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How the Tungurahua volcano dropped heavy metals into Ecuador’s food supply

Luis Egas farms the land under Tungurahua in central Ecuador; The mountain’s mineral-rich soils are good for the corn and fruit he grows on his farm. But the volcano has been restless, spewing ash regularly between 1999 and 2016. An eruption in 2006 was particularly destructive, depositing up to 20 millimeters of ash. ‘We lost almost everything: crops, animals and houses; the ash caused the roofs to collapse,” Egas said.

After the eruptions largely subsided in 2016, Egas and his neighbors breathed a sigh of relief and continued rebuilding their farms. But they were concerned about the long-term effects of the ash.

Working with the farmers, researchers discovered that Tungurahua had brought dangerous levels of heavy metals such as nickel and cadmium to the soil below, contaminating wild plants and crops. The findings were recently published in Ecotoxicology and environmental safety.

Pollution in the fields

The effort began when Egas and others were put in touch with investigators from the Escuela Superior Politécnica de Chimborazo (ESPOCH) in Riobamba, Ecuador. “The farmers themselves took us to the sampling sites, and then we returned to report our results to them,” says the paper’s first author, Lourdes Cumandá Carrera Beltrán, a chemist at ESPOCH.

A person squats in a cultivated field.
Student Erika Lisbeth Erazo Macas samples agricultural fields under the Tungurahua volcano to identify heavy metal pollution. Credit: Lourdes Cumandá Carrera Beltrán/GAIBAQ

The ESPOCH team sampled agricultural fields, livestock fields and natural areas near the volcano in 2020, focusing on vegetables and plants in both cultivated and uncultivated plots to account for possible chemical differences related to pesticide use and fertilizer. They also sampled soil and ash in both types of cultivated land.

The researchers dried, sieved and ground the samples and then analyzed them for a range of heavy metals, including cadmium.

The analysis found that cadmium concentrations averaged 1.76 milligrams per kilogram in potatoes and 1.38 milligrams per kilogram in corn, well exceeding the internationally recognized limit of 0.1 milligrams per kilogram. The cadmium and lead levels in small reed grass and kikuyu grass outside the cultivated plots were even higher than levels previously found in plants growing in mine waste in central Peru, the researchers noted.

“Pollutants such as cadmium can lead to major metabolic changes, as well as major health consequences in the future.”

Environmental contamination such as that found near Tungurahua is “of concern for vulnerable populations,” said co-author Antonio Jose Signes-Pastor, a researcher from the Universidad Miguel Hernández de Elche in Spain who specializes in the health effects of contamination. “Pollutants such as cadmium can lead to major metabolic changes, as well as major health consequences in the future,” he said.

The researchers have not yet conclusively analyzed the levels of heavy metals in cow’s milk or human urine from the region, explains co-author and food scientist Angel Antonio Carbonell Barrachina, also from Universidad Miguel Hernández de Elche. In the future, these analyzes could help the group understand the extent of pollution in the area. Some of the group plan to return to Ecuador later this year to continue the work.

Future for farmers

Farmers in volcanic areas face “unique challenges,” said Octavio Pérez Luzardo, a toxicologist at the Universidad de Las Palmas de Gran Canaria in Spain, who was not involved in the new research. “Although soils can be enriched with useful minerals thanks to volcanoes, there is a risk of contamination with heavy metals, especially in the short term, which can be dangerous for both human health and the health of the ecosystem,” he said. Pérez Luzardo noted that the Tungurahua study was similar to a 2022 study he co-authored on the effect of volcanic ash on bananas in the Canary Islands.

“Fortunately, we were all very satisfied with the results of the study.”

“Not all volcanic materials are the same,” says Budiman Minasny, a soil scientist at the University of Sydney in Australia, who has studied volcanic ash and soil from recent volcanic eruptions in Indonesia but was not involved in the Tungurahua work. “The research in Ecuador is valid,” he said, adding that given that some volcanic materials have elevated levels of heavy metals, precautionary monitoring such as that done in Tungurahua, as well as establishing a baseline of these metals in the soil , is important.

International studies have shown that compost can help clean up pollution, says co-author and project leader Irene Del Carmen Gavilanes-Terán, a chemist at ESPOCH. “Compost contains a large cocktail of microorganisms that can remove heavy metals,” says Gavilanes-Terán. Researchers are studying bioremediation in the area using compost.

“Fortunately, we were all very satisfied with the results of the study,” said Egas.

—Andrew J. Wight, science writer

Quote: Wight, AJ (2024), How the Tungurahua Volcano dropped heavy metals into Ecuador’s food supply, Eos, 105, https://doi.org/10.1029/2024EO240213. Published on May 13, 2024.
Text © 2024. The authors. CC BY-NC-ND 3.0
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