Iodinated contrast media electro-degradation: process performance and degradation pathways

One-step electrodeposition preparation of boron nitride and samarium co-modified Ti/PbO2 anode with ultra-long lifetime: highly efficient degradation of lincomycin wastewater

Lincomycin (LC) is an extensively applied broad-spectrum antibiotic, and its considerable residues in wastewater have caused a series of environmental problems, which makes degradation of LC wastewater extremely urgent. In this work, we have constructed a novel boron nitride (BN) and samarium (Sm) co-modified Ti/PbO2 as anode for high-performance degradation of LC wastewater. Compared with Ti/PbO2, Ti/PbO2-Sm, and Ti/PbO2-BN electrodes, Ti/PbO2-BN-Sm electrode with smaller pyramidal particles possesses higher oxygen evolution potential (2.32 V), excellent accelerated service life (103 h), and outstanding electrocatalytic activity. The single-factor experiments demonstrate that under optimized conditions (current density of 20 mA.cm-2, 6.0 g L-1 Na2SO4, pH 9, and temperature of 30°C), removal rate and COD degradation rate of LC at 3 h have reached 92.85% and 89.11%, respectively. At the same time, degradation of LC is in accordance with the primary kinetic model. Based on the analysis of high-performance liquid chromatography-mass spectrometry (HPLC-MS), four possible degradation pathways are hypothesized. Therefore, efficient electrochemical degradation of LC by using an extremely long-life Ti/PbO2 electrode with high catalytic activity may be a promising method.

Anaerobic Transformation of the Iodinated X-ray Contrast Medium Iopromide, Its Aerobic Transformation Products, and Transfer to Further Iodinated X-ray Contrast Media

The iodinated X-ray contrast medium (ICM) iopromide and its aerobic transformation products (TPs) are frequently detected in the effluents of wastewater treatment plants and in different compartments of the aquatic environment. In this study, the anaerobic transformation of iopromide and its aerobic TPs was investigated in water-sediment systems. Iopromide, its final aerobic TP didespropanediol iopromide (DDPI), and its primary aniline desmethoxyacetyl iopromide (DAMI) were used as model substances. Five biologically formed anaerobic TPs of iopromide and DAMI and six of DDPI, and the respective transformation pathways, were identified. The TPs were formed by successive deiodination and hydrolysis of amide moieties. Quantification of the iodinated TPs was achieved by further development of a complementary liquid chromatography (LC)-quadrupole time-of-flight mass spectrometry (Q-ToF-MS) and LC-inductively coupled plasma - mass spectrometry (ICP-MS) strategy without needing authentic standards, despite several TPs coeluting with others. A database with predicted anaerobic TPs of ICMs was derived by applying the transformation rules found for the anaerobic transformation pathways of iopromide and diatrizoate to further ICMs (iomeprol and iopamidol) and their aerobic TPs already reported in the literature. The environmental relevance of the identified transformation pathways was confirmed by identifying an experimental TP and two predicted TPs using suspect screening of water taken from anaerobic bank filtration zones.

Fate of new three anti-influenza drugs and one prodrug in the water environment

We evaluated the environmental fate of new three anti-influenza drugs, favipiravir (FAV), peramivir (PER), and laninamivir (LAN), and an active prodrug of LAN, laninamivir octanoate (LANO), in comparison with four conventional drugs, oseltamivir (OS), oseltamivir carboxylate (OC), amantadine (AMN), and zanamivir (ZAN) by photodegradation, biodegradation, and sorption to river sediments. In addition, we conducted 9-month survey of urban rivers in the Yodo River basin from 2015 to 2016 (including the influenza season) to investigate the current status of occurrence of these drugs in the river environment. The results clearly showed that FAV and LAN rapidly disappeared through photodegradation (half-lives 1 and 8 h, respectively), followed by LANO which gradually disappeared through biodegradation (half-life, 2 days). The remained PER and conventional drugs were, however, persistent and transported from upstream to downstream sites. Rates of their sorption to river sediments were negligibly small. Detected levels remained were in the range from N.D. to 89 ng/L for the river waters and from N.D. to 906 ng/L in sewage effluent. However, all of the remained drugs were effectively removed by ozonation after chlorination at a sewage treatment plant. These findings suggest the importance of introducing ozonation for reduction of pollution loads in rivers, helping to keep river environments safe. To the best of our knowledge, this is the first evaluation of the removal effects of natural sunlight, biodegradation, and sorption to river sediments on FAV, PER, LAN, LANO, and a conventional drug, AMN.

Sulfate-mediated electrooxidation of X-ray contrast media on boron-doped diamond anode

Recently, electrochemical activation of sulfate ions to sulfate radical species and nonradically activated persulfate has been demonstrated at boron-doped diamond (BDD) anode, which enhanced the electrooxidation kinetics of several persistent contaminants. In this study, we investigated the transformation pathways of two X-ray contrast media (ICM), diatrizoate and iopromide, in electrooxidation at BDD anode using sulfate and inert nitrate anolyte. Sulfate anolyte yielded a seven-fold increase in apparent rate constants for ICM oxidation compared to inert nitrate anolyte, and a two-fold increase for the removal of organic carbon. Higher iodine release was observed in electrooxidation of diatrizoate compared to iopromide. In the case of diatrizoate, around 80% of deiodination efficiency was achieved in both anolytes. Deiodination efficiency of iopromide was somewhat lower in nitrate anolyte (≤75%) and significantly reduced in sulfate anolyte (≤46%) due to a larger steric hindrance of alkyl side chains. Moreover, a considerable lag phase of iopromide deiodination was observed in sulfate anolyte, indicating that initial oxidation reactions took place almost exclusively at the alkyl side chains. Several transformation products (TPs) of ICM were identified in electrooxidation in sulfate anolyte, and only three TPs in the case of nitrate anolyte. The main mechanistic steps in the oxidation of iopromide were H-abstraction and bond cleavage in the alkyl side chains. Diatrizoate was mainly transformed through oxidative cleavage of iodine substituent and inter-molecular cyclization. Two hydroxylamine derivatives of iopromide and a nitro-derivative of diatrizoate were observed in sulfate anolyte. These products have not been reported previously for hydroxyl radical-mediated oxidation of ICM. Given that electron-transfer mechanism is more typical for sulfate than for hydroxyl radicals, formation of hydroxylamine and nitro-derivatives of ICM was assigned to one-electron charge transfer to sulfate radical species and formation of N-centered radicals.