The toxic tyre chemical no one is measuring

A chemical used to make tyres last longer turns into 6PPD-quinone, a toxin linked to mass deaths of salmon in the U.S.
With vehicle and tyre sales rising in India, experts warn the problem could grow, but no data exists on the toxin’s levels in Indian road dust, stormwater or water bodies.
Experts call for regulating 6PPD and better stormwater management, as poor drainage and sewage-laden storm drains in Indian cities could carry the toxin into water bodies.

Every time a vehicle moves, its tyres shed tiny particles. Some of these particles carry a chemical that, in the U.S., was found killing salmon in urban streams after rain. India is selling more vehicles than ever before, yet experts say there is no data on how much of this chemical reaches the country’s rivers.

The chemical is 6PPD (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine), an additive used worldwide to increase tyre durability. It became a concern after researchers from the U.S. published a study in the journal Science in December 2020, linking a compound formed from 6PPD to mass deaths of coho salmon in urban streams after rain.

“6PPD is used to neutralise ozone, prevent cracks in the rubber, and extend the lifespan of the tyre,” according to a January review article in RSC Advances by the Royal Society of Chemistry. The review opens by noting that India’s tyre market is expanding with its automotive industry, then examines the toxic effects of 6PPD-quinone (6PPD-Q), a byproduct formed when 6PPD reacts with ozone.

Echoing the same, Paul Sharp, a chemist and Professor Emeritus, University of Missouri, Columbia, USA, says, “6PPD-Q is the ozonisation byproduct of 6PPD and formed as a tyre wear particle. It has no boundaries and is ubiquitous all over the motorised world. These can make their way into water bodies during rainstorms, leading to rapid/mass death of aquatic species.”

Responding to Mongabay-India’s email interview, Sharp explains that as tyres wear down, 6PPD reacts with ground-level ozone to form 6PPD-Q. Edward Kolodziej, a professor of the University of Washington, says that 6PPD-quinone was one of the most toxic compounds known to aquatic organisms.

The toxic tyre chemical no one is measuring — Every time a vehicle moves, its tyres shed tiny particles, some of which carry 6PPD, a chemical used worldwide to increase tyre durability. In the USA, it was found killing salmon in urban streams after rain. Image via Public Domain.

Global finding, local concerns

The identification of 6PPD-Q as a lethal toxin was a long journey, says Sharp. Scientists worked for 20 years to understand the “urban runoff mortality syndrome,” in which 90% of coho salmon returning to urban creeks died rapidly after rainstorms.

Scientists studied various possibilities for the death of unspawned salmon, such as higher temperatures, pathogens, low dissolved oxygen, zinc and pesticides. It was clear that these parameters were not the reason for mass death. One clue was that the salmon died after it rained. Something in the stormwater runoff was killing the coho salmon, Sharp says.

Jen McIntyre, Assistant Professor of Washington State University and her colleagues studied stormwater from various creeks and found chemicals associated with tyre-wear particles. Through toxicity studies, they narrowed the culprit down to an unknown compound closely related to 6PPD. Further studies confirmed that 6PPD reacts with ozone to form 6PPD-Q, the toxin killing the salmon.

Since then, the finding has led to several studies, but few have examined the impact of 6PPD-Q in India.

“To the best of our knowledge, no scientific data exists on the 6PPD-Q levels in Indian road dust, stormwater or water bodies,” says N. Jayaraman, Professor and the Chair of the Department of Organic Chemistry at the Indian Institute of Science (IISc) in Bangalore. However, a global air-monitoring study conducted in 2022 quantified tyre-derived chemicals in the air using passive samplers. It included 18 megacities worldwide, including Kolkata. Notably, Kolkata ranked first among all global cities in diphenylguanidine concentration. The study did not report quantified data on 6PPD-Q, he adds.

When asked whether there is any reason to think Indian tyres are made differently, he says, “No. 6PPD is the goldilocks of the tyre industry so Indian tyres use them and it’s backed up by literature.”

Jayaraman says that as it is a recent issue, awareness in India may be low. The COVID-19 pandemic, followed by recent geopolitical turmoil, diverted resources and public attention. Besides, because India has relatively fewer privately owned cars than the Western world, this problem might not have received much attention. However, with rising middle-class incomes and urbanisation, more cars are on Indian roads, and he says this could become a bigger problem in the coming years.

Commuters drive through rain. Experts say no scientific data exists on the 6PPD-Q levels in Indian road dust, stormwater or water bodies. Image by Jorge Royan via Wikimedia Commons (CC BY-SA 3.0).

More vehicles, more tyre dust

India is now the world’s third-largest market for automobiles, surpassing Japan. In 2025-26, the automobile sector saw record growth of 10.4%, with passenger and commercial vehicles, two-wheelers, and three-wheelers all at their highest-ever annual sales. With increased automobile sales, the tyre industry also grew steadily. According to the Automotive Tyre Manufacturers’ Association (ATMA) India, total tyre production in India rose 21% in 2022 and 6% in 2023.

Old tyres also find a second life. Scrap tyres are shredded into crumb rubber, which is used as infill in some artificial turf, particularly on sports fields, to cushion the surface. Researchers have detected 6PPD and 6PPD-quinone in artificial turf athletic fields in the U.S. There are several estimates indicating that the artificial turf lawn sector in India is expanding.

Given the increasing use of these materials, Jayaraman says there is an urgent need for policy measures to regulate 6PPD in Indian’s tyre industry.

He argues that India has weaker law enforcement than the Western world and lacks effective regulatory bodies to safeguard rivers, lakes and ponds. “Our water bodies are already in poor shape, so regulation becomes very important to save the water bodies from 6PPD-Q pollution,” he says.

India lacks proper stormwater management (SWM). In most Indian cities, stormwater drains invariably carry sewage because the sewage network is not properly managed. Most Indian cities lack a dedicated SWM system. As a result, storm drains carry untreated sewage and rainwater. As rainfall patterns become erratic and intense, stormwater runoff mixed with sewage could worsen contamination of water bodies by 6PPD-Q.

Sharp says that 6PPD-Q ranks second among the 10 listed toxic chemical compounds to aquatic life worldwide.

Until India starts measuring 6PPD-Q in its road dust, drains and rivers, experts say the scale of the problem will remain unknown.

Banner image: A taxi on the move in Kolkata, West Bengal. A global air-monitoring study quantified tyre-derived chemicals in the air using passive samplers. Kolkata ranked first among all global cities in diphenylguanidine concentration. Image by Dharamveer via Pexels.