“Combustion remains a source of air pollution across the world, both indoors and outdoors. We found that cooking on your gas stove produces large amounts of small nanoparticles that get into your respiratory system and deposit efficiently,” said Brandon Boor, an associate professor in Purdue’s Lyles School of Civil Engineering, who led this research.

Based on these findings, the researchers would encourage turning on a kitchen exhaust fan while cooking on a gas stove.

The study, published in the journal PNAS Nexus, focused on tiny airborne nanoparticles that are only 1-3 nanometers in diameter, which is just the right size for reaching certain parts of the respiratory system and spreading to other organs.

Recent studies have found that children who live in homes with gas stoves are more likely to develop asthma. But not much is known about how particles smaller than 3 nanometers, called nanocluster aerosol, grow and spread indoors because they’re very difficult to measure.

“These super tiny nanoparticles are so small that you’re not able to see them. They’re not like dust particles that you would see floating in the air,” Boor said. “After observing such high concentrations of nanocluster aerosol during gas cooking, we can’t ignore these nano-sized particles anymore.”

Using state-of-the-art air quality instrumentation provided by the German company GRIMM AEROSOL TECHNIK, a member of the DURAG GROUP, Purdue researchers were able to measure these tiny particles down to a single nanometer while cooking on a gas stove in a “tiny house” lab. They collaborated with Gerhard Steiner, a senior scientist and product manager for nano measurement at GRIMM AEROSOL.

Called the Purdue zero Energy Design Guidance for Engineers (zEDGE) lab, the tiny house has all the features of a typical home but is equipped with sensors for closely monitoring the impact of everyday activities on a home’s air quality. With this testing environment and the instrument from GRIMM AEROSOL, a high-resolution particle size magnifier — scanning mobility particle sizer (PSMPS), the team collected extensive data on indoor nanocluster aerosol particles during realistic cooking experiments.

This magnitude of high-quality data allowed the researchers to compare their findings with known outdoor air pollution levels, which are more regulated and understood than indoor air pollution. They found that as many as 10 quadrillion nanocluster aerosol particles could be emitted per kilogram of cooking fuel — matching or exceeding those produced from vehicles with internal combustion engines.

This would mean that adults and children could be breathing in 10-100 times more nanocluster aerosol from cooking on a gas stove indoors than they would from car exhaust while standing on a busy street.

“You would not use a diesel engine exhaust pipe as an air supply to your kitchen,” said Nusrat Jung, a Purdue assistant professor of civil engineering who designed the tiny house lab with her students and co-led this study.

Purdue civil engineering PhD student Satya Patra made these findings by looking at data collected in the tiny house lab and modeling the various ways that nanocluster aerosol could transform indoors and deposit into a person’s respiratory system.

The models showed that nanocluster aerosol particles are very persistent in their journey from the gas stove to the rest of the house. Trillions of these particles were emitted within just 20 minutes of boiling water or making grilled cheese sandwiches or buttermilk pancakes on a gas stove.

Even though many particles rapidly diffused to other surfaces, the models indicated that approximately 10 billion to 1 trillion particles could deposit into an adult’s head airways and tracheobronchial region of the lungs. These doses would be even higher for children — the smaller the human, the more concentrated the dose.

The nanocluster aerosol coming from the gas combustion also could easily mix with larger particles entering the air from butter, oil or whatever else is cooking on the gas stove, resulting in new particles with their own unique behaviors.

A gas stove’s exhaust fan would likely redirect these nanoparticles away from your respiratory system, but that remains to be tested.

“Since most people don’t turn on their exhaust fan while cooking, having kitchen hoods that activate automatically would be a logical solution,” Boor said. “Moving forward, we need to think about how to reduce our exposure to all types of indoor air pollutants. Based on our new data, we’d advise that nanocluster aerosol be considered as a distinct air pollutant category.”

This study was supported by a National Science Foundation CAREER award to Boor. Additional financial support was provided by the Alfred P. Sloan Foundation’s Chemistry of Indoor Environments program through an interdisciplinary collaboration with Philip Stevens, a professor in Indiana University’s Paul H. O’Neill School of Public and Environmental Affairs in Bloomington.

According to the Ancient Greek philosopher Pythagoras, ‘consonance’ — a pleasant-sounding combination of notes — is produced by special relationships between simple numbers such as 3 and 4. More recently, scholars have tried to find psychological explanations, but these ‘integer ratios’ are still credited with making a chord sound beautiful, and deviation from them is thought to make music ‘dissonant’, unpleasant sounding.

But researchers from Cambridge University, Princeton and the Max Planck Institute for Empirical Aesthetics, have now discovered two key ways in which Pythagoras was wrong.

Their study, published in Nature Communications, shows that in normal listening contexts, we do not actually prefer chords to be perfectly in these mathematical ratios.

“We prefer slight amounts of deviation. We like a little imperfection because this gives life to the sounds, and that is attractive to us,” said co-author, Dr Peter Harrison, from Cambridge University’s Faculty of Music and Director of its Centre for Music and Science.

The researchers also found that the role played by these mathematical relationships disappears when you consider certain musical instruments that are less familiar to Western musicians, audiences and scholars. These instruments tend to be bells, gongs, types of xylophones and other kinds of pitched percussion instruments. In particular, they studied the ‘bonang’, an instrument from the Javanese gamelan built from a collection of small gongs.

“When we use instruments like the bonang, Pythagoras’s special numbers go out the window and we encounter entirely new patterns of consonance and dissonance,” Dr Harrison said.

“The shape of some percussion instruments means that when you hit them, and they resonate, their frequency components don’t respect those traditional mathematical relationships. That’s when we find interesting things happening.”

“Western research has focused so much on familiar orchestral instruments, but other musical cultures use instruments that, because of their shape and physics, are what we would call ‘inharmonic’.

The researchers created an online laboratory in which over 4,000 people from the US and South Korea participated in 23 behavioural experiments. Participants were played chords and invited to give each a numeric pleasantness rating or to use a slider to adjust particular notes in a chord to make it sound more pleasant. The experiments produced over 235,000 human judgments.

The experiments explored musical chords from different perspectives. Some zoomed in on particular musical intervals and asked participants to judge whether they preferred them perfectly tuned, slightly sharp or slightly flat. The researchers were surprised to find a significant preference for slight imperfection, or ‘inharmonicity’. Other experiments explored harmony perception with Western and non-Western musical instruments, including the bonang.

Instinctive appreciation of new kinds of harmony

The researchers found that the bonang’s consonances mapped neatly onto the particular musical scale used in the Indonesian culture from which it comes. These consonances cannot be replicated on a Western piano, for instance, because they would fall between the cracks of the scale traditionally used.

“Our findings challenge the traditional idea that harmony can only be one way, that chords have to reflect these mathematical relationships. We show that there are many more kinds of harmony out there, and that there are good reasons why other cultures developed them,” Dr Harrison said.

Importantly, the study suggests that its participants — not trained musicians and unfamiliar with Javanese music — were able to appreciate the new consonances of the bonang’s tones instinctively.

“Music creation is all about exploring the creative possibilities of a given set of qualities, for example, finding out what kinds of melodies can you play on a flute, or what kinds of sounds can you make with your mouth,” Harrison said.

“Our findings suggest that if you use different instruments, you can unlock a whole new harmonic language that people intuitively appreciate, they don’t need to study it to appreciate it. A lot of experimental music in the last 100 years of Western classical music has been quite hard for listeners because it involves highly abstract structures that are hard to enjoy. In contrast, psychological findings like ours can help stimulate new music that listeners intuitively enjoy.”

Exciting opportunities for musicians and producers

Dr Harrison hopes that the research will encourage musicians to try out unfamiliar instruments and see if they offer new harmonies and open up new creative possibilities.

“Quite a lot of pop music now tries to marry Western harmony with local melodies from the Middle East, India, and other parts of the world. That can be more or less successful, but one problem is that notes can sound dissonant if you play them with Western instruments.

“Musicians and producers might be able to make that marriage work better if they took account of our findings and considered changing the ‘timbre’, the tone quality, by using specially chosen real or synthesised instruments. Then they really might get the best of both worlds: harmony and local scale systems.”

Harrison and his collaborators are exploring different kinds of instruments and follow-up studies to test a broader range of cultures. In particular, they would like to gain insights from musicians who use ‘inharmonic’ instruments to understand whether they have internalised different concepts of harmony to the Western participants in this study.

The report, “Endocrine Disrupting Chemicals: Threats to Human Health” provides a comprehensive update on the state of the science around EDCs, with increasing evidence that this large group of toxic substances may be implicated in rising global health concerns.

The report from the Endocrine Society, co-produced with the International Pollutants Elimination Network (IPEN), includes detailed analyses on exposure to EDCs from four sources: plastics, pesticides, consumer products (including children’s products), and per-and polyfluoroalkyl substances (PFAS), a class of thousands of chemicals known or suspected to be EDCs.

The Endocrine Society-IPEN report is being released during the U.N. Environment Assembly (UNEA-6) meeting in Nairobi. At UNEA key agenda items include welcoming the newly adopted Global Framework on Chemicals, advancing global action on highly hazardous pesticides, and threats to the circular economy from plastics and toxic chemicals. The groups’ report anticipates an update from UNEP and the WHO expected later this year on their 2012 Report on State of the Science of Endocrine Disrupting Chemicals.

“A well-established body of scientific research indicates that endocrine-disrupting chemicals that are part of our daily lives are making us more susceptible to reproductive disorders, cancer, diabetes, obesity, heart disease, and other serious health conditions,” said the report’s lead author, Andrea C. Gore, PhD, of the University of Texas at Austin. Gore is also a member of the Endocrine Society’s Board of Directors. “These chemicals pose particularly serious risks to pregnant women and children. Now is the time for the UN Environment Assembly and other global policymakers to take action to address this threat to public health.”

Hormones are natural chemicals that contribute to normal development, adaptation, and maintenance of bodily processes and health. By interfering with hormones and their actions, EDC exposure can impact many health-related functions, with consequences for increased risks of many serious conditions. Evidence suggests that EDCs in the environment contribute to disorders such as diabetes, neurological disorders, reproductive disorders, inflammation, and compromised immune functioning.

Two of the four analyses in the report look at EDCs used in plastics and as pesticides. Global production of plastics and pesticides is increasing even as scientists warn that chemical and plastic pollution is an escalating crisis. Glyphosate is the world’s most widely used herbicide, and a recent study found that glyphosate has eight of ten key characteristics of an EDC. Other studies have found links between glyphosate and adverse reproductive health outcomes. Plastics are made with thousands of known toxic substances, some of which are known or suspected EDCs. The report examines bisphenols and phthalates, two toxic chemical groups found in many plastics. Exposures to EDCs from plastics occur at all phases of plastics production, use, disposal, and even from recycled plastics.

The Endocrine Society-IPEN report notes that, while evidence of health threats from EDCs is mounting, current regulations have not kept pace. “EDCs are different than other toxic chemicals, but most regulations fail to address these differences,” said IPEN Science Advisor Sara Brosché, Ph.D. “For example, we know that even very low doses of endocrine disrupting chemicals can cause health problems and there may be no safe dose for exposure to EDCs. However, regulations typically do not protect against low-dose effects. We need a global approach to controlling EDCs based on the latest science with a goal of protecting the human right to a healthy environment.”

At the UNEA-6 meeting, IPEN is also releasing a new report on “The Global Threat from Highly Hazardous Pesticides,” highlighting ongoing health and environmental risks from HHPs, especially in low- and middle-income countries. DDT, glyphosate, and chorpyrifos, three HHPs reviewed in the Endocrine Society report, are also highlighted in the new IPEN report as they continue to pose health threats especially in the Global South.

In addition to plastics and pesticides, the report looks at EDC exposures from arsenic and lead, and from widely used per- and polyfluoroalkyl substances (PFAS), humanmade “forever chemicals” used as oil and water repellents and coatings. Lead remains in use in paint in many countries, as documented in recent IPEN reports. Endocrine-related conditions from lead exposure may include delayed onset of puberty and early menopause. Arsenic is a common metal that has long been linked to cancer and other health conditions, and more recent evidence shows that arsenic can disrupt multiple endocrine systems. PFAS are used in hundreds of products including clothing and food packaging, but recent studies show that some PFAS can disrupt hormones such as estrogen and testosterone and impair thyroid hormone functions.