(FORT COLLINS, CO) Imagine an ordinary Tuesday. You wash your hair, put on deodorant, drink coffee, pack lunch in a plastic container and commute through traffic to get to work. At work, the custodial staff wipes down a shared table with disinfectant. At home, you cook dinner, clean the kitchen and run the dishwasher.
Each of these ordinary moments can involve exposure to chemicals. By itself, that is not a reason for concern. After all, chemicals make up the entire physical world.
But depending on the dose, timing and circumstances of exposure, some chemicals in our environment – both naturally occurring and human-made ones – may affect health.
Most everyday exposures occur at low levels, and many products are designed and regulated with safety in mind. But as a board-certified toxicologist who studies how chemical exposures affect human health, I rarely ask whether a single chemical is safe in isolation.
A more realistic question is: What might the health effects be when many low-level exposures overlap?
Mixtures are the rule, not the exception
Decades of research on the health effects of individual chemicals have helped scientists identify hazards, estimate safe exposure levels and develop regulations.
But the challenge is that people are rarely exposed to one chemical at a time.
Air is a changing mixture of particles, gases and vapors. Indoor air can differ from outdoor air because of cooking, cleaning, building materials, ventilation and chemical reactions that occur inside enclosed spaces.
Food often contains residues from multiple pesticides, as monitoring programs in Europe and the United States have identified. This reflects the fact that crops may be exposed to more than one pesticide during production.
Household products add another layer. Cleaning products, cosmetics and personal care products can contain fragrances, preservatives and other ingredients that contribute to everyday chemical exposures. Researchers have identified hormone-disrupting and asthma-associated chemicals in some consumer products and continue to investigate combinations of chemicals that may warrant closer testing.
Even drinking water, which is carefully treated and monitored, can contain trace amounts of contaminants from multiple sources, including pharmaceuticals, industrial chemicals and compounds formed during water treatment. Studies have reported pharmaceuticals and hormone-disrupting compounds in U.S. drinking water, and researchers continue to investigate emerging contaminants in water as analytical methods improve.
Why combinations can be hard to predict
In many cases, chemicals in a mixture have the same effects as they do on their own, contributing a predictable share of the overall effect. This idea, known as additivity, gives researchers and regulators a practical starting point for predicting chemical mixture risk.
But chemicals do not always behave so neatly. Sometimes a combination has a larger effect than expected. Sometimes one chemical reduces another’s effect. So it’s not always possible to predict a chemical’s risk when other chemicals affecting the same biological system are present too.
Hormone-active chemicals illustrate why this matters. Hormones such as estrogen and thyroid hormone are chemical messengers that regulate growth, metabolism, reproduction and many other essential functions through the endocrine system.
Some chemicals, known as endocrine disruptors, can interfere with how these hormones are produced, transported or recognized by the body. Individually, exposures may be too low to raise concern, but multiple chemicals acting on the same hormonal system may have a combined effect.
Two well-studied examples are phthalates and parabens. Phthalates are used in some plastics and are also associated with fragrance mixtures, while parabens are preservatives found in some cosmetics and personal care products. People may encounter these chemicals repeatedly through products they use daily.
This does not mean that every scented lotion or shampoo is harmful. But everyday product choices can measurably influence personal chemical exposures. In one study, for example, switching to personal care products labeled free of certain phthalates, parabens and related compounds reduced some of these chemicals’ presence in urine.
New methods for testing chemical mixtures
Thousands of chemicals are used in commerce and released into the environment. People encounter different combinations depending on where they live, what they eat, the products they use, the work they do and how much time they spend indoors or outdoors.
Testing every possible combination of chemicals is impossible. But researchers like me are tackling the problem by studying mixtures that reflect real-world exposures and grouping chemicals with similar biological effects. They are using rapid automated laboratory testing and computer models, including artificial intelligence, to predict which chemicals are most likely to interact and to identify mixtures that deserve closer investigation.
A newer approach, called exposomics, aims to measure the many chemical and environmental exposures people accumulate throughout their lives and relate them to health outcomes.
These tools are becoming increasingly powerful, and mixture science is advancing rapidly. But it is unlikely that every question will ever have a simple answer.
What you can do
None of this means you should throw out every product in your home or try to live a “chemical-free” life. That would be impossible. A more practical goal is to reduce unnecessary and repeated exposures when doing so is easy and inexpensive, and does not create new problems.
Start with indoor air, where pollutants can accumulate during cooking, cleaning and the use of fragranced products. Opening windows when outdoor air quality is good, using kitchen and bathroom exhaust fans and increasing ventilation during cleaning can all help reduce indoor pollutant levels. A review of indoor air studies concluded that improving ventilation and reducing pollution at its source are among the most effective strategies for improving indoor air quality.
Next, look at product routines rather than individual products. If you regularly use several scented personal care or cleaning products, consider whether you need all of them. Fragranced consumer products like cleaning agents, air fresheners and skin lotions are a common source of indoor air pollution. Choosing fragrance-free alternatives, using fewer overlapping products or reserving strongly scented products for occasional use can reduce repeated exposure to some fragrance-related chemicals.
For food, focus on habits that already make sense for overall health. Wash fruits and vegetables under running water and eat a varied diet instead of relying heavily on the same foods every day. Because pesticide residues differ among foods, eating a variety of foods may help reduce repeated exposure to residues from the same foods, although it does not eliminate pesticide exposure.
If you drink water from a public system, review your local water quality report to understand what has been detected in your community. If you decide to use a water filter, choose one certified to reduce the contaminants you want to remove. Check the certification label to verify which contaminants it has been tested to reduce, and replace cartridges according to the manufacturer’s instructions.
Informed and straightforward steps like these can help limit exposures while scientists continue studying how the many small exposures of everyday life combine to influence health.
This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Brad Reisfeld, Colorado State University
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Brad Reisfeld received funding from US Environmental Protection Agency and the National Institute of Environmental Health Sciences.
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