Environment Minister Anil Madhav Dave in a written reply in the Lok Sabha said a number of studies have been carried out by various research teams regarding discolouring of the Taj Mahal.
"According to one such research, open burning of municipal solid waste in the vicinity of the Taj Mahal could contribute to discolouring," he said, adding the discolouring is not necessarily permanent and the colour can be regained significantly by simple cleaning and washing treatments.
For conservation and cleaning of the monument, one of the measures is mud pack therapy to remove surface deposits and black and yellow spots on the marble.