TEMPORETTI pedro Felix
Trace metal partitioning and potential mobility in the naturally acidic sediment of Lake Caviahue, Neuquén, Argentina
CABRERA, J.M.; TEMPORETTI, P; PEDROZO, F
SERVICIO NACIONAL GEOLOGIA MINERVA
Lugar: Santiago de Chile; Año: 2020 vol. 47 p. 46 - 60
>Lake Caviahue, in Patagonia (Argentina), is a very acid water body (Patagonia, Argentina) due to theinflux of volcanic fluids. Over the past 18 years, the lake has been progressively alkalinizing and pH is close to the ferriciron precipitation threshold (pH>3,0). Should iron precipitate, water and sediment composition will be altered. To set abaseline, trace metal partitioning (Cu, Cd, Cr, Pb, Zn and Mn) was studied for three sediment cores (0 to 16 cm depth) atthree sampling stations using a sequential extraction procedure (SEP) and the acid volatile sulfide/simultaneously extractedmetals (AVS/SEM) protocol. The total metals content of the sediments ranged between 0 to 408 µg g-1 of dry sediment,with Pb>Cr>Mn>Cu>Zn>Cd. No Cd was measured above the limit of detection. The sediment was richest in Mn andCr, two non-toxic metals at the pH / Eh combination of the lake basin. Total Pb was at a moderate contamination levelalthough it is associated with the most recalcitrant fraction and therefore has low mobility. The sediment fractions withhigher metal content were the oxidizable and residual, the former commonly associated with labile organic matter andpyrite while the latter are related to recalcitrant organic matter and rock forming minerals. In addition, a high correlationwas found between Cr, Pb and Mn, thus these metals may be subject to analogous precipitation processes and possibly toco-variation in the volcano effluents. Furthermore, no metals were detected in the exchangeable/carbonates fraction, whichis the most labile of all the sediment fractions. The metal content in (SEM) was likewise below the toxicity thresholdsof two international sediment quality guidelines and the ratio AVS/SEM was over one, indicative of non-toxicity. Bothresults indicate that metal mobility in the acidic sediments of lake Caviahue is very low.