Indonesian environmental activist Muhammad Rosidi shudders as he recalls the horrific moment two men on a motorbike threw acid through the open window of his car as he was driving on Sumatra island in February.

He was instantly consumed by a burning pain as the corrosive liquid ate into his hands, legs and groin.

¡°I knew right away it was acid. It felt like being doused in boiling water,¡± said the 43-year-old.