MERCURY CONCENTRATIONS IN SEDIMENTS OF THE SUQUIA RIVER BASIN, CORDOBA, ARGENTINA

From its headwaters in the Sierras Grandes range until its outfall in Laguna del Plata Lake, the chemical composition of the Suquía River suffers alterations due to urban and industrial wastewaters and agricultural discharges that diminish the water quality along its path (1, 2).

Exchanges at the air-water interface and atmospheric transport are important features in the global mercury cycle (3), in which sediments can represent efficient Hg traps and archives of past contamination (4) and act as secondary sources, releasing Hg again into solution under suitable environmental conditions (5). The aim of this work is to identify human impact traces in the Suquía River basin in the last century. For this we analyzed Hg concentrations in present riverbed sediments and Laguna del Plata and Mar Chiquita Lakes bottom sediments, as well as in a sediment core from Laguna del Plata, where Suquía River mouths. Total particulate mercury (HgTp) was determined by cold vapour atomic absorption spectrometry and the measures threw values between 2-131µg/kg. Concentrations in riverbed sediments were in the lower range of observed levels (~17-72µg/kg), with higher values in the headwaters before entering into the San Roque dam and next to the city of Córdoba. In Laguna del Plata Lake Hg concentrations are higher (~38µg/kg) compared to Mar Chiquita Lake (~20µg/kg) that does not receive direct inputs from the Suquía River basin, suggesting riverborne Hg transport to the lake. The data obtained from the core sediments show fluctuations between 40-60µg/kg Hg in the first 25 cm, followed by a 131µg/kg HgTp peak at 35 cm. In the lower part of the core, i.e. between 75 to 120 centimetres, HgTp concentrations become almost constant around 50µg/kg.The pH of the river and the lake range from 7.62 to 8.90 and from 8.27 to 9.25, respectively. According to the first results in the core dating using ²¹⁰Pb and ¹³⁷Cs, the highest HgTp concentrations were related to river inputs after the end of the major drought period of the Laguna del Plata lake that took place in the early 1970s.

(1) Pesce SF, DA Wunderlin, 2000. Wat. Res.34, 2915±2926.

(2) Wunderlin DA et al.2000. Wat. Res. 35, 2881–2894.

(3) Fitzgerald W et al., 1991. Water, Air, Soil Pollut. 56, 745–767.

(4) Castelle S et al., 2007.Appl. Geochem. 22, 1359-1370.

(5) Schäfer J, et al. 2010. Est. Coast. Shelf Sci., 90, 80-90.