Prolonged defoamer use to rid Yamuna of froth triggers ecological worries

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.

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.

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