Identification of transformation products during advanced oxidation of diatrizoate: Effect of water matrix and oxidation process.

Removal of micropollutants from reverse osmosis (RO) brines of wastewater desalination by oxidation processes is influenced by the scavenging capacity of brines components, resulting in the accumulation of transformation products (TPs) rather than complete mineralization. In this work the iodinated contrast media diatrizoate (DTZ) was used as model compound due to its relative resistance to oxidation. Identification of TPs was performed in ultrapure water (UPW) and RO brines applying nonthermal plasma (NTP) and UVA-TiO2 as oxidation techniques. The influence of main RO brines components in the formation and accumulation of TPs, such as chloride, bicarbonate alkalinity and humic acid, was also studied during UVA-TiO2. DTZ oxidation pattern in UPW resulted similar in both UVA-TiO2 and NTP achieving 66 and 61% transformation, respectively. However, DTZ transformation in RO brines was markedly lower in UVA-TiO2 (9%) than in NTP (27%). These differences can be attributed to the synergic effect of RO brines components during NTP. Moreover, reactive species other than hydroxyl radical contributed to DTZ transformation, i.e., direct photolysis in UVA-TiO2 and direct photolysis + O3 in NTP accounted for 16 and 23%, respectively. DTZ transformation led to iodide formation in both oxidation techniques but it further oxidized to iodate by ozone in NTP. In total 14 transformation products were identified in UPW of which 3 were present only in UVA-TiO2 and 2 were present exclusively in NTP; 5 of the 14 TPs were absent in RO brines. Five of them were new and were denoted as TP-474A/B, TP-522, TP-586, TP-602, TP-628. TP-522 (mono-chlorinated) was elucidated only in presence of high chloride titer-synthetic water matrix in NTP, most probably formed by active chlorine species generated in situ. TPs accumulation in RO brines was markedly different in comparison to UPW. This denotes the influence of RO brines components in the formation of reactive species that could further attack DTZ/TPs and/or scavenging performed by these brine components that could limit further TPs degradation. Five plausible degradation pathways are proposed for DTZ transformation in UPW.

Effects of carbamazepine and two of its metabolites on the non-biting midge Chironomus riparius in a sediment full life cycle toxicity test.

The antiepileptic drug carbamazepine (CBZ) and its main metabolites carbamazepine-10,11-epoxide (EP-CBZ) and 10,11-dihydro-10,11-dihydroxy-carbamazepine (DiOH-CBZ) were chosen as test substances to assess chronic toxicity on the non-biting midge Chironomus riparius. All the three substances were tested in a 40-day sediment full life cycle test (according to OECD 233) in which mortality, emergence, fertility, and clutch size were evaluated. In addition, these parameters were considered to calculate the population growth rate which represents an integrated measure to assess population relevant effects. With an LC50 of 0.20 mg/kg (time-weighted mean), the metabolite EP-CBZ was significantly more toxic than the parent substance CBZ (LC50: 1.1 mg/kg). Especially mortality, emergence, and fertility showed to be sensitive parameters under the exposure to CBZ and EP-CBZ. By using classical molecular dynamics (MD) simulations, the binding of CBZ to the ecdysone receptor was investigated as one possible mode of action (MoA) but appeared to be unlikely. The second metabolite DiOH-CBZ did not cause any effects within the tested concentration rage (0.17-1.2 mg/kg). Even though CBZ was less toxic compared to EP-CBZ, CBZ is found in the environment at much higher concentrations and therefore causes a higher potential risk for sediment dwelling organisms compared to its metabolites. Nevertheless, the current study illustrates the importance of including commonly found metabolites into the risk assessment of parent substances.

Oxypurinol - A novel marker for wastewater contamination of the aquatic environment.

The anti-gout agent allopurinol is one of the most prescribed pharmaceuticals in Germany and is widely metabolized into oxypurinol (80%) as well as the corresponding riboside conjugates (10%) within the human body. To investigate the occurrence of allopurinol and oxypurinol in the urban water cycle an analytical method was developed based on solid phase extraction (SPE) and subsequent liquid chromatography electrospray-ionization tandem mass spectrometry (LC-MS/MS). In raw wastewater concentration levels of oxypurinol ranged up to 26.6 µg L(-1), whereas allopurinol was not detected at all. In wastewater treatment plant (WWTP) effluents, concentrations of allopurinol were

Electrochemical oxidation of tramadol in low-salinity reverse osmosis concentrates using boron-doped diamond anodes.

The electrochemical treatment of low-salinity reverse osmosis (RO) concentrates was investigated using tramadol (100 µM) as a model substance for persistent organic contaminants. Galvanostatic degradation experiments using boron-doped diamond electrodes at different applied currents were conducted in RO concentrates as well as in ultra-pure water containing either sodium chloride or sodium sulfate. Kinetic investigations revealed a significant influence of in-situ generated active chlorine besides direct anodic oxidation. Therefore, tramadol concentrations decreased more rapidly at elevated chloride content. Nevertheless, reduction of total organic carbon (TOC) was found to be comparatively low, demonstrating that transformation rather than mineralization was taking place. Early stage product formation could be attributed to both direct and indirect processes, including demethylation, hydroxylation, dehydration, oxidative aromatic ring cleavage and halogenation reactions. The latter led to various halogenated derivatives and resulted in AOX (adsorbable organic halogens) formation in the lower mg/L-range depending on the treatment conditions. Characterisation of transformation products (TPs) was achieved via MS(n) experiments and additional NMR measurements. Based on identification and quantification of the main TPs in different matrices and on additional potentiostatic electrolysis, a transformation pathway was proposed.

Transformation of iopamidol during chlorination.

The transformation of the iodinated X-ray contrast media (ICM) iopamidol, iopromide, iohexol, iomeprol, and diatrizoate was examined in purified water over the pH range from 6.5 to 8.5 in the presence of sodium hypochlorite, monochloramine, and chlorine dioxide. In the presence of aqueous chlorine, only iopamidol was transformed. All other ICM did not show significant reactivity, regardless of the oxidant used. Chlorination of iopamidol followed a second order reaction, with an observed rate constant of up to 0.87 M(-1) s(-1) (±0.021 M(-1) s(-1)) at pH 8.5. The hypochlorite anion was identified to be the reactive chlorine species. Iodine was released during the transformation of iopamidol, and was mainly oxidized to iodate. Only a small percentage (less than 2% after 24 h) was transformed to known organic iodinated disinfection byproducts (DBPs) of low molecular weight. Some of the iodine was still present in high-molecular weight DBPs. The chemical structures of these DBPs were elucidated via MSn fragmentation and NMR. Side chain cleavage was observed as well as the exchange of iodine by chlorine. An overall transformation pathway was proposed for the degradation of iopamidol. CHO cell chronic cytotoxicity tests indicate that chlorination of iopamidol generates a toxic mixture of high molecular weight DBPs (LC50 332 ng/µL).

Biotransformation of the UV-filter sulisobenzone: challenges for the identification of transformation products.

The UV-filter substance Sulisobenzone (BP-4) is widely employed in sunscreens and other personal care products. In the current study, its behavior during biological wastewater treatment was investigated. In contact with activated sludge BP-4 was degraded in aerobic batch experiments forming at least nine transformation products (TPs). The mass balance in the batch experiments was closed, as measurements with LC-UV underlined that the quantity of the TPs was comparable to the BP-4 quantity transformed. The chemical structures of the nine TPs could be proposed based on accurate mass measurements by high resolution mass spectrometry (LTQ-Orbitrap-MS), several fragmentation experiments up to MS(6) and synthesis of one TP. NMR analyses of the main TP confirmed its proposed chemical structure. At the beginning of the biotransformation of BP-4, a benzhydrol analogue was formed due to the reduction of the keto moiety. Further reactions (e.g., oxidation, demethylation, decarboxylation) led to the formation of extremely polar TPs. A biodegradation pathway was proposed based on the TP structures identified and the sequence of the TP formation. The isolated TPs exhibited higher toxic effects on Vibrio fischeri than BP-4. The results contribute to a better general understanding and prediction of the biotransformation of aromatic sulfonic acids in WWTPs.

Palladium-catalyzed pentannulation of polycyclic aromatic hydrocarbons.

We present a new and versatile one-step synthesis of a series of small molecular chromophores based on cyclopentannulated polycyclic aromatic hydrocarbons (PAH). Easily available pyrene, anthracene, and perylene bromides serve as starting materials for the reactions. The formation of the five-membered ring is achieved by the straightforward palladium(0)-catalyzed carbannulation with various substituted acetylenes. This approach is applicable either to single or multiple annulation procedures leading to hitherto inaccessible PAH topologies. According to the resulting products of the diverse reactions, a mechanistic explanation is proposed. UV/Vis absorption as well as cyclovoltammetric measurements were performed for characterization demonstrating the value of this annulation technique. Optical absorptions of up to 780 nm and absorption coefficients ranging from 8000 to 34,000 M(-1) cm(-1) were detected.