Silver nanoparticles, like the ones being prepared here, are incorporated into many building products for their antimicrobial and antibacterial properties.

Two new studies suggest that silver nanoparticles in building products not only kill harmful bacteria and microbes but also may contribute to improper sperm function and disrupt beneficial microbial activity in ecosystems. Touted for their antimicrobial benefits, silver nanoparticles have been incorporated into dozens of products such as air and water purifiers, handrails, door handles, washing machines, refrigerators, paints, fabrics, cleaning products, plastics, and electronics.

Previous studies have shown that silver nanoparticles between 10–25 nanometers (nm—one billionth of a meter) in size can reduce male sperm stem cell growth when cells are exposed to more than 10 micrograms per milliliter (μg/ml). A more recent study, published in the August 2010 issue of Toxicological Sciences, revealed that silver nanoparticles stunt sperm stem cell growth—with the greatest damage (stem cell death) resulting from exposure to the smallest nanoparticles.

Another recent study contends with the ecosystem-related effects of nanoparticles being released from materials, entering the wastewater system, and accumulating in sewage sludge—some of which is used as fertilizer. Benjamin Colman, a postdoctoral researcher at Duke University, shared his findings on the disruptive nature of nanosilver in August at an Ecological Society of America conference.

Colman observed the effects of nanoparticles on plants and soil using field model ecosystems containing 0.2 kg of sewage slude and 11 mg of silver nanoparticles, He found that once in the ground, silver nanoparticles continue to do just what they were designed to—kill bacteria and microorganisms, which plants require to thrive. Colman told EBN, “Decreases in microbial biomass, if they persist, could slow decomposition and decrease nutrient availability to plants.” One species of plant grown in soil contaminated with silver nanoparticles was found to be 22% less productive than those in uncontaminated soil. Colman also found different bacteria in the contaminated soil, a decrease in microbes and a 34% reduction in microbial enzyme activity. Colman also noted “an increase in emission of the greenhouse gas N2O [nitrous oxide], which not only contributes to [global] warming but also destroys stratospheric ozone. While the magnitude of these impacts was small, it was detectable.”

Although manufacturers using nanotechnology often contend that nanoparticles such as nanosilver are bound up in materials, they may become dislodged and enter the ecosystem through natural use or as materials are washed or abraded.

Simon Silver, Ph.D., professor of microbiology at the University of Illinois-Chicago offered his perspective on these studies: “Monitoring for unwanted effects is a good thing to do. [But] strong concern about widely used products with an amazingly safe track record [is unnecessary]. Building products are a long way from tissue culture cells in lab plastic containers.”

A consortium has been created with funding from the U.S. Environmental Protection Agency to further research and address the effects of nanomaterials entering ecosystems through the land application of sewage sludge.

– Emily Catacchio