Category: Analysis

Source: The Conversation – USA – By Linda Bartoshuk, Research Professor of Psychology, George Washington University

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

Why does orange juice taste bad after you brush your teeth? – Seth G., age 10, Bloomington, Indiana

It’s a mistake you hopefully only make once. In your morning rush to get ready, you brush your teeth before you head to the kitchen and down a big glass of orange juice. Yuck!

What makes your clean, minty mouth taste so gross when it meets OJ?

The short answer is that toothpaste contains a detergent that dissolves fat. And since your taste buds are partly made of fat, they are disrupted whenever you brush your teeth.

Before you decide you need to stop brushing your teeth to save your taste buds, know that this disruption is temporary, lasting only a few minutes. Brushing with toothpaste is still important for your health.

But how does this change in taste happen? And how are the taste receptors that are all over the surface of your tongue supposed to work?

I’m a psychologist, and I’ve spent more than 40 years researching the science of how people experience taste and flavor.

Let’s look at the science behind this phenomenon:

A bittersweet symphony

Thanks to evolution, your brain is wired to make you love the sweet sugars your body and brain need for fuel and hate the bitter poisons than could kill you. So your receptors for these two particular tastes are vital to your survival.

All of the cells in your body are held together by an outer layer, known as the membrane, that is made up of fats called lipids. And in sweet or bitter taste receptor cells, the cell membranes also contain a special molecule called a G protein-coupled receptor, or GPCR.

Some GPCRs are designed to detect sweet tastes. They tune out all compounds that aren’t sweet and respond only to the sugars your body can use. Others detect bitter tastes, tuning in to the large number of compounds in nature that are poisonous. They act as a built-in alarm system.

Salty chips and sour candies

Your perception of saltiness and sourness happens a little differently. These tastes are detected when positively charged ions called cations pass through tiny openings in the cell membrane of your salty and sour receptors.

In the case of saltiness, the cation is the positively charged sodium found in sodium chloride – common table salt.

For acidic, or sour, tastes, the cation is a positively charged hydrogen ion. While different types of acids may contain different chemical compounds, they all contain the hydrogen cation.

When you eat potato chips, the positively charged sodium cations from the salt pass through special openings in a receptor’s membrane, producing the salty taste. Similarly, the hydrogen cations in your favorite sour candy slip through other special openings in your sour receptor’s membrane and send a “sour” signal to your brain.

Toothpaste and OJ

The orange juice that many people like to drink with breakfast is naturally high in sugar. But it also contains citric acid, with its hydrogen cations. As a result, it’s a delicious combination of both sweet and a little sour.

But if you brush your teeth before breakfast, your OJ tastes terrible. What’s changed?

It’s not just that minty tastes clash with sweet ones. Toothpaste contains the detergent sodium lauryl sulfate, which helps remove dental plaque from your teeth. Plaque is the sticky film of germs that can cause cavities and make your breath smell bad.

If you ever do the dishes, you’ve probably seen what happens when you squirt detergent into a sink full of greasy water: The detergent breaks up the greasy fat, making it easy to wipe it off the dishes and rinse them clean.

But there’s another type of fat in your mouth that the detergent in toothpaste disrupts – the lipids in the cell membranes of your taste receptors. Brushing your teeth breaks up that layer of lipids, temporarily changing how you perceive taste.

Testing it out

Back in 1980, I conducted a study with a couple of my colleagues who were studying chemistry. We wanted to know how the tongue responds to sweet, bitter, salty and sour after being exposed to sodium lauryl sulfate, the detergent in toothpaste.

We conducted an experiment with seven student volunteers at Yale. They tasted very high concentrations of sweet sucrose, sour citric acid, salt and bitter quinine, both before and after holding a solution (0.05%) of sodium lauryl sulfate in their mouths for one minute.

You could conduct your own version of this experiment with something sweet like sugar, a little table salt, orange juice and tonic water. Taste them before you brush your teeth and then after, and see what happens!

We found that the intensity of the tastes of sucrose, salt and quinine were reduced by a small amount, but the most important change was that a bitter taste was added to the sour taste of citric acid.

This is why, instead of tasting sweet with a bit of nice tanginess, your OJ tastes bitter after you brush your teeth.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Linda Bartoshuk has received funding from NIH.

– ref. Why does orange juice taste bad after you brush your teeth? – https://theconversation.com/why-does-orange-juice-taste-bad-after-you-brush-your-teeth-271741

Source: The Conversation – USA (2) – By James Salzman, Professor of Environmental Law, Bren School of Environmental Science & Management, University of California, Santa Barbara; University of California, Los Angeles

Growing up in the 1970s, I took for granted the trash piles along the highway, tires washed up on beaches, and smog fouling city air. The famed “Crying Indian” commercial of 1971 became a symbol of widespread environmental damage across the United States.

That’s why the first Earth Day on April 22, 1970, energized the nation. In the largest single-day public demonstration in U.S. history, roughly 10% of the population took to the streets to shout together: “Enough is enough!”

Republican and Democratic politicians alike listened. Over the decade that followed, all the nation’s foundational environmental laws were passed with strong bipartisan support – the Clean Air Act, Clean Water Act, Endangered Species Act and more.

These laws are taking a beating at the moment, including from the Environmental Protection Agency – the federal government agency created in 1970 to protect the environment. The agency’s own leader, Lee Zeldin, boasted of “driving a dagger straight into the heart” of environmental regulations. President Donald Trump regularly derides environmental laws as job killers and government overreach.

But the conditions that made these laws necessary have largely been forgotten. This environmental amnesia allows critics to focus entirely on costs while ignoring the laws’ very real benefits and achievements.

I’m an environmental law professor, so I was excited to learn recently about the Documerica project, courtesy of a wonderful article by writer Gideon Leek. It shows in clear photographic evidence how dirty the U.S. used to be and wakes people up to how much better the environment is today.

An inspired origin

Environmental protection was a bipartisan effort in the 1970s: The EPA was created by President Richard Nixon, a Republican. The agency’s first leader was Bill Ruckelshaus, a Republican congressman from Indiana.

Inspired by the famous photographs of Depression-era farmworkers commissioned in the 1930s by the Farm Security Administration, Ruckelshaus’ newly created EPA commissioned a nationwide photo record. The goal, as Leek put it, was to “provide the EPA with a great deal of qualitative environmental data, create a ‘visual baseline’ against which to judge their efforts, and introduce the agency to the country through art.”

In its few short years of operation, from 1972 through 1978, the Documerica project produced over 20,000 photographs of rivers and farms, highways and city streets. The photos provide a vivid window into the state of the U.S. environment in the 1970s. Now, looking back, they highlight the progress made in the decades since, a demonstration of environmental laws’ successes far more powerful than graphs and statistics.

Solid waste

As a kid, every Sunday my father and I would load the back of our station wagon with trash barrels and drive to the town dump – literally a hole in the ground. My dad would back up to the edge of the pit, and I would enthusiastically run out for what we called “The Olympic Trash Throw!” pouring the barrels’ contents down to where a bulldozer rumbled back and forth, compacting the trash while gulls circled overhead.

To say America’s landscape was littered in the 1970s is not merely poetic phrasing. Waste disposal was a matter of local law, and illegal dumping was commonplace. Drums of pesticides and chemicals could be sent to the local dump along with tires and just about anything else people and companies wanted to get rid of. When the dump was full, it was covered with topsoil and became open land, ready for recreation or building construction.

One place where this happened was Love Canal, a neighborhood near Niagara Falls, New York. A dump holding decades of chemical drums from the Hooker Chemical Co. was lightly covered and sold to the town for just $1. The town was grateful. A neighborhood was built on the land.

Only when people noticed high levels of miscarriages and cancer clusters among the residents – and saw oozing waste – did opinion change.

In 1976, Congress passed the Resource Conservation Recovery Act, which was the first law that tracked waste materials from their creation to their disposal and set tough standards for how to dispose of them. But by then, decades of unregulated waste disposal had contaminated sites all over the country. The contaminants, toxicity and people responsible were often unknown.

Four years later, the 1980 law known as “Superfund” set standards and assigned financial responsibility for cleaning up hazardous waste sites. The law created a multibillion-dollar fund that could pay for the cleanups and required potentially responsible parties to reimburse the government or clean up the sites on their own.

Faced with requirements to track their waste and heavy fines if the disposal resulted in hazardous sites, companies paid much more careful attention to their waste disposal. No one wanted to pay for cleaning up a Superfund site.

Water pollution

I had the misfortune in 1978 to capsize while sailing a boat on the Charles River in Boston. My shame turned to a dermatologist’s visit when I broke out in rashes the next day. You fell in the Charles at your peril.

Environmental advocates weren’t kidding when, in the 1960s and 1970s, they declared “Lake Erie is a dead lake” because of all the industrial pollution pouring into its waters. An oil slick on Cleveland’s Cuyahoga River famously caught fire in 1969, but it was actually the 12th time the river had burned in a century.

Just as with dumps on land, all kinds of waste was being disposed of in rivers, lakes and harbors. There was a federal law in place, but it was ineffective and relied on states to set limits and enforce them.

The Clean Water Act of 1972 sought to create a national standard, requiring companies that wanted to discharge waste into waterways to get a federal permit and use the best available technology to reduce the amount and toxicity of what they did dump. The act also provided billions of taxpayer dollars to upgrade sewage treatment plants so they didn’t just dump untreated sewage into the water.

The ambitious goal was to end water pollution entirely and make all of the nation’s waters safe for swimming and fishing within a decade. Those aspirational goals for the country’s waters still have not been fully met, though Ruckelshaus used to quip that at least they are not flammable.

Even more telling, the Charles River and other urban rivers that people avoided in the 1970s now boast all manner of recreation, with little or no risk of rashes even while swimming.

Air pollution

Perhaps the most obvious improvement since the 1970s has been in air quality around the U.S.

The horrible smog around Los Angeles is well known. But many other cities were blanketed in polluted air that led to respiratory illnesses and millions of early deaths across the nation over the decades. In Pittsburgh it was only half-jokingly said that you had to floss your teeth after breathing.

The Clean Air Act of 1970 was the first law to require the EPA to set uniform nationwide standards for air quality to protect the air people breathe. In short order, lead was phased out of gasoline, catalytic converters were required on cars, acid rain was ended, and the sources of smog were stringently regulated. An EPA study found that the benefits under the law exceeded costs by a factor of more than 30 to 1 and in 2020 alone prevented over 230,000 early deaths.

I could go on with photos and stories about laws from the 1970s that protected wetlands, conserved open space, reduced pesticide use, increased recycling and made many other changes to how Americans treat our lands and waters.

But it all boils down to two simple facts. First, with the exception of greenhouse gases, which have been effectively unregulated, every major measure of environmental health has improved significantly over the past five decades. And second, those improvements all occurred during times of strong economic growth, with inflation-adjusted gross domestic product increasing fivefold.

Calling these laws “job killers” misses the point entirely. They created jobs and stopped environmental killers. The laws now being demonized are the very reason the Documerica photos are images of the past, not the present. Environmental laws and regulations have their costs, to be sure, but these photographs still hold visceral power: They show just how far the nation has come and what is at risk if we forget.

James Salzman does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. The US used to be really dirty – environmental cleanup laws have made a huge difference – https://theconversation.com/the-us-used-to-be-really-dirty-environmental-cleanup-laws-have-made-a-huge-difference-271277

Source: The Conversation – USA (2) – By Yifang Zhu, Professor of Environmental Health Sciences, University of California, Los Angeles

When wildfires began racing through the Los Angeles area on Jan. 7, 2025, the scope of the disaster caught residents by surprise. Forecasters had warned about high winds and exceptionally dry conditions, but few people expected to see smoke and fires for weeks in one of America’s largest metro areas.

Environmental health scientist Yifang Zhu studies air quality at UCLA and began collecting samples from inside and outside homes the day after the fires began. In this Q&A, she describes findings by her team, a consortium of universities and local projects, that are painting a picture of the health risks millions of Los Angeles-area residents faced.

Their research offers both a warning and steps people everywhere can take to protect their homes and themselves from wildfire smoke in the future.

What made the LA fires unusual?

Urban fires are unique in a sense that it’s not just trees and other biomass burning. When homes and vehicles catch fire, plastics, electronics, cleaning chemicals, paints, textiles, construction material and much more burns, releasing chemicals and metals into the air.

More than 16,000 buildings burned in LA. Electric vehicles burned. A dental clinic burned. All of this gets mixed into the smoke in complicated ways, creating complex mixtures that can have definite health risks.

One thing we’ve found that is especially important for people to understand is that the concentration of these chemicals and metals can actually be higher inside homes compared with outside after a fire.

What are your health studies trying to learn?

To understand the health risks from air pollution, you need to know what people are exposed to and how much of it.

The LA Fire HEALTH Study, which I’m part of, is a 10-year project combining the work of exposure scientists and health researchers from several universities who are studying the long-term effects of the fire. Many other community and health groups are also working hard to help communities recover. A local program called CAP.LA, or Community Action Program Los Angeles, is supporting some of my work, including establishing a real-time air quality monitoring network in the Palisades area called CAP AIR.

During an active wildfire, it’s extremely difficult to collect high-quality air samples. Access is restricted, conditions change quickly, and research resources are often limited and take time to assemble. When the fires broke out not far from my lab at UCLA, my colleagues and I had been preparing for a different study and were able to quickly shift focus and start collecting samples to directly measure people’s exposure to metals and chemicals near and around the fires.

My group has been working with people whose homes were exposed to smoke but didn’t burn and collecting samples over time to understand the smoke’s effects. We’re primarily testing for volatile organic compounds off-gassing from soft goods – things like pillows, textiles and stuffed animals that are likely to absorb compounds from the smoke.

Our testing found volatile organic compounds that were at high levels outdoors during the active fire were still high indoors in February, after the fires were contained. When a Harvard University team led by environmental scientist Joe Allen took samples in March and April, they saw a similar pattern, with indoor levels still high.

What health risks did your team find in homes?

We have found high levels of different kinds of volatile organic compounds, which have different health risks. Some are carcinogens, like benzene. We have also found metals like arsenic, a known carcinogen, and lead, which is a neurotoxin.

Mike Kleeman, an air quality engineer at the University of California Davis, found elevated levels of hexavalent chromium in the nanometer-size range, which can be a really dangerous carcinogen. In March, he drove around collecting air samples from a burn zone. That was testing which government agencies would not have routinely done.

Fires have a long list of toxic compounds, and many of them aren’t being measured.

What do you want people to take away from these results?

People are exposed to many types of volatile organic compounds in their daily lives, but after wildfires, the indoor VOC levels can be much, much higher.

I think that’s a big public health message from the LA fires that people really need to know.

In general, people tend to think the outdoor air is worse for their health, particularly in a place like LA, but often, the indoor air is less healthy because there are several chemical emission sources right there and it’s an enclosed space.

Think about cooking with a gas stove, or burning candles or spraying air fresheners. All of these are putting pollutants into the air. Indoor pollution sources like cleaning fluids and PFAS from furniture and carpets are all around.

We often hear from people who are really worried about the air quality outside and its health risk during fires, but you need to think about the air indoors too.

What are some tips for people dealing with fires?

The LA fires have given us lots of insights into how to restore homes after smoke damage and what can be cleaned up, or remediated. One thing we want to do is develop an easy-to-follow decision tree or playbook that can help guide future fire recovery.

When the fires broke out, even I had to think about the actions I should take to reduce the smoke’s potential impact, and I study these risks.

First, close all your windows during the wildfire. If you have electricity, keep air purifiers running. That could help capture smoke that does get into the home before it soaks into soft materials.

Once the outside air is clean enough, then open those windows again to ventilate the house. Be sure to clean your HVAC system and replace filters, because the smoke leaves debris. If the home is severely impacted by smoke, some items will have to be removed, but not in every case.

And you definitely need to do testing. A home might seem fine when you look at it, but our testing showed how textiles and upholstery inside can continue off-gassing chemicals for weeks or longer.

But many people don’t have their homes tested after wildfires. They might not know how to read the results or trust the results. Remediation can also be expensive, and some insurance companies won’t cover it. There are probably people who don’t know whether their homes are safe at this point.

So there needs to be a clear path for recovery, with contamination levels to watch for and advice for finding help.

This is not going to be the last fire in the Los Angeles area, and LA will not be the last city to experience fire.

Yifang Zhu is working with CAP.LA (Community Action Project Los Angeles), which is funded by the R&S Kayne Foundation, and the LA Fire Health Study, which is funded by private philanthropists, including the Speigel Family Fund. Her work has also been partially funded by the Gordon and Betty Moore Foundation, the Danhakl Family Foundation, and the California Air Resources Board.

– ref. LA fire studies show the risks as wildfire smoke lingered inside homes – https://theconversation.com/la-fire-studies-show-the-risks-as-wildfire-smoke-lingered-inside-homes-272473