6PPD is one of many chemicals added to tires and other rubber products to improve their durability. 6PPD prevents cracks in the rubber, making tires last longer and safer for driving. 6PPD reacts with the air and creates new chemicals called transformation products. One transformation product is called 6PPD-quinone (pronounced “quih-known”; 6PPDQ) and is most known for being deadly to coho salmon (Oncorhynchus kisutch). We are currently learning how 6PPD and 6PPDQ may cause human health effects, and how effects on salmon harm human well-being.
Sources of 6PPD and 6PPDQ
Tires driving on the road leave behind tiny pieces of rubber called tire wear particles. When it rains, these tire wear particles run off the roads and enter waterways. As they are ground down into dust they can also spread from the roadway into water and air. Water and air carry 6PPD and 6PPDQ away from the source and into contact with people.
Recycled tires are often used to make other products, such as filler for athletic fields. 6PPD and 6PPDQ have been detected in artificial turf athletic fields in the U.S. that contain this crumb rubber.
6PPD can be added to other rubber products, such as some sneaker soles, door mats, garden hoses, kneepads, and the rubber parts of faucets. We are still learning about what rubber products contain 6PPD and 6PPDQ, and whether people are exposed by using these products.
Exposure to 6PPD and 6PPDQ
Both 6PPD and 6PPDQ have been found in people, so we know we can be exposed to these chemicals. 6PPD and 6PPDQ have been found in urine, blood, and breast milk. 6PPDQ has been found in the fluid around the ovaries, in umbilical cord blood, and in brain and spinal fluid. 6PPD, but not 6PPDQ, has been found in the fluid that surrounds a fetus during pregnancy.
In the Environment
Studies have found 6PPD and 6PPDQ in the air and dust in several places, mainly in China, with some data from Europe, Canada, and the U.S. These studies find higher amounts in dusts than in air. So far, no studies have looked for 6PPD and 6PPDQ in air or dust in Washington state.
Home and Workplace
6PPD and 6PPDQ have been found in indoor dusts from workplaces, homes, commercial buildings, and inside of vehicles. Babies and young children are more likely to be exposed to dust because they crawl on the floor and put their hands in their mouths. We are also concerned about the health effects of people who live or work near highways due to possible 6PPD and 6PPDQ exposure from the roadway, but more research is needed. People working in direct contact with tires can be exposed to 6PPD or 6PPDQ through touching or accidentally eating the chemicals left on their hands. People in contact with products made from used tires may also get these chemicals on their skin. People who use artificial turf athletic fields may accidentally ingest the tire crumb rubber during or after recreation. See Synthetic Turf and Crumb Rubber for more information about chemicals in synthetic turf.
Food and Water
We are still learning if 6PPD and 6PPDQ are in the food we eat. 6PPDQ has been found in fillets of salmon caught in Washington state, but we don’t know if 6PPD was also present. We don’t yet know if the 6PPDQ levels found in fish cause health problems in people, so we still recommend people eat fish for their health benefits. For locally caught fish advise, see our fish consumption advisories. Learn more about 6PPD and fish, Washington Department of Fish and Wildlife.
A single report found trace levels of 6PPD in some leafy green vegetables grown in Europe and Israel. Crops in Washington state have not been tested. Leafy greens are a great source of many vitamins and minerals, so we still recommend eating them.
6PPD has also been detected in tap water in Singapore and both chemicals have been detected in tap water in China. While studies in Canada have not found either chemical in drinking water, no research has been done on drinking water in the U.S. We keep track of emerging information and are working with partners to learn if 6PPD or 6PPDQ are a concern for drinking water in Washington state.
Both chemicals have been found in creeks and lakes in Washington state, but we don’t think there is a health risk to people who swim or play in these waters from these chemicals.
Possible Health Effects
6PPD
6PPD has been used in tires and other products for decades, so we understand more about its human health effects than 6PPDQ, which was discovered more recently.
6PPD can cause skin allergies according to studies that looked at workers in rubber manufacturing and other similar jobs. Having a skin allergy to other chemicals in the same class of chemicals (PPDs) can sometimes mean you’re also allergic to 6PPD.
6PPD may cause risk to human reproduction. Studies in female rats show that 6PPD can make giving birth more difficult, and other research suggests it may cause reproductive problems. We don’t yet know if the levels of 6PPD that people are currently exposed to are high enough to cause any reproductive health effects.
New research suggests that 6PPD could be bad for the liver. A study found that people with a common liver condition had slightly more 6PPD in their blood than those without it, along with signs of liver damage. Harm to the liver from 6PPD has been observed in animals and human cells in lab tests; however, it's still unclear if the amount of 6PPD in the environment is enough to cause liver problems in people.
We don’t think 6PPD causes cancer.
6PPDQ
Most of the research on 6PPDQ so far has focused on its harmful effects on fish and its presence in the environment. However, as interest in this chemical grows, research looking at 6PPDQ in humans and laboratory animals is rapidly emerging.
Higher levels of 6PPDQ have been found in people with polycystic ovarian syndrome (PCOS) compared to people without PCOS. However, we don't know if 6PPDQ causes PCOS. Additional laboratory experiments in human cells, rodents, and roundworms all show 6PPDQ can cause reproductive issues in both genders.
People with liver disease have been found to have high levels of 6PPDQ, along with signs of liver damage. Long term studies in mice and human liver cells show that 6PPDQ can harm the liver. For example, research in mice found that it can cause fat to build up in the liver.
6PPDQ has been found at higher levels in the brain and spinal fluid of people with Parkinson’s disease compared to those without it. Supporting studies in laboratory rodents show 6PPDQ can harm brain cells, but we don’t know if this happens in human brains or if 6PPDQ has any role in causing nervous system damage.
Laboratory mice that ate 6PPDQ for several weeks had damage to their intestines. 6PPDQ weakened their intestinal lining and increased inflammation. Other studies found similar effects, including increased intestinal leakage in roundworms and signs of intestinal damage in zebrafish.
We don’t currently know if 6PPDQ causes cancer.
Overall, studies in laboratory animals suggest that 6PPDQ may impact health, and some studies have found that 6PPDQ is higher in people with certain diseases. More research is needed to know how much exposure could be harmful to people and whether 6PPDQ causes any health conditions.
Human Well-Being
Human well-being also depends on healthy aquatic life. We know that 6PPDQ is deadly to coho salmon and that it is also toxic for other fish, such as coastal cutthroat trout (Oncorhynchus clarkii), brook trout (Salvelinus fontinalis), rainbow trout (Oncorhynchus mykiss), and lake trout (Salvelinus namaycush). The declining health of salmon and other aquatic life harms the holistic health and lifeways of people who rely on these species for:
- Economic or commercial purposes
- Food (subsistence, balanced nutrition, food sovereignty)
- Culture
- Tradition
- Spiritual or emotional well-being
- Recreation
Limit Your Exposure
DOH toxicologists are still learning whether levels of 6PPD and 6PPDQ in the environment are high enough to cause health effects in people. If you're still concerned, you can limit your contact with these chemicals by following these tips:
- Clean dust from your home and vehicle, particularly if you have children. If you’re pregnant, make sure to wear a mask while dusting and using cleaning products, and follow product safety label requirements. See our Safe Cleaning Practices in Your Home.
- Bring your children to parks that don’t use tires as play structures when possible. Do your best to prevent children from putting unknown objects in their mouths or swallowing artificial turf bits. For more information about chemicals in turf, see Synthetic Turf and Crumb Rubber.
- There are no dietary restrictions on these chemicals. We recommend eating fish as part of a balanced diet and following our healthy fish guide and advisories.
- If possible, place home gardens away from the roadside.
- If you work with tires or on busy roadways follow appropriate workplace protective measures and personal protective equipment requirements.
Addressing 6PPD and 6PPDQ in Washington
DOH toxicologists are learning about the public health impacts of new findings on 6PPD, 6PPDQ, and other similar chemicals. We collaborate with state, federal, and tribal partners to further understand these chemicals. Through this partnership we stay up to date with the latest research on human health and exposure relevant to Washington state in order to share what we know with the public. For example, our Fish Advisories Program works closely with the Department of Ecology, Washington Department of Fish and Wildlife, and other partners to monitor levels of 6PPD and 6PPDQ in fish from Washington waterways. You can find presentations we’ve given and reports we’ve contributed to, such as the ITRC guidance chapters, in the resources below.
In 2024, an advisory committee including DOH toxicologists, the Washington State Department of Ecology, and other state agencies developed Phase 1 of the 6PPD Action Plan for Washington State. An Action Plan is a set of recommendations for protecting humans and the environment from hazardous chemicals. In Phase 1 of the 6PPD Action Plan, we created a set of recommendations aimed at identifying data gaps and research needs to inform and prioritize future work on 6PPD and 6PPDQ. For more information and to read the recommended actions that DOH is leading, please visit Data Gaps, Research Needs, and Recommendations to inform 6PPD Action Plan work (PDF).
More Resources
6PPD and 6PPD-quinone, Interstate Technology and Regulatory Council (ITRC)
6PPD, Washington State Department of Ecology
6PPD-quinone, Environmental Protection Agency
Contacts
If you have a question or would like information on any of the references used to inform this page, email the Office of Environmental Public Health Sciences or call 360-236-3385.