dezembro, 19 2024

By WWF-Brazil

Using a modeling approach to project the distribution and bioaccumulation of mercury in rivers, researchers have identified that sub-basins of the Tapajós, Xingu, Mucajaí, and Uraricoera Rivers—home to Indigenous territories threatened by illegal mining—are at high risk of mercury contamination exceeding safe levels. Mercury concentrations tend to be lower at river headwaters and increase progressively downstream. Across all analyzed basins, major rivers and longer waterways exhibit greater potential for mercury bioaccumulation.

The modeling study covered the Tapajós basin, spanning the states of Pará, Mato Grosso, and Amazonas; the Xingu basin, encompassing Pará and Mato Grosso; and the Mucajaí and Uraricoera basins in Roraima. It utilized a probabilistic model developed by the U.S. Environmental Protection Agency (EPA).

An analysis of sub-basins against maximum mercury thresholds set by Brazilian regulations revealed a high probability of non-compliance. Results show an alarmingly high contamination risk for men and women in over 50% of the sub-basins examined, with particularly severe implications for Indigenous and riverine populations who rely on fish for sustenance.

Tapajós Basin

In the Tapajós basin, over half (51.77%) of its 3,791 sub-basins fail to meet Brazilian environmental standards. Further analysis highlights greater non-compliance in areas like Baixo Teles Pires, Rio Apiacás, and Alto and Médio Teles Pires, all exceeding 59%. Men face a significantly higher risk (49.4%) due to greater fish consumption compared to women (45.1%). For Indigenous populations, who depend on fish as a primary protein source, 49.6% of sub-basins pose very high risk.

Uraricoera and Mucajaí Basins

The Uraricoera and Mucajaí basins exhibit contamination levels exceeding 0.31 µg g-1 for non-piscivorous fish and 1.79 µg g-1 for piscivorous fish in multiple sub-basins. Rivers such as Parima, Uraricaá, Amajari, and their tributaries show elevated bioaccumulation potential. The Lavrado wetlands in the northeastern Uraricoera basin play a significant role in mercury methylation, amplifying contamination risks.

Among 540 sub-basins analyzed, 56.7% fail to meet Brazilian environmental standards. In the Uraricoera basin, this figure reaches 57.87%, while in the Mucajaí basin, it is 53.94%. Indigenous and riverine communities face particularly severe risks due to their reliance on fish, with 51.1% of sub-basins classified as very high risk for women and 53.7% for men.

Xingu Basin

Despite a lower presence of mining, the Xingu basin also demonstrates concerning levels of mercury bioaccumulation in fish. Metal vapor emissions may significantly influence contamination dynamics. Elevated mercury levels are projected in the Macrobacias of Rio Fresco and Rio Iriri, attributed to higher mining activity. Even sub-basins in the Rio Ronuro and Nascentes do Xingu regions show significant contamination levels.
Floodplains, particularly in regions like the Volta Grande do Xingu, amplify contamination risks. While average mercury levels in fish remain within regulatory limits, projections raise concerns about future contamination potential and its impact on local ecosystems and communities.

Recommendations and Study Insights

Using the SERAFM model, developed by the U.S. EPA, the study provides new insights into the dynamics of mercury in the Amazon biome. Vitor Domingues, an environmental analyst and study co-author, notes, "One of the major challenges of studying the Amazon is the lack of sample data. Modeling studies help address this by offering insights into mercury dynamics in such a complex and sensitive biome."

The study, published in the scientific journal Toxics in August this year, provides scientific grounds for planning effective interventions in affected regions. Marcelo Oliveira, WWF-Brazil conservation expert, emphasizes the need for integrated approaches to monitor and mitigate the impacts of gold mining and other activities on Amazonian water quality. "Considering the complexities of ecosystems and local populations is essential for evaluating the environmental and social implications of projects, especially in areas already affected by mercury pollution," he adds.

The study recommends implementing a broad contamination monitoring program tailored to regional conditions, enhancing Brazilian regulations with risk-based parameters, and establishing a standardized information system to improve data availability and inform decision-making processes. Data from the Mercury Observatory, developed by WWF-Brazil in partnership with other institutions, played a pivotal role in shaping these findings.

About WWF-Brazil

WWF-Brazil is a 28-year-old Brazilian NGO that works collectively with civil society, academia, governments, and businesses nationwide to combat socio-environmental degradation and advocate for people and nature. The organization is part of an interdependent network seeking urgent solutions to the climate emergency.