If you haven’t heard of nanosilver, you’re definitely not alone. But that doesn’t mean these tiny silver particles intended to kill bacteria aren’t ending up in your food. There are now over 400 consumer products [PDF] on the market made with nanosilver. These include many intended for use with food, among them cutting boards, cutlery, pans, storage containers, espresso machines, water filters, baby bottles, and refrigerators.

The U.S. Environmental Protection Agency (EPA) considers nanosilver a pesticide and requires products that contain–or are treated with this germ-killer–to be registered with and approved for use by the agency. But most of the nanosilver products now on the market have not been reviewed, let alone approved by the EPA.

Just a few weeks ago, in an attempt to close this loophole, the Center for Food Safety, the Center for Environmental Health, Clean Production Action, the Institute for Agriculture and Trade Policy, and other nonprofits filed suit against the EPA for failing to respond to their 2008 petition [PDF], asking the agency to regulate all products containing nanosilver as pesticides.

Why all the fuss?

As the name implies, nanosilver is silver used at the nanoscale, in the realm of billionths of a meter. To put this in perspective, one strand of human hair is about 50,000 to 80,000 nanometers wide. What makes nanomaterials so interesting to scientists designing new materials is that at this infinitesimal scale, materials can behave entirely differently than they do at either the macro or micro scales.

At the nanoscale, materials can take on chemical, physical, and biological properties that they might not otherwise have. And there are still many of unknowns, even in the scientific community, about how nanomaterials behave.

It is known that nanosilver can kill bacteria and microbes, so manufacturers are including it as a sort of antiseptic safeguard in food contact products that might harbor bacteria (i.e., that pesky cutting board on your kitchen counter.) But exactly how nanosilver behaves once released into the environment or absorbed into the human body, is not yet well understood. A number of studies show that consumer products, including textiles and plastics, can shed nanosilver particles. In fact, these particles have been detected in wastewater and sewage sludge.

Recent studies also show that nanosilver has the potential to harm and stress cells in ways that include causing damage to DNA.

Among the concerns raised by the growing use of nanosilver as antimicrobial agents in consumer products, explains Center for Food Safety’s Senior Policy Analyst Jaydee Hanson, is that it, like other antibacterial ingredients, “may lead to bacteria becoming increasingly resistant to antibiotics.”

Despite the many gaps in understanding the environmental and human health impacts of nanomaterials, the EPA has already granted what’s called “conditional approval” to some nanosilver products, saying the silver released will not cause unreasonable adverse effects.

This brings us back to EPA oversight and approval. So far, the EPA has only reviewed the few nanosilver products that manufacturers have submitted to the agency for registration as pesticides. Under the law, manufacturers must have EPA approval to make claims about a product’s germ-killing ability. The agency has enforced this law, taking a number of nanosilver products off the market, as it did earlier this year with some   sold widely by retailers that included Amazon, Pathway, Sears, and Walmart.

According to the recent lawsuit, however, other manufacturers have simply changed their product labels to remove germ-killing claims, in an effort to avoid EPA enforcement or product scrutiny. These products, however, may still contain nanomaterials.

In short, the plaintiffs contend that EPA is not regulating nanosilver products comprehensively as required under the U.S. law governing pesticides.

Asked about any EPA approval of nanosilver for use in food-contact products, an EPA spokesperson responded by email explaining that the agency “has approved nanosilver for use as a non-food-contact preservative to protect plastics and textiles … from odor and stain causing bacteria, fungi, mold, and mildew.” But they did not respond about food contact products directly.

Meanwhile, the U.S. Food and Drug Administration (FDA), which regulates chemicals used in food contact products, responded by saying it has “not approved the use of silver nanomaterial for use as a food ingredient added to food or as a food contact substance.” So while EPA has approved some nanosilver products for use in plastics, its approval does not cover food-contact products of the type that are now being sold–without FDA approval.

To make matters more confusing, in a “guidance document” issued last June, the FDA said it had “not established regulatory definitions of “nanotechnology,” “nanomaterial,” “nanoscale,” or other related terms.” The same document also says safety evaluations of such products should consider their “unique” characteristics.

The bottom line appears to be that both EPA and FDA–the agencies responsible for regulating chemicals used in consumer products–acknowledge significant gaps in understanding the behavior and toxicity of nanomaterials, including nanosilver. Yet such products–including those for use with food–are growing in number and availability while research shows that nanosilver can indeed escape from these items.

So what happens next? “The EPA hopefully will say they want to settle,” and develop a legally binding “timeline to respond to the petition,” says CFS’ Hanson. In the meantime, nanosilver may be finding its way from these materials into the food we eat. If you’re concerned about their potential environmental and health effects, you might want to stay away from kitchen items that claim to kill germs and follow good food safety practices instead.