The campaign text is short and hard. It comes from Avaaz, an organisation that gathers signatures and donations on the internet. In Bolivia, it reads, children are born sick, lacking fingers, with ear malformations. Parents fear the mercury used in illegal gold mines that ends up in the Madre de Dios river. Communities are collecting water and hair samples for a court case. The campaign says it paid for the first tests. Thirty-six communities remain to be sampled before the November rains cut off the farthest villages.
Part of this story has long been documented. In the 1990s a team from the French institute IRD measured mercury in the hair of eighty people in the Bolivian Amazon. The work, led by Laurence Maurice-Bourgoin, appeared in 2000 in The Science of the Total Environment. The Esse Ejja of the Beni river had the highest values, from 4.30 to 19.52 micrograms per gram of hair, with a mean of 9.81. The reference used by the WHO and the US Environmental Protection Agency is one microgram per gram. Three Esse Ejja children aged two to five reached 8.56, 14.68 and 15.65.
In the same study the gold miners of the Kaka river, who handle mercury, averaged 0.28. It looks like a paradox and is not. In the mines mercury is used to capture the gold and is then burned off. What reaches the water is turned by bacteria into methylmercury, a form that enters fish and climbs the food chain. The Esse Ejja are fishermen. In the predatory fish sampled by the French team mercury averaged 0.986 micrograms per gram, and 86 per cent exceeded the WHO limit.

The more recent measurements say the same. In 2021 the IPEN network and the Biodiversity Research Institute in Maine published hair results for 64 Esse Ejja women from two communities, Eyiyoquibo and Portachuelo. The mean was 7.58, the maximum 32.4, and 60 of the 64 women were above the reference. In June 2023 the Central de Pueblos Indígenas de La Paz and the Universidad Mayor de San Andrés released 302 tests from 36 communities in six territories. The overall mean was 3.93, that of the Esse Ejja 6.9.
Mercury reaches Bolivia legally. According to UN customs data compiled by the World Bank, the country imported 91,667 kilograms in 2021 and 103,214 in 2023. In 2023 it was the world’s third largest importer. Bolivia ratified the Minamata Convention, the treaty meant to cut mercury use, in 2015.
What methylmercury does to the fetus is known. It crosses the placenta and attacks the brain. At Minamata, in Japan, in the 1950s, the children of women who had eaten poisoned fish were born with mental retardation, ataxia, stunted growth, speech difficulties and limb deformities, in a picture resembling cerebral palsy. The psychiatrist Masazumi Harada followed them for decades. The WHO fact sheet of 2024 calls mercury a threat to the development of the child in the womb and speaks of cognitive damage. It names no malformations.
Missing fingers and malformed ears are a different matter. They are defects of form that arise in the first weeks of pregnancy, when the limbs and the outer ear are built. The reviews by the WHO, the US EPA and the US health agency ATSDR do not list them among the effects of mercury. ATSDR reports cases of extra or fused fingers at Minamata, not missing ones. In animals methylmercury causes cleft palate and skeletal anomalies, but at doses of milligrams per kilogram of body weight, thousands of times above human exposure. In the literature consulted for this article there is no study linking a mother’s mercury to missing fingers or to microtia, the small and malformed ear.

These malformations have known causes. Microtia affects about 2 in 10,000 births worldwide, according to a 2011 review by Danielle Luquetti and Pierpaolo Mastroiacovo. Among Native American populations it rises to 4–12 per 10,000, in Ecuador to 17.4. Maternal diabetes, some drugs, altitude and genetics all play a part. For limb defects there are also amniotic bands, strands of membrane that can strangle a finger in the womb. A cluster of cases in a few villages must therefore be examined, diagnosed and compared with these figures before a poison is blamed.
From the villages come mostly other signals. On 28 September the newspaper Opinión reported from Eyiyoquibo, 501 people in 104 families on the Beni river. The village has at least ten children with severe developmental delays, without a formal diagnosis and without a doctor. These are the signs the literature associates with mercury. Even in Peru, on the Peruvian stretch of the Madre de Dios, the CONAMAD cohort of 198 mother and child pairs did not look for malformations. It measured birth weight and length of pregnancy.

The legal front is further ahead than the campaign says. On 4 December 2025 the full bench of Bolivia’s Agro-environmental Tribunal upheld the case brought by Esse Ejja, Tacana and Cavineño communities of the Multiethnic Indigenous Territory II. It ordered mining outside authorised areas to stop and recognised the Madre de Dios as a «sujeto colectivo de derechos», a collective subject of rights, under the 2012 Mother Earth law, Law 300. The river’s legal personhood, which Avaaz presents as a possible victory, already exists.
What is missing is an examination of the children. On 25 September 2026 the same tribunal ordered the health ministry to send mobile brigades within ten working days to diagnose the indigenous communities exposed to mercury. That diagnosis will say how many children are ill and with what. The mercury of the Esse Ejja comes with thirty years of figures. The missing fingers, for now, are only in the text of a fundraising appeal.

References
Maurice-Bourgoin L., Quiroga I., Chincheros J., Courau P., «Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations», The Science of the Total Environment, 260, 1–3, pp. 73–86, 2000. doi: 10.1016/S0048-9697(00)00542-8
Bell L., Evers D. (BRI), «Mercury Exposure of Women in Four Latin American Gold Mining Countries», IPEN e Biodiversity Research Institute, June 2021, open access. ipen.org
National Research Council, «Toxicological Effects of Methylmercury», chapter «Health Effects of Methylmercury», National Academies Press, Washington, 2000. nationalacademies.org
World Health Organization, «Mercury and health», fact sheet, 24 October 2024. who.int
Luquetti D.V., Leoncini E., Mastroiacovo P., «Microtia-anotia: a global review of prevalence rates», Birth Defects Research Part A, 91, 9, pp. 813–822, 2011. doi: 10.1002/bdra.20836
Berky A.J. et al., coorte CONAMAD, Madre de Dios (Peru), Environmental Health Perspectives, 131, 9, 097008, 2023, open access. doi: 10.1289/EHP10557
World Bank WITS su dati UN Comtrade, mercury imports (HS 280540), 2021 and 2023. wits.worldbank.org
«Tribunal Agroambiental ordena suspender minería ilegal en el río Madre de Dios en Pando», La Región, 5 December 2025. laregion.bo
«Tribunal Agroambiental instruye intervención de áreas afectadas por minería», Los Tiempos, 30 September 2026. lostiempos.com
Carrasco M., Carrasco A., «Mercurio: la vida que se apaga en Eyiyoquibo», Opinión, 28 September 2026. opinion.com.bo
«Estudio de cabellos revela altos niveles de mercurio en comunidades indígenas de Bolivia» (CPILAP and Universidad Mayor de San Andrés study), Opinión, 13 June 2023. opinion.com.bo
Avaaz, «Support the urgent plan to stop mercury pollution in Bolivia», campaign page. avaaz.org
Previous articles on ScienceOnline
Donati G., «Mercury in the bones», ScienceOnline, 10 August 2026.

*Board Member, SRSN (Roman Society of Natural Science)
Past Editor-in-Chief Italian Journal of Dermosurgery