Roadway Pollution More Toxic Than Freeway Pollution

November 01, 2021

In Utero Exposure to Near-Roadway Air Pollution May Be Tied to ASD

A large, representative retrospective birth cohort study has discovered that in utero exposure to near-roadway air pollution (NRAP) from non-freeways was associated with an increased risk of autism spectrum disorder (ASD). This work was supported by the National Institutes of Environmental Health Sciences and by Kaiser Permanente as well as the Environmental Protection Agency. The new study theorizes that pollutants in the NRAP mixture include ultrafine particles (UFP) and associated high particle number concentrations from on-road vehicular sources. UFPs are particularly insidious because they can be found in blood after inhalation. Furthermore, exposures to these tiny particles have been linked to increased inflammation and pro-inflammatory cytokines. A previous animal study has already determined that in utero exposure to UFPs can cause neurodevelopmental damage and autism-like behaviors, showing that this study’s findings are biologically plausible. The research team points out that NRAP is a complex mixture of many chemicals in addition to UFP. They additionally reported that other studies have demonstrated that offspring of rats exposed to traffic emissions near automobile tunnels exhibited delayed growth and social behavior as well neurodevelopmental dysfunction. The study’s authors also call attention to the potential dangers of gasoline fumes opposed to diesel exhaust (more common on freeways) by pointing out that the vehicular fleet on non-freeway roads in Southern California, where the study took place, is almost exclusively fueled with gasoline. They go on to report that gasoline exhaust effects have not been studied adequately at this time. One possible reason for roadway pollution containing higher levels of toxins than freeway pollution is the difference in the pollutant mixture near fast moving freeway automobiles opposed to the slower stop-and-go traffic where particles can settle more easily. Cold starts, which are more common on secondary roadways, are another possible factor. The authors also point to problematic brake dust and metals produced in stop-and-go traffic experienced on streets. Earlier research has shown brake dust and metals to be highly toxic in cellular systems. Additionally, the researchers indicated that only a small proportion of the study’s subjects lived very close to a freeway but almost all the subject’s residences were located very close to arterial, collector or local roads. The study ends with a call for more toxicological investigation on NRAP effects on ASD and gasoline-fueled emissions characteristic of non-freeway roads. 

Original Study

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