Bhopal, Jan 24 (ANI): Victims of 1984 Bhopal gas tragedy, world's worst industrial disaster, called upon US President Barack Obama to ensure justice for survivors by directing Dow Chemicals to appear for hearings and clean toxic waste. In the early hours of December 3, 1984, around 40 tons of methyl isocyanate gas accidentally leaked from a pesticide factory owned by US multinational Union Carbide Corp. and was carried by the wind into the surrounding slums. Social activist Satinath Sarangi said they have called upon Obama and demanded extradition of John Macdonald, secretary of Union Carbide. Obama will arrive in India on Sunday for the second time during his tenure, to build on what he calls one of the defining relationships of the 21st century.