Environmental fate of nanoparticles depends on properties of water car...(the environment. To study the flow a...)

To study the flow and retention of the nanoparticles in simulated soil and filtration systems, Pennells 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.

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, its unlikely that they will come off as long as the conditions dont 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
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