Study suggests single-walled carbon nanotubes exhibit limited transport in soil columns
The increased production and commercial use of nanomaterials combined with a lack of regulation to govern their disposal may result in their introduction to soils and ultimately into groundwater systems. In a study published this week in Environmental Science & Technology, researchers at Yale University in the United States have investigated the transport behaviour of carboxyl-functionalised single-walled carbon nanotubes (SWCNT) in natural soil.
Their results show that, in general, SWCNT deposition (filtration) rate increased with increasing solution ionic strength, with divalent cations (Ca2+) being more effective in increasing SWCNT retention than monovalent cations (K+). However, SWCNT deposition rate over a very wide range of monovalent and divalent cation concentrations (0.03 to 100 mM) was relatively high and changed only slightly above 0.3 mM KCl or 0.1 mM CaCl2.
In contrast, filtration of another type of engineered carbon-based nanomaterial, aqueous fullerene (C60) nanoparticles (radius of 51 nm), was more sensitive to solution ionic strength, displaying lower deposition rate and more effective transport in soil than SWCNT.
Authors Jaisi et al. conclude that physical straining governs SWCNT filtration and transport under all the solution chemistries investigated in their study study. The researchers propose that SWCNT shape and structure, particularly their very large aspect ratio and highly aggregate state in aqueous solutions, as well as the soil properties (such as soil particle size, porosity, and permeability), collectively contribute to its retention in natural soil media.
Jaisi et al. conclude that their results 'suggest that SWCNTs of comparable properties to those used in the present study will not exhibit substantial transport and infiltration in soils because of effective retention by the soil matrix'.
Click here to access the article through ACS Publications.
Source: ACS