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A while back, I wrote about the US regulatory system’s strange attitude toward nanotechnology and food.

On the one hand, the Food and Drug Administration is on record stating that nanoparticles-which are microscopically tiny pieces of common materials like silver and clay-pose unique safety concerns. The particles, which measure in at a tiny fraction of the width of a human hair, “can have significantly altered bioavailability and may, therefore, raise new safety issues that have not been seen in their traditionally manufactured counterparts,” the FDA wrote in a 2012 draft proposal for regulating nanoparticles in food. On the other hand, its solution-that the food industry conduct safety testing that is “as rigorous as possible” and geared specifically to nano-materials before releasing nano-containing products onto the market-will be voluntary.

But what about packaging-the wrappers and bags and whatnot that hold food to keep it fresh? Nano-sized silver has powerful antimicrobial properties and can be embedded in plastic to keep food fresh longer; and nanoparticles of clay can help bottles and other packaging block out air and moisture from penetrating, preventing spoilage. Yet research has suggested (see here and here) that nanoparticles can migrate from packaging to food, potentially exposing consumers.

So how widely is nanotech used in the containers that contact our food? Back in 2010, the Environmental Protection Agency released a “State of the Science Literature Review” on nanosilver (PDF; warning: 221 pages). The report confirms that nano-materials, including silver, are being used in food packaging, but shows why it’s hard to get a grip on how just widely. “Current labeling regulations do not require that the nanomaterial be listed as an ingredient,” neither in food or in food packaging, the EPA report states. And “manufacture of nanosilver-containing products is shifting to the Far East, especially China, South Korea, Taiwan and Vietnam,” making it even harder to track nano-containing products that come in from abroad.