A chemical preservative widely used in vehicle tyres is causing significant mortality in coho salmon populations in the Pacific Northwest and raising concerns about potential human health impacts. The compound, known as 6PPD, reacts with ozone in the atmosphere to form 6PPD-quinone, a toxic substance that enters waterways through stormwater runoff. This has been identified as a primary factor in the decline of salmon returning to spawn in urban streams.
Researchers have observed that coho salmon exposed to stormwater runoff exhibit erratic swimming behavior, loss of orientation, and ultimately die within hours. Investigations traced these acute mortality events to 6PPD-quinone, which is lethal to coho salmon at concentrations as low as 0.095 micrograms per liter. The chemical’s toxicity varies among species; for instance, brook trout and rainbow trout have higher lethal concentration thresholds of 0.59 and 1.0 micrograms per liter, respectively.
The implications of tyre wear particles extend beyond aquatic life. Studies indicate that these particles contribute significantly to air pollution, releasing a complex mix of microplastics, heavy metals, and other toxic chemicals into the environment. In urban areas, where vehicle traffic is dense, the concentration of these pollutants is particularly high. Inhalation of fine particulate matter from tyre wear has been associated with respiratory and cardiovascular issues, including increased risks of strokes and coronary heart disease.
The health concerns are not limited to respiratory ailments. Emerging evidence suggests that microplastics and associated chemicals from tyre wear may interfere with reproductive health. A comprehensive review highlighted strong evidence linking microplastic exposure to damage in reproductive systems and moderate evidence pointing to adverse effects on ovarian follicles and hormonal balance. These findings underscore the pervasive nature of microplastic pollution and its potential impact on human health.
Regulatory bodies are beginning to address these concerns. In the United States, the Environmental Protection Agency has initiated a review of 6PPD following petitions from West Coast Native American tribes advocating for its ban due to its detrimental effects on salmon populations. Additionally, lawsuits have been filed against major tyre manufacturers, seeking to prohibit the use of 6PPD or to compel companies to fund stormwater mitigation efforts to protect aquatic life.
The tyre industry faces the challenge of balancing product performance with environmental and health considerations. While 6PPD enhances tyre longevity by preventing degradation, its transformation into a toxic compound poses significant ecological and health risks. Researchers and manufacturers are exploring alternative additives and materials, such as bio-based compounds like guayule and dandelion rubber, to reduce the environmental footprint of tyres without compromising their durability and performance.
The rise of electric vehicles introduces additional complexities. Despite their zero tailpipe emissions, EVs tend to be heavier than their internal combustion counterparts, leading to increased tyre wear and, consequently, higher emissions of tyre-derived particulates. This underscores the need for developing tyres specifically designed for EVs that minimize wear and associated pollution.
Beyond tyres, other vehicle components contribute to non-exhaust emissions. Recent studies have revealed that microscopic particles emitted from brake pads can be more toxic than those from diesel exhaust emissions. These findings highlight the necessity of addressing all sources of vehicular pollution to mitigate their cumulative impact on environmental and human health.