The Amazon is the largest river basin globally and contains about 40% of the world’s remaining tropical rainforest, hosting a vast diversity of terrestrial and aquatic organisms. It is estimated that about 30 million people live in the Amazon nowadays, most of whom live in Brazil. About two thirds of the people in the Brazilian Amazon live in large cities such as Manaus or Belém, which account for about 2 million inhabitants each. The socioeconomic development model of the region supports the continued migration to such urban areas, so it is expected that their population doubles within the next decades. The borders of Amazonian cities form dynamic frontiers between modern societies and nature, which may be responsible for significant direct and indirect impacts on ecosystems and indigenous people. Such impacts include habitat loss, but also freshwater contamination. Freshwater contamination is of critical importance because more than 90% of households are not served by any sewage collection or treatment facilities, and discharge tons of solid and liquid waste directly into the Amazon River network.
The SILENT AMAZON project (led by Dr Andreu Rico and financed by the National Geographic Society, in partnership with several research centers from Europe and Latin America), was initiated to understand the impact that organic and inorganic wastes consumed by modern societies could have on Amazonian freshwater ecosystems. Through this project we are investigating the emission and exposure to pharmaceuticals, pesticides, metals, microplastics and persistent organic pollutants in the Amazon River and its main tributaries, as well as in the streams crossing the main urban areas of the Brazilian Amazon. We aim to provide the first large-scale dataset of contaminants in the Amazon and to quantify their risks for freshwater organisms. Ultimately, we would like to create awareness about the impact that chemical pollution has on Amazonian ecosystems and on the people that depend on them, and support the creation of sustainable development plans for the region.
The first results of our investigations show that Amazonian waters contain complex mixtures of pharmaceuticals and other substances consumed by modern societies (e.g. licit and illicit drugs, personal care products). A screening analysis shows that the streams crossing the urban areas of Manaus, Santarém, Belém and Macapá contain residues of up to 30-40 substances, primarily analgesics, antihypertensives, stimulants (such as caffeine or nicotine) and antibiotics. In such areas, chemical contamination may result in long-term risks for 50-80% of freshwater species. The potential decrease of freshwater invertebrates and fish next to urban areas of the Brazilian Amazon can be intrinsically related to a loss of food for reptiles, birds and humans (by reducing fish captures), and may also have detrimental effects for basic ecological functions. The environmental impacts caused by these chemicals should be added to those created by other contaminant groups, such as pesticides used in urban and peri-urban agriculture, metals or plastics. Follow-up studies will be dedicated to quantifying the emission of these contaminant groups and their risks for freshwater biodiversity.