For two decades, coho salmon kept dying in West Coast streams whenever it rained, and nobody could say why. Scientists put fish in water containing old and new tire particles. The salmon died. Then came the slow job of testing a long list of chemicals that had washed out of the rubber.
A 2020 paper named the culprit: 6PPD, an additive that keeps tires from cracking and breaking down. Tire dust carries it, and when ozone at ground level reaches it, it turns into several other chemicals, among them 6PPD-quinone. Yale Environment 360 reported that the compound is sharply toxic to four of the 11 fish species tested, coho among them.
A new question about the brain
Now a different group of researchers is asking whether the same chemical matters for people. Zhang and Zhang, reporting in Open Medicine, a de Gruyter Brill journal, say their paper is the first to look at a possible link between 6PPD-quinone and Alzheimer’s disease in a systematic, data-driven way.
The starting point is that 6PPD-quinone has been detected in human biological samples as well as in water and soil, so people are plainly exposed through traffic pollution. Earlier work found it toxic to fish and able to reach the brains of mice. The authors used machine learning to chart how it might act on the brain’s molecular machinery. They picked out five genes that predict Alzheimer’s and found that the chemical binds strongly to three of them. In their model, that sets off oxidative stress, inflammation and a breakdown in communication between brain cells.
Caution is needed. The authors describe a theoretical framework, built mostly on computation, gene datasets and brain tissue from only a few people with Alzheimer’s. Lab work on cells and human tissue, plus animal studies, would have to confirm it. Epidemiological studies would then be needed to show how much everyday exposure actually raises the risk. The researchers say their work offers “the first systematic characterization of the molecular mechanisms by which 6PPD-Q may contribute to Alzheimer’s disease pathogenesis”.
A very large source
The scale is part of the worry. Some 2 billion tires are sold worldwide each year, Yale Environment 360 said, a pile that would stretch to the moon if stood on edge, and the market is expected to climb to 3.4 billion annually by 2030. One estimate it cited, from the Pew Charitable Trust, is blunt: Seventy-eight percent of the ocean’s microplastics are tire rubber of the synthetic kind.
Pressure for rules has been building. The legal nonprofit Earthjustice, acting for the fishing industry, served notice that it intends to sue tire makers under the Endangered Species Act over their use of 6PPD, and a coalition of tribes asked the EPA to ban it. “We have witnessed firsthand the devastation to the salmon species we have always relied upon to nourish our people,” the Puyallup Tribal Council said.
Sources
- Invisible Tire Dust Hijacks Alzheimer's Predictor Genes
- Emerging evidence links tire pollution to Alzheimer's risk
- Road Hazard: Evidence Mounts on Toxic Pollution from Tires
