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Silver Nanoparticles Not Green, But Threat to Ecosystems

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ecosystemSilver nanoparticles, used in various consumer products, were found to reduce the biomass of plants and microbes by one third, only five days after application.

The study that revealed these findings was conducted by a team at Duke University. The scientists are convinced that although the findings are preliminary, they explain much of the unknown effects that silver has on the environment.

The element is found in many textiles, clothing, toys, pacifiers, disinfectants and even toothpaste. According to Benjamin Colman, a post-doctoral fellow in Duke’s biology department and a member of the Center for the Environmental Implications of Nanotechnology (CEINT), the effect of these nanoparticles is not yet fully explored.

The use of silver nanoparticles in such variety of consumer products is common because  they kill bacteria, which inhabits unwanted odors. These nanoparticles adopt different mechanisms to destroy or damage microbial DNA without harming human cells.

Silver nanoparticles are introduced to the environment as a by-product of sewage treatment plants. They cannot be filtered out and end up in the wastewater treatment “sludge”, used as a fertilizer.

The study, which was published in the latest issue of the journal PLOS One, is difficult to extrapolate to ecosystems. As Colman states, this is because exposure is likely to be at low concentrations, while the diversity of organisms makes it even harder.

But the scientists found a way to estimate it. They used the so-called mesocosms- small structures, comprised of different plants and microorganisms, to simulate the environment. The researchers then applied sludge containing silver nanoparticles to some of the mesocosms and compared the biomass of these with untreated samples.

Colman pointed out that species, such as the common annual grass, decreased its biomass by as much as 32%, when the sludge is applied. But not only plants suffered- enzymes in microbes were found to decrease too.

The findings indicate that silver nanoparticles in biosolids have high negative impact on ecosystems. These include changes in microbial community composition, decrease in biomass, and extracellular enzyme activity among others.

The team is now working towards establishing the long-term effects and examining other abundant nanoparticles.

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