Bridgestone, Michelin, Pirelli and 10 other tire manufacturers in the United States are facing off in court against the Institute for Fisheries Resources and the Pacific Coast Federation of Fishermen's Associations, who are represented by the environmental group Earthjustice.
Plaintiffs argue that usage of the additive 6PPD can devastate coho salmon and other fish populations who live off the coasts of California and Alaska.
The suit charges that the use of the additive constitutes an illegal "taking" under the US Endangered Species Act, affecting 24 populations of coho, Chinook salmon and steelhead trout listed as threatened.
The 13 tire companies have argued that 6PPD provides an essential safety function by ensuring the integrity of tires when they come into contact with ozone and oxygen.
But plaintiffs say the use of 6PPD, when combined with ozone, produces 6PPD-quinone or 6PPD-q, which moves into waterways after storm events, with devastating consequences for fish populations.
Scientific studies published by prestigious journals have shown such substances to be damaging to fish populations, even at low doses.
6PPD-q "can kill coho salmon within hours and the chemical is largely responsible for 'urban runoff mortality syndrome,' which can kill up to 100 percent of salmon returning to freshwater streams to spawn in the Pacific Northwest before they can lay eggs," Earthjustice says on its website.
On Monday, researcher Edward Kolodziej testified before US Judge James Donato that just one automobile could do tremendous damage.
A car contains four tires with enough of the chemical that, after interacting with ozone, could produce enough to 6PPD-q to kill more than 11 million salmon, said Kolodziej, whose testimony followed video of a salmon flailing in the water in distress.
Countering that testimony were remarks from scientist Tiffany Thomas of consultancy Exponent, who told the court that the findings presented by plaintiffs' scientists were based on laboratory conditions rather than real life and therefore were "limited and speculative."
Concentrations of 6PPD-q found in waterways are well below lethal doses, according to Thomas.
Tire companies maintain, further, that there is no substitute for 6PPD, adding that other possible options would have worse environmental impacts.
Hearings in the case will continue on Wednesday and Thursday with further testimony from scientists. A ruling is expected at a later time.
Beyond the California case, the European Chemicals Agency is also weighing potential restrictions on 6PPD in tires.
Health threat of global plastics projected to soar
Paris, France (AFP) Jan 26, 2026 - The threat posed by plastic production, usage and disposal to human health will skyrocket in the coming years unless the world does something to address this global crisis, researchers warned Tuesday.
A British-French team of researchers attempted to cover all the different ways that plastic affects health, from oil and gas extraction during production to all the products that end up in landfills.
However they said that their modelling study still does not take into account an array of other ways plastic could harm health, such as microplastics or chemicals that can leach out of food packaging.
"This is undoubtedly a vast underestimate of the total human health impacts," lead study author Megan Deeney of the London School of Hygiene & Tropical Medicine told AFP.
The study, published in The Lancet Planetary Health, said it was the first to estimate the number of healthy years of life lost due to the lifecycle of plastic worldwide.
The researchers used a measure called DALYs, which represents the number of years lost to either early death or diminished quality of life from illness.
Under a business-as-usual scenario, the number of DALYs caused by plastic was projected to more than double from 2.1 million in 2016 to 4.5 million in 2040.
Planet-heating greenhouse gas emissions from plastic production had the biggest health impact, followed by air pollution and toxic chemicals.
- 'Public health crisis' -
Deeney gave the example of a plastic water bottle.
Like more than 90 percent of all plastic, its production begins with the extraction of oil and gas.
A series of chemical processes then transform those fossil fuels into Polyethylene terephthalate -- or PET -- which the bottle is made from.
Deeney pointed out that a stretch of more than 200 petrochemical plants involved in plastic production in the US state of Louisiana is known as "cancer alley".
Once made, the plastic bottle is transported across the world to a shop.
Then it gets chucked in the rubbish -- or littered.
Despite recycling efforts, most plastic ends up in landfills where it can take centuries to decompose, leaching out chemicals during that time, Deeney said.
The researchers also modelled a scenario where the world tried harder to fight the health effects of plastic.
They found that plastic recycling made little difference.
The most effective measure was reducing the amount of "unnecessary" plastic created in the first place, Deeney said.
Talks to seal a world-first treaty to fight plastic pollution fell apart in August under opposition from oil-producing countries.
However Deeney emphasised that countries can still act at a national level to address this "global public health crisis".
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