic amendments (materials rich in iron oxides and calcium carbonate). Different amendment combinations were grouped in four treatments (T1 to T4) and applied in different sectors depending on the soil properties and the degree of initial contamination. To assess the degree of soil recovery, physicochemical properties, total, water-soluble, and bioavailable concentrations of the main contaminants (Pb, As, Zn, and Cu) were determined over time. Applied treatments increased pH, calcium carbonate, and organic carbon content of soils, reduced electrical conductivity, and decreased mobility of contaminants, indicating that remediation treatments were efficient recovering soils contaminated by potentially harmful elements (PHEs).However, 20 years after the accident, total concentrations of Pb and As still exceed the intervention levels of the current regulations in certain areas. These areas are located in the sectors closest to the mine and where treatments T1 and T2 were applied. In these cases, the added doses of organic amendments, iron oxide-rich soils, and carbonate amendments were not sufficiently effective, so the application of new treatments is recommended to complete the total recovery of the Guadiamar Green Corridor.
<p>The present study evaluates the potential toxicity of the soils of the Guadiamar Green Corridor (GGC) (Seville, SW Spain) affected by the Aznalc&#243;llar mine spill, one of the most important mining accidents in Europe in recent decades. Twenty years after the accident, soils affected by residual contamination are still present in the area, for which their potential toxicity was assessed by carrying out bioassays with lettuce (<em>Latuca sativa</em> L.), earthworms (<em>Eisenia andrei</em>) and determining the microbial activity by measuring the basal respiration and the microbial metabolic quotient (qCO2) of these soils at surface level (0-10 cm). A total of 84 soil samples were taken along the GGC, which were divided into four types (SS1-SS4) according to their physicochemical properties. Soils SS1 and SS2 showed a higher environmental toxicity risk, with a reduction in root elongation of lettuce seeds of 57% and 34% compared to the control, as well as a higher metabolic quotient (23.9 and 18.1 ng Cc<sub>O2</sub> &#181;g C<sub>microb</sub><sup>-1 </sup>h<sup>-1</sup>), significantly higher than those measured in SS3 and SS4.</p><p>The potential risk to humans of these soils through ingestion, inhalation, and skin exposure routes for the main potentially toxic elements (PTEs) present in the GGC (Pb, and As) was also evaluated based on EPA empirical models, in which the total exposure through each of the three routes was considered. The results obtained indicate that there is no potential risk for human health throughout the GGC considering the exposure for both adults and children, although there are areas of the corridor where the Guideline values for both Pb and As are exceeded. This, together with the potential toxicity of the soils to the ecosystem shown by the bioassays, indicate the need to monitor over time the human and environmental risks in the area to guarantee the safety and enjoyment of this natural area.</p>
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