Speaking after the US Environmental Protection Agency took its first step to regulate a nanomaterial -- near atomic-sized particles of silver being used as pesticide in products from shoes to a washing machine -- experts told AFP that nanotechnology is already producing materials that can harm the environment and human health.

"There are some very serious concerns about potential health consequences," said Patrice Simms of the US Natural Resources Defense Council (NRDC).

"We know next to nothing about their potential health effects," said Simms.

Nanotechnology is the creation and use of materials barely larger than atomic in scale, measuring usually between one and 100 nanometers. A nanometer is one-billionth of a meter, and a human hair is roughly 80,000 nanometers in width.

At that size -- small enough to pass through cell membranes in the body -- many materials can take on physical and chemical properties not seen in their larger forms, giving them uses never imagined before.

A Washington-based group, The Project on Emerging Nanotechnologies, has catalogued 356 products already using nanotechnology, including "breathable" bedsheets, lighter, stiffer golf clubs, skin care creams, computer chips and antibacterial socks.

The technology also promises more substantial "miracle" uses, from health applications like cancer treatments, to drinking water filtration systems for poor countries, to longer-life batteries.

But materials at that size may also pose dangers when they are inhaled, ingested, absorbed through the skin, or spread through nature by wind and water, scientists warn.

"Something different happens when you begin to work at a very small scale," said Andrew Maynard, chief science advisor at the Project on Emerging Technologies.

"We know that a lot of materials like asbestos and particles affect the health because of their shapes and sizes as well as their chemistry.

"It's reasonable to assume that some of these new materials are going to do the same thing," noting that there are a number of new nanomaterials in filament form, like asbestos which causes lung disease.

The problem is that both industry and the government have assumed the existing regulatory framework for chemicals and other materials is adequate, Simms pointed out.

"You cannot pretend that nano-carbon is the same as regular carbon," he said.

"Nanomaterials are fundamentally different from their macroscopic counterparts."

The EPA took an initial step last week when it said it would require manufacturers using silver nano-particles to provide evidence that their products won't harm the environment.

Nano-silver meant to act as pesticide is found in several dozen products, including socks and shoes and plastic storage containers, to prevent fungus and bacteria growth.

But the EPA was mainly targeting a washing machine built by Samsung which releases nano-engineered silver ions into the wash cycle to kill bacteria. The silver would clearly flow into the environment, and the NRDC points out that silver in its macroscopic form is already known to damage aquatic organisms.

But environmentalists say the EPA and US health authorities need to move more aggressively on nano-materials.

"It's certainly a step in the right direction," Simms said of the EPA move. "That having been said, it's a pretty small step in the right direction."

A groundbreaking article authored by Maynard in Nature magazine earlier this month on the safety challenges of nanotechnology stressed that the dangers remain mostly theoretical but highly plausible.

"Recent studies examining the toxicity of engineered nanomaterials in cell cultures and animals have shown that size, surface area, solubility and possibly shape all play a role in determining the potential for nanomaterials to cause harm," the report said.

Maynard told AFP he worried that private researchers are not paying enough attention to the possible impact of nano-materials.

"My biggest concern is that people are very rapidly developing a lot of new materials without asking critical questions about how they are going to behave," he said.

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