Seasonal dynamics of trace elements in water and sediments (suspension and bottom) in the Madeira River Basin, Western Amazon

Trace elements are ubiquitous global pollutants in modern society and are present in water and biota associated with natural and anthropogenic sources. In this context, this study reports the dynamics of trace elements in the Upper Madeira River Basin, a region that has undergone major environmental changes in the past decades, such as deforestation, mining, and the installation of two large hydroelectric power plants. Bottom sediment, water, and suspended particulate matter (SPM) were collected to determine water quality parameters and trace elements concentrations, quantified by ICP-OES. The average electrical conductivity of water was higher in the Madeira River (110.6 +/- 44.4 mu S cm-1) than in its tributaries (59.0 +/- 49.1 mu S cm-1). The Madeira River water has a pH close to neutral (7.0 +/- 0.8), compared to the slightly acidic water of the tributaries (6.3 +/- 0.9). The average dissolved oxygen in the Madeira River water samples was 6.9 mg L-1, significantly higher than in the tributaries (3.9 mg L-1). The sediment from the Madeira River has higher concentrations of As, Cu, Mn, Ni, Sr, and Zn than the tributaries but lower concentrations of Ba, Mn, Pb, Sr, V, and Zn in the SPM. Trace elements concentrations in the SPM remained relatively constant during the study period and were controlled by seasonality. The average concentrations of trace elements in water, suspended solids, and bottom sediments of the Madeira River Basin were comparable to other non-impacted aquatic ecosystems and can be considered regional environmental background values. In addition, concentrations were below the limits established by the World Health Organization and Brazilian regulations, for human consumption and conservation of aquatic life except, for occasional peaks of Ni and Pb concentrations.