Stephen E. Duirk

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).

Reaction of benzophenone UV filters in the presence of aqueous chlorine: kinetics and chloroform formation.

The transformation of two benzophenone UV filters (Oxybenzone and Dioxybenzone) was examined over the pH range 6-11 in the presence of excess aqueous chlorine. Under these conditions, both UV filters were rapidly transformed by aqueous chlorine just above circumneutral pH while transformation rates were significantly lower near the extremes of the pH range investigated. Observed first-order rate coefficients (k(obs)) were obtained at each pH for aqueous chlorine concentrations ranging from 10 to 75 μM. The k(obs) were used to determine the apparent second-order rate coefficient (k(app)) at each pH investigated as well as determine the reaction order of aqueous chlorine with each UV filter. The reaction of aqueous chlorine with either UV filter was found to be an overall second-order reaction, first-order with respect to each reactant. Assuming elemental stoichiometry described the reaction between aqueous chlorine and each UV filter, models were developed to determine intrinsic rate coefficients (k(int)) from the k(app) as a function of pH for both UV filters. The rate coefficients for the reaction of HOCl with 3-methoxyphenol moieties of oxybenzone (OXY) and dioxybenzone (DiOXY) were k(1,OxY) = 306 ± 81 M⁻¹s⁻¹ and k(1,DiOxY) = 154 ± 76 M⁻¹s⁻¹, respectively. The k(int) for the reaction of aqueous chlorine with the 3-methoxyphenolate forms were orders of magnitude greater than the un-ionized species, k(2,OxY) = 1.03(±0.52) × 10⁶ M⁻¹s⁻¹ and k(2_1,DiOxY) = 4.14(±0.68) × 10⁵ M⁻¹s⁻¹. Also, k(int) for the reaction of aqueous chlorine with the DiOXY ortho-substituted phenolate moiety was k(2_2,DiOxY) = 2.17(±0.30) × 10³ M⁻¹s⁻¹. Finally, chloroform formation potential for OXY and DiOXY was assessed over the pH range 6-10. While chloroform formation decreased as pH increased for OXY, chloroform formation increased as pH increased from 6 to 10 for DiOXY. Ultimate molar yields of chloroform per mole of UV filter were pH dependent; however, chloroform to UV filter molar yields at pH 8 were 0.221 CHCl₃/OXY and 0.212 CHCl₃/DiOXY.

An acetylcholinesterase-inspired biomimetic toxicity sensor

This work demonstrates the ability of an acetylcholinesterase-inspired biomimetic sensor to accurately predict the toxicity of acetylcholinesterase (AChE) inhibitors. In surface waters used for municipal drinking water supplies, numerous pesticides and other anthropogenic chemicals have been found that inhibit AChE; however, there is currently no portable toxicity assay capable of determining the potential neurotoxicity of water samples and complex mixtures. Biological assays have been developed to determine the toxicity of unknown samples, but the short shelf-life of cells and other biological materials often make them undesirable for use in portable assays. Chemical methods and structure-activity-relationships, on the other hand, require prior knowledge on the compounds of interest that is often unavailable when analyzing environmental samples. In the toxicity assay presented here, the acetylcholinesterase enzyme has been replaced with 1-phenyl-1,2,3-butanetrione 2-oxime (PBO) a biomimetic compound that is structurally similar to the AChE active site. Using a biomimetic compound in place of the native enzyme allows for a longer shelf-life while maintaining the selective and kinetic ability of the enzyme itself. Previous work has shown the success of oxime-based sensors in the selective detection of AChE inhibitors and this work highlights the ability of an AChE-inspired biomimetic sensor to accurately predict the toxicity (LD50 and LC50) for a range of AChE inhibitors. The biomimetic assay shows strong linear correlations to LD50 (oral, rat) and LC50 (fish) values. Using a test set of eight AChE inhibitors, the biomimetic assay accurately predicted the LC50 value for 75% of the inhibitors within one order of magnitude.

The impact of iodinated X-ray contrast agents on formation and toxicity of disinfection by-products in drinking water

The presence of iodinated X-ray contrast media (ICM) in source waters is of high concern to public health because of their potential to generate highly toxic disinfection by-products (DBPs). The objective of this study was to determine the impact of ICM in source waters and the type of disinfectant on the overall toxicity of DBP mixtures and to determine which ICM and reaction conditions give rise to toxic by-products. Source waters collected from Akron, OH were treated with five different ICMs, including iopamidol, iopromide, iohexol, diatrizoate and iomeprol, with or without chlorine or chloramine disinfection. The reaction product mixtures were concentrated with XAD resins and the mammalian cell cytotoxicity and genotoxicity of the reaction mixture concentrates was measured. Water containing iopamidol generated an enhanced level of mammalian cell cytotoxicity and genotoxicity after disinfection. While chlorine disinfection with iopamidol resulted in the highest cytotoxicity overall, the relative iopamidol-mediated increase in toxicity was greater when chloramine was used as the disinfectant compared with chlorine. Four other ICMs (iopromide, iohexol, diatrizoate, and iomeprol) expressed some cytotoxicity over the control without any disinfection, and induced higher cytotoxicity when chlorinated. Only iohexol enhanced genotoxicity compared to the chlorinated source water.

Quantitative Analysis of Earthy and Musty Odors in Drinking Water Sources Impacted by Wastewater and Algal Derived Contaminants

The goal of this study was to develop a robust method capable of quantifying taste and odor compounds (i.e., geosmin and 2-methylisoborneol) at very low aqueous concentrations in the presence of wastewater and algal derived contaminants. A polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber was used to perform headspace-solid phase microextraction (HS-SPME) to extract and analyze taste and odor compounds from model, source water, and finished drinking water samples. Gas chromatography coupled with mass spectrometery (GC/MS) in full scan mode was used to analyze the compounds desorbed from the fiber in the GC inlet. The following parameters were optimized in order to enhance analyte recovery: extraction temperature, extraction time, desorption time, sonication temperature, sonication time and GC/MS configuration/temperature program. After optimization, the method provided a linear response from 1 to 300 ng L(-1) and yielded limit of detections (LODs) of 1 ng L(-1) for both 2-MIB and geosmin. In MS full scan mode, wastewater contaminants and other algal derived volatile organic compounds (ADVOCs) relevant to cyanobacterial bloom dynamics were detected and monitored in real source water samples. In the presence of known interferents with similar mass/charge fragments and elution times, the optimized method yielded low detection limits as well as exact molecular confirmation for taste and odor compounds in impacted source water samples. This method could be used as a tool to aid in the development of source water protection plans by identifying potential sources of anthropogenic and algal derived contamination in drinking water sources.

Detection of halogenated organics by their inhibitory action in a catalytic reaction between dimethyl acetylenedicarboxylate and 2-methyl-4-nitroaniline

The purpose of this paper is to report on the detection of toxic halogenated organic compounds in water using their inhibitory action on a pyridine-catalyzed reaction between dimethyl acetylenedicarboxylate (DMAD) and 2-methyl-4-nitroaniline (MNA). Previous work has shown that similar techniques can successfully lower the detection limit of sulfides and arsines in water samples, compared to their standard photometric detection methods. This paper highlights the optimization, selectivity, and sensitivity studies of the proposed sensing scheme. Optimization shows that the pyridine-catalyzed reaction is more favorable at 4 mM DMAD and 8 mM MNA. It was also determined that the inhibitory effect of halogenated organic compounds is more pronounced when carried out at 60°C. Using optimized reaction conditions, the limit of quantification for the four regulated trihalomethanes (THMs) was approximately 80 ppm. In addition, the sensing method is selective to THMs and a few other halogenated organics. These promising results demonstrate the further success of this technique for sensitive, selective detection, and future work will be carried out to incorporate the technique in sensing applications for THMs in drinking water.

Formation of DBPs and halogen-specific TOX in the presence of iopamidol and chlorinated oxidants

Iopamidol is a known direct precursor to iodinated and chlorinated DBP formation; however, the influence of iopamidol on both iodo/chloro-DBP formation has yet to be fully investigated. This study investigated the effect of iopamidol on the formation and speciation of halogen-specific total organic halogen (TOX), as well as iodo/chloro-DBPs, in the presence of 3 source waters (SWs) from Northeast Ohio and chlorinated oxidants. Chlorination and chloramination of SWs were carried out at pH 6.5-9.0 and, different iopamidol and dissolved organic carbon (DOC) concentrations. Total organic iodine (TOI) loss was approximately equal (22-35%) regardless of SW. Total organic chlorine (TOCl) increased in all SWs and was substantially higher in the higher SUVA254 SWs. Iopamidol was a direct precursor to chloroform (CHCl3), trichloroacetic acid (TCAA), and dichloroiodomethane (CHCl2I) formation. While CHCl3 and TCAA exhibited different formation trends with varying iopamidol concentrations, CHCl2I increased with increasing iopamidol and DOC concentrations. Low concentrations of iodo-acids were detected without discernible trends. Total trihalomethanes (THMs), total haloacetic acids (HAAs), TOCl, and unknown TOCl (UTOCl) were correlated with fluorescence regional volumes and SUVA254. The yields of all these species showed a strong positive correlation with fulvic, humic, and combined humic and fulvic regions, as well as SUVA254. Iopamidol was then compared to the 3 SWs with respect to DBP yield. Although the SUVA254 of iopamidol was relatively high, it did not produce high yields of THMs and HAAs compared to the 3 SWs. However, chlorination of iopamidol did result in high yields of TOCl and UTOCl.

Development of an Enhanced Ozone-hydrogen Peroxide Advanced Oxidation Process

Advanced chemical oxidation processes (AOP’s), particularly processes using.ozone, involve a rapidly growing area of environmental research and applications. A need exists, however, for improvements to AOP’s to make them less costly and more effective. This paper evaluated the addition of a fixed bed of sand to the conventional H2O2-O3 process as a function of reactor configuration, pH, and sand type. The West Liberty sand consisting of the greatest concentrations of iron and manganese yielded the best results, showing 15% more phenol removal than Muscatine sand and 28% more removal than no sand (i.e. H2O2-O3). Phenol degradation product formation and disappearance rates in comparison to the direct ozonation and O3-H2O2 processes indicate metal-oxide sand surface-catalyzed H2O2 decomposition improves the conventional O3-H2O2 advanced oxidation process at pH 7. Analysis of results suggests the enhancement is a result of increased formation of essential oxygen radical intermediates (i.e. hydroxyl radical). Direct ozonation, however, was equally effective at phenol removal at pH 8.9 because the conjugate base of phenol (i.e. phenate ion) has a direct ozonation reaction rate constant six orders of magnitude greater than phenol.

Impact of chlorine exposure time on disinfection byproduct formation in the presence of iopamidol and natural organic matter during chloramination

Chloramines, in practice, are formed onsite by adding ammonia to chlorinated drinking water to achieve the required disinfection. While regulated disinfection byproducts (DBPs) are reduced during chloramine disinfection, other DBPs such as iodinated (iodo-) DBPs, that elicit greater toxicity are formed. The objective of this study was to investigate the impact of prechlorination time on the formation of both halogen-specific total organic halogen (TOX) and iodo/chlorinated (chloro-) DBPs during prechlorination/chloramination in source waters (SWs) containing iopamidol, an X-ray contrast medium. Barberton SW (BSW) and Cleveland SW (CSW) containing iopamidol were prechlorinated for 5-60 min and afterwards chloraminated for 72 hr with ammonium chloride. Chlorine contact time (CCT) did not significantly impact total organic iodine (TOI) concentrations after prechlorination or chloramination. Concentrations of total organic chlorine (TOCl) formed during prechlorination did not significantly change regardless of pH and prechlorination time, while TOCl appeared to decrease after 72 hr chloramination period. Dichloroiodomethane (CHCl2I) formation during prechlorination did not exhibit any significant trends as a function of pH or CCT, but after chloramination, significant increases were observed at pHs 6.5 and 7.5 with respect to CCT. Iodo-HAAs were not formed during prechlorination but were detected after chloramination. Significant quantities of chloroform (CHCl3) and trichloroacetic acid (TCAA) were formed during prechlorination but formation ceased upon ammonia addition. Therefore, prechlorination studies should measure TOX and DBP concentrations prior to ammonia addition to obtain data regarding the initial conditions.

Encapsulation of Nitrate Salts Using Vinylmethylpolysiloxane

The Department of Energy has an immediate need for multiple technologies to transport and dispose of low level mixed waste. Solidification/stabilization (S/S) processes offer one possible solution that encapsulates sludge and dry hazardous wastes in a low permeability solid form. The advantage of vinylmethylpolysiloxane over other organic solidification processes is its ability to cure at ambient temperature. This paper examined compressive strength, metal leaching, and void area measurements of vinylmethylpolysiloxane-encapsulated waste as a function of waste loading (28–48wt%) for three surrogate wastes having compositions similar to those found at national laboratories. Compressive strength was greater than 4,390 kPa for all but one sample (48 wt% waste load-High Chloride waste). Image analysis shows void area increases linearly with increasing waste load, attributed to an increasing total sample volume physically occupied by the waste. Leaching test results indicate metal specific behavior and waste composition effects on Toxicity Characteristic Leaching Procedure (TCLP) concentrations. Cadmium diffusion from the encapsulated waste is slow (leach index >10 at all waste loads). Cost comparison of vinylmethylpolysiloxane to cement shows that it could be an economical waste disposal alternative.