After performing on-site drinking water analyses, researchers warned local residents of their very high levels of arsenic.

© Jacques Gardon-IRD

The Uros of Bolivia, adept at neutralising arsenic

A study of women from various Bolivian communities shows that these peoples drink water containing elevated levels of arsenic on a daily basis. While the toxic effects of the regular ingestion of this substance are well known, these women’s bodies seem particularly adept at “neutralising” the poison.

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These indigenous peoples of Bolivia drink water with arsenic levels that are on average ten times higher than the standards (1) advocated by the WHO, sometimes even up to fifty times higher. It is tragic that people drink this type of water in 2018!” deplores Jacques Gardon, research director with IRD. The physician-epidemiologist conducted this research in a particular area: the Altiplano, the world’s second highest inhabited region after the Tibetan plateau, in the heart of the Andes mountains.

The water in this highly mineralised area is known for its high levels of arsenic, and the situation is getting worse. Every day, 800 kg of arsenic are discharged into the water of Lake Poopó, one of the region’s largest lakes. This arsenic intake is partly linked to the mining activity in the region. Due to a series of biochemical reactions, ore mining triggers the formation of residual metal particles such as arsenic, which subsequently dissolves in nearby waters and contaminates the water table.

Stronger bodies than average

Researchers discussed water issues with Quechua and Aymara communities, for example during this meeting in Challapata. Up until then, arsenic had not been identified by the population because, once it dissolves in water, it becomes tasteless, odourless an

© IRD/Jacques Gardon

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The consequences of the regular consumption of arsenic-containing water are well known: skin condition, skin, bladder, kidney and lung cancer, heart diseases, compromised immune system in children.

Several countries are affected by this water contamination (Bangladesh, China, Mexico Argentina, Chile, etc.), “but Swedish colleagues had already found, in Argentina, that the metabolism of Andean populations seemed slightly different”, indicates Jacques Gardon. “It appears that these populations are better than most at excreting arsenic in urine. This is confirmed by the results of our study.

The researchers focused on ten villages around Lake Poopó. They tested the urine and blood of 201 women. “We decided to study women only, as they stay in their villages more, which makes it easier to track their water consumption”, adds the researcher. The results(2) show that women who participated in the study manage to make arsenic less toxic by chemically transforming 80% of it – this is referred to as dimethylation - when these rates are generally around 60%! Their hepatic metabolism seems to perform better than average.

Amplified genetic mutation

The Altiplano region is naturally highly mineralised, and the researchers found arsenic on many sites, even in surface water, as seen here in the immediate vicinity of Lake Poopó.

© IRD/Jacques Gardon

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More interestingly for Jacques Gardon, “Within the ethnic groups of Bolivia, we were able to do something that was not feasible in Argentina, where people are of very mixed origins. We studied the Uros group, a very ancient and isolated people from the Altiplano.” By comparing them with other Andean peoples such as the Aymara and Quechua, the researchers found that the Uros were even better at metabolising arsenic and reducing its toxicity. In their urine, scientists identified 85% dimethylated forms of arsenic (i.e. less toxic), i.e. 5% more than in others.

 “As the Uros have lived in this region for millennia, they have always drunk this arsenic-containing water. A genetic mutation conferring the ability to “process” arsenic has been observed in many peoples across the globe. But it has never been amplified as appears to be the case here. The study therefore supports the fact that it is a skill acquired under selective pressure.” In other words, the Uros’ bodies adapted to their environment, and the daily consumption of arsenic-containing water over 10,000 years selected a mutation with beneficial effects.

This discovery should not obscure the fact that, according to Jacques Gardon, “the situation of these peoples is very worrying. Such exposure to toxic substances in water in 2018 is unacceptable. This is the purpose of target 3.9 of the sustainable development goals?By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.

Notes :
  The limit value currently recommended by the WHO in terms of arsenic in drinking water is 10 µg/l.

2. Jessica De Loma, Noemi Tirado, Franz Ascui, Michael Levi, Marie Vahter, Karin Broberg, Jacques Gardon, Elevated arsenic exposure and efficient arsenic metabolism in indigenous women around Lake Poopó , Bolivia, Science of the Total Environment , 2 décembre 2018.

Contact : jacques.gardon@ird.fr