Even very low concentrations of one tire chemical can kill certain fish. Studies have shown it, and the chemical is called 6PPD-quinone, or 6PPD-q. Nobody adds it to a tire. It forms on its own, after the rubber starts to wear.
Here’s the chemistry in plain terms. Tire makers put 6PPD into rubber so it lasts longer. It belongs to the phenylamine family and works as both an antioxidant and an antiozonant. Think of it like sunscreen for a tire: it reacts with ozone first, so the ozone never gets a chance to crack the rubber.
From protector to poison
As a tire wears down, 6PPD moves to its surface and meets ozone there. The reaction produces 6PPD-q. Tire wear particles carry the new compound into the environment, according to AccuStandard, a supplier of chemical reference materials, and from there it reaches waterways where fish and other aquatic animals take it in.
The damage is best documented in coho salmon. 6PPD-q raises the risk of death among aquatic organisms, particularly that species, and is linked to a condition called urban runoff mortality syndrome. AccuStandard also notes possible implications for people who eat fish that contain the compound.
Not the only breakdown product
6PPD-q is one of the best-known metabolites, but it is not the only one. It is well established that 6PPD can transform in the environment into several products, and some of them may be more toxic than 6PPD itself. AccuStandard lists 4-hydroxydiphenylamine, 4-Nitrosodiphenylamine, 1,3-dimethylbutylamine and p-Benzoquinone among the examples.
Swapping in a substitute is not a simple fix. Other antioxidants used in consumer products to protect rubber have similar structures. Among the common alternatives to 6PPD are 7PPD, CPPD, DPPD and IPPD. That resemblance suggests they could produce similar transformation products with comparable toxicity.
Testing and regulation
The EPA and other regulators have published test methods to measure 6PPD-q, aiming to monitor it and limit its presence in the environment. EPA Draft Method 1634 determines 6PPD-q in surface water using LC-MS/MS. AccuStandard sells certified reference materials for 6PPD, its transformation products and replacement candidates, and has synthesized an extended list of 6PPD metabolites to help researchers trace the breakdown pathways.
