Bioavailability of phenanthrene and nitrobenzene sorbed on carbonaceous materials

Abstract

To better understand the mechanisms regarding effects of the interactions between organic contaminants (ORCs) and carbonaceous materials (CMs) on bioavailability of ORCs, 22 mg/kg of phenanthrene and nitrobenzene were spiked onto various CMs, and their microbial mineralization by the bacterium Mycobacterium vanbaalenii PYR-1 was investigated. The results showed that as sorption of phenanthrene and nitrobenzene to CMs increased 4.5 and 42.3 times, their freely dissolved concentrations (Cfree) decreased by 80.4% and 97.0%, respectively. Correspondingly, the maximum mineralization rate was reduced by 99.6% for phenanthrene and 98.2% for nitrobenzene. Functionalization of multiwalled carbon nanotubes (CNTs) with hydrophilic polar moieties greatly weakened sorption of phenanthrene and nitrobenzene. Correspondingly, the reduction in mineralization of them preloaded on CNTs was more modest. However, bioavailability of CM-sorbed phenanthrene and nitrobenzene was not solely controlled by Cfree. Model calculations of mineralization kinetics data and electron microscopy observations of CMs evidenced that bacteria access to sorbed phenanthrene and nitrobenzene through cell attachment to the particle surfaces, but this process was CM dependent. This work highlights the factors and underlying mechanisms governing microbial availability of ORCs sorbed on CMs, which is significant for risk assessment of ORCs and possible application of CMs for ORC pollution control through sequestration.