October 2008, Vol. 20, No.10

Research Notes

SJWP Winner Investigates Silver Nanoparticles

Joyce Chai is making a big impact in the water community by looking at something no bigger than a billionth of a meter wide. Chai was named the 2008 winner of the U.S. Stockholm Junior Water Prize (SJWP) for her work on nanomaterials.

These minute materials are becoming increasingly common in more than 1000 manufactured products, as diverse as deodorant and wound dressings. Although they have proven to offer countless benefits and scientific advances, little is known about their possible environmental effects. Chai’s investigation took steps toward understanding and quantifying the potential environmental consequences and risks of using nanoparticles.   

Chai’s research found that silver nanoparticles induce highly toxic effects, including overwhelming cell death and cell inactivity in a short period of time. Also, when water containing these nanoparticles was run through a filtration system, the toxicity decreased, but did not disappear. This ongoing toxic effect and the relatively high corresponding concentrations, even after filtration, may prove to be harmful to the environment.

Her investigation attempts to model and quantify the toxicity of silver nanoparticles under varying environmental conditions and to measure the toxicity of “nanosilver” in a model consumer product. Chai quantified the percentage of dead cells using a fluorescene intensity ratio and analyzed the data with an AJAVA computer program written specifically for the investigation.

“To me, the most intriguing aspect was that silver nanoparticles were more toxic than silver ions,” Chai said. She explained that while the exact mechanism used by silver nanoparticles to kill bacteria is not known, additional research could help in understanding this phenomenon.

Chai’s research concluded that the bacterial toxicity assay technique used throughout the investigation is a reliable, reproducible approximation of the potential toxicity of silver nanoparticles. She believes that this assay can be applied to almost any research that focuses on the toxicity of a substance to an environment bacterium. However, additional bacteria strains would need to be tested using the same method to determine the reproducibility of the investigation, she said. 

 “Because they are nanosized, it is almost impossible to physically filter out the silver nanoparticles, but perhaps a chemical reaction between silver nanoparticles and another substance can be used to completely prevent any release of silver nanoparticles,” she added.

“The presence of silver nanoparticles in the [water/wastewater] system may be harmful to the beneficial bacteria used in water recycling treatment. As a result, the quality of the recycled water may be greatly reduced,” she said. In addition, silver nanoparticles released from consumer products may be easily transmitted through air, water, and soil and eventually diffuse into the oceans and rivers, she said. “The potential risks of silver nanoparticle release into the environment are mind-boggling.” 

 “The research suggests that more measures need to be taken by the [U.S. Environmental Protection Agency] to regulate the presence of silver nanoparticles in our industry in order to protect our environment,” she said.

Chai began research on water purification in the 10th grade, forming a natural water purification device that reduced turbidity down to 1.5 nephelometric turbidity units (ntu), short of the World Health Organization’s potable water standards of 1.0 ntu. She initially wanted to integrate silver nanoparticles into her filtration system to create a more efficient purification system. She then decided to focus on the toxicity of silver nanoparticles to the environment, she said.