- A database built by Mongabay Latam, based on the analysis of scientific studies that gathered more than 7,000 samples from humans and 5,900 from fish, identified the areas most affected by mercury contamination in the Madeira River, one of the main tributaries of the Amazon.
- Mongabay Latam investigated the impact of mercury contamination on the health of the most affected communities: Lake Puruzinho in the state of Amazonas, and the riverside community of Calama and the Karipuna Indigenous Territory, in Rondônia state.
- Studies show that mercury concentrations among residents of Lake Puruzinho are among the highest recorded in the Madeira River Basin and well above what the World Health Organization considers safe, prompting residents to change their eating habits.
- High levels of mercury in Amazonian communities are related to fish consumption, their main source of protein; the accumulation of mercury in humans can cause serious health damage, such as motor and neurological problems, researchers say.
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An analysis of 42 scientific studies published between 1997 and 2024 found evidence of mercury exposure among residents of at least 249 Indigenous and riverside communities over that 27-year period. Another 702 communities are at risk because they’re located near illegal mining hotspots, in addition to communities where residents have already tested positive for mercury. In Brazil, at least 286 Indigenous and riverside communities don’t know how much mercury is in their bodies, or the danger posed by continued exposure.
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It takes two hours by regular boat, or 40 minutes by speedboat, to reach the Lake Puruzinho community from Humaitá. The river journey offers a quintessential Amazonian scene: the noise of the engine, the sound of the water, and the green of the forest reflected on the surface of a river teeming with life.
There’s no gold mining at Lake Puruzinho, and at first glance it appears to be a natural refuge. However, currents from the Madeira River carry fish into the lake that have been contaminated by mercury from mining sites in the region. The mercury accumulates in fish tissue and eventually ends up in people’s bodies, resulting in high concentrations in residents’ hair, blood, and feces, studies show.
“Fish is, unfortunately, the main route of entry for the ingestion of mercury,” De Almeida, the UNIR researcher, tells Mongabay Latam during a visit to his office at the campus in Porto Velho, the Rondônia state capital. Among the studies to which he contributed was a paper published in 2021 examining the relationship between high fish consumption and mercury levels in the blood of residents of communities in the Brazilian Amazon.
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According to De Almeida, contamination by organic mercury in food, in the form of methylmercury, is much more serious than direct exposure to metallic mercury. “When someone uses metallic mercury — which is elemental mercury and is liquid — if you leave it here on the bench, it will evaporate. If you inhale this mercury, will it cause some damage to your health? Yes, it will, but your organism will eliminate it at a much higher rate than organic mercury,” he says. “Now organic mercury, methylmercury, when we ingest it through some type of food, it enters the organism and its elimination rate is very low. So it stays retained in the organism, it will accumulate over time, and it will cause serious damage to health: neurological problems, cardiological problems, orientation problems.”
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Protection that doesn’t arrive
Brazil has been a party to the Minamata Convention since 2013; the agreement establishes regulations on the use, trade, and production of mercury. In 2018, the federal government formally incorporated the convention into Brazilian law.
However, Mongabay Latam found that Brazil has yet to implement restrictions on mercury use in the states of Amazonas and Rondônia, where it’s still used in illegal gold mining. The government also hasn’t set a date for implementing the restrictions, according to statements from the ministries involved in the Minamata Convention, obtained through access-to-information requests and from their press offices.
“Brazil does not have a [current] sectoral implementation plan for the Minamata Convention on mercury,” said the Ministry of the Environment and Climate Change.
In 2023, Brazil presented its Minamata Initial Assessment (MIA), a study of the country’s use, emissions, and releases of mercury. According to the environment ministry, the assessment identified regulatory gaps and sources of mercury releases, and helped establish priorities for meeting the convention’s obligations. The ministry did not provide a timeline for implementing those measures.
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Scientists say a dedicated system for detecting mercury-related disease is important because damage to the central nervous system causing motor, sensory, or cognitive problems can’t be cured. Early detection and appropriate intervention are therefore important to help maintain quality of life, the experts added.
Given the scale of the contamination, De Almeida says the priority should be to stop mercury emissions. “The [main] thing is to stop emitting, it is the first thing. We need to do that.”
In Lake Puruzinho, Raimundo dos Santos says his dream is to be able to enjoy the beauty of the lake and live from its riches — without mercury. “We love this nature that God left for us,” he says, looking at the water’s mirrored surface. “It is my dream to raise fish within the region itself.”
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