Ecological concerns have been raised over the prolonged use of silicone-based defoamers to prevent frothing in the Yamuna, with a Delhi-based environmental group pointing that the spraying this year has continued far longer than in the previous years.
In a letter sent to Lieutenant Governor VK Saxena and CM Rekha Gupta, among others on Monday, Earth Warrior, a nonprofit, claimed that the practice has been carried out “for more than 40 days till date (November 23, 2025)” and that it had “commenced in the second week of October 2025,” unlike the shorter duration associated with the Chhath Puja period in earlier years.
According to the letter, the group maintains that “for the last three years (2022–2024), the Delhi Jal Board (DJB) restricted the spraying… to only 7–10 days immediately before and during Chhath Puja,” and that this year’s timeline represents a significant departure from that pattern.
The group has also requested clarity from the DJB on whether any scientific or ecological assessment was conducted before approving prolonged spraying, noting that the key question that arises is the basis on which such an extended operation has been undertaken.
The DJB has not yet issued an official response to the concerns raised in the letter.
A senior DJB official, speaking on condition of anonymity with The Indian Express, said that excessive defoaming can potentially pose ecological risks. The official noted that international research has documented instances where silicone-based defoamers may settle on the gills of fish or form thin films on the water surface that could interfere with oxygen transfer. The official also said the dosing of a defoamer is typically determined by factors such as the thickness of the foam, bubble size and whether the foam is compact or loose.
Meanwhile, Earth Warrior has requested that the DJB release, within seven days, any scientific study or risk assessment undertaken before the spraying; the methodology used for calculating dosage; date-wise permissible dose versus actual quantities used since October 10; daily consumption data of the concentrated defoamer; and water-quality assessments before and after the spraying. The group has urged that the spraying be suspended until such information is made public and independently reviewed.
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In its letter, Earth Warrior stated that its members observed spraying “even when little or no foam is visible on the river surface,” particularly between October 15 and 30. These observations, the group said, have prompted concerns about the need for clearer protocols and publicly available information on dosage calculations and ecological safeguards. “Such indiscriminate and prolonged application far exceeds any reasonable temporary measure and poses grave risks to the river ecosystem,” the letter read.
The group cited international studies on polydimethylsiloxane (PDMS), the silicone compound used in many defoamers, pointing to research that has reported reduced oxygen transfer, slow biodegradation, and potential impacts on fish and aquatic organisms at high concentrations. One study referenced in the letter reported “100% mortality within 24 hours at 0.5% and 0.25% concentrations” in Tilapia guineensis, with a lethal concentration of 50% of organisms at 0.176% after 96 hours. The letter also mentioned the possibility of bioaccumulation and interactions with existing pollutants.
Sophiya Mathew is a Correspondent at The Indian Express, based in New Delhi. She joined the Delhi bureau in 2024, and has specialization in Integrated Multimedia Journalism from the Asian College of Journalism (ACJ), Chennai.
Professional Background
Core Beats: Her reporting is primarily focused on the Environment and Education.
Specialization: She has gained recognition for her ground-level reporting on the Yamuna floodplains and the socio-economic challenges faced by those living on its banks. She also focuses on the disparities in Delhi's education system, ranging from elite private schools to government institutions and refugee education.
Recent Notable Articles (December 2025)
Her recent work has been heavily centered on Delhi's severe winter pollution crisis and the government's regulatory responses:
1. The Air Pollution Crisis
"A tale of two cities: Delhi govt schools choke in bad air, private classrooms set up air filters" (Dec 20, 2025): A high-impact feature contrasting the "Clean Air Bubbles" in elite schools with the reality of government school students who are exposed to an equivalent of 17 cigarettes a day due to outdoor exposure.
"Delhi sees season's worst air day, second worst December AQI in nearly a decade" (Dec 15, 2025): An analytical report on the meteorological patterns trapping pollutants in the NCR.
"Delhi bans non-BS VI vehicles from outside: Why curbing vehicular pollution is key" (Dec 17, 2025): Explaining the science behind targeting specific vehicle vintages to lower particulate matter.
2. Enforcement & Regulations
"No fuel at pumps in Delhi without valid PUC certificate from December 18" (Dec 17, 2025): Breaking the news on the environment ministry's strict "No PUC, No Fuel" policy.
3. Education Policy
"Law to regulate school fee in Delhi risks becoming procedural, say parents" (Dec 13, 2025): Investigating the loopholes in the new Delhi School Education (Transparency in Fixation and Regulation of Fees) Bill, 2025.
"Monsoon Session: Private school fee regulation Bill cleared after four-hour debate" (Aug 9, 2025): Covering the legislative passage of the controversial fee hike regulation.
Signature Style
Sophiya is known for her observational depth. Her reporting often includes vivid details from school corridors, hospital waitlists, or the banks of the Yamuna to illustrate how policy failures affect the city's most vulnerable residents. She is a frequent expert guest on the 3 Things podcast, where she explains the complexities of Delhi’s environmental laws.
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