Vehicle brakes produce charged particles that may harm public health

Scientists know relatively little about particles released into the air when a vehicle driver brakes, though evidence suggests those particles may be more harmful to health than particles exiting the tailpipe.

In a new study in Proceedings of the National Academy of Sciences, University of California, Irvine researchers show how most of these particles emitted during light braking carry an electric charge -- something that could potentially be exploited to help reduce air pollution from vehicles.

"We found that up to 80% of aerosol particles emitted from braking are electrically charged, and that many of them are in fact highly charged," saidAdam Thomas, a doctoral candidate in the lab of Jim Smith, professor of chemistry, who led the study alongside UCI postdoctoral researcher Paulus Bauer.

To do the work, the team used a large lathe to spin a detached brake rotor and caliper.

They then measured the electric charge of the aerosols emitted into the air and discovered the 80 percent figure.

"I was very surprised," said Smith. "We were also surprised that this has not really been studied given how common cars are in human societies."

The research is part of a broader team effort at UCI to understand the public health impacts of non-tailpipe emissions in areas beset by car traffic, including many areas in Southern California.

"The toxicity and health effects of brake wear particles are largely unknown," said Manabu Shiraiwa, professor of aerosol chemistry at UCI and one of the researchers behind the university-wide project.

"Recent results from my lab indicate that they may induce oxidative stress, but more research is needed."

The new study reveals a problem that may grow as electric cars become more and more common over the next several decades.

Electric cars, Smith explained, are not truly zero-emission vehicles, so municipalities need to think about strategies to reduce emissions from brake use as well as tailpipes.

The team found that the percentage of charged particles emitted largely depended on the material makeup of brake pads.

Because the particles carry an electric charge, this should make it relatively easy to remove from the air.

"If they are charged, they can be removed easily from the air before they have a chance to have an impact at all on health," said Smith.

"All you would need to do is to collect them with an electrostatic precipitator -- a device that exposes the charged particles to an electric field and efficiently sweeps them away."

The public health risk posed by brake emissions is not borne equally by a population -- lower-income parts of cities tend to be more traffic-heavy than others, which creates an environmental justice issue wherein certain socioeconomic classes are more exposed to brake emissions than others.

According to Professor Barbara Finlayson-Pitts, Distinguished Emeritus Professor of chemistry and the principal investigator of the project at UCI, emissions from braking are not well-characterized but are potentially significant in high-traffic areas.

"These areas are often in poorer communities and highlight an important aspect of environmental justice that has been largely overlooked," Finlayson-Pitts said.

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Can we save more lives if we let resistant bacteria live?

Antibiotic resistance is a ticking bomb under public health. WHO predicts that in 2050 more people will die from infections than from cancer -- and we are talking about infections that we today consider harmless; infections that occur in a cut or wound -- or perhaps cystitis.

The reason is that bacteria are masters at adapting. When their existence is threatened, they mutate into a new and improved version of themselves that can no longer be threatened by eg antibiotics. Consequently, many disease-causing bacteria today are resistant to antibiotics.

"That's bacteria for you. They always find a way! Of course, resistance will occur; that's how evolution works," says professor and head of research, Birgitte Kallipolitis, who studies disease-causing bacteria at the Department of Biochemistry and Molecular Biology at University of Southern Denmark.

The talents of fatty acids

And that's exactly why, like other researchers around the world, she thinks it's time to find new ways to fight or neutralize the perpetually mutating bacteria.

For some years now, she and her research group have studied a particular type of fatty acid, which has proven itself interesting in this context. The researchers use listeria as a bacterial model to test the effect of these fatty acids. Elsewhere in the world, colleagues are using salmonella and cholera bacteria for similar tests.

The particular fatty acids are interesting not only because they can kill the listeria bacteria in Kallipolitis' laboratory, but they can also turn off their ability to infect and spread infection.

The researchers' experiments have shown that the fatty acids have an antimicrobial effect, ie that they can kill listeria bacteria. At first, this sounds good, but then there is the mutation thing; trying to kill the bacteria only makes it mutate into a new and resistant version of itself.

Enter the special talent of the fatty acids: They can make the resistant bacteria harmless, so that no infection occurs at all.

"Thus, the resistant bacterium is no longer a bacterium that we must try to kill -- instead, we prevent it from spreading and making us sick," Birgitte Kallipolitis explains.

No more spreading

The concept of making a disease-carrying bacterium unable to spread or make us sick is called turning off its virulence.

When you turn off the virulence of a bacterium, you prevent it from producing proteins like adhesins and invasins, which the bacterium needs to attach to a cell so that it can enter the cell.

"If a listeria bacterium cannot enter a cell, it cannot spread, and then no infection will occur," Birgitte Kallipolitis explains.

Extra help for the elderly and weak

The Listeria bacteria in Kallipolitis' experiments are only harmless as long as their virulence is switched off. When they are no longer exposed to the fatty acids that turn off their virulence, they regain the ability to spread

"But this may be the extra help that allows a patient to cope with an infection. Antivirulent medication or supplements could be good for the prevention of infections, especially in the elderly and weak," says Birgitte Kallipolitis.

The fatty acids that she and her colleagues work with, are so-called medium and long free fatty acids.

In nuts, plants and seeds

"We have especially focused on the free fatty acids, palmitoleic acid and lauric acid, which are found in nuts, seeds, plants and milk, etc. In our experiments, they show an antivirulent effect," she says.

Kallipolitis points out that you cannot eat your way to an antivirulent effect by, for example, eating nuts and seeds containing palmitoleic acid and lauric acid.

"The fatty acids must be in the free form, and that does not generally occur in food. You can buy free fatty acids as supplements but be aware that most fatty acids in supplements are locked and not in the free form.

"We do not yet know if you can achieve the effect by consuming free fatty acids. Maybe the fatty acids are metabolized before they reach the battle ground in the intestinal system, where the fight against many resistant bacteria takes place. Maybe we need pharmacists or chemists to find a way to transport the fatty acids to the scene of the battle," she explains.

Hence, a special dietary supplement or tablet is not just around the corner, she emphasizes. Before we get there, a number of tests are needed.

"The next step will be to test the antivirulence effect in a laboratory system reminiscent of the human intestinal system; here we will add listeria bacteria and see if the fatty acids will make them avirulent. If this works, it goes on to mouse experiments, and eventually it can hopefully be used prophylactically in humans," says Birgitte Kallipolitis.

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Hyena scavenging provides public health and economic benefits to African cities

Hyenas are frequently vilified and often feared. Hemingway once described the hyena as a stinking, foul devourer of the dead, with jaws that crack the bones the lion leaves.

But a new study concludes that spotted hyena scavenging provides significant public health and economic benefits to the African cities they roam.

In a study conducted in and around the Ethiopian city of Mekelle, home to 310,000 people and 120,000 livestock animals, a University of Michigan conservation ecologist and two colleagues found that spotted hyenas annually remove 207 tons of animal carcass waste.

Mekelle is the capital of northern Ethiopia's Tigray region. The carcasses of livestock animals that are slaughtered for food there, or that die naturally, are often dumped at the local landfill or on roadsides, where hyenas feed on the waste. The researchers wanted to know whether hyenas -- by removing this waste from the environment -- might also prevent pathogens from jumping into people and livestock.

They determined that hyena scavenging annually prevents five infections of anthrax and bovine tuberculosis in Mekelle residents and 140 infections in cattle, sheep and goats. This disease-control service potentially saves the city $52,000 annually in treatment costs and livestock losses avoided.

The study, published online Sept. 26 in the Journal of Applied Ecology, is the first to quantify the public health and economic benefits of scavenging by spotted hyenas.

"Yes, the effects are modest. Even so, this study totally upends the traditional narrative around hyenas -- that they are a nuisance and should be removed," said U-M's Neil Carter, senior author of the study and an assistant professor at the School for Environment and Sustainability. "This is an important contribution to a growing body of work that highlights the benefits of predators and scavengers, rather than focusing only on their costs to humanity."

The authors emphasize that these sanitation and disease-control services are particularly valuable in low-income and rural areas. In Mekelle, the scavenging behavior of hyenas advances three U.N. Sustainable Development Goals: ensuring good health and well-being, providing clean water and sanitation, and promoting terrestrial biodiversity.

To estimate the benefits of spotted hyenas, the researchers examined their feeding habits and the population size around Mekelle. During the daytime, the Mekelle hyenas rest at sites outside the city to avoid human disturbances; they come into the city at night to feed.

The field data were collected and analyzed by study lead author Chinmay Sonawane, a former student of Carter's who is now a doctoral student at Stanford University.

Those data were integrated into a disease transmission model used to predict the number of anthrax and bovine tuberculosis infections arising in humans and livestock from infected carcass waste, as well as the costs associated with treating those infections and losing livestock. The researchers compared these public health and economic outcomes under two scenarios: hyenas present and hyenas absent.

"In comparison to the large cattle enterprises in the Global North, the benefits that we found are quite small," Sonawane said. "However, losing even a single cow to anthrax or bovine tuberculosis can cause significant financial stress to cattle owners in Ethiopia, who tend to own much smaller herds of cattle than cattle owners in other parts of the world.

"In addition, we only estimated the benefits accrued from hyenas within 5 kilometers of the city. It is very, very likely that hyenas much further than 5 kilometers are coming into Mekelle and consuming even more waste."

For Sonawane, the fieldwork involved spending nights at the Mekelle landfill and recording the number and type of animal carcasses (mostly cattle, horses, chickens, sheep and goats) available to the scavengers.

He counted the hyenas and watched them feed, using night-vision binoculars that operate at infrared wavelengths. The black-and-white photos and video clips he captured are haunting: the eyes of the hyenas glow with an unearthly fire.

The study authors determined that an individual Mekelle hyena annually scavenges about 2,100 pounds of carcass waste around the city. For hyenas feeding at the landfill, horse carcasses accounted for about 80% of that total, while poultry waste was the most frequently consumed type of animal carcass waste.

The researchers estimated a population size of 210 hyenas around Mekelle using "call-in surveys." This field method involved broadcasting prerecorded hyena distress calls with a 45-watt megaphone from the top of a vehicle at five locations around the city. During each hour-long survey, the researchers counted the number of hyenas attracted to the sounds and visible with the night-vision binoculars.

Given the consumption rate and the estimated population size, the Mekelle hyenas were expected to annually remove 207 metric tons of animal carcass waste, which is 4.2% of the total animal carcass waste thrown away by residents and businesses.

Waste generation in Mekelle is expected to increase with the exponentially growing human population there, Carter and his colleagues wrote: "Given the financial constraints on waste collection and disposal services, sanitary conditions are expected to deteriorate further." Hyena scavenging may, therefore, be even more valuable in the future.

The authors note that the benefits of hyena presence must be weighed against the costs. A 2011 study reported 10 nonfatal hyena attacks on humans annually in Mekelle, along with an estimated economic loss of $2,928 from 33 fatal attacks on cattle and small ruminants annually.

To preserve the public health and financial benefits provided by hyenas into the future, nonlethal management actions that minimize risks and enable hyenas to coexist with humans are necessary, according to the authors.

"By maintaining the hyenas' access to waste, human-hyena conflict can be mitigated in Mekelle, and the sanitation and disease control benefits provided by hyena scavenging can be preserved or even increased," they wrote.

But excluding hyenas from scavenging animal carcass waste may compel them to hunt livestock and could increase human-hyena conflict, as a previous study in Mekelle has shown.

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