Longitudinal Gradient and Historical Trends of Arsenic and Metals in a Tropical Reservoir

This study aimed to establish the longitudinal gradient and historical trends of arsenic and metals in a tropical reservoir. Water and sediment samples were collected along the Rio Bonito reservoir (Espírito Santo, Brazil), and a sediment core was obtained from the lacustrine zone. Plasma spectrometric techniques were employed to determine concentrations of As, Cd, Co, Cu, Fe, Mn, Ni, and Pb in water and sediment samples, and the sediment samples were dated using high-resolution gamma spectrometry. Higher concentrations of elements were observed in surface water samples from the riverine zone and bottom water samples from the transition zone. Concerning surface sediment samples, elevated concentrations were noted in the transition and lacustrine zones, where deposition is more intense. The sediment core was dated to 1940, before the reservoir dam construction, utilizing 210Pb dating. Certain elements exhibited progressively increasing concentrations over time. Enrichment factor, pollution load, and ecological risk indexes indicated the need for continuous monitoring of this reservoir