Seasonal Variations in Arsenic Distributions and Mobility in a Shallow Pampean Lagoon

CHIODI BOUDET, L.N.; DOLAGARATZ CARRICAVUR, ARANTXA; POLIZZI PAULA; BUZZI, NATALIA; MEDICI, S.; BRAMBILLA, E; FERNANDEZ, E; MARCOVECCHIO, JORGE; GERPE, M.

Congreso; SETAC Latin America 14th biennial meeting; 2021

The presence of arsenic (As) in surface and groundwater is a seriousenvironmental concern because of its high toxicity and globaloccurrence in the environment. The Chaco-Pampean plain, is one of thelargest areas in the world with elevated As levels (geogenic origin), aswell as one of the most important agricultural-livestock regions ofArgentina, constituting a high risk for the human health. The pampeanlagoons are shallow and highly dynamic, where there are wide range ofphysical, chemical, and biological factors that affect the mobilization ofAs in the freshwater–sediment interface. The mobility of As in suchwater bodies can be of concern, particularly in water bodies withprobable use as drinking water, livestock water and/or crop irrigation.The aims of this research were to elucidate: 1) the seasonal variations inthe distribution of total and labile As fractions in the surface sedimentsof Los Padres lagoon located in Buenos Aires province, Argentina 2)their mobility to water column in relation to its availability in sediments,and 3) the possible risk of using this resource of water. Surface sedimentand water samples were taken from the lagoon and associated streamsduring the four seasons of the year (2018-2019). Arsenic weredetermined by atomic absorption spectroscopy. Total As in sedimentsdid not show a clear seasonal pattern, with a range between 3.6-14.8mg/kg and a positive linear relationship (r2=0.79, p< 0.05) with iron (Fe)concentrations was observed. Labile concentrations varied between0.85-7.1 mg/kg, showing the following order of lability: summer(44%)> spring (29%)> winter (26%)> autumn (16%). The closerelationship between As - Fe, under the oxidant conditions and alkalinepH of the lagoon, would suggest As co-precipitation and adsorption onFe oxides as probable route of immobilization in sediments, determiningits low lability. The As levels in water varied between 10.9-24.8 µg/L,with maximum values during summer, in accordance with that reportedfor other shallow lakes. This increase coincided with the maximumlability in sediments (44%), evidencing the release of As into the watercolumn. All water samples exceeded the limit establish in Argentina forhuman consumption (10µg/L) while not those of livestock (67µg/L) andcrop irrigation (100µg/L), but were very close to Canadian limit forlivestock (25µg/L). These results constitute the first report on seasonalvariations of As concentrations in a pampean lagoon.