The transformation of triclosan by laccase: Effect of humic acid on the reaction kinetics, products and pathway.

This study systematically explored the effect of humic acid (HA) (as model of natural organic matter) on the kinetics, products and transformation pathway of triclosan (TCS) by laccase-catalyzed oxidation. It was found that TCS could be effectively transformed by laccase-catalysis, with the apparent second-order rate constant being 0.056 U-1 mL min-1. HA inhibited the removal rate of TCS. HA-induced inhibition was negatively correlated with HA concentration in the range of 0-10 mg L-1 and pH-dependent from 3.5 to 9.5. FT-IR and 13C NMR spectra showed a decrease of aromatic hydroxyl (phenolic) groups and an increase of aromatic ether groups, indicating the cross-linking of HA via C-O-C and C-N-C bonds during enzyme-catalyzed oxidation. Ten principle oxidative products, including two quinone-like products (2-chlorohydroquinone, 2-chloro-5-(2,4-dichlodichlorophenoxy)-(1,4)benzoquinone), one chlorinated phenol (2,4-dichlorophenol (2,4-DCP)), three dimers, two trimmers and two tetramers, were detected by gas chromatograghy/mass spectrometry (GC-MS) and high performance liquid chromatography/quadrupole time-of-flight/mass spectrometry (HPLC/Q-TOF/MS). The presence of HA induced significantly lesser generation of self-polymers and enhanced cross-coupling between HA and self-polymers via C-O-C, C-N-C and C-C coupling pathways. A plausible transformation pathway was proposed as follows: TCS was initially oxidized to form reactive phenoxyl radicals, which self-coupled to each other subsequently by C-C and C-O pathway, yielding self-polymers. In addition, the scission of ether bond was also observed. The presence of HA can promote scission of ether bond and further oxidation of phenoxyl radicals, forming hydroxylated or quinone-like TCS. This study shed light on the behavior of TCS in natural environment and engineered processes, as well provided a perspective for the water/wastewater treatment using enzyme-catalyzed oxidation techniques.

[Toxicities of 30 ionic liquids to Vibrio qinghaiensis sp. Q67].

To systematically and effectively assess the toxic effects of "green solvent" ionic liquid (ILs) to a novel freshwater luminescent Vibrio qinghaiensis sp. Q67 (Q67), the toxicities of 30 ILs with different alkyl chain lengths, anions and cation skeletons (methylimidazolium, dimethylimidazolium and pyridinium) were determined using the microplate toxicity analysis. The observed dose-response curves (DRCs) were fitted by using the nonlinear least square regression. It was shown that the DRCs of 30 ILs could be well described by the Logit or Weibull function (R > 0.98, RMSE < 0.053). The toxicities of 30 ILs varied greatly and the pEC50 values of 30 ILs ranged from 1.01 to 5.48. The toxicities of ILs to Q67 mainly depended on the alkyl chain length and every two-carbon augment on the alkyl chain made the toxicity duplicate. The anions, cation skeletons and light absorbance of ILs showed no significant effect on the toxicities of ILs to Q67.

A novel direct equipartition ray design (EquRay) procedure for toxicity interaction between ionic liquid and dichlorvos.

BACKGROUND, AIM AND SCOPE: Pollutants always co-exist in the environment. Determining and characterizing the interaction among chemicals is an important issue. Experimental designs (ED) play an important role in evaluating the interactions. The main aim of our study is to provide the test and analysis of the toxicity interaction with a novel ED method. MATERIALS AND METHODS: A novel direct equipartition ray design (EquRay) procedure was proposed to effectively and systematically determine the toxicities of binary mixtures on Vibrio qinghaiensis sp.-Q67. Here, one component is ionic liquid, 1-butyl-2,3-dimethylimidazolium chloride (IL1), 1-butylpyridinium bromide (IL2) or N-hexylpyridinium bis(trifluoromethylsulfonyl)imide (IL3), and another is dichlorvos (DIC). The toxicity interaction was evaluated by comparing experiment and additive model together with three-dimension deviation response surface (DRS) analysis. RESULT: Selecting CA as a reference model, the binary mixtures exerted less than additive (antagonism). Most of the deviations occurred in the centre portion of the DRS where the dCA (deviation from CA) values are between -15% and -26% for IL1-DIC and IL2-DIC mixtures and -10% and -15% for IL3 and DIC. Selecting IA as a additive model, IL1-DIC and IL2-DIC mixtures exhibited less than additive (antagonism) while IL3-DIC displayed an addition action and the absolute values of dIAs (deviation from IA) were less than 10%. CONCLUSION: A novel EquRay procedure was developed in this study and the EquRay can provide us with the information about the toxicity interaction between binary mixture components (such as DIC and IL) in different concentration regions across different mixture ratios.

Evaluation on the toxicity of ionic liquid mixture with antagonism and synergism to Vibrio qinghaiensis sp.-Q67.

Ionic liquids (ILs) are a fascinating group of new chemicals with the potential to replace the classical volatile organic solvents, stimulating many applications in chemical industry. In case ILs are released to the environment, possible combined toxicity should be taken into account and it is, however, often neglected up to now. In this paper, therefore, the concentration-response curves (CRCs) of four groups of IL mixtures with various mixture ratios to Vibrio qinghaiensis sp.-Q67 were determined using the microplate toxicity analysis and were compared to the CRCs predicted by an additive reference model, the concentration addition (CA) or independent action (IA), to identify the toxicity interaction. It is showed that most of the IL mixture rays displayed the classical addition while the remaining rays exhibited antagonism or synergism. Moreover, it is found that the pEC50 values of the mixture rays exhibiting antagonism or synergism are well correlated with the mixture ratio of a certain IL therein.