At the recent Geological Society of America (GSA) annual meeting in Denver, Mike Hochella, a geochemist at Virginia Tech, gave a couple of talks about nano-particles, an area of research he thinks is the next big thing in the geosciences. In fact, he thinks understanding them is a key to understanding the workings of many major Earth systems in a fundamental way.
What are nano-particles? You probably figured out they are really small, between 1 and 100 nanometers, or 1-100 x 10-9 meters. They can be single or multiple mineral crystals, amorphous materials, or a combination. They are extremely reactive, and readily adsorb metals. Hochella noted that this reactivity is significant greater than would be expected just due to their relatively large surface area. Their effects on the health of humans and other organisms is largely unknown.
Much of the research done by Hochella’s group is at the Clark Fork River Superfund Complex in Montana, a mining area that has been substantially contaminated with heavy metals, such as copper, zinc, arsenic, and lead. It’s the largest Superfund site in the U.S., 1,600 square kilometers. They found that the metal behavior is driven by the presence of nano-particles, and their properties are different from what would be expected by thermodynamic equilibrium predictions. Abstracts of Hochella’s talks are here and here.
In water quality studies, we typically filter our samples in order to get dissolved samples. We generally use a 0.45 micrometer pore sized filter (450 x 10-9 meters), which is the operationally defined size separating dissolved from suspended materials. You can see that nano-particles are not trapped by these filters, and thus dissolved water samples may contain material that is not truly dissolved.
Hochella cautioned that these are extremely difficult materials to study. And to do it right, you need powerful, expensive (several million $) transmission electron microscopes.
