Sorption to biofilms is thought to be a crucial process controlling the fate of trace
organic contaminants in aquatic systems. The organic composition of biofilms is regarded
as the determining factor in the sorption mechanism of biolilm organic carbon fractions;
however, its role is not well known. Here, the sorption of phenanthrene and ofloxacin
was modeled with classic and emerging organic contaminants, respectively, by comparatively
investigating nine type of freshwater biofilms cultured in a river, lake, and reservoir
in spring, summer, and autumn. The chemical features of the nine biofilms were analyzed
using elemental analysis, infrared spectroscopy, X-ray photoelectron spectroscopy,
and carbon-13 nuclear magnetic resonance. Results showed that the freshwater biofilms
were aliphatic-rich natural amorphous solid substances with O-containing functional
groups, and their surface polarity was significantly lower than their bulk polarity.
All the isotherms of phenanthrene and ofloxacin sorption by the biofilms were linear.
The organic carbon-normalized partition coefficient values for phenanthrene and ofloxadn
on the nine biofilms ranged from 91.9 to 364.2 L g(-1) and 32 to 43.2 L g(-1), respectively.
The van der Waals interaction between a majority of aliphatic carbon (73.4%-83.9%)
in biofilms and the two sorbates was much stronger than pi-pi interactions between
a minority of aromatic carbon (12.7%-21.7%) and sorbates. The surface polarity of
the biofilms regulated polar interactions induding the hydrogen bonding and electron
donoracceptor interactions. Both the aliphatic carbon and surface polarity in the
biofilms enhanced the sorption of phenanthrene and ofloxacin. The sorption characteristics
and mechanisms of polycyclic aromatic hydrocarbons and antibiotics on biofilms shown
in our present and previous studies are different from those of other ubiquitous natural
solid materials such as soils and sediments. This study provides insight into the
importance of aliphatic carbon fractions of freshwater biofilms for the sorption of
classic and emerging organic contaminants. (C) 2019 Elsevier B.V. All rights reserved.