Nanoparticles containing hazardous elements and the spatial optics of the Sentinel-3B OLCI satellite in Amazonian rivers: a potential tool to understand environmental impacts

The Amazon River is the longest river in the world. The Tapajós River is a tributary to the Amazon. At their junction, a marked decrease in water quality is evident from negative impacts from the constant activity of clandestine gold mining in the Tapajós River watershed. The accumulation of hazardous elements (HEs), capable of compromising environmental quality across large regions is evident in the waters of the Tapajós. Sentinel-3B OLCI (Ocean Land Color Instrument) Level-2 satellite imagery with Water Full Resolution (WFR) of 300 m was utilized to detect the highest potential for the absorption coefficient of detritus and gelbstoff in 443 m −1 (ADG443_NN), chlorophyll-a (CHL_NN) and total suspended matter concentration (TSM_NN), at 25 points in the Amazon and Tapajós rivers (in 2019 and 2021). Physical samples of riverbed sediment collected in the field at the same locations were analyzed for NPs and ultra-fine particles to verify the geospatial findings. The riverbed sediment samples collected in the field were studied by Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), with selected area electron diffraction (SAED), following laboratory analytical procedures. The Sentinel-3B OLCI images, based on the Neural Network (NN) were calibrated by the European Space Agency (ESA), with a standard average normalization of 0.83 µg/mg, containing a maximum error of 6.62% applied to the sampled points. The analysis of the riverbed sediment samples revealed the presence of the following hazardous elements: As, Hg, La, Ce, Th, Pb, Pd, among several others. The Amazon River has significant potential to transport ADG443_NN (55.475 m −1 ) and TSM_NN (70.787 gm −3 ) in sediments, with the possibility of negatively impacting marine biodiversity, in addition to being harmful to human health over very large regions.