Victims of Brazil’s worst environmental disaster were taking their case for compensation to a UK court on Monday, almost nine years after tons of toxic mining waste poured into a major waterway, killing 19 people and devastating local communities.

The class action lawsuit at the High Court in London seeks an estimated 36 billion pounds ($47 billion) in damages from the global mining giant BHP. That would make it the largest environmental payout ever, according to Pogust Goodhead, the law firm representing the plaintiffs.

BHP owns 50% of Samarco, the Brazilian company that operates the iron ore mine where a tailings dam ruptured on Nov. 5, 2015, releasing enough mine waste to fill 13,000 Olympic-size swimming pools into the Doce River in southeastern Brazil. The case was filed in Britain because one of BHP’s two main legal entities was based in London at the time.