What is TIP doing about 6PPD-quinone?

On 3 December 2020 (Science), Tian et al., published research that suggested a link between 6PPD-quinone (a transformation product of the tire ingredient 6PPD) and mortality in coho salmon.

6PPD is used in tires and in other rubber products due to its antioxidant and antiozonant effects which slow the aging process. 6PPD is covered by chemicals regulations worldwide (including the EU Regulation on the registration, evaluation, authorization and restriction of chemicals (REACH) and the US Toxic Substances Control Act (TSCA)), and its use is regulated accordingly.

6PPD-quinone had not been identified before the Tian et al., paper, but its identification prompted TIP to expand its program of sponsored research to further scientific understanding of the transformation process that results in this newly identified chemical, and the potential for impacts on other salmonids (a family of fish species that includes coho salmon). Our research has so far identified that 6PPD-quinone is formed in air and not water.

Understanding the origins and fate of 6PPD-quinone in water and air can help guide any necessary mitigation; therefore, we sponsored a study to understand the process of transformation of 6PPD in water and air. The study found that 6PPD-quinone is a product of the transformation of 6PPD in air – in a process that appears to be accelerated by exposure to sunlight – whereas 6PPD-quinone was not found to be produced by reaction with water.

In order to better understand how 6PPD-quinone might impact certain fish species – which can be useful in guiding the design of potential alternative molecules – TIP is sponsoring in-vitro toxicity assessments of tire particles and tire-associated chemicals into the gill, gut, and brain cell-lines of rainbow trout. Rainbow trout are a common freshwater test species and – like coho salmon – are a member of the salmonid family. 6PPD-quinone was not found to be toxic to rainbow trout gill and gut cell-lines at environmentally relevant concentrations. The preliminary results of the brain-cell tests have not ruled out the potential for neurotoxic effect, which underscores the need for continued research.