Study finds single exposure to roadway PM induces transient pulmonary stress; possible need to regulate non-tailpipe-related pollution
A study by researchers in Israel and the US has found that single (“sub-clinical”) exposure to extracts from particulate material (PM) collected in a near roadway environment can induce a transient oxidative stress and inflammation in mice’ lungs. The researchers attributed this largely to the dissolved metals (such as Cu, Fe, Mn, V, Ni, and Cr) that are part of roadway emissions.
The local response was largely self-resolved by 48 h, suggesting that it could represent a subclinical response to everyday-level exposure. Removal of soluble metals by chelation markedly diminished the pulmonary response. The paper appears in the ACS journal Environmental Science & Technology.
The effect of near roadway air pollution on human health is especially significant in major cities, and respiratory and cardiovascular diseases are mostly implicated in response to continued/repeated exposure to air pollution. In an effort to limit roadway-related air pollution, the common regulations have focused on reducing tailpipe emissions. Among the various particulate matter (PM) constituents, some metals are potentially cytotoxic and can contribute to organ and tissue damage and injury. Yet, because tailpipe emissions from mobile sources are not major sources of these metals it is expected that their roadway emissions are largely associated with resuspended road dust that contains brake wear, tire wear, and crustal elements.
… The heterogeneity of chemical species and different roadway sources presents a major challenge in identifying specific components that are most biologically active, lead to pathogenesis of disease, or both. Identifying these components is essential for appropriate mitigation policies that could reduce their public health impact.—Pardo et al.
The study by the team from Weizmann Institute of Science, Ben-Gurion University of the Negev and the University of Wisconsin-Madison focused on identifying the in vivo role PM-derived transition metals from collected roadside PM.
They collected PM samples from a roadside monitoring site in central London in early July 2012. Metals present in water-soluble extracts from collected roadway particles were either chelated from the extracts, or in complementary experiments, a water metal solution containing the same composition and concentrations of the PM-derived metals was used to assess the effect on pulmonary and systemic inflammation and oxidant stress and defense.
They used a single, low-dose exposure by intratracheal instillation (IT) to elicit a transient inflammatory/oxidative response rather than a toxic/full-blown disease-promoting exposure level, to model pulmonary response to common levels of daily exposure to roadway PM in an urban environment.
They found that the aqueous extracts induced a 24 h inflammatory response characterized by increased broncho-alveolar lavage fluid (BALF) cells and cytokines (IL-6 and TNF-α), and increased reactive oxygen species production.
The associated the self-resolving nature of the response with the activation of antioxidant defense mechanisms.
this low-dose, compensated and short-lived response may elucidate the sequence of events that occur in the respiratory system by normal daily life exposure to roadside-derived air pollution. Metals in resuspended roadway PM are largely derived from brake and tire wear and the resuspension of road dust. These roadway sources are typically not a focus of emission controls measures, which are largely targeted at tailpipe emissions.
Future studies should unravel whether repeated low-dose exposure eventually results in decompensated biological response and accumulated damage that could explain air-pollution-associated morbidity and mortality. In such case, regulating non-tailpipe-related pollution sources must be considered to alleviate the impact of traffic-associated air pollution on human health.—Pardo et al.
Michal Pardo, Martin M. Shafer, Assaf Rudich, James J. Schauer, and Yinon Rudich (2015) “Single Exposure to near Roadway Particulate Matter Leads to Confined Inflammatory and Defense Responses: Possible Role of Metals” Environmental Science & Technology doi: 10.1021/acs.est.5b01449