ORCID ID

0000-0003-3005-8177

Date Awarded

Spring 2024

Document Type

Capstone Project

Degree Name

Master of Arts (M.A.)

Department

Virginia Institute of Marine Science

Advisor

Molly Mitchell and Robert Hale

Committee Member

Jacques Oliver

Abstract

Around 3.1 billion tires are produced around the world annually1. The antioxidant additive, 6PPD (i.e., N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine) is widely employed in passenger and commercial vehicle tires at 0.4-2% by mass to impede tire degradation2. Antioxidants are intended to migrate to tire surfaces and form protective films to prevent rubber oxidation. 6PPD is designed to react with oxidant species like ozone, intentionally forming chemical transformation products that can then escape from the tire and into the environment. 6PPD-Q (i.e., 2-anilino-5-[(4-methylpentan-2-yl)amino]cyclohexa-2,5-diene-1,4-dione) is one such transformation product.

After release and disbursement in the environment, 6PPD-Q is bioavailable to aquatic animals and mammals and acute exposure to 6PPD-Q can be lethal to some organisms. Additionally, exposure at environmentally relevant concentrations can induce neuro-, cardio-, intestinal, respiratory, and reproductive toxicity. 6PPD-Q was discovered to be the cause of massive coho salmon (Oncorhynchus kisutch) die-offs in the U.S. Pacific Northwest in 20213. Following this discovery, many publications have further documented its toxicity to diverse organisms including fish, invertebrates, bacteria, and mice. The presence of 6PPD and 6PPD-Q have been reported in a variety of environmental matrices worldwide. The potential risks to human and environmental health posed by 6PPD-Q has only recently been investigated. There is, however, a deficiency of publications regarding policy and regulation of this chemical.

Despite its widespread detection, much is unknown about 6PPD-Q. Yet understudied is its toxicity to humans, species specific toxicity mechanisms of action, long-term exposure impacts, and sublethal and developmental toxicity endpoints. Its impact on other organisms and ecosystems, such as freshwater invertebrates, amphibians, and aquatic plants, also remains uncertain. More information regarding bioaccumulation and biotransformation are also needed. With so much being unknown about 6PPD-Q, it is important for responsible policies to be developed and implemented quickly. The benefit of enacting policies early outweighs any potential added costs of action.

Considering the decades of harm its use has likely caused, quick actions should be taken to reduce future impacts. Failure to implement policies in a timely manner regarding environmental pollution is too often the norm and it allows for much harm to come to the inhabitants of the natural environment – including humans. While it is too late to work proactively to prevent all releases of 6PPD and 6PPD-Q, it is imperative to put policies and other mechanisms in place to stem their release, protect sensitive populations, and to ensure the chemicals replacing 6PPD as rubber additives do not pose additional threats.

DOI

https://doi.org/10.25773/5fey-8x40

Rights

© The Author

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