title: Binding of dicamba to soluble and bound extracellular polymeric substances (EPS) from aerobic activated sludge: a fluorescence quenching study.
abstract: Binding of dicamba to soluble EPS (SEPS) and bound EPS (BEPS) from aerobic activated sludge was investigated using fluorescence spectroscopy. Two protein-like fluorescence peaks (peak A with Ex/Em=225 nm/342-344 nm and peak B with Ex/Em=275/340-344 nm) were identified in SEPS and BEPS. Humic-like fluorescence peak C (Ex/Em=270-275 nm/450-460 nm) was only found in BEPS. Fluorescence of the peaks A and B for SEPS and peak A for BEPS were markedly quenched by dicamba at all temperatures whereas fluorescence of peaks B and C for BEPS was quenched only at 298 K. A dynamic process dominated the fluorescence quenching of peak A of both SEPS and BEPS. Fluorescence quenching of peak B and C was governed a static process. The effective quenching constants (logK(a)) were 4.725-5.293 for protein-like fluorophores of SEPS and 4.23-5.190 for protein-like fluorophores of BEPS, respectively. LogK(a) for humic-like substances was 3.85. Generally, SEPS had greater binding capacity for dicamba than BEPS, and protein-like substances bound dicamba more strongly than humic-like substances. Binding of dicamba to SEPS and BEPS was spontaneous and exothermic. Electrostatic force and hydrophobic interaction forces play a crucial role in binding of dicamba to EPS.
authors.affiliation: Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, Xinjiang, 830011, China.
authors.forename: Xiangliang
authors.initials: X
authors.lastname: Pan
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Daoyong
authors.initials: D
authors.lastname: Zhang
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Wenjuan
authors.initials: W
authors.lastname: Song
authors.forename: Fengchang
authors.initials: F
authors.lastname: Wu
mesh_terms: D003996:Dicamba / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D006812:Humic Substances; D012722:Sewage / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D006540:Herbicides; D006812:Humic Substances; D012722:Sewage; D003996:Dicamba