The scientific wing of Archeological Survey of India (ASI) has started cleaning the stains with normal water as they don’t want to use chemicals which could damage the intricate designs, floral mosaics and the marble surface of the monument. However, final cleaning is being done with distilled water.
Confirming this, superintending archaeological chemist MK Bhatnagar said that though stains were spotted on the wall, they are still less as compared to earlier years.
“Black and green patches appear due to excreta deposited by a particular species of insect, Goeldichironomus, during the months of April and October at the time of variation in temperature,” he said, adding that it will disappear once mercury starts rising.
TOI had in May last year reported that the insects attacking the 17th century monument had stayed away due to a cleaner Yamuna and minimal human activity around the premises owing to the Covid-induced lockdown.
Talking to TOI, superintending archaeologist in ASI’s Agra circle, Vasant Swarnkar, said, “We regularly monitor and observe the developments but a long-term solution to the issue is to clean the river properly and maintain flowing water levels in the Yamuna.”
A study by ASI’s science branch in 2016 to look into the reasons behind the phenomenon had revealed that a polluted Yamuna is responsible for green patches on the iconic monument.