It seemed like a small thing when Paul Westerhoff’s 8-year-old son appeared, with his tongue and lips coated bright white. The boy had just polished off a giant Gobstopper, a confectionery made of sugary, melt-in-the-mouth layers. Curious about the white coating, Westerhoff, an environmental engineer, pored over the jawbreaker’s contents and discovered just how incredibly small the matter was.
Among the Gobstopper’s ingredients were submicroscopic particles of titanium dioxide, a substance commonly added to plastics, paint, cosmetics and sunscreen. At the time, Westerhoff’s lab group at Arizona State University was actively tracking the fate of such particles in municipal wastewater systems across the nation.
Titanium dioxide is also a food additive approved by the U.S. Food and Drug Administration. Ground to teensy particles measuring just tens of billionths of a meter in size — much smaller than a cell or most viruses — titanium dioxide nanoparticles are frequently added to foods to whiten or brighten color.
Weeks after his son’s candy-coated encounter, Westerhoff went to the supermarket, pulled more than 100 products off the shelves and analyzed their contents. His findings, published in 2012 in Environmental Science & Technology, show that many processed foods contain titanium dioxide, much of it in the form of nanoparticles. Candies, cookies, powdered doughnuts and icing were among the products with the highest levels. Titanium dioxide is also found in cheese, cereal and Greek yogurt.
“I began to question why we care about things in the environment — at a few micrograms per liter in water — if we’re freely ingesting these materials,” Westerhoff says.
Titanium dioxide isn’t the only nanoingredient added to food. Various other materials, reduced to the nanoscale, are sprinkled into food or packaging to enhance color, flavor and freshness. A dash of nano will smooth or thicken liquids or extend the shelf life of some products. Scientists have designed nano-sized capsules to slip beneficial nutrients, such as omega-3 fish oil, into juice or mayonnaise, without the fishy taste.
Food scientists aren’t stopping there. They are downsizing the structure of a wide array of ingredients with bold plans to help tackle obesity, malnutrition and other health issues (see “Nanocreativity,” below).
But as scientists cook up ways to create heart-healthy mayo and fat-fighting ice cream, some are also considering the potential risks that might accompany the would-be benefits. Because of their small size, ingested nanoparticles may interact with cells or behave differently than their bulkier counter-parts. So far, less-than-perfect laboratory studies offer contradictory results.
Researchers, including those developing nanofoods, say more information is needed on the ingredients’ potential impacts. Current studies, limited to mice or lab dishes, often analyze megadoses of particles far beyond what any normal diet would include. Scientists need a better handle on what happens when people nosh on nanolaced foods daily, taking in small doses at a time, says Ohio State University pathologist James Waldman. He and others are devising tests to find out.
A pinch of nano
Over the last two decades, nano-sized components — smaller than 100 nanometers — have found their way into a wide range of products: clothing, electronics and cosmetics as well as food. But people have been exposed to, and have inevitably ingested, nanoparticles for much longer, says Andrew Maynard, director of the Arizona State University Risk Innovation Lab in Tempe. Since prehistoric times, people have been consuming nanoparticles found in natural foods such as milk (casein micelles, for example, are nano-sized particles that help calves readily digest their mother’s milk). Nanoparticles also creep into the food supply from environmental sources. Burning wood, oil and coal; wildfires; volcanic activity; and crashing of ocean waves release ultrasmall particles of metal, carbon or silica into the atmosphere and into the food chain.
Even with this long history of nanoparticle exposure, Maynard says, it’s highly unlikely that people had been eating the kinds of particles added to foods today. The distinction is important, he says. “Our bodies have always been exposed to nanoparticles, but they’re now being exposed to different types. We just need to make sure that our bodies can deal with the ones we’re putting in food.”
What makes particles different today is not only their size, but also their specificity. The amino acids and proteins that coat a nanoparticle determine its shape and surface properties, which can enhance or reduce the particle’s propensity to bind to certain molecules. By fine-tuning surface features, scientists can control where or how quicklynanoparticles release their contents.
So far, only a few nanoingredients are added directly to foods or packaging: Titanium dioxide, silicon dioxide and zinc oxide are the most common. Larger versions of these ingredients have been used in food and medicines for decades and are considered “generally recognized as safe” by the FDA, which requires that any substance added to food be evaluated for safety.
Scientists have developed numerous ways to test the safety of substances that go into food, but most of the tests were designed decades ago, before ingredients began to go nano. Titanium dioxide, for example, was evaluated in the late 1960s, using particles larger than 100 nanometers. Human cells were exposed to the substance to test for toxic effects and to work out how much of it can be safely consumed.
But those safety tests may not apply to some nano-substances. Size and surface features can improve or impair a nanoparticle’s ability to enter cells. Some nanoparticles — including those considered safe by the FDA — interact with cells in odd or unexpected ways, according to several recent studies.
This article appears in the October 31, 2015, Science News with the headline, “Noshing on nano: The tiny particles in what we eat raise big questions.”
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