6PPD and 6PPD-quinone

What are 6PPD and 6PPD-quinone?

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”) and is most known for being deadly to coho salmon (Oncorhynchus kisutch). We are currently learning how 6PPD and 6PPD-quinone may cause human health effects, and how effects on salmon harm human well-being.

What are the sources of 6PPD and 6PPD-quinone?

Hand holding crumb rubber over a turf soccer field. — *Turf fields often contain crumb rubber created from recycled tires which are a common source of 6PPD and 6PPD-quinone.*

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 6PPD-quinone away from the source and into contact with people.

Manufacturers often use recycled tires to make other products, such as filler for athletic fields. Researchers have detected 6PPD and 6PPD-quinone 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 6PPD-quinone, and whether people are exposed by using these products.

What are the possible health effects?

6PPD

Tire and other rubber product manufacturers have used 6PPD for decades, so we understand more about its human health effects than 6PPD-quinone, which was discovered more recently.

Skin Allergies: Image

Some people have a skin allergy to 6PPD.

6PPD can cause skin allergies according to studies that looked at workers in rubber manufacturing and other similar jobs. If you’re allergic to other chemicals in the same class (PPDs), you may also react to 6PPD.
Reproductive and Developmental Effects: 6PPD may cause risk to human reproduction and development. Studies in female rats show that 6PPD can make giving birth more difficult, and other research suggests it may cause reproductive problems. Laboratory tests show that 6PPD might be able to alter development of the nervous system. We don’t yet know if the levels of 6PPD that people are currently exposed to are high enough to cause any reproductive or developmental health effects.
Liver 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. Lab tests in animals and human cells show liver harm. It's still unclear if the amount of 6PPD in the environment is enough to cause liver problems in people.
Cancer: We don’t think 6PPD causes cancer, based on our review of the available science.

6PPD-quinone

Most of the research on 6PPD-quinone 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 6PPD-quinone in humans and laboratory animals is rapidly emerging.

Overall, studies in laboratory animals suggest that 6PPD-quinone may be toxic to people, and some studies have found that 6PPD-quinone is higher in people with certain diseases. More research is needed to know whether 6PPD-quinone causes any health conditions and how much exposure could be harmful.

Reproductive and Developmental Effects: Researchers have found higher levels of 6PPD-quinone in people with polycystic ovarian syndrome (PCOS) compared to people without PCOS. However, we don't know if 6PPD-quinone causes PCOS. Additional laboratory experiments in human cells, rodents, and roundworms all show 6PPD-quinone can cause reproductive issues in both genders.
Liver Effects: Researchers have found high levels of 6PPD-quinone and signs of liver damage in people with liver disease. Long term studies in mice and human liver cells show that 6PPD-quinone can harm the liver. For example, research in mice found that it can cause fat to build up in the liver.
Nervous System Effects: Researchers studying people with Parkinson’s disease have found higher levels of 6PPD-quinone in the brain and spinal fluid compared to those without the disease. Supporting studies in laboratory rodents show 6PPD-quinone can harm brain cells, but we don’t know if this happens in human brains or if 6PPD-quinone causes nervous system damage or Parkinson’s disease in people.
Intestinal Effects: Laboratory mice that ate 6PPD-quinone for several weeks had damage to their intestines. 6PPD-quinone weakened their intestinal lining and increased inflammation. Other lab experiments found similar effects, including increased intestinal leakage in roundworms and signs of intestinal damage in zebrafish.
Cancer: We don’t currently know if 6PPD-quinone can cause cancer.

How does the health of fish affect human well-being?

Salmon swimming. — *The declining health of salmon and other aquatic life harms the health and well-being of people who rely on these species.*

Human well-being also depends on healthy aquatic life. We know that 6PPD-quinone 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

Are people exposed to 6PPD and 6PPD-quinone?

When scientists test people’s bodily fluids, they often find both 6PPD and 6PPD-quinone, so we know people can be exposed to these chemicals. Researchers have found 6PPD and 6PPD-quinone in urine, blood, and breast milk. They have also detected 6PPD-quinone in the fluid around the ovaries, umbilical cord blood, and brain and spinal fluid. They have found 6PPD—but not 6PPD-quinone—in the fluid that surrounds a fetus during pregnancy. None of the studies on people’s bodily fluids were done in Washington or the U.S. and amounts of chemicals here might be different.

How can people be exposed to 6PPD and 6PPD-quinone?

Researchers find 6PPD and 6PPD-quinone in many different parts of indoor and outdoor environments.

View the illustrations below along with information about different ways we can come into contact with these chemicals in the environment, indoors, in waterways and fish, and at recreational fields and playgrounds.

The Environment

6PPD and 6PPD-quinone can be present in air that people breathe. So far, no studies have looked for 6PPD and 6PPD-quinone in air in Washington state; most of the available information comes from other locations across the world.

Exposure Through Food

Researchers found trace levels of 6PPD and 6PPD-quinone in leafy greens and other vegetables such as bell peppers, carrots, onions, and potatoes grown in Europe and Israel. 6PPD and 6PPD-quinone may be absorbed by crops grown in soils containing these chemicals. 6PPD and 6PPD-quinone in the air may drop onto crops, and rain runoff from nearby roads may also add these chemicals to agricultural soils and crops.

Crops in Washington state have not been tested but it is possible that people could be exposed through their diet. Vegetables are a great source of nutrients and fiber and DOH recommends eating a varied diet rich in fruits and vegetables.

Exposure Through Work

People who live or work near highways and other busy roads may come into contact with more 6PPD and 6PPD-quinone, but researchers need to do more studies to confirm this.

People working in direct contact with tires can be exposed to 6PPD or 6PPD-quinone through touching the tires and then accidentally ingesting the chemicals left on their hands while eating. We don’t think that the chemicals cross through skin into the body.

Exposure Through Soil

Researchers found 6PPD and 6PPD-quinone in soils from schools and farms in China. People may be exposed to these chemicals in soil by accidentally eating small amounts of soil when it gets on their hands or food.

Researchers have also found 6PPD and 6PPD-quinone in biosolids in the U.S. and in China. Biosolids are processed waste materials that come from wastewater treatment and are sometimes added to soil to increase nutrients and improve soil.

Exposure to 6PPD and 6PPD-quinone from the environment — 6PPD and 6PPD-quinone in tire particles on the road can be released into the air or stormwater runoff and carried to nearby soils, crops and waterways. Roadside workers may also be exposed through the air.

Waterways and Fish

High traffic roads, typically in urban settings but not always, have high levels of tire wear particles carrying 6PPD and 6PPD-quinone. Water running off roads when it rains can carry particles and chemicals into lakes and streams. Researchers have found 6PPD and 6PPD-quinone in creeks and lakes in Washington state, but we don’t think they pose a health risk to people who swim or play in these waters.

Fish, shellfish, and aquatic plants that live and grow in waterways near high traffic areas may absorb 6PPD and 6PPD-quinone from the water. The Washington Department of Fish and Wildlife, in partnership with other state and federal agencies report that detectable levels of 6PPD-quinone have been found in aquatic species in Washington state such as mussels, juvenile Chinook salmon, fillets of salmon, and English sole. 6PPD has not been tested yet. We don’t yet know if the 6PPD-quinone levels found in fish cause health problems in people, and only a few of the fish, shellfish and aquatic plants that we harvest and eat have been tested. We recommend people eat fish for their many health benefits.

Visit 6PPD, Washington Department of Fish & Wildlife to learn more. For locally caught fish, please consult DOH’s fish consumption advisories.

Exposure to 6PPD and 6PPD-quinone from Waterways and fish — *People may be exposed to 6PPD and 6PPD-quinone through fish and other aquatic life in waterways, especially near high traffic roads.*

Baby crawling on floor. — *Babies and young children are vulnerable to 6PPD and 6PPD-quinone due to more frequent contact with floor dust and hand-to-mouth behavior.*

Indoors

Researchers have measured 6PPD and 6PPD-quinone in indoor air and dusts from workplaces, schools, 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. Airborne dust coming from indoors or outdoors may also land onto food.

Exposure Through Rubber Products

6PPD can be added to rubber products other than tires, such as floor mats and sneaker soles. As these products wear down, the small particles of rubber can potentially contribute 6PPD and 6PPD-quinone to indoor dust. We are still learning whether dust exposure to these chemicals is a concern for health.

Exposure Through Drinking Water

Tap water may contain 6PPD or 6PPD-quinone if it comes from a source that has been contaminated. There is no evidence at this time that any Washington drinking water is affected. A single U.S. study found some 6PPD in New York state tap water samples, but not 6PPD-quinone, and we don’t know the source of the 6PPD. Researchers also found 6PPD, but not 6PPD-quinone, in a small number of bottled water samples purchased in New York state.

6PPD has also been detected in tap water in Singapore and both chemicals have been detected in tap water in China. We are working with state agency partners to learn more about whether 6PPD or 6PPD-quinone could be a concern for drinking water in Washington state.

Exposure to 6PPD and 6PPD-quinone from the indoors — *People may be exposed to 6PPD and 6PPD-quinone indoors through dust, rubber products, and drinking water.*

Recreational Fields and Playgrounds

People who use artificial turf athletic fields may accidentally consume small amounts of tire crumb rubber particles and dusts when they play and eat on or near crumb rubber surfaces. Please see our Synthetic Turf and Crumb Rubber page for more information about chemicals in synthetic turf.

Playground equipment is sometimes made from recycled tires. People in contact with products made from used tires may also get these chemicals on their skin and transfer them to their mouths. We are not worried about 6PPD or 6PPD-quinone absorbing into skin and causing health effects.

Exposure to 6PPD and 6PPD-quinone from Recreational Fields and Playgrounds — *People may be exposed to 6PPD and 6PPD-quinone when using artificial turf fields made with recycled tires.*

How do we limit our exposure?

DOH toxicologists are still learning whether levels of 6PPD and 6PPD-quinone 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 label safety requirements.
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.
Wash hands after playing on artificial turf and before eating. See our Synthetic Turf and Crumb Rubber page for more information about chemicals in synthetic turf.
There are no dietary restrictions on these chemicals. We recommend eating fish, fruits and vegetables as part of a balanced diet. Here is more advice on which fish are safe to eat.
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 and wash hands before eating.

How is Washington addressing 6PPD and 6PPD-quinone?

DOH toxicologists track the latest research on possible public health impacts of 6PPD, 6PPD-quinone, and other related chemicals. We collaborate with state, federal, and tribal partners to further understand these chemicals in the environment and we share what we know with the public. The DOH 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 6PPD-quinone in fish from Washington waterways and assesses any potential concerns for human health.

In 2024, an advisory committee including DOH toxicologists, the Washington State Department of Ecology, and other state agencies developed Phase 1 of a 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 6PPD-quinone. 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.

You can find other presentations and reports we’ve contributed to in the More Resources section below.

More Resources

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.