“In some cases, the nanoparticles move very little and you would get complete retention in the soil,” said Kurt Pennell, a professor in the School of Civil and Environmental Engineering at the Georgia Institute of Technology. “But in different solution conditions or in the presence of a stabilizing agent, they can travel just like water. The movement of these nanoparticles is very sensitive to the solution conditions.”
“It will be difficult to control the waste stream, so these nanoparticles are likely to get everywhere,” said Pennell. “We want to figure out now what will happen to them and how toxic they will be in the environment.”
The nanoparticles retained were tightly bound to the sand or beads and could only be removed by changing the pH of the water.
“That would be a good thing if you were trying to filter these particles from a water system and were worried about them moving into the environment,” Pennell said. “Once they go onto the soil system, it’s unlikely that they will come off as long as the conditions don’t change.”
The researchers observed that up to 77 percent of the nanoparticle mass was retained by the sand, while the glass beads retained between 8 and 49 percent. Preparation of the solutions containing C60 dramatically affected the retention; when no salt was added, the particles flowed through the columns like water.
“We want to make a mechanistic assessment of why the particles are attaching,” Pennell said. “When we look at real soils with finer particles, we will expect to see more retention.”
For municipal drinking water filtration, the sensitivity to solution characteristics means local conditions may play a key role.
“Under most conditions, you should be able to remove nanoparticles from the water,” Pennell explained. “But you will have to be careful if the nanoparticles are stabilized by a natural surfactant or humic acid. If those are present in the water, the nanoparticles could go right through.”
In a continuation of the work, Pennell and his Georgia Tech collaborators – Joseph Hughes, John Fortner and Younggang Wang – are now studying more complicated transport issues in real soils and with other types of nanoparticles. In field conditions, the nanoparticles are likely to be found with other types of carbon – and potentially with other nanostructures.
“When we study systems with real soil, we will have background interference with humics and other materials,” Pennell noted. “Ramping up the complexity will make this research a real challenge.”
Ultimately, Pennell hopes to develop information about a broad range of nanoparticles to predict how they’ll be retained and transported under a variety of conditions. Facilitating that is mathematical modeling being done by collaborators Linda Abriola and Yusong Li at Tufts University in Medford, Mass.
“We want to build up to the point that we can systematically vary properties and parameters,” Pennell explained. “Over time, we should be able to classify nanoparticles based on their properties and have a good idea of how they will behave in the environment.” ###
Technical Contact: Kurt Pennell (404-894-9365); E-mail: (email@example.com). Contact: John Toon firstname.lastname@example.org 404-894-6986 Georgia Institute of Technology Research News