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Faculty for Biology, Chemistry, and Earth Sciences

Environmental Geochemistry Group - Prof. Dr. Britta Planer-Friedrich

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Master Thesis

Characterization of metal(loid)s stored in the salt marshes of Rio Tinto and Rio Odiel, Spain

Nathalia Paola Ceron Espejo (07/2019-12/2020)

Support: Britta Planer-Friedrich, Andrea Colina Blanco

Extensive mining of the Iberian Pyritic Belt has contaminated the salt marshes of the Río Tinto and Río Odiel. In order to assess the pollution levels in the sediments of these rivers´ estuaries, seven 25 to 40 cm long cores were characterized at a spatial resolution of 1 to 7 cms for total contents of various metal(loid)s, their association with different soil fractions as determined by sequential extraction, organic carbon percentage, color, grain size estimates, and pH. The soils exceeded from 13 up to 58 times the Andalusian soil contamination thresholds for As, Cu, Pb, and Zn. Additionally, from 0 to 37% of soil-bound Zn, Cu, and Pb was detected in the mobile and easily mobilizable fractions. The main parameters driving this mobilization were higher pH values than 4.7, closer proximity to the ocean, and high contents of Fe and C%. Moreover, the spatial distribution of the contaminants was linked to finer grain size soils. pH values lower than 4.0 and the presence of Fe and S were indicators of high contents of As, Sb, and Pb. These soils were predominantly yellow (schwertmannite) and brown (goethite and ferrihydrite). On the other hand, higher pH values enhanced Mn, Al, Co, Ni, Cu, Zn, and La accumulation. Nickel, Co, La, Zn, Cr, and V were mostly related to Mn and Al crystalline or amorphous oxides or clay minerals in grayish layers (Mn-Goethite and birnessite), preferentially in the base of the cores. However, no systematic trend was found in the depth distribution of the contaminants in the studied cores. Overall, these findings show that the rivers´ contaminant load reaches the salt marshes and represents a risk for the environment in the area, also suggest muddy to clayey structures, presence of Fe, Mn and Al, pH, and color of the sediments as indicators for the metal(loids) accumulation.

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