Distribution and seasonality of potentially toxic elements (PTEs) in the waters of the Negro river in Manaus, Amazonas, Brazil

Population growth and urbanization have led to critical environmental challenges worldwide. Chemical pollutants, especially Potentially Toxic Elements (PTEs) such as Cd (Cadmium), Cu (Copper), Zn (Zinc), Al (Aluminum) and Mn (Manganese), as well as macroelements like P (Phosphorus), affect physicochemical and ecological parameters, posing risks to both human health and biodiversity. This study evaluates the influence of seasonality on the concentration of these PTEs in the waters of the Negro River, Manaus, Amazonas. Sampling was conducted at 60 sites along the river in January 2023, September 2023, and March 2024. Sampling, storage, and analyses followed the procedures established in the Standard Methods for the Examination of Water and Wastewater. Results revealed elevated mean Al and P concentrations (above 1250 µg/L and 250 µg/L, respectively), suggesting significant inputs of organic matter and surface urban pollution. Principal Component Analysis (PCA) revealed distinct patterns in January, higher levels of Na, Mg, Ca, Al, P, Ti, Be, and Cu; in September, predominance of K, Rb, and Ba; and in March, Li and Fe. Contamination by PTEs is multifactorial: although seasonality is a key driver, other factors, such as urbanization, proximity to agricultural areas, and industrial discharges, strongly modulate water quality.