Consider an ordinary day. A person washes their hair, applies deodorant, drinks coffee, stores lunch in a plastic container and travels through traffic to work. At the office, staff clean a shared surface with disinfectant. At home, dinner is prepared, the kitchen is cleaned and the dishwasher runs.
These routine actions can involve contact with chemicals. Alone, this raises no alarm since chemicals form the physical world.
Yet depending on dose, timing and conditions, some environmental chemicals, both natural and synthetic, might influence health.
Most daily exposures are at low levels, and many items are made and overseen with safety considerations. As a certified toxicologist examining how chemical contacts affect health, the focus is rarely on one substance alone.
A more practical question involves possible health outcomes when numerous low-level exposures coincide.
Mixtures represent the norm
Years of study on single chemicals have allowed identification of risks, estimation of safe levels and creation of rules.
The issue remains that individuals seldom encounter one chemical in isolation.
Indoor air varies
Food can hold residues from several pesticides, as programs in Europe and the United States have found. This occurs because crops may receive multiple pesticides.
Household items add further exposure. Cleaners, cosmetics and personal care goods may include fragrances, preservatives and other components. Studies have noted hormone-disrupting and asthma-linked substances in some products.
Even treated drinking water can hold trace contaminants from various origins, such as medicines, industrial compounds and treatment byproducts. Research has detected pharmaceuticals and hormone-related substances in U.S. water supplies.
Why mixtures prove difficult to forecast
Often chemicals in a mixture act as they would separately, adding a foreseeable portion to the total impact. This concept of additivity aids prediction of mixture risks.
Yet chemicals may not interact predictably. A combination can produce a greater effect than anticipated, or one may lessen another’s impact.
Hormone-active chemicals show the relevance. Hormones like estrogen and thyroid hormone regulate growth, metabolism and reproduction.
Endocrine disruptors can alter hormone production, transport or recognition. Individual exposures might seem minor, but several acting on the same system could combine.
Phthalates and parabens provide examples. Phthalates appear in some plastics and fragrances, while parabens serve as preservatives in cosmetics. Daily product use can lead to repeated contact.
This does not imply all scented items are harmful. Still, product selections can affect personal exposures. One study showed that switching to items free of certain phthalates and parabens lowered their levels in urine.
New testing approaches for mixtures
Thousands of chemicals enter commerce and the environment. People face varying combinations based on location, diet, products, occupation and time indoors or out.
Testing all possible mixtures is unfeasible. Researchers address this by examining realistic mixtures and grouping chemicals with similar effects. They employ automated lab tests and computer models, including artificial intelligence, to forecast interactions and flag mixtures needing study.
A newer method called exposomics seeks to measure the many chemical and environmental exposures accumulated over a lifetime.
