Mercury Poisoning Forces Amazon Families to Abandon Staple

Illegal gold mining is poisoning the staple fish of Amazonian riverside communities with mercury. A Mongabay Latam investigation, based on an analysis of over 7,000 human and 5,900 fish samples, identifies the Madeira River basin as a critical contamination zone, forcing families to abandon their traditional diet.

For decades, the roughly 170 residents of Lake Puruzinho in Amazonas state relied on fish from their local waters. That changed when studies from the Federal University of Rondônia (UNIR) revealed dangerous mercury contamination linked to mining dredges. An estimated 10 to 50 metric tons of mercury from gold mining enters the Madeira River, which feeds the lake.

Maria Rogelina Soares da Silva dos Santos, a fisher and homemaker, participated in the UNIR research for 26 years. She described the discovery as a "huge scare." The studies focused on pregnant women, breastfeeding women, and children in riverside communities. Researcher Ronaldo de Almeida, a co-author of several UNIR publications, says mercury levels in these communities are far above those found in urban populations.

Critical Exposure Levels

A 2024 study found mercury accumulation among Lake Puruzinho residents was among the highest reported in the Madeira River Basin. Concentrations in residents' hair ranged from 15.61 to 25.81 micrograms per gram. The World Health Organization's safe limit is 2 micrograms per gram.

After learning the results, Maria Rogelina dos Santos says her family drastically reduced eating fish like tucunaré, a former diet staple. The Mongabay investigation analyzed 42 scientific studies from 1997 to 2024, finding evidence of mercury exposure in at least 249 Indigenous and riverside communities over 27 years. Another 702 communities are at risk due to proximity to illegal mining.

The Contamination Pathway

No gold mining occurs at Lake Puruzinho itself. However, currents from the Madeira River carry contaminated fish into the lake. The mercury accumulates in fish tissue and eventually in human bodies, showing up in hair, blood, and feces. Researcher Ronaldo de Almeida explains that fish is the main route for mercury ingestion.

He distinguishes between metallic and organic mercury. Metallic mercury evaporates and can be inhaled, but the body eliminates it relatively quickly. Organic mercury, or methylmercury, enters through food. "Its elimination rate is very low," says De Almeida. "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."

Raimundo Nonato dos Santos, president of the Lake Puruzinho Community Development Association, lived by the lake for 55 years. He and his wife ate fish like pintado and tucunaré for years unaware. "It’s as if we were in innocence, without knowing anything that was happening," he told Mongabay Latam.

A Widespread Health Crisis

Scientific studies in the database include 76 human samples and over 2,000 fish samples from Lake Puruzinho. Results show mercury levels three to seven times the WHO limit. Fish like tucunaré and curimatã are both highly affected and key to the local diet. The problem extends beyond Puruzinho.

Teacher Renata Vieira Guacebe, 41, is a research fellow on UNIR studies in the region. She still eats fish three or four times a week but is concerned. "I like to eat fish. If it’s contaminated, what are we going to do to continue eating fish?" she says. "How are we going to be able to drink water?"

The situation is complicated further as some community members work in gold mining to support their families.