Today I learned that vehicle tires produce toxic dust that enters the air, rivers, and oceans spreading massive amounts of toxicity and is the largest source of ocean microplastics.
One specific tire-rubber additive called 6PPD turns out to be uniquely toxic even at remarkably low levels in Coho salmon, specifically.
It's the breakdown product of 6PPD into its quinone derivative when altered by ozone that is specifically toxic to Coho salmon at very low concentrations; Coho are about 800 times more sensitive than Chinook salmon.
Several non-toxic replacements are being evaluated, and are mandated to replace the toxic compound before 2035. In the meantime, environmental agencies are relying on stormwater solutions like rain gardens and bioretention soils to trap tire particles before they reach salmon streams.
The estimated per capita emission from tires ranges from 0.23 to 4.7 kg/year, with a global average of 0.81 kg/year. The emissions from car tires (100%) are substantially higher than those of other sources of microplastics, e.g., airplane tires (2%), artificial turf (12–50%), brake wear (8%) and road markings (5%).
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Car tires are one of the single largest sources of microplastics in our environment, accounting for roughly 28% of all microplastics found in the world's oceans. Scientists refer to this pollution as Tire and Road Wear Particles (TRWP). Unlike standard microplastics (like a degrading plastic water bottle), tire microplastics are uniquely dangerous because they act as "toxic sponges." They are packed with chemical preservatives, heavy metals (like zinc and lead), and anti-cracking agents (like 6PPD). As the microplastics sit in the water or inside an organism's stomach, these toxic chemicals leach out into the surroundings.
Another study suggested that microplastics specifically derived from tire dust accounts for approximately 78% of the total mass of ocean microplastics. Ref
Rainfall washes more than 7 trillion pieces of microplastics, much of it tire particles left behind on streets, into San Francisco Bay each year — an amount 300 times greater than what comes from microfibers washing off polyester clothes, microbeads from beauty products and the many other plastics washing down our sinks and sewers...a local rain garden was found to capture more than 90% of the microplastics before they reach the ocean.
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