6PPD Quinone and Its Impact on the Environment
6PPD is an antioxidant and antiozonant primarily used during the manufacturing process of rubber tires for vehicles. This chemical helps prevent the degradation and cracking of the tires by reacting with the ozone before the latter can react with the rubber, prolonging the life of the tires.
On its own, 6PPD is not hazardous; however, when it reacts with ozone – usually when tires heat up during driving – 6PPD is converted to 6PPD-quinone, the toxic chemical recently found to be harmful to fish, particularly the coho salmon. [1]
6PPD-quinone enters streams and waterways via any water runoff point from roads and other places where tires have been present; such as, storm drains, catch basins, recreational trails, playfields, or so-called tire graveyards. As the tires breakdown, increased concentrations of the hazardous 6PPD-quinone accumulate.
Salmon plays a crucial role in the health and function of freshwater ecosystems by benefiting other species as a rich source of food and nutrients. Citing the factors above, the chances of streams and waterways becoming contaminated with 6PPD-quinone are highly probable.
Identification and subsequent tests on 6PPD-quinone
The recent identification of 6PPD-quinone as the prime cause of toxicity in coho salmon has naturally led to significant concerns about the chemical’s potential for harming other aquatic creatures. However, studies on 6PPD-quinone and its toxicity have revealed a rather unexpected pattern, as closely related species showed varying responses to this compound. Some species exhibited extreme sensitivity, while others did not react at all. These varied observations indicate that the compound’s toxicity targets specific species; only complicating urgently needed environmental risk assessment.
Several research laboratories have begun testing 6PPD-quinone’s acute toxicity on other fish, such as Atlantic salmon and brown trout alevins (newly spawned trout still carrying the yolk sac). These fish species had not undergone testing previously for the compound.
The research labs exposed the fish in static conditions, with initial 6PPD-quinone concentrations ranging from 0.095 to 12.16 micrograms per liter (μg/L) and then observed the fish for 48 hours while monitoring every change in 6PPD-quinone concentrations throughout the experiment. The findings reported no mortalities or significant changes in behavior in either the Atlantic salmon or brown trout. This analysis provided a crucial step in assessing 6PPD-quinone’s effects on salmon and trout, both economically and culturally important fish species. [2]
A study in 2022 also identified 6PPD-quinone’s toxicity in other fish species like brook trout and rainbow trout. The following lethal concentrations have been published so far: [3]
- Coho salmon – LC50 = <0.1 μg/L
- Brook trout – LC50 = 0.59 μg/L
- Rainbow trout – LC50 = 1.0 μg/L
Other research labs detected 6PPD-quinone in stormwater draining into waterways, such as streams and creeks with levels high enough to raise concerns; although, fortunately, the concentrations were still low in the receiving bodies of water, lessening the overall impact. Furthermore, the compound was detected in storm drainages, but fortunately again, the levels observed remained below concern. Researchers will continue to study the local waterways, especially those along highly used traffic corridors.
Currently, the Pacific Northwest is the most studied region as it is the most affected. But 6PPD-quinone’s impact may also be considered a global problem. Over 1.6 billion new tires are produced annually, and about a billion waste tires are generated yearly, with the majority accumulating in tire graveyards. Considering these significant numbers, 6PPD-quinone begs elevated attention from scientists and continual studies.
Will there be an alternative to 6PPD?
Tire producers have used 6PPD as an essential component in manufacturing products since the mid-1960s but have become increasingly aware of the seriousness of the issue. The global tire industry has established a joint task force to address the rising concerns and have vowed to continue working with researchers regarding 6PPD-quinone’s impact on the environment.
However, this mission will be a tricky one; addressing environmental matters caused by 6PPD-quinone is one thing, finding a solution is another. Again, 6PPD is an antioxidant and antiozonant. It prevents tire degradation; vital to driver and passenger safety. If solving the problem means eliminating 6PPD from the tire rubber formulations, there should be more suitable – and safer – chemical alternatives. However, to-date, no known chemical alternatives have been found as effective.
6PPD-quinone’s solubility
As expected, 6PPD-quinone is sufficiently water-soluble to enter waterways and streams by way of surface runoff, where the compound is toxic to coho salmon and other fish. Despite 6PPD being used in tire production since the mid-1960s, 6PPD’s harmful breakdown into 6PPD-quinone was only identified in 2020. [4]
What does 6PPD-quinone’s toxicity mean to food production and human health?
6PPD-quinone’s toxicity to coho salmon is now well established. 6PPD-quinone is especially highly toxic to juvenile coho salmon (median lethal concentration [LC50] 0.79 ± 0.16 μg/liter) [5] and can kill adult fish before they spawn in freshwater streams.
But as the experiment on the Atlantic salmon and brown trout has proven, not all aquatic animals may not react sensitively to 6PPD-quinone, concluding that its toxicity may target particular fish species.
The mechanism for this toxicity has yet to be well known. The broader impact of 6PPD-quinone’s contamination on drinking water, food production, or human health is inconclusive. Multiple studies are still underway to understand the kinetics and broaden the toxicological understanding of this compound, but scientists admit it will take some time before they have the answers. For now, they say it is far too early to speculate on food production or 6PPD-quinone’s impact on drinking water and human health.
In response to the growing concern and need for an analytical method to achieve the desired level of concern, Caltest has developed an analysis for 6-PPD quinone (CAS # 2754428-18-5) by EPA 632 using high pressure liquid chromatography (HPLC).
Environmental samples are collected in 1-liter amber glass bottles to protect them from photodegradation. These samples are extracted within 14 days of sample collection and brought to a 1 milliliter final volume. All analyses are performed within 28 days of extraction, and include standard batch QC (Method Blank, Laboratory Control Sample (LCS), Matrix Spike and Matrix Spike Duplicate (MS/MSD). It is important in collection of samples to provide at least two additional 1-liter bottles for the Matrix Spike and Spike duplicates, (total of three liters required; preferably four to allow for an extra volume in the event sample re-extraction is necessary).
The developed method currently achieves a method detection limit (MDL) of 0.0069 µg/L (6.9 ng/L) with a low calibration point and Reporting Limit (RL) of 0.010 µg/L (10 ng/L).
For more information or a quote for 6PPD Quinone analyses, please email us at info@caltestlabs.com.
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| Analyte | RL | MDL* | Units | |
| 6PPD Quinone | 0.010 | 0.0069 | μg/L | |
*MDL values listed on the website may not be reflective of the most current MDL study. Check with the lab for the most current list.
References
[1] Anchorage Waterways Council, undated. “6PPD-quinone and its impact on coho salmon.” Available on: https://www.anchoragecreeks.org/single-project (accessed on February 1, 2023)
[2] Andres Foldvik, Fedor Kryuchov, Roar Sandodden, Silvio Uhlig, 2022. “Acute Toxicity Testing of the Tire Rubber-Derived Chemical 6PPD-quinone on Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta).” Pubmed.com. Available on: https://pubmed.ncbi.nlm.nih.gov/36148925/ (accessed on February 1, 2023)
[3] Markus Brinkmann, David Montgomery, Summer Selinger, Justin G. P. Miller, Eric Stock, 2022. “Acute Toxicity of the Tire Rubber-Derived Chemical 6PPD-quinone to Four Fishes of Commercial, Cultural, and Ecological Importance,” Environmental Science & Technology Letters, vol. 9, no. 4, pp. 333–338, doi: 10.1021/acs.estlett.2c00050, S2CID 247336687 (accessed on February 1, 2023)
[4] Sean Dixon, Chen-Yeh Goh, 2020. “Tire-driven stormwater toxicity and salmon mortality from 6PPD-quinone.” American Bar Association. Available on: https://www.americanbar.org/groups/environment_energy_resources/publications/trends/2022-2023/september-october-2022/tire-driven-stormwater-toxicity/ (accessed on February 1, 2023).
[5] Science.org authors, 2020. “A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon.” Science.org. Available on: https://www.science.org/doi/10.1126/science.abd6951. (accessed on February 1, 2023).