The recent Nyiragongo (Democratic Republic of Congo) eruption: the impact of volcanic ash fallout on drinking water and edible plants

Nyiragongo is an active intraplate volcano well known for its fascinating persistent lava lake inside the crater and is recognized as one of the most dangerous volcanoes in the world as more than two million people live on its slopes, 18-25 km far from the main crater. It is located in the Virunga Volcanic Province (VVP), in the western branch of the East African Rift System (EARS), at the intersection between the Democratic Republic of Congo, Rwanda, and Uganda. Unexpectedly, on 22 May 2021, Nyiragongo produced three different lateral lava flows in the low flanks and significant amounts of volcanic gas and ash were emitted from the summit crater. For several weeks, the ash fallout strongly impacted the main city of Goma and the numerous villages located in the vicinity of the volcano. During and after the eruption, 22 samples of volcanic ash, 135 drinking waters, and 32 leaf samples of different edible plants were collected in rural villages at different distances from the volcano. The samples were analyzed for the major, minor and trace constituents, including all those elements recognized as potentially toxic (PTEs) to human health and the ecosystem in general. The preliminary results are particularly alarming as most of the drinking water sampled was found to be heavily contaminated with fluoride, chloride, sulphur, and many trace metals (As, Cd, Cr, Cu, Mo, Pb, Sb, Se, Te, Tl, and V), potentially toxic to human health. The plants analyzed were also found to be strongly contaminated by the extensive deposition of volcanic ash, and by the consequent release of water-soluble ash-borne species (mainly sulphates and chlorides). The two processes that caused the heavy environmental contamination are mainly due to the interaction of rainwater with the volcanic plume and the leaching of the emitted ash. Further studies are still in progress to define the risk factors for the population exposed to the important event in the VVP.