Removal of the iodinated X-ray contrast medium diatrizoate by anaerobic transformation.

The iodinated X-ray contrast medium diatrizoate is known to be very persistent in current wastewater treatment as well as in environmental compartments. In this study, the potential of anaerobic processes in soils, sediments, and during wastewater treatment to remove and transform diatrizoate was investigated. In anaerobic batch experiments with soil and sediment seven biologically formed transformation products (TPs) as well as the corresponding transformation pathway were identified. The TPs resulted from successive deiodinations and deacetylations. The final TP 3,5-diaminobenzoic acid (DABA) was stable under anaerobic conditions. However, DABA was further transformed under air atmosphere, indicating the potential for the mineralization of diatrizoate by combining anaerobic and aerobic conditions. With the development of a methodology using complementary liquid chromatography-electrospray ionization-tandem mass spectrometry and liquid chromatography-inductively coupled plasma-mass spectrometry techniques, all identified TPs were quantified and the mass balance could be closed without having authentic standards for four of the TPs available. The detection and quantification of diatrizoate TPs in groundwater, in technical wetlands with anaerobic zones, and in a pilot wastewater treatment plant established for anaerobic treatment highlights the transferability and up-scaling of the results attained by laboratory experiments to environmental conditions.

Removal of the X-ray contrast media diatrizoate by electrochemical reduction and oxidation.

Due to their resistance to biological wastewater treatment, iodinated X-ray contrast media (ICM) have been detected in municipal wastewater effluents at relatively high concentrations (i.e., up to 100 µg L(-1)), with hospitals serving as their main source. To provide a new approach for reducing the concentrations of ICMs in wastewater, electrochemical reduction at three-dimensional graphite felt and graphite felt doped with palladium nanoparticles was examined as a means for deiodination of the common ICM diatrizoate. The presence of palladium nanoparticles significantly enhanced the removal of diatrizoate and enabled its complete deiodination to 3,5-diacetamidobenzoic acid. When the system was employed in the treatment of hospital wastewater, diatrizoate was reduced, but the extent of electrochemical reduction decreased as a result of competing reactions with solutes in the matrix. Following electrochemical reduction of diatrizoate to 3,5-diacetamidobenzoic acid, electrochemical oxidation with boron-doped diamond (BDD) anodes was employed. 3,5-Diacetamidobenzoic acid disappeared from solution at a rate that was similar to that of diatrizoate, but it was more readily mineralized than the parent compound. When electrochemical reduction and oxidation were coupled in a three-compartment reactor operated in a continuous mode, complete deiodination of diatrizoate was achieved at an applied cathode potential of -1.7 V vs SHE, with the released iodide ions electrodialyzed in a central compartment with 80% efficiency. The resulting BDD anode potential (i.e., +3.4-3.5 V vs SHE) enabled efficient oxidation of the products of the reductive step. The presence of other anions (e.g., chloride) was likely responsible for a decrease in I(-) separation efficiency when hospital wastewater was treated. Reductive deiodination combined with oxidative degradation provides benefits over oxidative treatment methods because it does not produce stable iodinated intermediates. Nevertheless, the process must be further optimized for the conditions encountered in hospital wastewater to improve the separation efficiency of halide ions prior to the electrooxidation step.

Determination of iodinated X-ray contrast media in sewage by solid-phase extraction and liquid chromatography tandem mass spectrometry.

A method for the quantitative determination of five iodinated X-ray contrast media (ICMs) in sewage was developed by solid-phase extraction and high-performance liquid chromatography-tandem mass spectrometry. A fused-core analytical column was successfully applied for the first time for the separation of ICMs. Oasis HLB was selected from the sorbents tested because of its higher recoveries. The optimized method allowed the determination of the ICMs at low ng/L levels in both influent and effluent sewage, with detection limits of 40 ng/L and 10 ng/L for most compounds in influent and effluent sewage, respectively. The five ICMs studied were determined in all samples analysed, with iopromide being the analyte found at the highest concentration (8.9 µg/L), while iopamidol was the analyte found at lowest concentration (1.3 µg/L) in influent sewage. Effluent sewage did not show a significant decrease in ICM concentrations.

Investigating the fate of iodinated X-ray contrast media iohexol and diatrizoate during microbial degradation in an MBBR system treating urban wastewater.

The capability of a moving bed biofilm reactor (MBBR) to remove the iodinated contrast media (ICM) iohexol (IOX) and diatrizoate (DTZ) from municipal wastewater was studied. A selected number of clones of microorganisms present in the biofilm were identified. Biotransformation products were tentatively identified and the toxicity of the treated effluent was assessed. Microbial samples were DNA-sequenced and subjected to phylogenetic analysis in order to confirm the identity of the microorganisms present and determine the microbial diversity. The analysis demonstrated that the wastewater was populated by a bacterial consortium related to different members of Proteobacteria, Firmicutes, and Nitrisporae. The optimum removal values of the ICM achieved were 79 % for IOX and 73 % for DTZ, whereas 13 biotransformation products for IOX and 14 for DTZ were identified. Their determination was performed using ultra-performance liquid chromatography-tandem mass spectrometry. The toxicity of the treated effluent tested to Daphnia magna showed no statistical difference compared to that without the addition of the two ICM. The MBBR was proven to be a technology able to remove a significant percentage of the two ICM from urban wastewater without the formation of toxic biodegradation products. A large number of biotransformation products was found to be formed. Even though the amount of clones sequenced in this study does not reveal the entire bacterial diversity present, it provides an indication of the predominating phylotypes inhabiting the study site.

Doping of biogenic Pd catalysts with Au enables dechlorination of diclofenac at environmental conditions.

By using the metal reducing capacities of bacteria, Pd nanoparticles can be produced in a sustainable way ('bio-Pd'). These bio-Pd nanoparticles can be used as a catalyst in, for example, dehalogenation reactions. However, some halogenated compounds are not efficiently degraded using a bio-Pd catalyst. This study shows that the activity of bio-Pd can be improved by doping with Au(0) ('bio-Pd/Au'). In contrast with bio-Pd, bio-Pd/Au could perform the removal of the model pharmaceutical compound diclofenac from an aqueous medium in batch experiments at neutral pH and with H(2) as the hydrogen donor (first order decay constant of 0.078 ± 0.009 h(-1)). Dehalogenation was for both catalysts the only observed reaction. For bio-Pd/Au, a disproportional increase of catalytic activity was observed with increasing Pd-content of the catalyst. In contrast, when varying the Au-content of the catalyst, a Pd/Au mass ratio of 50/1 showed the highest catalytic activity (first order decay value of 0.52 ± 0.02 h(-1)). The removal of 6.40 µg L(-1) diclofenac from a wastewater treatment plant effluent using bio-Pd was not possible even after prolonged reaction time. However, by using the most active bio-Pd/Au catalyst, 43.8 ± 0.5% of the initially present diclofenac could be removed after 24 h. This study shows that doping of bio-Pd nanoparticles with Au(0) can be a promising approach for the reductive treatment of wastewaters containing halogenated contaminants.

Degradation mechanisms and kinetic studies for the treatment of X-ray contrast media compounds by advanced oxidation/reduction processes.

The presence of iodinated X-ray contrast media compounds (ICM) in surface and ground waters has been reported. This is likely due to their biological inertness and incomplete removal in wastewater treatment processes. The present study reports partial degradation mechanisms based on elucidating the structures of major reaction by-products using gamma-irradiation and LC-MS. Studies conducted at concentrations higher than observed in natural waters is necessary to elucidate the reaction by-product structures and to develop destruction mechanisms. To support these mechanistic studies, the bimolecular rate constants for the reaction of OH and e(-)(aq) with one ionic ICM (diatrizoate), four non-ionic ICM (iohexol, iopromide, iopamidol, and iomeprol), and the several analogues of diatrizoate were determined. The absolute bimolecular reaction rate constants for diatrizoate, iohexol, iopromide, iopamidol, and iomeprol with OH were (9.58 +/- 0.23)x10(8), (3.20 +/- 0.13)x10(9), (3.34 +/- 0.14)x10(9), (3.42 +/- 0.28)x10(9), and (2.03 +/- 0.13) x 10(9) M(-1) s(-1), and with e(-)(aq) were (2.13 +/- 0.03)x10(10), (3.35 +/- 0.03)x10(10), (3.25 +/- 0.05)x10(10), (3.37 +/- 0.05)x10(10), and (3.47 +/- 0.02) x 10(10) M(-1) s(-1), respectively. Transient spectra for the intermediates formed by the reaction of OH were also measured over the time period of 1-100 micros to better understand the stability of the radicals and for evaluation of reaction rate constants. Degradation efficiencies for the OH and e(-)(aq) reactions with the five ICM were determined using steady-state gamma-radiolysis. Collectively, these data will form the basis of kinetic models for application of advanced oxidation/reduction processes for treating water containing these compounds.

Removal of diatrizoate with catalytically active membranes incorporating microbially produced palladium nanoparticles.

There is an increasing concern about the fate of iodinated contrast media (ICM) in the environment. Limited removal efficiencies of currently applied techniques such as advanced oxidation processes require more performant strategies. The aim of this study was to establish an innovative degradation process for diatrizoate, a highly recalcitrant ICM, by using biogenic Pd nanoparticles as free suspension or immobilized in polyvinylidene fluoride (PVDF) and polysulfone (PSf) membranes. As measured by HPLC-UV, the removal of 20mg L(-1) diatrizoate by a 10mg L(-1) Pd suspension was completed after 4h at a pH of 10. LC-MS analysis provided evidence for the sequential hydrodeiodination of diatrizoate. Pd did not lose its activity after incorporation in the PVDF and PSf matrix and the highest activity (k(cat)=30.0+/-0.4h(-1) L g(-1) Pd) was obtained with a casting solution of 10% PSf and 500mg L(-1) Pd. Subsequently, water containing 20mg L(-1) diatrizoate was treated in a membrane contactor, in which the water was supplied at one side of the membrane while hydrogen was provided at the other side. In a fed batch configuration, a removal efficiency of 77% after a time period of 48h was obtained. This work showed that membrane contactors with encapsulated biogenic nanoparticles can be instrumental for treatment of water contaminated with diatrizoate.

Bank filtration: a suitable process for the removal of iodinated X-ray contrast media?

After bank filtration, effluent influenced surface waters are often used as raw drinking water. It is known that high concentrations of iodinated X-ray contrast media are detectable in such surface waters and thus, more knowledge about the behaviour of the contrast media during bank filtration is necessary and the subject of investigations in this study. The adsorbable organic iodine (AOI), four widely used iodinated X-ray contrast media and four possible transformation products were quantified in an influenced lake, five groundwater wells and a drinking water well. Under anoxic conditions the AOI as well as the concentration of the contrast media are decreased by bank filtration, whereby the AOI is decreased by 64% and the contrast media concentration can be reduced up to 95%, depending on the compound. In the raw drinking water the following average concentrations were determined: lopromid < 20 ng/L, Diatrizote 166 ng/L, lopamidol 166 ng/L and lohexol 34 ng/L. Instationary conditions during the sampling period indicate that, at least under anoxic conditions, a large part of the contrast media and transformation products, which are still iodinated, may be associated to colloids and/or humic material.

Assay and purity analysis of diatrizoate sodium in drug product by LC.

An LC procedure was developed to separate diatrizoate sodium from three known impurities. These impurities are 2,4- and 2,6-diiodo-3,5-diacetamidobenzoic acid (DDZA), and the free amine (5-acetamido-3-amino-2,4,6-triiodobenzoic acid). The separation was achieved using a Hamilton, PRP-X100, anion exchange column. The retention of diatrizoate sodium and the impurities was dependent on pH, potassium chloride concentration and phosphate concentration. Increasing any of these mobile phase modifiers decreased the retention time of all of the components. The eluent for assay and purity determination of drug product consisted of 0.1 M potassium chloride and 0.05 M potassium phosphate dibasic in water/acetonitrile (900:100). The mean concentration of diatrizoate sodium in Hypaque Sodium 50% determined over 3 days was 102.3% of label claim with an R.S.D. of 1.3. The accuracy of the purity method, determined by spiking known amounts of the impurities at five concentrations ranging from 0.025 to 0.06% (w/w) into drug product, was 100.1% for DDZA and 94.2% for the free amine. The decomposition of diatrizoate sodium in 0.1 N potassium hydroxide at 85 degrees C followed pseudo first-order kinetics. The calculated half-life was 2 days.