Abstract
Dredging and disturbance of sediments in rivers with redox-sensitive conditions, such as the Araguaia River, can pose environmental and health risks, especially in areas with high concentrations of toxic metals like iron and mercury. These metals accumulate in sediments under reducing conditions, and their disturbance can lead to their release into the water column, affecting the food web and human health. The Araguaia River floodplain is composed of alluvial deposits and igneous and metamorphic rocks rich in chromium, nickel, iron, magnesium, and mercury. Land use change, particularly for agriculture, accelerates weathering and the transport of these elements into the river. Sediment dredging disrupts the chemical stability of metals such as iron and mercury, increasing their bioavailability. Mercury, in particular, can be converted into methylmercury, a highly toxic and bioaccumulative form that enters the aquatic food web, impacting fish, wildlife, and humans. Methylmercury biomagnifies through the food chain, posing risks to top predators, including piscivorous birds and humans. Studies show that fish consumption by riverine communities can lead to significant mercury exposure, increasing the risks of neurological damage, cardiovascular disease, and developmental problems in children. Furthermore, dredging can worsen water quality by increasing turbidity and mobilizing other toxic elements such as arsenic and cadmium. The environmental impacts of dredging go beyond immediate contamination, affecting biodiversity, ecosystem resilience, and fisheries, which are vital to local livelihoods. Socioeconomic consequences include food insecurity, income loss for fishers, and increased water treatment costs.