What's in Rubber?

When you enter a tire store or a bike shop, what do you smell? To me it is the distinctive odor of rubber, and it makes me want to hold my breath, or better yet, evacuate. So I always wonder: what are the chemicals that are off-gassing from all that rubber and how does it affect the health of everyone breathing it, especially the employees who may breathe it all day?

Interestingly, as I researched this topic I found a number of references to air purifiers manufactured/engineered to specs that prevented off-gassing from their rubber filters. And I found mattresses and SCUBA gear advertised as healthy alternatives to conventional products because of no rubber off-gassing. In fact, there are a multitude of references to the toxic chemicals in rubber, but finding out exactly what chemicals are off-gassing, and their health effects, is elusive. The air quality issue is being raised, but without offering answers to my questions.

So I can't tell you exactly what's in the room with you and the rubber, but I can tell you what MIGHT be. I think you'll agree that my flee response was the appropriate one!

RUBBER CHEMICAL SAMPLER:
Benzene is in rubber. Tire manufacturing facilities provide workers with a significant exposure to benzene (although about half of this nation's exposure comes from cigarette smoke!). The National Toxicology Program (NTP) has classified benzene as a human carcinogen. Breathing high levels of the chemical can cause irreversible brain damage and a whole bunch of other undesirable and/or debilitating symptoms. 1

Toluene is an aromatic hydrocarbon found in rubber. It is toxic by inhalation, affecting the CNS (central nervous system, i.e. brain & nerves), the blood, muscles, and internal organs including the heart. “Long-term toluene exposure or abuse is devastating.” 2

Toluene diisocyanate, also found in rubber, is a carcinogen, is extremely toxic from acute and chronic inhalation exposures, affects the CNS, and chronic inhalation can significantly compromise lung function. 3

INGREDIENTS:
According to the US Environmental Protection Agency (USEPA), the list presented here includes chemicals typically used in synthetic rubber production that are subject to reporting under Title III Section 313. Details can be found in EPA’s Release Reporting Guidance, Estimating Chemical Releases From Rubber Production and Compounding4

Monomers:
1,3-butadiene. styrene, acrylonitrile, ethylene, ethylene glycol, propylene glycol, propylene, 1,3-toluene diisocyanate [it appears this should be 2,4-toluene diisocyanate ~cv], ethylene dichloride, epichlorohydrin, acrylic acid, ethyl acrylate, butyl acrylate, chloroprene, ethylene oxide
Retarders:
Phthalic anhydride, n-nitrosodiphenylamin
Catalysts:
Cobalt compounds, nickel compounds, titanium tetrachloride
Antioxidants:
Phenylene diamine
Short stops:
Hydroquinone
Solvents:
Toluene, methyl chloride (chloromethane), 1,1,2-trichloroethane
Cooling tower corrosion inhibitors:
Chromium compounds, zinc compounds
Miscellaneous chemicals:
Sodium hydroxide, sulfuric acid, various additives
Rubber compounding Processing aids:
Zinc compounds
Accelerators:
Zinc compounds, ethylene thiourea, diethanolamine
Agy restorers:
Nickel compounds, hydroquinone, phenol, alpha-naphthylamine, p-phenylenediamine
Vulcanizing agents:
Selenium compounds, zinc compounds, lead compounds
Initiator:
Benzoyl peroxide
Accelerator activators:
Zinc compounds, lead compounds, ammonia
Plasticizers:
Dibutyl phthalate, dioctylphthalate, bis (2-ethylhexyl adipate)
Miscellaneous ingredients:
Titanium dioxide, cadmium compounds, organic dyes, antimony compound

If this were a detective story, this is where the plot would thicken. Hexachlorobenzene (HCB) is a nasty chemical: carcinogen, liver & kidney toxicant, developmental & reproductive toxicant, liver & skin toxicant, endocrine & blood toxicant, neurtotoxicant, immunotoxicant. According to the Environmental Defense Fund Scorecard, it is ranked as one of the most hazardous compounds (worst 10%) to ecosystems and human health.5 Until 1965 HCB was used in pesticides, and was used in the manufacture of rubber. It is formed as a by-product in the production of other chemicals, in the waste streams of wood-preserving plants, and in municipal waste incineration. It persists in the environment for a long time. 6

In 1998 tire production was regulated under the Clean Air Act because of its status as a major contributor of hexachlorobenzene emissions. Then in 2000, the EPA issued a notice regarding these same emissions, stating that now there was no HCB contamination in tire manufacturing emissions. The reason for the turnaround? Perhaps it can be attributed to the fox-guarding-the-henhouse phenomenon. It turns out that The Rubber Manufacturer's Association (RMA) designed and conducted their own emissions test for HCB, then analyzed and compiled the test results which were promptly accepted by the EPA. This resulted in a reversal of EPA stance on the regulation of tire manufacturing.7

So now it is proclaimed that there is no extremely toxic hexachlorobenzene in rubber. And who knows, maybe it's true.

But I digress. Considering just the toxic ingredients we know are in rubber, WHAT IF toxic chemicals from rubber are in the air in a tire store. Are they also in the air from the friction and heat of tires wearing on highways and city streets? piles of old tires heating in the sun? synthetic turf fields made of crumbled up old tires?... And can you even imagine what toxins are in the air when tires are incinerated?! Somebody ought to look into this, don't you think?

Citations

1. Please click the superscripted reference links in the body of the text above.