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24
Sep

Send Your Comments to EPA as Scientists Examine the Fate of Silver Nanoparticle Waste

(Beyond Pesticides, September 24, 2010) Researchers from Virginia Tech discovered, for the first time, a way to detect nanosilver particles in the environment, finding that the particles leaching from consumer products can transform into silver sulfide in sewer sludge. Despite their widespread use, scientists still know very little about how nanomaterials move from consumer manufactured products into the environment and what impact they might have. These findings provide new information about the life cycle of silver nanoparticles, which are used in a number of consumer products as antimicrobial agents, including cosmetics, sunscreens, sporting goods, clothing, electronics, baby and infant products, food, and food packaging.

Previous studies have shown that the particles, which are between one and 100 nanometers in size and smaller than many viruses, can enter the environment through wastewater, where they can accumulate in biosolids at wastewater treatment plants. These biosolids, also known as sewage sludge, are often sold to consumers as fertilizer, despite the fact that they can contain toxic contaminants, including another antibacterial, triclosan, which was recently found to persist in the environment. Nanosized particles can be released from impregnated materials via washing or or as a result of sweating, posing unknown adverse effects to humans and water systems. There is much reason to be concerned, especially since a recent study found that nanosilver can interrupt important cell signaling within male reproductive sperm cells, causing them to stop growing.

Though scientists were previously aware that many publicly-owned wastewater treatment facilities had silver in their sludge, identifying and characterizing these microscopic particles among countless other chemicals was another matter. The Virginia Tech researchers used x-ray transmission electron microscopy, an extremely sensitive technique that can identify both composition and structure. With micrographs of sludge from a Midwest treatment plant, they identified nanoparticles 5 to 20 nm in diameter and determined that the particles had a 2-to-1 silver-to-sulfur ratio. The scientists also obtained a crystal structure to confirm that the particles were Ag2S.

“What we start with is not what ends up in nature,” says Michael Hochella, Ph.D., one of the researchers. He believes this work underscores the complexity in studying the environmental effects of nanoparticles and suggests that the nanomaterials most likely enter the treatment plant in the form of silver nanoparticles and then transform into silver sulfide, because silver readily binds to sulfer and wastewater plants contain high concentrations of sulfide.

But, the environmental impact of nanoparticles is still unclear. Researchers also do not know how much incoming silver turns into silver sulfide. The Virginia Tech teams plans to analyze samples from each stage of the treatment process at the same wastewater plant as their next step.

With an increasing number of scientific studies looking at these antibacterial substances, two basic, yet important, questions arise: Are they safe for human health and the environment? And, are they necessary?

For more information on nanomaterials, see Beyond Pesticides’ nanosilver page.

Take Action: EPA announced a 45-day public comment period for the draft document “Nanomaterial Case Study: Nanoscale Silver in Disinfectant Spray” (EPA/600/R-10/081). The document is being issued by the National Center for Environmental Assessment within EPA’s Office of Research and Development. EPA is releasing this draft document solely for the purpose of pre-dissemination review under applicable information quality guidelines. This document has not been formally disseminated by EPA. It does not represent and should not be construed to represent any agency policy or determination. The draft document is available via the Internet on the NCEA home page under the Recent Additions and the Data and Publications menus at http://www.epa.gov/ncea.

The draft is intended to serve as part of a process to help identify and prioritize scientific and technical information that could be used in conducting comprehensive environmental assessments of selected nanomaterials. It does not attempt to draw conclusions regarding potential environmental risks of nanoscale silver; rather, it aims to identify what is known and unknown about nanoscale silver to support future assessment efforts. When finalizing the draft document, EPA intends to consider any public comments that EPA receives in accordance with this notice. Technical comments should be in writing and must be received by EPA by September 27, 2010

For more information, please see our Watchdogging the Government page.

Source: Chemical and Engineering News

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