Environmentally Induced Changes of Commercial Carbon Nanotubes in Aqueous Suspensions. Adaptive Behavior of Bacteria in Biofilms

Abstract

The effects of environmental factors such as sunlight 7 irradiation and the presence of humic acid (HA) on the physicochemical 8 properties of a commercial multiwall carbon nanotube (MWCNT) 9 suspended in a simulated ionic matrix (SIM) and their impacts on 10 bacteria growing in biofilms were evaluated. Both solar irradiation and 11 the presence of HA lead to the dissolution of adsorbed metals on the 12 MWCNT, which are residues of synthesis catalysts. Also, preferential 13 adsorption of certain HA components on the MWCNT induces 14 important modifications in the aliphatic/aromatic relationship of HA 15 components in solution and the generation and release of new moieties. 16 Results demonstrated that the variation of such physicochemical 17 parameters strongly affects the interactions of MWCNT with 18 Pseudomonas aeruginosa sessile bacteria. Thus, the number of attached 19 bacteria increased, and stress responses such as decrease in bacterial size 20 were found in the presence of sunlight-irradiated MWCNT with a particular distribution of EPS strands. A shielding effect was 21 observed when HA was added. It was concluded that physicochemical alterations caused by environmental conditions (with/without 22 irradiation, presence/absence of HA) on MWCNT-containing SIM trigger distinctive adaptive behavior of bacteria in biofilms. This 23 information must be taken into account in the development of biologically assisted treatments for organic metal co-contamination of 24 MWCNT-containing media since MWCNT discharge alters the physicochemical properties and composition of the aqueous 25 environment and the response of the biofilms that interact with it.