Small rubber particles, forms of micro- and nanoplastics, are released into the air when tyres from cars and trucks wear down. These particles contribute to a complex mix of airborne air pollution, which we are exposed to when cycling or walking next to a busy road. As the amount of traffic on our roads is still increasing, the POLYRISK project has launched a study to investigate whether these plastic particles found in traffic-related air pollution have a negative impact on people’s immune system.

Polluted air is a significant environmental health risk in Europe. According to the World Health Organization (WHO), around 97% of the European population is exposed to fine particulate matter (PM2.5) concentrations above the WHO air quality guideline level. Estimates indicate that the degradation of vehicles’ tyres could contribute about 0.1 up to 10% of the total mass of fine particulate matter in Europe. In Germany, for example, a 2018 report by Fraunhofer Institute for Environmental, Safety and Energy Technology looked at 70 primary sources releasing microplastics into the environment and found that the biggest contributor was the abrasion of vehicle tyres. In the Netherlands, it has been calculated that up to 1040 tonnes of rubber particles are released into the atmosphere each year as a result of the wear and tear of car tyres on the road.

However, actual exposure data on how much of these microplastics contribute to fine particulate matter mass in air is still unclear. While scientists have made a clear connection between air pollution and health effects such as lung function decline or impacts on the immune system, little is yet known about airborne microplastics. That is why POLYRISK researchers have set out to investigate whether exposure to traffic-related microplastics is potentially associated with acute immuno-toxicological effects within healthy, young adults. Secondly, they are investigating whether these microplastics could cross the alveolar lining, into the bloodstream.

Studying real-life traffic-related exposure to microplastics

While evidence of the presence of microplastics within our bodies exists, there is limited knowledge about the possible health effects of the microplastics that people are exposed to on a daily basis. The POLYRISK project examines occupational and consumer exposure to microplastics to better understand their potential adverse effects on the immune system. In a dedicated project work package, external and internal exposures to micro- and nanoplastic particles in humans are studied in five real-life scenarios settings, which include microplastics from artificial sports pitches and traffic-related exposure to microplastics.

Over the past months, POLYRISK partners at the University of Utrecht in the Netherlands asked a group of 24 young people between the ages of 18 and 31 to participate in a  controlled repeated study to assess the presence of micro- and nanoplastics in blood, and whether this could have short-term immuno-toxicological health effects. 

Volunteers participating in the study were exposed to varying traffic conditions at three locations within and around Utrecht, all during the same time of day. These locations included a highway, an area characterised by stop-and-go traffic, and a city park as an urban background location. The locations were selected for the possible variation in microplastic concentrations when compared to other well-known air pollutants, which can be attributed to both driving style and the amount of traffic on the road. For example, at the stop-and-go spot, cars were seen breaking and accelerating more frequently compared to the other locations. This could result in a higher release of rubber microplastic particles, due to the additional friction, compared to the highway location with more continuous driving.

Photo: Test locations in and around the city of Utrecht

At each of the three test sites, volunteers were asked to cycle on static bicycles for a set period of time. The researchers from the University of Utrecht monitored their heart rates and collected a variety of air samples, including filters for future microplastic and polymer analyses. Moreover, directly before and after the test, and the following morning, a variety of health measurements were collected. Saliva and blood samples were sampled, a lung function test was executed and the volunteers were asked to fill out a questionnaire about previous exposure and symptoms.

Photo: Volunteers performing intermittent exercise near a highway to measure the levels of micro- and nanoplastics in their blood.

Now that the fieldwork has been finalised, an evaluation of the exposure to rubber and other polymers within air and blood samples is underway. Additionally, other major air pollutants like PM10, black carbon, ultrafine particles, metals, plasticizers, phthalates and PAHs (class of organic compounds found in coals and gasoline), will also be analysed. This research aims to find out if there is a connection between microplastics and these air pollutants, and if any resulting health impacts are caused by microplastics, a mix of pollutants, or something else. 

Blood and saliva samples will also be screened for different characteristics related to the exposure and their potential immunotoxicological health effects. These analyses are expected to be finalised by the beginning of 2024.

Researching the potential adverse health impacts of microplastics can be challenging, explains Esther Lenssen, PhD candidate Toxicology and Environmental Health at Utrecht University and a partner of the POLYRISK project: Microplastics are not just small; they are also potentially everywhere. This means that every step, including gathering samples outside the lab, can cause contamination, potentially skewing our results. Overcoming this obstacle requires careful planning, meticulous attention to detail, and the development of stringent protocols including loads of blanks, to ensure the integrity of our findings.”