Environmental fate of nanoparticles depends on properties of water carrying them

Researchers Kurt Pennell (standing) and Younggang Wang examine glass microbeads and sand used to study the transport and retention of C60 particles in water. Click here for more information.

“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.”

To study the flow and retention of the nanoparticles in simulated soil and filtration systems, Pennell’s research team filled glass columns with either glass microbeads or sand, and saturated the columns with water. They then sent a “pulse” of water containing C60 nanoparticles through the columns, followed by additional water containing no nanoparticles.

They measured the quantity of nanoparticles emerging from the columns and analyzed the sand and glass beads to observe the quantity of C60 retained there. They also extracted the contents of the columns to measure the distribution of retained nanoparticles.

“In sand, we saw a uniform distribution of the nanoparticles throughout the column, which suggests that under the circumstances we examined, there is a limited retention capability due to filtration,” Pennell explained. “Once that capacity is reached, the particles will pass through until they are retained by other grains of soil or sand.”

Traditional theories regarding the activity of such packed-bed filters suggest that particles would build up near the column entrance, with concentrations falling off thereafter. The study findings suggest that the predictions of “filter theory” will have to be modified to explain the transport of nanoparticles in soil, Pennell said.

The nanoparticles retained were tightly bound to the sand or beads and could only be removed by changing the pH of the water.