Distinguishable co-transport mechanisms of phenanthrene and oxytetracycline with oxidized-multiwalled carbon nanotubes through saturated soil and sediment columns: vehicle and competition effects.

To date mechanisms underlying co-transports of engineered nanomaterials (ENMs) with contaminants have not been adequately explored, which involve complex interactions among ENMs, contaminants, and soils. This study investigated co-transport behaviors of 3 oxidized-multiwalled carbon nanotubes (o-MWCNTs) with phenanthrene (PHE) and oxytetracycline (OTC) in soil and sediment columns. Sorptions and desorptions of PHE and OTC by the o-MWCNTs were examined to facilitate the discussion of co-transport mechanisms. The results showed that mobilities of PHE and OTC in the columns were significantly enhanced by the presences of o-MWCNTs in the influents; the eluted o-MWCNTs were positively correlated to the eluted total PHE but negatively correlated to the eluted total OTC; the eluted PHE was mainly in the o-MWCNTs-associated form, while it was mainly the dissolved OTC breaking through the columns. It was thus concluded that the o-MWCNTs acted as vehicles facilitating the PHE transport, while besides the vehicle effect the o-MWCNTs also competed for the adsorption sites on soil particles with OTC and thereby enhancing the OTC mobility. These findings provide new insight into the mechanisms regulating co-transports of ENMs and contaminants in porous media.