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New study shows daily intake of mercury exceeds safe limits in six Amazon states


Ensp/ Fiocruz


A new study carried out in the main urban centers of the Amazon, covering six states and 17 municipalities, reveals that fish in the region are contaminated by mercury. The results show that fish from all six Amazonian states had contamination levels above the acceptable limit of ≥ 0.5 µg/g established by the WHO, World Health Organization. The worst indexes are in Roraima, with 40% of fish presenting mercury above the recommended limit, and Acre, with 35.9%. The lowest indicators are in Pará, with 15.8%, and in Amapá, with 11.4%. On average, 21.3% of the fish sold in the area and that reach the table of families in the Amazon region have mercury levels above safe limits.

In all population groups analyzed, the daily intake of mercury exceeded the recommended reference dose. In the most critical municipality, Rio Branco (AC), the potential intake of mercury exceeded 6.9 to 31.5 times the reference dose indicated by the EPA - Environmental Protection Agency of the US government (0.1 μg/kg/day). Women of childbearing age - the most vulnerable public to the effects of mercury - would be ingesting up to 9 times more mercury than the recommended dose; while children aged 2 to 4 years up to 31 times more than that advised.

In Roraima, the second most critical state, the potential intake of mercury extrapolated from 5.9 to 27.2 times the reference dose. Considering the population strata most vulnerable to contamination, women of childbearing age would be ingesting up to 8 times more mercury than the indicated dose, and children aged 2 to 4 years up to 27 times more than that recommended.

This information is from a study carried out by researchers from the National School of Public Health Sérgio Arouca of the Oswaldo Cruz Foundation (Ensp/Fiocruz), the Federal University of the West of Pará (UFOPA), Greenpeace Brazil, Iepé, the Socio-environmental Institute and WWF-Brazil. The survey sought to assess the risk to human health due to consumption of contaminated fish - and, for that, visited markets and fairs in 17 Amazonian cities, where the samples used in this research were purchased. “This is the first study that evaluates the main Amazonian urban centers spread across six states. It reinforces a warning for an already known but unresolved issue, which is the risk to food security in the Amazon region coming from the use of mercury in mining activities. It is concerning that the main source of protein in the territory, if ingested without control, will cause health damage because it is contaminated", says Decio Yokota, coordinator of the Information Management Program at Iepé.

“We are facing a public health problem. We know that contamination is more serious for pregnant women, since the fetus can suffer neurological disorders and damage to the kidneys and cardiovascular system. Children may have motor and cognitive difficulties, including speech and learning process problems. In general, the effects are dangerous, often irreversible; symptoms may appear after months or years of exposure. It is urgent to create public policies to assist people already affected by mercury contamination and preventive measures regarding use control”, warns Dr. Paulo Basta, researcher at the National School of Public Health of Fiocruz.

The survey was carried out from March/2021 to September/2022 in the states of Acre, Amapá, Amazonas, Pará, Rondônia and Roraima. The samples were collected in the municipalities of Altamira (PA), Belém (PA), Boa Vista (RR), Humaitá (AM), Itaituba (PA), Macapá (AP), Manaus (AM), Maraã (AM), Oiapoque (AP), Oriximiná (PA), Porto Velho (RO), Rio Branco (AC), Santa Isabel do Rio Negro (AM), Santarém (PA), São Félix do Xingu (PA), São Gabriel da Cachoeira (AM) and Tefé (AM). We evaluated 1,010 specimens of fish, from 80 different species, purchased in markets, fairs and directly from fishermen, simulating the daily lives of local consumers.

Of the overall sample, 110 were herbivorous fish, 130 detritivores, 286 omnivores and 484 carnivores. Carnivores, which are more appreciated by end consumers, had higher levels of contamination than non-carnivorous species. Comparative analysis between species indicated that contamination is 14 times higher in carnivorous fish compared to non-carnivorous ones. Therefore, the study brings a consumption indication for the main fish species sampled, considering level of contamination and locality.

The main recommendation that researchers make is to have greater control of the Amazon territory and eradicate illegal mining and other sources that emit mercury to the environment. “In addition to environmental degradation, illegal mining carries a trail of destruction that includes drug, weapon and wildlife trafficking, as well as sexual exploitation. Therefore, the State needs to ensure greater control and security for local populations. However, other actions such as monitoring deforestation and burning can also reduce exposure to mercury, since they impact the dynamics of soils, rivers and streams”, says Marcelo Oliveira, conservation expert at WWF-Brazil.

About the study

Fish samples were collected in 17 Amazonian municipalities, totaling six sampled states. The fish were acquired in public markets, street markets or from fishermen during fishing landing from March 2021 to September 2022. Whenever possible, at least three different species were sampled in each trophic guild (carnivore, omnivore, detritivore and herbivore) and at least three individuals of each species, with different sizes.

The detection of Hg levels was carried out by atomic absorption spectrometry in the laboratories of CETEM - Center for Mineral Technology (RJ) and IEC - Evandro Chagas Institute (PA). The assessment study of the health risk attributed to the consumption of contaminated fish was calculated according to parameters of the US.EPA - United States Environmental Protection Agency. For that, four population strata were considered: women of childbearing age (10 to 49 years); adult men (≥ 18 years); children aged 5 to 12 years; and children aged 2 to 4 years.

The estimated consumption of fish per person was based on the report on fish consumption in the Amazon region of Brazil, with an average per capita of 100 grams of fish per day in urban environments. The calculation of the risk ratio (RR), which indicates the potential for damage to health caused by the consumption of contaminated fish, and the health risk assessment were also evaluated.

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