- © The Mineralogical Society Of America
Mineral particles with diameters on the scale of nanometers (nanoparticles) are important constituents of natural environments. The small size of such particles has a host of consequences for biogeochemical systems, which we will review in this chapter. We begin by briefly reviewing what is known about how and when nanoparticles form and the ways in which nanoparticles impact natural processes.
Nanoparticles form via a variety of inorganic and biological pathways and may be introduced into the environment as a consequence of human activity. They are widespread in the environment (Banfield and Navrotsky 2001; Penn et al. 2001; Kennedy et al. 2003a,b; van der Zee et al. 2003), although few quantitative studies of their abundance are available. While all crystals begin as very small particles, an important subset retain small size at the Earth’s surface over relatively long time scales, because the combination of low temperature and low solubility inhibits growth. As a consequence, nanoparticles have the potential for a long lifetime in the environment, and widespread transport under certain circumstances.
Processes that result in the removal of nanoparticles from an environment include dissolution, settling from air, transport in solution, and crystal growth. Particle aggregation may be an important component of these processes because it will promote settling, limit dispersal via solution transport, and can lead to aggregation-based crystal growth.
The presence of nanoparticles can profoundly influence biological systems. Because they are frequently formed in environments that are populated by microorganisms, nanoparticles often adhere to cell surfaces or cell-associated polymers (see Fig. 1⇓ for examples). These coatings can have important consequences for metabolic activity, for example, by restricting communication between the cell and its surroundings. They may also provide protection from predators, inhibit desiccation, screen cells from ultraviolet radiation, and alter the cell buoyancy (e.g., …