Over the years, visitors to the Taj Mahal have been complaining of a foul smell that is ruining their experiences at the majestic 17th-century Mughal architecture listed as one of the New Seven Wonders of the World. The gas responsible for the odour may in fact be doing greater harm – it is likely the culprit behind the discolouration of the Taj’s glorious white marbles.

The stink coming from the black waters of the Yamuna river that flows prompted a group of scientists to explore if the gas that was responsible for the odour – hydrogen sulphide – also had corrosive effects. They found that the gas released from polluted Yamuna water had a more corrosive impact than sulphur dioxide released by industrial pollution in Agra city.

The findings assume significance, as initiatives around protecting the Taj from being affected by pollution have largely been concerned with tackling industrial and vehicular pollution, while Yamuna pollution has not got as much attention until five years ago.


For over three decades now, sulphur dioxide has been considered to be the main pollutant behind the decay in the glorious white marbles. Yamuna pollution was also blamed for the impact on the marble structure, in a 2016 report of the Archaeological Survey of India submitted before the Supreme Court of India, but from a different perspective – it highlighted the growth of the insect of the genus Goeldichironomus, in stagnant Yamuna water devoid of aquatic life and blamed the insect excreta for the green and brownish patches on the Taj marbles.

The recent study, however, indicates that the polluted Yamuna might be harming the Taj in more than one way.

The white marbles of the Taj Mahal have been stained and fading over the years. A new study suggests that pollution, mainly hydrogen sulphide is the cause for corrosion. Photo credit: Kathuria Films & Production/Mongabay

“We tried corrosion deformation studies using various air pollutants like sulphur dioxide, nitrogen dioxide, ammonia, carbon monoxide, carbon dioxide and hydrogen sulphide. Most interestingly, hydrogen sulphide was found to be the most problematic among all.

Polluted river

Our preliminary investigation establishes that river Yamuna, which carries untreated wastewater of the entire Agra, was responsible for the generation of hydrogen sulphide,” Dipankar Saha, a former additional director of the Central Pollution Control Board and one of the co-authors of the paper, told Mongabay-India.

“Hydrogen sulphide gas is acidic and corrosive therefore much attention is needed to clean river Yamuna,” added Saha, who had also served as head of the Central Pollution Control Board’s air laboratory for 12 years.

Published recently in the International Journal of Environmental Science and Technology, the study also noted, “The wind rose diagram developed during the period of the study suggests that the direction of the wind opposed the industrial pollutants moving towards the monument” and that “hydrogen sulphide emitted from the polluted Yamuna River… has a dominant role”.

The study titled Role of air pollutant for deterioration of Taj Mahal by identifying corrosion products on the surface of metals, is co-written by four others, apart from Saha – Achal Pandya, head of the conservation unit at Indira Gandhi National Center for Arts, New Delhi and Jitendra Kumar Singh, Sharma Paswan and DDN Singh from the Corrosion and Surface Engineering Division of the National Metallurgical Laboratory, Jamshedpur.

Pandya told Mongabay-India that it was necessary, for the protection of the Taj from discolouration, that the Yamuna is cleaned and the city’s sewage is allowed into the river only after treatment. “It is no longer a river, its water is unusable,” Pandya said. “But we should remember that the Yamuna included the original Taj Mahal landscape. The river was very much part of the planning of the entire premises.”

The corrosion deformation study was conducted on metals – samples of carbon steel, zinc and copper left exposed at the Taj Mahal premises – and the report concluded that “all evidence suggests that hydrogen sulphide emitted from the polluted Yamuna river flowing very close to the exposure site (the premise of Taj Mahal) has a dominant role on the corrosion rate of metals”.

“The finding of this study leads to the conclusion that the fading of white marbles of the Taj Mahal may be due to the corrosive effect of hydrogen sulphide emitted from the polluted Yamuna River,” the report said.

Untreated domestic sewage entering the Yamuna river in Agra. Photo credit: Kathuria Films & Production/Mongabay

According to Agra-based environmentalist Sharad Gupta, the findings of the study are not surprising.

“The whole city’s sewage and industrial waste, including solid waste, flow into the Yamuna mostly untreated,” he told Mongabay-India. “There are 90 nullahs in Agra, of which the water of only 25 get treated by four plants but these plants do not function at night. The sewage of 65 other drains flows into Yamuna untreated. The materials include leather and synthetic leather waste from about 3,000 shoe factories and these leather wastes help form many gases.”

He added that acids used for washing in the imitation jewellery industry of Agra are also released into the drains untreated.

Not acid rain?

The impact of Yamuna pollution on the Taj has remained little discussed, though not entirely ignored. The focus of Taj-protection initiatives has mostly been on the industrial units, resulting in a series of measures since the 1980s to curb Agra’s industrial pollution, including the relocation and closure of some polluting industrial units.

The battle to save the Taj from the impact of pollution has been ongoing since the 1970s, and particularly since 1984 when environmentalist MC Mehta approached the Supreme Court of India, drawing its attention to the yellowing and blackening of the Taj marbles in several places, suspected to have been a result of “acid rains” caused by sulphur dioxide emissions.

“It is inside the Taj that the decay is more apparent,” the petitioner told the court. “Yellow pallor pervades the entire monument. In places, the yellow hue is magnified by ugly brown and black spots. Fungal deterioration is worst in the inner chamber where the original graves of Shah Jahan and Mumtaz Mahal lie.” This case resulted in the apex court’s landmark judgment of 1996 and many other orders over the next two and a half decades.

The recent paper on corrosion questioned the popular theory that blames sulphuric acid-induced “acid rain” – caused by the sulphur dioxide emitted by the Mathura refinery and the local industries in and around Agra and Firozabad – for the corrosion on the gleaming white marbles.

It cited a 2008 paper that revealed that the corrosion rate of steel exposed at Agra recorded an almost similar rate of corrosion as recorded at the other distant places considered to be free from industrial pollution and added, “Had the sulphur dioxide evolved from refineries and foundries a dominant role, the steel exposed at Agra should have shown a much higher rate of corrosion than at the other locations having comparatively lower industrial pollution in the atmosphere.”

Industrial units in Agra on the banks of the Yamuna river. Photo credit: Kathuria Films & Production/Mongabay

Corrosive effect

The analysis presented in the paper is based on a study conducted at the Taj Mahal site between 2006 and 2010 and, subsequently, an analysis of the retrieved samples was performed at the National Metallurgical Laboratory, Jamshedpur.

The corrosion products on the metals were analysed using Raman spectroscopy and X-ray diffraction and oxides and sulphides were found to be the main constituents. The researchers argued that reaction with acid rain would have formed sulphates and nitrates, but not sulphides. Agra’s climatic data for the period was also taken into consideration.

The authors, however, said the study needed to be further extended, “Exposing the samples of marble having similar composition, structure and porosity as used for the erection of the monument at the premise of the Taj Mahal.”

Since the process of the formation of tarnished patina on the surface of marbles is very slow, it is recommended that the duration of exposure should be long enough – about 10 years – to have meaningful findings and reach a definitive conclusion.

Study co-author Pandya said that since the Taj Mahal is quite tall (73 metres), metallic samples should also be placed at a higher elevation while conducting further studies to estimate the impact of the gas at different heights.

“If a scientific study claims Yamuna pollution is affecting the Taj Mahal, then it is a serious claim and this needs to be thoroughly investigated with further studies,” said Anurag Sharma of water conservation group, Jaladhikar Foundation, Agra.

While answering a question in the Lok Sabha in February, Prahlad Singh Patel, who at that time was the Minister of State (Independent Charge) for Culture and Tourism, said that the Archaeological Survey of India’s recommendations for ending the insect menace included scientific cleaning and preservation of the monument fabric, de-silting of Yamuna river, increase the water flow, prevent stagnation of the water and cleaning and removal of vegetation growth from the river banks.

This article first appeared on Mongabay.