We’re inhaling, eating, and drinking toxic chemicals. Now we need to figure out how they’re affecting us.

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What are chemical pollutants doing to our bodies? It's a question that's been on my mind this week, for a few reasons. Last week, people in Philadelphia cleared grocery shelves of bottled water after a toxic leak from a chemical plant spilled into a tributary of the Delaware River, a source of drinking water for 14 million people. And it was only last month that a train carrying a suite of other hazardous materials derailed in East Palestine, Ohio, unleashing an unknown quantity of toxic chemicals into the environment.

Earlier this week, I spoke to scientists about the potential impacts of microplastic pollution, too. A research team examining seabirds that have accidentally eaten plastic found that their gut microbiomes seem to have been transformed. Birds with more plastic in their guts also have more potentially harmful bacteria, including antibiotic-resistant bugs, as well as others that can break down plastic. Scientists don't yet know what microplastics are doing to humans. Given that they've been found in human blood, placentas, and feces, it's a pressing question.

There's no doubt that we are polluting the planet. In order to find out how these pollutants might be affecting our own bodies, we need to work out how we are exposed to them. Which chemicals are we inhaling, eating, and digesting? And how much? Enter the field of exposomics.

The term exposome" was first coined a couple of decades ago. The idea is that it should capture all the things we are exposed to that might affect our health, whether we encounter them in our diets or in our environment. We already know that our genomes help determine our risk of various diseases, but that's only part of the story. The exposome should help fill the gaps.

As you might expect, this is a huge field that covers everything from the effect of a pregnant person's diet on a fetus to the impact of structural racism on people's health. But let's focus on one of the trickier areas of study-understanding our exposure to pollutants.

Carmen Marsit is one of the scientists trying to work out how to measure our exposure to chemicals and what they might be doing to us. Marsit is a molecular epidemiologist and directs the Hercules Exposome Research Center at Emory University in Atlanta, Georgia.

The most detailed and accurate tests look for traces of chemicals, and their breakdown products, in blood, Marsit says. Once a chemical gets into your body, it doesn't stay in its original form for very long. It might get broken down by enzymes in your liver or acids in your stomach, for example. Scientists have learned which breakdown products to look for to estimate a person's exposure to lots of chemicals, but not all of them.

[When] factories release chemicals into the environment, they're going to transform," says Marsit. The chemicals might react with bacteria or fish in water, for example. Or they might react with sunlight or with other chemicals in the air, especially if they are burned. These reactions will produce new chemicals.

To test your exposure to different chemicals, scientists only need a tiny amount of blood-around 100 to 200 microliters. That small sample can be run through a couple of lab tests. Techniques like gas chromatography, liquid chromatography, and mass spectrometry work to separate individual chemicals and metabolites from a blood sample and identify them by weight. These tests can provide a pretty detailed list of chemicals you might have been exposed to, says Marsit. Today, researchers can check your exposure to potentially thousands of chemicals in one test, he says.

These kinds of tests aren't available to the public yet, but they are being honed in multiple labs, and researchers are working on ways to test for even more chemicals.

That's especially important because new chemicals are being developed all the time, and companies don't usually need to put them through rigorous safety tests before they start using them, says Marsit. They're coming on the market almost every day," he says. [We need to] understand what they are, and what's being released, before we can even measure them."

Getting to grips with the health effects of these chemicals is going to take a lot of work. We're often trying to understand the impact of chronic exposures to low levels of pollutants, says Ian Mudway, who investigates the health effects of air pollution at Imperial College London in the UK. It's like thinking about cigarette smoking," he says. The cigarette doesn't kill you, but the long-term cumulative effect of the toxic load ... drives forward diseases."

It's really tricky to work out a person's long-term exposure to chemicals from blood or other body tissues, says Mudway. Most measures will only indicate a person's short-term exposure.

Some researchers are working on personal sensors that can monitor a person's exposure to a set of chemicals over time. And some of these sensors-such as air quality monitors-are available to buy. But neither Mudway nor Marsit uses them.

That's partly because they provide very limited information. An air quality monitor might tell you about the level of certain particulates or indicate how much air flow there is in a room. But it won't tell you whether or how these pollutants are getting into your body. That is likely to depend on variables such as your breathing rate, your metabolism, and the amount of skin that's exposed to the air, says Mudway: All of these factors become critically important."

The more sensitive tests being developed are, for the time being, restricted to research labs-your doctor won't be able to run them. Even if clinics could run exposure tests, it would be difficult to know what to do with the results. While we're getting better at working out how to measure our exposure to various chemicals, we've got a long way to go to understand how they might be affecting our health.

We can measure a lot of these [exposures], but, for a lot of these chemicals, we may not even know what a safe level is," says Marsit. Our estimates for even relatively well understood pollutants can end up being wrong. We tend to set a safe level, but really it ends up being much lower than that," he says.

Take lead, for example. While the US Centers for Disease Control and Prevention (CDC) states that there is no safe level" of lead in children's blood, the organization sets a blood lead reference value (BLRV) to help determine when levels are high enough to require medical intervention. In 2012, this level was set at 5 micrograms per deciliter of blood. But the cutoff was lowered to 3.5 L/dL in 2021, after more research demonstrated the harmful effects of even low levels of lead on a child's brain, heart, and immune system. As new findings emerge, this cutoff could be lowered even further, says Marsit.

Getting a handle on the exposome might seem like an impossible challenge. As Mudway puts it, we're trying to understand the impact of everything, everywhere, at all times."

But we are making good progress. Some research teams are focusing on groups of people who are especially vulnerable to diseases, and trying to work out how chemical exposures might play a role. Others are investigating the effects of specific pollutants in the lab. And tests that measure chemical exposures are improving over time. Perhaps the bigger challenge is to convince polluters to stop pumping so many of these chemicals into our environment in the first place.

Read more from Tech Review's archive

Seabirds that eat microplastics have altered gut microbiomes. We ingest microplastics too-a credit card's worth a week, by one estimate-so scientists are wondering what they might be doing to our own microbiomes, as I reported earlier this week.

When it comes to regulating emissions in the US, the Environmental Protection Agency has limited powers. These were further diminished last summer, when the US Supreme Court ruled that the EPA did not have the authority to cap carbon emissions, as my colleague Casey Crownhart reported.

Casey has also explored technologies that might help us cut down the emissions associated with air travel. (This article is from her excellent weekly newsletter, The Spark, which you can sign up for here.)

Unfortunately, reducing air pollution could have unintended consequences for climate change. Research suggests that as we clean up the air, droughts will get even more severe, as my colleague James Temple reported in 2019.

Less pollution, more art. That was the goal of startup Graviky Labs, which developed a system to collect soot and turn it into ink or paint for artists, as Rob Matheson reported in 2018.

From around the web

Getting reinfected with mpox is thought to be extremely unlikely. But this unfortunate man caught it twice within a matter of months. (The Lancet)

Weight-loss drugs could soon be considered essential medicines" by the World Health Organization. The move could help make the drugs more accessible to those living in poorer countries. (Reuters)

Italy's government is looking to ban lab-grown meat and other synthetic foods." Lab-made foods won't have the quality of Italian food and wine, argued a minister in support of the ban. (BBC)

Dozens of people in the UK are launching legal action against AstraZeneca over a rare side effect of the company's covid vaccine. Around 75 claimants are seeking compensation following the development of blood clots, some of which resulted in stroke, heart failure, or leg amputations. (BMJ)

Could you fall asleep cuddling a stranger in virtual reality? My colleague Tanya Basu has a firsthand report on the cozy but creepy" world of VR sleep rooms. (MIT Technology Review)