Banca de DEFESA: IURI APARECIDA DA SILVA OLIVEIRA

POTENTIAL BIOMAGNIFICATION OF METHYLMERCURY IN THE PLANKTONIC COMMUNITY OF ALTO RIO MADEIRA (RO)

Keywords: Contamination; Mercury; Methyl mercury; Aquatic ecosystem.

Mercury (Hg) participates in numerous chemical reactions in aquatic ecosystems, being able to transform from an inorganic chemical form to an organic one and quickly be incorporated into the biota. In this way, the monitoring of aquatic environments, with emphasis on reservoirs in which the natural dynamics of rivers is altered, is necessary, to enable intervention actions in cases of environmental imbalances, which may occur due to the presence of this element in aquatic ecosystems. The objective of the study was to evaluate the dynamics of mercury (HgT) and methylmercury (MeHg) concentrations in the planktonic community, in the tributaries of the upper Madeira River over the years 2009 to 2019. Data from the database provided by the laboratory were used. of Environmental Biogeochemistry WCP/UNIR. The samples were collected in nylon nets of three size fractions, 25µm, 70µm and 160µm, by dragging them on the surface of the water, stored in 2 liter PET bottles, refrigerated and transported to the laboratory, to later be prepared for quantification of mercury levels. The Biota-Sediment Accumulation Factors (BSAF) varied according to seasonality and were higher in the Jatuarana II creek in the three analyzed sizes (25µm, 70µm and 160µm). The Jatuarana II stream showed the highest average concentrations over time. The average concentrations of MeHg in general were lower in the Jaci Paraná River and higher in the Jatuarana II creek, zooplankton (160µm) stood out with the highest average concentrations in all seasonal periods and over time the average concentrations increased after creation of the reservoir (2011). In general, the average concentrations of HgT, seasonally and over time, did not show large variations between the studied affluents, seasonality affected the average concentrations of each affluent differently. The highest mean MeHg percentages were found in zooplankton (160µm). The results obtained in this work are similar to the results of other studies carried out in the Amazon region and in the Madeira River basin, and demonstrate that MeHg biomagnification occurs in the studied planktonic community. The higher concentrations of MeHg downstream of the hydroelectric reservoir may be an indication that the export of methylmercury produced in the reservoir is taking place. Seasonality, atypical flood and dry periods and the year 2012 (post-dam) influenced the availability and incorporation of HgT and MeHg in the planktonic community.