Natural and Incidental Nanoparticles

Overview: 

We have derived a global budget (whole Earth distribution and movement) for natural, inorganic nanomaterials (Hochella et al., 2011).  This is the first global budget of its kind, and it provides a basis for fundamental understanding such as sources and sinks, reservoir residence and transfer times, and a basis for comparing natural vs. anthropogenic nanomaterials on a global basis.    This is our most important achievement in the past two years with underlying consequences for all that CEINT does.

TiO2 is the most extensively used engineered nanoparticles to date, yet its fate in the soil environment has been investigated only rarely.  We conducted two field-scale investigations to address the most likely route presently for TiO2 NPs entering the soil environment, i.e., application of biosolids derived from waste water treatment plants to field soils.  First, we analyzed three sewage sludge products and the presence of TiO2 NPs was repeatedly identified using analytical TEM.  The TiO2 NPs identified are in the size range of 44 – 320 nm, have faceted shapes with the rutile atomic structure, and form small, loosely packed aggregates.  Secondly, we examined surface soils in mesocosms that had been amended with Ag NP-spiked sewage sludge-derived biosolids for the occurrence of TiO2 particles. The TiO2 particles were again determined to have the rutile structure, but this time containing Ag on their surfaces. This suggests that TiO2 NPs from biosolids can interact with toxic trace metals that would then enter the environment if the biosolids were used as a soil amendment.

In our continuing and extensive efforts to understand the detailed, complex, and global nature of natural and incidental nanomaterials, two sets of precipitates collected from stream sediments in the Iberian Pyrite Belt (IPB) of Spain were identified as the iron oxyhydroxysulfate nanomineral schwertmannite.  Extensive HRTEM observations suggest that schwertmannite should not be described as a single phase mineral with a repeating unit cell, but as a polyphasic nanomineral with crystalline areas spanning less than a few nanometers within an amorphous matrix. Arsenic is the most abundant trace element in these samples, keeping in mind that schwertmannite has been shown to be a key player in the global metal cycling of this element. Furthermore, arsenic is associated with crystalline areas within schwertmannite’s nano-needle matrix, implying that schwertmannite-derived goethite nanocrystals may be an important host of arsenic globally.