Pharmaceutical water pollution detected deep in the Brazilian Amazon

  • Major rivers in the Amazon Basin of Brazil are contaminated with a wide range of pharmaceuticals as well as with sewage and wastewater, largely coming from urban centers in the region, according to recent research.
  • Water samples taken along the Amazon, Negro, Tapajós and Tocantins rivers, and small urban tributaries that pass through the region’s cities, including Manaus, Santarém, Belém and Macapá contained 40 pharmaceuticals out of 43 in concentrations that have the potential to affect 50-80 % of the local aquatic species.
  • Experts explain that a major cause of freshwater contamination is the Amazon Basin’s rapidly growing population along with the government’s failure to provide adequate sanitation infrastructure — even though that has long been promised. Most of the region’s sewage is untreated, a solvable problem if properly funded.

Many of us imagine the Brazilian Amazon to be pristine. But evidence of humanity’s modern lifestyle flows downstream through the rainforest every day from the region’s major population centers.

According to findings published last year, urban streams and tributaries feeding into the Amazon River are highly contaminated with pharmaceuticals, including analgesics, psychostimulants and anti-diabetics, as well as with antibiotics and anti-inflammatories, in concentrations up to a hundred times larger than in the mainstem rivers into which they flow.

Those results come from the Silent Amazon Project, whose researchers’ long-term goal is to create a complete dataset documenting the chemical pollution status of the Amazon River.

“Our goal was to quantify current occurrence, exposure and risks of a group of contaminants, which is usually understudied in tropical regions. What we see is that the demographic pressures and the lack of sanitation and wastewater treatment allows them to reach areas of high ecological value,” Andreu Rico told Mongabay. He is an ecotoxicologist at the IMDEA Water Institute and the study’s chief researcher.

The study team collected water samples at 40 points along 1,500 kilometers (932 miles) of the Amazon, Negro, Tapajós and Tocantins rivers, and in small tributaries that pass through the cities of Manaus in Amazonas state; Santarém and Belém both in Pará; and Macapá in Amapá state, to assess the presence of 43 pharmaceuticals and other urban contaminants.

Sample collection sites in the Amazon (A), Negro (N), Tapajós (TA) and Tocantins (TO) rivers, and in small urban tributaries in the Brazilian Amazon. The region’s sharp urban population growth and lack of sanitation infrastructure explain the findings of the Silent Amazon pharmaceutical pollution study. Image courtesy of Silent Amazon.

Of this total, 40 were found in the study area waters to be above the limit of detection (the lowest concentration of a pollutant that can be revealed via a given analytical method). In addition to the already mentioned drugs, anti-arrhythmics, anti -hypertensives, antidepressants, anti-epileptics, anxiolytics, hormones (synthetic and natural) and fragrances, among other contaminants, were identified in the waterways.

“The number of substances was notably higher in the tributaries crossing urban areas (23–40 per sample) than in the Amazon River and its major tributaries (9–17),” says the study. “The concentrations in [the first group] were, on average, about two orders of magnitude higher than those measured in the [second one].”

Another study, published in 2022 and carried out internationally along 258 rivers in 104 countries, classified the Amazon River “downstream from Manaus city” as a “site with low active pharmaceutical ingredient (API) concentrations, due to “high riverine flows with a large dilutional component.” Sampling for the 2022 study was done exclusively on the Amazon mainstem, so concentrations were lower than in the Silent Amazon study.

Exposure concentrations in the urban discharge areas of the Amazon River are about two orders of magnitude lower than those measured in urban streams, and decrease farther downstream. Despite the Amazon River’s high dilution potential, the study identified contaminants that are ubiquitous in several parts of the river, such as caffeine, nicotine, and acetaminophen. Image courtesy of Silent Amazon.

Amazon waters increasingly polluted

Among the contaminants found by the Silent Amazon team is metformin, the most commonly prescribed medication used to treat type 2 diabetes, and measured by the 2021 study for the first time in surface waters of Latin America. “The concentrations in the streams of Manaus and Belém constitute the maximum values ​​reported in the literature so far (Fekadu et al., 2019).”

According to the Silent Amazon investigation, the biggest threats to aquatic organisms in the analyzed waters may be acetaminophen (an anti-inflammatory that can cause genetic alterations and impair the reproduction of aquatic invertebrates and fish), estrone (a steroid reported to contribute to the feminization of fish), ibuprofen (which has negative impacts on fish reproduction), and 17β-estradiol (a natural estrogen hormone with a high potential toxicity).

“In view of the results, we can conclude that pharmaceuticals are widespread contaminants in the Amazon basin and that urban areas contain concentrations that can result in long-term effects in a large number of aquatic species (50-80%),” said the chief researcher.

Rico notes that other pollutants are affecting the Amazon Basin’s aquatic biodiversity. “The discharge of organic matter [from sewage] and heavy metals are important drivers of ecosystem deterioration, as well as pesticides, microplastics and PAHs,” a chemical compound whose main source is the smoke and soot produced when solid fuels, such as wood, are burnt.

The rapid growth of the Amazon urban population and the lack of basic sanitation explains a good part of the current water pollution. In the last 50 years, the population of large Brazilian Amazon cities (about two thirds of the region’s total population of 28.1 million people ), more than doubled. The region’s sewage collection is the lowest in the country.

According to the National Sanitation Information System (SNIS), of Brazil’s Ministry of Regional Development, only 13.1% of the Amazon’s municipalities have sewage collection and only 21.3% of the Amazon’s existing sewage networks go to sewage treatment plants for the removal of at least some of the pollutants. The rest of the existing Amazonian sewage networks (78.7%) dump directly to rivers and streams without treatment.

“Basic sanitation has never been a priority in Brazil, and the northern region is an example of that. In the 1970s, the military regime created a national sanitation plan, in which the first stage was to bring water to everyone. The second, the construction of sewage treatment [infrastructure]never happened,” said Édison Carlos, former president of the Instituto Trata Brasil (ITB), in a 2020 interview.

According to Sanitation Ranking 2021, published by ITB, out of Brazil’s 100 largest cities, Manaus, Santarém, Belém and Macapá are among the 20 worst cities for sanitation in the country – respectively, at the 89th, 95th, 96th and 100th rankings.

The team of scientists found a lower contamination level in the samples taken from the Santarém River in Pará state, as compared to the other three mainstem rivers assessed (the Amazon, Tapajós and Tocantins rivers). Image courtesy of Silent Amazon.

Radical change needed

These studies and reports show that the Amazonian region is far behind the Sustainable Development Goal 6.3 set by the United Nations: “By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.”

“Measures should be initiated urgently to reduce the chemical burden created by urban areas in the Amazon,” Rico concluded. “If enough investment is [made]the construction of wastewater treatment plants or other water purification methods should not take very long.”

Gisela Umbuzeiro, coordinator of the Laboratory of Ecotoxicology and Toxicity (LAEG) at the State University of Campinas (UNICAMP), points to the risks posed by urban water pollution. “Imagine, for instance, what the urine of a person undergoing chemotherapy is like ; this treatment uses highly mutagenic compounds,” capable of generating genetic mutation in cells, she says. But that waste needn’t enter Amazonian waters. “There is technology to deal with huge contamination… but there is no common articulation and initiative [in the country to solve the problem].”

“Those technologies, which are expensive but very advanced, need to be developed in Brazil. Nanomaterials [for example, can] remove even viruses and bacteria from the water. We need to come together for the same goal — academia, control agencies, sanitation companies, NGOs, the Public Ministry, governments. Otherwise nothing will ever change.”


Wilkinson, JL, Boxall, ABA, Kolpin, DW, Leung, KMY, Lai, RW S,… Teta, C. (2022) Pharmaceutical pollution of the world’s rivers. Proceedings of the National Academy of Sciences of the United States of America.

Coˆrtes, JC, D’Antona, A ́.DO, Ojima, R., 2020. Extended urbanization and rural reconfiguration in the Amazon: a theoretical-methodological proposal based on demographic and spatial indicators. Rev. Bras. Est. Urb. Reg . twenty two.

Fekadu, S., Alemayehu, E., Dewil, R., Van der Bruggen, B., 2019. Pharmaceuticals in freshwater aquatic environments: A comparison of the African and European challenge. Sci. Total Environ. 654, 324–337.

Banner image: Forty out of 43 pharmaceutical drugs and other contaminants were found in the Amazon River and important tributaries that run through large urban areas in the Brazilian Amazon. Image by U3204694 CC BY-SA 4.0.

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Chemicals, Environment, Freshwater Ecosystems, Freshwater Fish, Health, Pollution, Public Health, Research, Rivers, Tropical Rivers, Waste, Water, Water Crisis, Water Pollution


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