Surface Interactions of Engineered (fullerene and gold) Nanoparticles and the Pyrogenic Carbon Components of Agricultural Soil.

Engineered nanomaterials are increasingly becoming available off the shelf for the direct application on agricultural soils.  Examples of the commercially available fertilizers and pesticides claiming to contain engineered nanomaterials include Primo Maxx (plant growth regulator by Syngenta), Nano-Gro (Agro Nanotechnology), nano-Ag answer (PKN fertilizer by Urth Agriculture), and nano-5 organic fertilizer (Uno Fortune).  Land application of sludge (containing nanosilver from industrial waste streams) and manure (containing silver and zinc nanoparticles from feed additives) represent additional routes of entry into the agricultural soils.  This study investigated the surface interactions between engineered (fullerene and gold) nanoparticles and charcoal black carbon, a ubiquitous soil constituent originating from the wildfire and intentional biochar amendment.  Charge transfer upon the close approach of surfaces, and van der Waals interactions resulted in irreversible retention of over 22 mg nano-gold per g biochar.  In a distinctive contrast, less than 20 μg/g fullerene was retained by biochar, and lead to an unusual phenomenon: physical disintegration of mm-scale biochar pellets into amorphous carbon nanoparticles in water, in the absence of external energy such as the sonication or laser ablation.  Importance of physical disintegration on the black carbon cycles, including the off-site migration of sorbed pollutants, will be discussed.