The claim relates to Rio Tinto's QIT Madagascar Minerals (QMM) mine. Communities near the site have previously protested over water releases from the mine into the surrounding environment, according to law firm Leigh Day, which is representing the claimants.
The claimants allege acidic wastewater containing uranium, lead and other metals was discharged into lakes and waterways used for drinking, cooking, washing and irrigation.
More than 2000 of the claimants are children, the law firm said.
Rio Tinto - a British–Australian multinational mining company - said it had been notified of the claim but had not yet received details.
"We have yet to receive any documents or details of the claim so cannot comment further at this time," a spokesperson said.
The company said QMM carries out extensive water monitoring and publishes results annually. Its 2025 Water Report found "most regulated metals were consistently below laboratory detection limits" in surrounding rivers.
"All uranium samples tested were below laboratory detection limits, while the majority of lead samples were also below detection limits," Rio Tinto said in a written comment.
The mine halted operations for five days in May 2022 after local communities protested over a water release that was followed by the discovery of dead fish. Rio Tinto said water sampling found no link between the release and the fish deaths.
The mine, which is 80 per cent-owned by Rio Tinto, produces ilmenite, which is processed into titanium dioxide, a white pigment used in products including paint, food and toothpaste.
The claimants are seeking compensation and court orders requiring Rio Tinto and QMM to remediate damage and halt further contamination.
The Jesuits in Britain, a Catholic religious order, said in May it may sell its stake in Rio Tinto after unsuccessful engagement with the company over environmental concerns in Madagascar and Guinea.
