Traffic can be dangerous, but the risks of congested highways may go beyond road rage and car accidents.
Credit: R&D
Traffic-related air pollution (TRAP) presents a significant health risk, said Patrick H. Ryan, Ph.D., an associate professor of Pediatrics and Environmental Health Division of Biostatistics and Epidemiology at Cincinnati Children’s Hospital Medical Center, University of Cincinnati.
“The emission from the tail pipes of gas and diesel-powered vehicles are complex and consist of multiple pollutants,” said Ryan, in an exclusive interview with R&D Magazine. “It has been recognized for a long time that pollution exposure is really high near the major roads and that exposure isn’t captured with background regulatory-type monitoring.”
Diesel exhaust specifically, falls under an unregulated class of nano-sized particles known as ultrafine particles, (UFP), which have been linked to increased respiratory issues, allergies and asthma development. In addition, emerging evidence from toxicology studies suggests that UFP can actually cross the blood-brain barrier, reaching the brain either directly through the olfactory vault or by inducing neuro-inflammation.
UFPs may pose particular dangers because of their composition, said Ryan, who recently spoke on the topic at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy (PITTCON) 2017.
Decreased particle size translates to increased surface area, which in turn increases the potential for the chemical compounds to be attached to the surface and be co-deposited in the airways. It is believed that UFP have the ability to get deeper into the lungs and deposited with greater efficiency than larger particles.
Challenges with UFP Measurement
However, most of the evidence regarding UFPs comes from laboratory-based studies and not field tests, said Ryan, because the small size of UFPs— less than 100 nanometres in diameter— makes them very difficult to capture and monitor.
“A big challenge with UFP is that the instrumentation hasn’t been there,” said Ryan. “We’ve been limited to very expensive desktop-size devices we can’t take into the field. It is also a challenge to get a real handle on the exposure because of the high spatiotemporal variability and the physical properties of these particles over distances.”
Stationary sampling of UFPs has been somewhat effective, but it is misses high concentration areas and doesn’t account for the variability of exposure. Because the average person moves from environment to environment throughout the day, personal exposure frequently exceeds monitored data of the environment, said Ryan. Personal monitoring is needed to truly understand the average person’s UFP exposure.
A Novel Device
Ryan and a team of scientists at the University of Cincinnati are working on just that. They are testing a wearable, novel sensor for measuring UFP exposure developed by Sang Young Son, Ph.D., an engineer from the University of Cincinnati and president and CTO of EnMont. The device, weighing about 750 grams, can measures particles as small at 6 nanometers in diameter and features a built-in GPS, a USB or Bluetooth data interface and a battery that lasts up to three hours without charging.
Most particles are measured by weight, if they are large enough, or counted optically by scatted light. UFPs however, are smaller than a wavelength of light and need to be enlarged to pass through an optical counter, explained Ryan. The device created by Son uses water to accomplish this.
“Particles as small as 4 to 6 nanometers enter the evaporation condensation tube where the temperature and humidity is such that it attaches water to the surface of the particle,” said Ryan. “This causes the particle to grow in size, so by the time it exits the tube it can cross the optical counter and be big enough to be counted.”
Ryan has conducted several studies of this device to test its effectiveness in collecting the UFPs and its usability in a pediatric population.
In the first, 20 kids age eight to 11 with previously diagnosed asthma wore the sensor at school, during transit periods between school and home and in their home for two to four hours on two consecutive days. The sensor recorded UFP number concentration at one second intervals as well as GPS location.
The overall total median personal exposure to UFP was 12,900 particles / cm3 (p/cc) and median UFP exposure at homes, schools, and during transit was 17,800, 11,900, and 13,600 p/cc, respectively
Surprisingly, kids that walked were found to have higher exposure than kids who got to school by bus or car. This was a result of increased exposure from crossing major intersections on foot, said Ryan.
Ryan’s team then conducted a second field test of the device, this one including 10 healthy adolescent volunteers with an average age of 16.
In this study, the participants were asked to wear the device for three hours each day for a week and to refill it with water and charge it as needed.
“This was a more realistic scenario,” said Ryan. “The goal was to see if the teens could use the device like we would in a study. They completed a questionnaire about their experience.”
Data was similar to the first study. The participants were able to wear the device over a week, with each participant wearing it for an average of 2.7 hours. The mean concentrations of UFP was again around 13,000 particles per CC.
Participants said it was easy to wear and only somewhat bothersome, said Ryan.
Next Steps
Now that previous studies have shown the device to be useable and effective for counting UFPs, the next step in Ryan’s research is to determine exactly how UFP exposure impacts health outcomes in children on a day-to-day basis.
For their next study, the team plans to recruit 100 children who will wear the device for two separate one week periods. In this study, which is expected to start this summer, the UFP exposure assessment will be looked at in conjunction with epidemiological health outcomes, including lung function. This will help determine if UFPs demonstrate the same health impacts they do in the labratory, in the field.
Ryan hopes this research will eventually be used to reduce UFP exposure for children. His team is collaborating with the Cincinnati Public Schools Safe Routes to School Program, and hopes to eventually help them develop walking routes to school that consider exposures to these containments. This type of research could also help determine zoning regulations, for example how far a school should be built from a busy highway to avoid pollution exposure, said Ryan.
“If we see something that is associated with a health effect, we have the opportunity to modify it,” said Ryan. “Whether that is through policy changes, regulatory actions, better engineering, lowering emissions, even down to personal changes people can make. The goal is always to improve public health.”