Toxic nanoparticles in Amazon River sediments: Microscopy and satellite-based assessment

Hazardous chemical elements in aquatic ecosystems pose a major threat to habitats and the environment. This study is based on two parallel analyses at different scales and innovates methodologically within this approach, with continental-scale analysis using satellite imagery. At the macroscale, it aims to spectrally detect chlorophyll-a (CHL), water turbidity (TSM), and potential for suspended pollution (ADG443), through 472 satellite sampling points distributed in the Solimões River, Amazon River, and the estuarine region, during the dry (February) and rainy (August) seasons between 2019 and 2024. At the microscale, it seeks to quantify the main chemical elements present in nanoparticles and ultrafine particles incorporated into sediments collected in the Amazon River. Sediment sampling was conducted at 18 sites, nine upstream and nine downstream of the city of Manaus, Brazil, during the dry season (February) and the wet season (August) of 2024. Sediment analyses were conducted using focused ion beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (HR-TEM), both of which were coupled with energy-dispersive X-ray spectroscopy (EDS). The results revealed the presence of toxic elements such as chromium (Cr) and vanadium (V) in nanoparticles smaller than 15 nm. The findings demonstrate that the convergence of high sediment contamination and increasing trophic instability pose a systemic risk to the world's largest freshwater system, necessitating urgent global environmental monitoring and the implementation of advanced conservation frameworks to safeguard both biodiversity and local riverside population.