ASI officials said that the stains damage the marble surface

AGRA: Green and black stains have again started appearing on the marble walls of the Taj Mahal due to insect attack. The Archaeological Survey of India's (ASI) superintending archaeologist ( Agra circle) Vasant Swarankar said the issue has become a permanent problem as filth in the Yamuna river provides a perfect breeding ground for insects to breed.

According to ASI experts, black and green patches appear due to excreta deposited by a particular species of insect, Goeldichironomus. This can damage the intricate designs and floral mosaics and the marble surface of the monument. Earlier, the monument used to face bug attacks only during the months of April and October, but now, this occurs regularly, said an expert.

The ASI has now started scrubbing the walls of the 17th century monument every Friday, when visitors are not allowed, to clean the stains. Swarankar says distilled water is being used to clean the walls to ensure that the marble surface is not damaged, adding that repeated scrubbing can damage the sheen of the marble.

A long-term solution to the issue is to clean the river properly, Swarankar added.

A study by ASI’s science branch in 2016 to look into the reasons behind the phenomenon had revealed that Yamuna pollution is responsible for green patches on the iconic structure. “However, we can't do anything outside the Taj Mahal as it is beyond our jurisdiction,” said an ASI official.

ASI officials had suggested in the report that there is need to increase the level of water in the Yamuna so that water does not stagnate and there is a continuous flow. “Small fishes that once kept insects in check are not found in the river now due to stagnation of river water. This has also disturbed the ecosystem,” said an official in the ASI.

The report also suggested desilting of the Yamuna, but nothing has been done so far. Besides, there is need to clean sewage and industrial effluent discharged into the river. A recent report of the Uttar Pradesh Pollution Control Board (UPPCB) revealed that about 807.53 MLD (millions of liters per day) of sewage and 43.80 MLD of industrial effluent are being discharged into the river. Treatment of sewage is a major area of concern, as out of the total estimated sewage discharge of 807.53 MLD, only 283.51 MLD is being treated.

An ASI scientist told TOI that another factor responsible for the growth of insects is phosphorous deposits, as ash is dumped from a nearby cremation ground on the riverbed. They said growth of algae is profuse due to phosphorous on the soil, and insects eat the algae and excrete on the walls of the Taj.

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In Video: Insects leave green & black stains on Taj Mahal marble