Influence of hydrological conditions on the availability of arsenic in alkaline lakes of the Pantanal of Nhecolândia

• Grant number: 19/14884-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2019
• End date: September 30, 2019
• Field of knowledge: Interdisciplinary Subjects
• Principal Investigator: Anne Helene Fostier
• Grantee: Júlia Pepino Leister
• Host Institution: Instituto de Química (IQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Associated research grant: 16/14227-5 - Climatic changes and environmental impacts in wetlands of Pantanal region (Brazil): quantification, control factors and long term temporal modeling, AP.PFPMCG.TEM

Abstract

High concentrations of Arsenic (As) were found in the waters of the alkaline lakes of the São Roque farm (Pantanal of Nhecolandia) collected during the dry season in October 2017 and September 2018. However, the concentrations of this element in the samples collected in 2017 were 9 to 49 higher than in the samples collected in 2018. These differences were attributed to the variation of the level of the water in the lakes and consequent effect of concentration or dilution of the solutions due to the exceptionally low level of water in 2017 and exceptionally high level in 2018. In both collection campaigns, sediment, phyto and zooplankton samples were also collected. The low concentrations of As in the sediment samples collected in 2017 showed that there was no significant transfer of As from the water column to the sediment, probably due to 1) the high pH that does not favor the adsorption of As (V) on the suspended particles, 2) adsorption competition with other anions (eg HCO3- and F-) by the active sites in the sediment, 3) possibly the presence of dissolved organic matter that can complexe As ions. Relatively low rates of phytoplankton and zooplankton bioaccumulation were observed, which may be related to the low bioavailability of As, at least under conditions found in 2017. Our hypothesis is that the large differences in hydrochemical conditions encountered between the two dry seasons 2017 and 2018 could influence the availability of As and significantly alter both concentrations of As in sediments and factors of bioaccumulation in phytoplankton and zooplankton. This project aims to verify this hypothesis from the determination of the concentration of As in sediment, phyto and zooplankton samples collected in September 2018. On the other hand, during a methane emission study (CH4) carried out by the team in 2018 and that happened soon after a strong rain event, "pulses" of black waters from the surface soil were observed. It was suspected that the black color could be linked to the presence of dissolved organic matter. Soil water samples were therefore collected in the proximity of the gas collection chambers in order to verify the dissolved organic carbon content (COD) and the possible COD / CH4 and COD / As ratio in these samples, which still need to be analyzed.This project of Scientific Initiation therefore aims to evaluate the influence of the water level on the concentrations of As in different compartments (sediment, phyto and zooplankton), as well as on the factors of bioaccumulation. It also aims to evaluate the possible relationships between COD / CH4 and COD / As.