Over the years, visitors to the Taj Mahal have complained of a foul smell that spoils their experience in the majestic 17th century Mughal architecture listed as one of the New Seven Wonders of the World. The gas responsible for the smell can actually do more harm – it’s likely the culprit behind the fading of the Taj’s beautiful white marbles.

The stench coming from the black waters of the flowing Yamuna River prompted a group of scientists to explore whether the gas that was responsible for the odor – hydrogen sulfide (H₂S) – also had corrosive effects. They found that H₂The S released by the polluted water at Yamuna had a more corrosive impact than sulfur dioxide (SO₂) released by industrial pollution in the city of Agra.

The results are gaining in importance, as initiatives to protect the Taj from pollution have largely concerned combating industrial and automotive pollution, while Yamuna’s pollution has not received as much attention until it. five years ago.

For more than three decades now, sulfur dioxide has been considered the main pollutant responsible for the decomposition of glorious white marbles. Yamuna’s pollution was also blamed for the impact on the structure of the marble, in a 2016 report by the Archaeological Survey of India submitted to the Supreme Court of India, but from a different perspective – he put in evidence the growth of the insect of the genus Goeldichironomus, in the stagnant water of Yamuna devoid of aquatic life and attributed to the insect excrement the green and brownish spots on the marbles of the Taj.

The recent study, however, indicates that the polluted Yamuna could harm the Taj in more than one way.

“We have tried corrosion deformation studies using various air pollutants such as SO₂, NO₂ (nitrogen dioxide), NH₃ (ammonia), CO (carbon monoxide), CO₂ (carbon dioxide) and H₂S. More interestingly, H₂S turned out to be the most problematic of all. Our preliminary investigation establishes that the Yamuna River, which carries untreated sewage from all of Agra, was responsible for the generation of H₂S, ”Dipankar Saha, former additional director of the Central Pollution Control Board (CPCB) and one of the co-authors of the article, told Mongabay-India.

“H₂S gas is acidic and corrosive, so a lot of attention is needed to clean up the Yamuna River, ”added Saha, who also ran the CPCB aerial lab for 12 years.

Recently published in the International Journal of Environmental Science and Technology, the study also noted: “The compass rose diagram developed during the study period suggests that the wind direction was against the moving industrial pollutants. towards the monument ”and that“ the hydrogen sulphide emitted by the polluted Yamuna river… has a dominant role.

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

Pandya told Mongabay-India that in order to protect the Taj from fading, it was necessary that the Yamuna be cleaned and that the city’s sewage was only allowed into the river after treatment. “It is no longer a river, its water is unusable. But we must remember that the Yamuna included the original landscape of the Taj Mahal. The river was an integral part of the planning of the whole premises.

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

“The discovery of this study leads to the conclusion that the discoloration of the white marbles of the Taj Mahal may be due to the corrosive effect of hydrogen sulfide emitted by the polluted Yamuna River,” the report said.

Agra-based environmentalist Sharad Gupta said the study’s results are not surprising.

“Sewage and industrial waste from all over the city, including solid waste, flows into the Yamuna for the most part untreated. There are 90 nullahs in Agra, of which only 25 water is treated by 4 factories but these factories do not work at night. Wastewater from 65 other drains flows into Yamuna untreated. The materials include leather and synthetic leather waste from around 3,000 shoe factories and this leather waste contributes to the formation of many gases, ”he told Mongabay-India.

He added that acids used for washing in Agra’s imitation jewelry industry are also discharged into untreated sewers.

No acid rain?

The impact of Yamuna’s pollution on the Taj has remained little discussed, but not entirely ignored. Taj protection initiatives have mainly focused on industrial units, which has resulted in a series of measures since the 1980s to reduce industrial pollution in Agra, including the relocation and closure of some polluting industrial units.

The battle to save the Taj from the impact of pollution has been going on since the 1970s, and especially since 1984 when environmentalist MC Mehta took the Supreme Court of India to India, calling its attention to the yellowing and darkening of the Taj marbles in several places, believed to have been the result of “acid rain” caused by sulfur dioxide emissions.

“It is inside the Taj that the degradation is most apparent. A yellow pallor pervades the whole monument. In places, the yellow tint is amplified by ugly brown and black spots. The fungal deterioration is worse in the inner chamber where the original graves of Shah Jahan and Mumtaz Mahal are located, ”the applicant told the court. This case culminated in the landmark 1996 Supreme Court judgment and numerous other orders over the next two and a half decades.

The recent article on corrosion challenged the popular theory of sulfuric acid-induced “acid rain” – caused by SO₂ issued by Mathura refinery and local industries in and around Agra and Firozabad – for corrosion on shiny white marbles. He cited a 2008 article which found that the corrosion rate of exposed steel at Agra had a corrosion rate almost similar to that recorded in other remote locations considered to be free from industrial pollution and added: “₂ Evolved from refineries and smelters a dominant role, the steel exposed at Agra should have shown a much higher corrosion rate than in other places with comparatively lower industrial pollution in the atmosphere.

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

Corrosion products on metals were analyzed using Raman spectroscopy and X-ray diffraction and oxides and sulfides were found to be the main constituents. The researchers argued that the reaction with acid rain would have formed sulfates and nitrates, but not sulfides. Agra climate data for the period was also taken into consideration.

The authors, however, said the study needs to be further extended, “Exhibit samples of marble having a composition, structure and porosity similar to those used for the erection of the monument on the premises of the Taj Mahal.” Since the process of forming a tarnished patina on the surface of the marbles is very slow, it is recommended that the exposure time be long enough – around 10 years – to have significant results and reach a definitive conclusion .

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

“If a scientific study claims that Yamuna’s pollution affects the Taj Mahal, then this is a serious claim and it needs to be investigated in depth with additional studies,” said Anurag Sharma of the water conservation group, Foundation. Jaladhikar, Agra.

Responding to a question at Lok Sabha in February 2021, Prahlad Singh Patel, who at the time was Minister of State (Independent Charge) for Culture and Tourism, said the ASI recommendations to end the threat of insects included scientific cleaning and preservation of monument fabric, de-silting the Yamuna river, increasing water flow, preventing water stagnation and cleaning and eliminating the growth of the vegetation of the river banks.

Read more: [Video] Creeping sand mining damages Yamuna’s ecology

Banner image: The Yamuna River flowing next to the Taj Mahal. Photo by David Castor / Wikimedia Commons.