Carcinogenic Car Tires?

Is there evidence to suggest that growing vegetables in old car tires filled with soil will contaminate them with carcinogenic substances?

Yes—but the evidence supports a plausible, probably low but uncertain risk, not a demonstrated finding that vegetables grown in intact old tires are necessarily contaminated with carcinogens.

What tires can contain

Tires contain complex mixtures of rubber, carbon black, oils, antioxidants, vulcanizing chemicals, metals, and other additives. Chemicals of concern include:

• Polycyclic aromatic hydrocarbons (PAHs), some of which are carcinogenic.
• Zinc and smaller amounts of metals such as lead, cadmium, chromium, and copper.
• Rubber additives such as benzothiazoles, 6PPD-related compounds, and vulcanization accelerators.

The EPA has found PAHs and metals in tire-derived rubber, although its exposure studies—primarily involving tire crumb used in athletic fields—found that only small fractions of many metals were bioaccessible under simulated exposure conditions. Those findings do not directly establish the safety of tire planters for food crops.^[1][2][3]

What is known about plant uptake

There is direct experimental evidence that some tire-derived chemicals can enter edible plants. In a hydroponic lettuce experiment, compounds associated with tire wear—including benzothiazole, diphenylguanidine, HMMM, 6PPD, and 6PPD-quinone—were taken up and transported into leaves. The study used controlled solutions containing tire-derived compounds rather than whole tires in ordinary garden soil, so it demonstrates biological possibility rather than proving that a typical tire garden produces harmful food.^[4][5]

A major limitation is that there appear to be few—or no well-controlled field studies measuring carcinogens in vegetables grown in intact tire planters over multiple seasons. McGill’s review reached the same basic conclusion: meaningful leaching is plausible, but the amount entering soil and vegetables from an intact tire is not well established. PAHs tend to be poorly water-soluble, whereas some metals and other additives may be more mobile.^[6]

Why intact tires differ from tire mulch

An intact sidewall or tread has relatively little surface area in contact with soil, and many chemicals remain bound in the rubber. That likely makes it less concerning than:

• Shredded or crumb rubber mixed into soil.
• Tires that are cut, abraded, or crumbling.
• Tire rubber exposed to acidic conditions.
• Burning tires or using tire ash.
• Long-term use in hot, sunny, wet conditions.

However, “less concerning” is not the same as “free of risk.” Aging, weathering, repeated wetting, and physical degradation can increase release of metals and organic additives. The strongest recent plant-uptake evidence concerns tire particles and leachates, not intact tires, so applying it quantitatively to a tire planter would be uncertain.^[7][8][4]

Practical recommendation

For vegetables intended for regular consumption, I would avoid using old tires as the actual soil container, especially for:

• Root crops such as carrots, potatoes, beets, and radishes.
• Leafy greens such as lettuce, spinach, and kale.
• Long-lived crops or perennial herbs.
• Tires that are cracked, deteriorating, oily, or heavily weathered.

The safer approach is to use untreated wood, masonry, galvanized metal designed for garden use, food-grade containers, or grow bags. If you want the tire appearance, put a separate food-safe growing container inside the tire so the soil does not contact the rubber.

If tires are used despite the uncertainty, reduce exposure by using intact tires only, keeping edible plant material away from the tire wall, avoiding root crops and leafy greens, using clean tested soil, and washing produce thoroughly. A plastic liner may reduce direct contact, but it introduces its own material and aging questions rather than eliminating uncertainty.

Bottom line

There is evidence that tire-derived chemicals—including some potentially carcinogenic PAHs and other toxic compounds—can leach under some conditions and that certain tire-derived chemicals can be taken up by lettuce. There is not yet strong evidence showing that ordinary vegetables grown in intact old tires routinely contain carcinogenic substances at dangerous concentrations. Given that safer containers are readily available, tires are best reserved for ornamental plants—or used only as an outer decorative shell around a separate food-safe planter.^[1][4][6]

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• https://www.epa.gov/chemical-research/public-webinar-part-1-tire-crumb-rubber-characterization  
• https://www.epa.gov/chemical-research/federal-research-recycled-tire-crumb-used-playing-fields-and-playgrounds 
• https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100QM90.TXT 
• https://pmc.ncbi.nlm.nih.gov/articles/PMC9835885/   
• https://pubs.acs.org/doi/10.1021/acs.est.2c05660 
• https://www.mcgill.ca/oss/article/health/are-vegetables-grown-tire-gardens-safe-eat  
• https://pubs.acs.org/doi/pdf/10.1021/acs.est.2c05660 
• https://downloads.regulations.gov/EPA-HQ-OPPT-2024-0403-0056/content.pdf 
• https://pmc.ncbi.nlm.nih.gov/articles/PMC10221668/ 
• https://louisville.edu/cepm/pdf-files/newpg28 
• https://ask.extension.org/kb/faq.php?id=784173 
• https://ask.extension.org/kb/faq.php?id=305496 
• https://www.mdpi.com/2071-1050/17/12/5433 
• https://swyg.nmsu.edu/2015/050215.html 
• https://www.echocommunity.org/en/resources/b1d9d1eb-afcb-4729-ae31-950e13872d1d 
• https://gardeningbeyond.com/how-to-make-a-tire-garden/ 
• https://www.eurekalert.org/news-releases/1111353 
• https://www.echocommunity.org/en/resources/39a9a5a2-47a2-4870-9beb-350ff6e7fbfa 
• https://gardeningbeyond.com/how-to-make-tire-garden/ 
• https://19january2021snapshot.epa.gov/sites/static/files/2019-12/documents/setac2019_tire_crumb_poster_final.pdf 
• https://www.epa.gov/chemical-research/tire-crumb-questions-and-answers 
• https://19january2021snapshot.epa.gov/chemical-research/tire-crumb-questions-and-answers_.html 
• https://www.epa.gov/sites/default/files/2019-08/documents/tc_public_webinar_-_august_6_2019.pdf 
• https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100X5RO.TXT 
• https://www.epa.gov/system/files/documents/2024-04/epa-atsdr-tire-crumb-study-response-to-external-peer-review-comments.pdf 
• https://19january2021snapshot.epa.gov/sites/static/files/2019-08/documents/synthetic_turf_field_recycled_tire_crumb_rubber_research_under_the_federal_research_action_plan_final_report_part_1_volume_1.pdf 
• https://www.uml.edu/docs/Tire-crumb-2017_tcm18-385461.pdf 
• http://i2.cdn.turner.com/cnn/2017/images/01/25/epa.on.chemicals.in.turf.also.found.in.soil.pdf 
• https://downloads.regulations.gov/EPA-HQ-OPPT-2024-0403-0110/attachment_8.pdf