NANOPARTICLES IN NATURAL SYSTEMS WHERE DO THEY COME FROM

Where do nanoparticles occur in natural systems Where do they come from Why should we distinguish them as a special state of matter deserving a volume in the RIMG series This chapter will (1) provide examples of the types of solids that are commonly encountered as nanoparticles in natural systems, (2) detail a subset of the inorganic and biological processes that generate nanoparticles in the environment, (3) review the ways in which nanoparticle stability and reactivity are modified as a consequence of their particle size in order to lay the foundation for consideration of the role of nanoparticles in natural processes and (4) consider some opportunities for future work on nanoparticles in geological systems. 

Pathways that produce abundant nanoparticles tend to involve geochemical processes that generate high degrees of supersaturation, leading to production of very many crystal nuclei. Supersaturation can occur as the result of inorganic or biological processes. 

Examples of environments where local high degrees of supersaturation are encountered include those associated with discharge of hydrothermal vent fluids into cold ocean water, regions where streams of highly acidic solutions mix with neutral pH water, zones of mixing between groundwater fluids, and sites of evaporation of soil water solutions. 

Acid mine drainage environments are weathering-dominated systems that generate very abundant nanoparticles. Consequently, we review the geochemistry and mineralogy of acid systems to provide specific examples of relevant processes. 

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