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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.

Resources

  • 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

Comments

Davemart

Regenerative braking should help to some extent, but the problem is a tough one.

HarveyD

This may disturb posters who claimed that ICEVs clean the air???

GdB

Regenerative braking can help a lot with massive ICE downsizing and increased electric power. BMW is leading in this area.

On my imiev EV I rarely use the brakes. There was a phone app developed that gives the driver predictive signal information. And could avoid brakes completely if the traffic phone app was available in my area. If widely adopted, traffic flow could increase as cars don't have to stop and signals turn green just in time.

Better flow through city allows shorter routes to be taken for some instead of highway.

So a software that saves time, fuel, pollution, health is still not available after how many years that it was invented. Why?

HarveyD

AWD EVs with more improved regenerative braking could greatly reduce the use of mechanical friction brakes while capturing valuable energy?

No doubt that Tesla and others will find ways to maximize it to reduce wear, improve e-range and reduce potential costly health hazards.

Peter_XX

Not all ICEVs clean the ambient air from particulate matter (as diesel engines with DPF can do) and one should note that particulate is a mixture of many different compounds. Only engines with DPF (possibly also GPF) clean also metal compounds in the exhaust that, for example, originate from the lube oil and engine wear but also from ambient air passing through the engine (although part of that will be trapped already in the inlet filter of the engine). In fact, the lifetime of the DPF is determined by accumulation of this “ash”. In contrast, a conventional gasoline engine without particulate filter will not trap any metal compounds in the exhaust.

One should also note that most of the total PM (mass, not number of particles) on the streets originates from road-tire wear and re-suspension from the road, not tailpipe PM. As the authors mention: “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.”, tailpipe emissions is not the main problem. In general, the bigger and heavier the vehicle is, the more it contributes to this type of PM. In fact, an EV, without any tailpipe emissions, will increase PM from re-suspension, tire wear and crustal elements compared to a conventional ICEV (which is, of course, much lighter). The EV advantage would be less brake wear but who knows if that fully compensates for the negative aspects mentioned. HEVs also have some advantage of reduced brake wear.

Hydraulic and kinetic hybrids will also reduce brake wear; potentially to a larger extent than electric hybrids provided that they are designed to absorb higher power. So-called “wet” brakes (used on off-road vehicles) do not emit any wear particles to the air but might have problems to cope with the high braking power necessary in on-road vehicles.

For sure, once tailpipe PM of modern cars is cleaned up (pretty soon, we can presume…), we will have to focus more attention to other sources of PM than the tailpipe.

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