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Hydroxyl radical ( OH) production in sunlit natural waters is known to be an important factor in pollutant degradation and nutrient cycling, and various probes have been developed to study this species in aquatic systems. Many of these probes have limitations in sensitivity and/or selectivity for OH, leaving room for improvement. Terephthalate (TPA) is a known probe for OH that produces a fluorescent product, hydroxyterephthalate (hTPA), upon hydroxylation, but its suitability for studying photochemical OH production has not been fully tested. To that end, the photochemical behavior of TPA and hTPA was characterized. TPA and hTPA react with OH with rate constants of (4.4 +/- 0.1) x 10(9) M(-1) s(-1) and (6.3 +/- 0.1) x 10(9) M(-1) s(-1), respectively. They were found to react with singlet oxygen ((1)O(2)) with significantly lower rate constants of <<10(4) M(-1) s(-1) and (5.0 +/- 0.1) x 10(4) M(-1) s(-1), respectively, indicating that TPA is selective for OH versus(1)O(2). TPA did not undergo direct photolysis, while hTPA was shown to undergo direct photochemical degradation with a Phi(direct,365nm) of (6.3 +/- 0.1) x 10(-3). TPA was applied to monitoring photochemical OH production by nitrate, nitrite and dissolved organic matter (DOM), and OH quenching rate constants measured for DOM were similar to results from previous studies. TPA provides a stable and sensitive probe for OH under significantly shorter photo-exposure times than similarly structured probe molecules, such as benzoate. However, the photoinstability of the analyte, hTPA, makes TPA an unsuitable probe for the study of photochemical systems under ultraviolet irradiation with wavelengths shorter than 360 nm.

N,N-Dimethylsulfamide (DMS), a newly identified, ubiquitous degradation product of the fungicide tolylfluanide, has been shown to be a N-nitrosodimethylamine (NDMA) precursor during ozonation. In this study, batch ozonation experiments in ultrapure buffered water, surface water, and tap water were performed to determine the kinetics and elucidate the mechanism of NDMA formation from DMS. It was found that at circumneutral pH, DMS reacts slowly with ozone (k approximately 20 M(-1) s(-1)) and moderately with hydroxyl radicals (k=1.5x10(9) M(-1)s(-1)). The reaction of DMS with these oxidants does not lead to NDMA. NDMA was only formed if bromide was present during ozonation of DMS-containing waters. Bromide is oxidized to hypobromous acid (HOBr) by ozone which then reacts with the primary amine of DMS to form a Br-DMS species. The rate limiting step of the formation of Br-DMS is the formation of HOBr. The reaction to form Br-DMS has an apparent second order rate constant at pH 8 of >3x10(4) M(-1)s(-1). The Br-DMS is transformed by ozone to NDMA and nitrate (k>or=5000 M(-1) s(-1)), with yields of 54% and 39%, respectively, based on the primary amine nitrogen of DMS. These reactions release bromide, making bromide a catalyst. NDMA is also formed during ozonation of DMS in the presence of hypochlorous acid (20-30% yield). The last step of NDMA formation is an intramolecular rearrangement with sulfur dioxide extrusion. On the basis of the mechanistic and kinetic information, it was possible to model NDMA formation in DMS-containing Lake Zurich water.

Triclosan, a widely used antimicrobial, is known to undergo phototransformation in aqueous solution to form 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD). Two sediment cores from a wastewater-impacted depositional zone of the Mississippi River were analyzed for triclosan by ultra performance liquid chromatography-triple quadrupole mass spectrometry (UPLC-MS-Q(3)) and for a suite of polychlorinated dioxins and furans by high resolution gas chromatography-mass spectrometry (HRGC-MS) to provide evidence of this photoreaction in the environment. 2,8-DCDD was detected at levels that trended with the historical use of triclosan since its introduction in the 1960s. Three other dioxin congeners, 2,3,7-TCDD, 1,2,8-TriCDD, and 1,2,3,8-TCDD, which are known photoproducts of chlorinated derivatives of triclosan, were also detected with similar trend profiles. These four congeners comprised the majority of di- through tetra-chlorinated dioxins. The trend profile of these specific dioxin congeners did not correlate with the trend profile of the higher-chlorinated dioxin homologues or any chlorinated furan homologues, suggesting a unique source. These results are fully consistent with the phototransformation of triclosan and its chlorinated derivatives that form during wastewater chlorine disinfection as the source of 2,8-DCDD, 2,3,7-TriCDD, 1,2,8-TriCDD, and 1,2,3,8-TCDD in this aquatic environment. As the levels of triclosan-derived dioxins increased over time and the total level of chlorinated dioxins decreased, the contribution of triclosan-derived dioxins to the total dioxin pool increased to as high as 31% by mass in recent years, indicating that their contribution to total dioxin toxicity may need consideration.

Background: Multiple trials have documented that myocardial blush grade (MBG) after primary percutaneous coronary intervention (PCI) for ST-elevation myocardial infarction (STEMI) has prognostic value for long-term clinical outcome. However, to the best of our knowledge, no study has determined the clinical use of MBG in routine clinical practice. We determined the prognostic value of MBG scored by the operator during primary PCI in consecutive patients with STEMI., Methods and Results: The prognostic value of MBG scored by the operator in relation to 1-year all cause mortality was evaluated in all patients with STEMI who underwent primary PCI between January 2004 and July 2008 in our hospital. The incidence of MBG 0, 1, 2, and 3 was 12%, 14%, 36%, and 38%, respectively, in 2118 consecutive patients with STEMI. Follow-up of all 2118 patients showed a 1-year all cause mortality rate of 8% (168 of 2118): 24%, 10%, 6%, and 4%, respectively, among patients with MBG 0, 1, 2, and 3 (P<0.001). In the 1763 patients with Thrombolysis in Myocardial Infarction (TIMI) flow grade 3 after PCI, these mortality rates were 17%, 10%, 6%, and 4%, respectively (P<0.001). MBG scored by the operator was a strong independent predictor of 1-year all cause mortality corrected for other well-known predictive variables, including TIMI flow grade., Conclusions: MBG scored by the operator during primary PCI has prognostic value for 1-year all cause mortality in patients with STEMI in routine clinical practice. Therefore, the MBG should be documented, in addition to the TIMI flow grade, during primary PCI in patients with STEMI in standard PCI reports in routine clinical practice.

A network of in situ sensors and nutrient analyzers was deployed to measure nitrate, specific conductance (surrogate for chloride), and turbidity (surrogate for total suspended solids (TSS)) for 28 days in two urban streams near Minneapolis, MN. The primary objectives of the study were: (1) to determine the accuracy associated with quantifying pollutant loading using periodic discrete (i.e., grab) samples in comparison to in situ near real-time monitoring and (2) to identify pollutant sources. Within a highly impervious drainage area (>35%) the majority of pollutant load (>90% for nitrate, chloride, and TSS) was observed to be discharged in a small percentage of time (<20%). Consequently, periodic sampling is prone to underestimate pollutant loads. Additionally, when compared to loads based on near real-time sampling, average errors of 19-200% were associated with sampling 1-2 times a month. There are also limitations of periodic sampling with respect to pollutant source determination. Resulting implications with regard to total maximum daily load (TMDL) assessments are discussed.

Breakthrough across high-density polyethylene (HDPE) was measured for 2,3',4',5-tetrachlorobiphenyl and a higher-solubility surrogate, 1,2,4-trichlorobenzene. Addition of powdered activated carbon (0.14 g carbon/cm(3) membrane) reduced pseudo-steady-state flux through thin HDPE membranes by approximately 60%. Breakthrough curves for activated carbon-containing membranes were best described by a model in which sorption to the carbon was limited by the rate of diffusion from the bulk membrane to the carbon particle surfaces. Field-scale estimates based on this model show a substantial (over 10 orders of magnitude) reduction in flux for the activated carbon-containing HDPE compared with pure HDPE. The flux of 2,3',4',5-tetrachlorobiphenyl through a composite membrane with thin layers of poly(vinyl alcohol) (PVA) with 0.05 g carbon/cm(3) and pure HDPE was 69% lower than expected for a similar layered membrane without the sorptive scavenger. This flux reduction was achieved with less than a third of the carbon used in the HDPE case, an improvement that is likely the result of better solute uptake in the hydrophilic PVA layer.

Triclosan (TCS; 5-chloro-2-(2,4-dichlorophenoxy)phenol), a common antimicrobial agent, may react with residual chlorine in tap water during transport to wastewater treatment plants or during chlorine disinfection of wastewater, generating chlorinated TCS derivatives (CTDs): 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol (4-Cl-TCS), 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol (6-Cl-TCS), and 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol (4,6-Cl-TCS). The photochemistry of CTDs was investigated due to the potential formation of polychlorodibenzo-p-dioxin (PCDD) photoproducts. Photolysis rates were highly dependent upon CTD speciation, because the phenolate species degraded 44 to 586 times faster than the phenol forms. Photolysis quantum yield values for TCS, 4-Cl-TCS, 6-Cl-TCS, and 4,6-Cl-TCS of 0.39, 0.07, 0.29, and 0.05, respectively, were determined for the phenolate species. Photolyses performed in Mississippi River and Lake Josephine (USA) waters gave similar quantum yields as buffered, pure water at the same pH, indicating that indirect photolysis processes involving photosensitization of dissolved organic matter are not competitive with direct photolysis. The photochemical conversion of the three CTDs to PCDDs under solar irradiation was confirmed in natural and buffered, pure water at yields of 0.5 to 2.5%. The CTD-derived PCDDs possess higher toxicities than 2,8-dichlorodibenzo-p-dioxin, a previously identified photoproduct of TCS, due to their higher chlorine substitution in the lateral positions. The load of TCS- and CTD-derived PCDDs to United States surface waters is estimated to be between 46 and 92 g toxicity equivalent units per year. Other identified photoproducts of each CTD were 2,4-dichlorophenol and reductive dechlorination products.

Chlortetracycline, an antibiotic commonly used as a growth promoter in livestock, enters the environment primarily through application of animal waste to open fields. The photochemical loss of chlortetracycline in sunlight-exposed soils is a potentially important process in its environmental fate, especially because it is photochemically labile and sorbs strongly to mineral surfaces. In this study, photolysis on kaolinite clay under simulated sunlight was used as a model system to elucidate the mechanistic kinetics of chlortetracycline photolysis on soil surfaces. The results suggest that photolysis may be an important loss process for chlortetracycline sorbed to sunlight-exposed soils, as well as to suspended clays in surface waters. Under direct irradiation equivalent to noon-time, summer sunlight in the midwestern United States, chlortetracycline at the outer clay surface (before light attenuation) degraded with a rate constant of k(0)(p) = 0.65 +/- 0.30 h(-1). The depth at which photochemical action was reduced by 50% (z(0.5)), one of the parameters of the mechanistic model, was found to be 0.014 +/- 0.004 mm. The quantum yield on the clay surface was estimated to be (1.3 +/- 0.7) x 10(-4), an order of magnitude lower than the quantum yield of the aqueous chlortetracycline zwitterion [(1.3 +/- 0.3) x 10(-3); pH 5], although still significant.

The potential photochemical formation of polybrominated and mixed halogenated dibenzo-p-dioxins (PBDDs and PXDDs) from hydroxylated polybrominated and polybrominated/ chlorinated diphenyl ethers (OH-PBDEs and OH-PBCDEs) in aqueous solution was studied. The ortho-hydroxylated BDE47 derivative 6-OH-BDE47, and chlorinated derivatives 3-Cl-6-OH-BDE47, 5-Cl-6-OH-BDE47, and 3,5-Cl-6-OH-BDE47 were photolyzed under sunlight at 45 degrees N latitude in buffered waters, Mississippi River water, Lake Josephine water, and ultrapure water adjusted to the pH of the natural waters. Chemical actinometry was used to determine reactant quantum yields which were calculated to be between 0.03 and 0.21, with lower yields for the chlorinated derivatives under all conditions. Quantum yields under natural water conditions were not significantly enhanced indicating that direct photolysis is the primary process of photochemical degradation. The formation of halogenated dioxins from the outdoor photolysis of the four OH-PBDEs/OH-PBCDEs under all conditions was confirmed. Dioxin yields of 0.7-3.6% were found, with higher yields for 6-OH-BDE47 under all conditions. This study suggests that photolysis of OH-PBDEs and OH-PBCDEs is a potential formation pathway of PBDDs and PXDDs in the environment.

Compound-specific nitrogen isotope analysis was shown to be a promising tool for the quantitative assessment of abiotic reduction of nitroaromatic contaminants (NACs) under anoxic conditions. To assess the magnitude and variability of 15N fractionation for reactions with dissolved reductants, we investigated the reduction of a series of NACs with a model quinone (anthrahydroquinone-2,6-disulfonate monophenolate; AHQDS-) and a Fe(II)-catechol complex (1:2 Fe(II)-tiron complex; Fe(II)L2(6-)) over the pH range from 3 to 12 and variable reductant concentrations. Apparent kinetic isotope effects, AKIEN, for the reduction of four mononitroaromatic compounds by AHQDS- ranged from 1.039 +/- 0.003 to 1.045 +/- 0.002 (average +/- 1sigma), consistent with previous results for various mineral-bound reductants. 15N fractionation for reduction of 1,2-dinitrobenzene and 2,4,6-trinitrotoluene by AHQDS- and that of 4-chloronitrobenzene by Fe(II)L2(6-), however, showed substantial variability in AKIEN-values which decreased from 1.043 to 1.010 with increasing pH. We hypothesize that the isotope-sensitive and rate-limiting step of the overall NAC reduction can shift from the dehydration of substituted N,N-dihydroxyanilines (large 15N fractionation upon N-O bond cleavage) to protonation or reduction of nitroaromatic radical anions (small 15N isotope effect upon electron transfer) consistent with calculations of semiclassical 15N isotope effects. Our results imply that a quantitative assessment of NAC reduction using compound-specific isotope analysis (CSIA) might need to account for homogeneous and heterogeneous reactions separately.

Compound-specific isotope analysis was used to monitor the delta(13)C signature of chloroform produced upon the chlorination of model compounds representing natural organic matter functional groups (resorcinol, acetylacetone, acetophenone, phenol, and 2,4,6-trichlorophenol) and a natural water sample. For each model compound, a different apparent kinetic isotope effect was found for chloroform formation. Normal isotope effects were found for resorcinol, acetylacetone, and acetophenone, and ranged from 1.009 +/- 0.002 to 1.024 +/- 0.004. For the two phenols, an inverse effect was found (0.980 +/- 0.004). Lake Zürich water also had a inverse effect (0.997 +/- < 0.001) indicating that phenols are likely chloroform precursors in NOM, but that other functional groups may also participate. The apparent 13C kinetic isotope effect for the addition/ elimination reaction of 1,1,1-trichloropropanone mediated by OH- to yield chloroform is 1.014 +/- 0.002. A comparison of this value to those found for the chlorination of the model precursors and an evaluation of the differences in chloroform production kinetics for the different model precursors argue against a mechanism in which all NOM precursors react via a common intermediate. Compound specific isotope analysis may give additional insights into chloroform formation mechanisms beyond those allowed by current techniques.

Halogenated disinfection byproducts (DBPs) may undergo reduction reactions at the corroded pipe wall in drinking water distribution systems consisting of cast or ductile iron pipe. Iron pipe corrosion products were obtained from several locations within two drinking water distribution systems. Crystalline-phase composition of freeze-dried corrosion solids was analyzed using X-ray diffraction, and ferrous and ferric iron contents were determined via multiple extraction methods. Batch experiments demonstrated that trichloronitromethane (TCNM), a non-regulated DBP, is rapidly reduced in the presence of pipe corrosion solids and that dissolved oxygen (DO) slows the reaction. The water-soluble iron content of the pipe solids is the best predictor of TCNM reaction rate constant. These results indicate that highly reactive DBPs that are able to compete with oxygen and residual disinfectant for ferrous iron may be attenuated via abiotic reduction in drinking water distribution systems.

Compound-specific analysis of nitrogen isotope fractionation is an important tool for assessing transformation pathways of N-containing organic contaminants. We investigated 15N-fractionation during the abiotic reduction of a series of nitroaromatic compounds (NACs) with intrinsic reactivities covering almost 6 orders of magnitude to evaluate substituent effects on 15N kinetic isotope effects, KIEN. Insights into reaction mechanisms and isotopic elementary reactions of NAC reduction were obtained from comparison of experimental results to density-functional theory (DFT) calculations of intrinsic KIEN. Apparent KIEN values for reduction of NACs by structural Fe(II) in octahedral layers of an iron-rich clay mineral were substantial (average +la of 1.038 +/- 0.003), independent of the NACs' reactivity and ring substituent, and larger than reported previously for reduction by Fe(II) species bound to Fe(III)(oxy)hydroxides and mercaptojuglone species (1.031 +/- 0.002). DFT-calculations accounting for semiclassical contributions and quantum-mechanical tunneling yielded a KIEN for N-O bond cleavage between 1.031 and 1.041, showed no substituent effect, and thus agreed well with experimental observations. Calculated transition-state structures of NAC reduction intermediates were consistent with H2O elimination from substituted N,N-dihydroxyanilines as the predominant 15N-fractionating elementary reaction. The absence of substituent effects on the apparent KIEN of NAC reduction may simplify the practical application of 15N-fractionation data for the quantification of contaminant transformation in the environment.

Many pharmaceuticals and personal care products (PPCPs) resist degradation in wastewater treatment plants. Thus, they may be transformed by chemical disinfectants in the final treatment stage, generating products that may possess enhanced toxicity/biological activity relative to the parent compounds. For this reason, the reaction of cimetidine, an over-the-counter antacid, with the frequently used disinfectant, free chlorine, was investigated. Cimetidine degraded rapidly in the presence of excess free chlorine, indicating that it will likely undergo significant transformation during wastewater disinfection. Four major products were isolated and extensively characterized by comparison of liquid chromatographic retention times to known standards, mass spectrometry, 1H- and 2D-nuclear magnetic resonance spectroscopy, and infrared spectroscopy. An expected sulfur oxidation product, cimetidine sulfoxide, was identified along with three unexpected products: 4-hydroxymethyl-5-methyl-1H-imidazole, 4-chloro-5-methyl-1H-imidazole, and a product proposed to be either a beta- or delta-sultam. The last three products are formed by transformations not frequently observed in free chlorine reactions of PPCPs such as C-C bond cleavage and intramolecular nucleophilic substitution. The unexpected transformations yielded compounds with more substantial structural changes than would be observed in common free chlorine reactions such as N-chlorination or electrophilic halogenation. The reaction pathway was elucidated by kinetic analysis and by independently treating isolated intermediates with free chlorine, and reaction mechanisms were proposed. Finally, the predicted no-effect concentration (PNEC) of the chlorination products was estimated, and the products 4-hydroxymethyl-5-methyl-1H-imidazole and 4-chloro-5-methyl-1H-imidazole were estimated to have lower PNECs than cimetidine.

The environmental photochemical kinetics of tylosin, a common veterinary macrolide antibiotic and growth promoter, were investigated under simulated sunlight. An efficient, reversible photoisomerization was characterized using kinetic, mass spectrometry, and proton nuclear magnetic resonance data. The photoisomerization was confirmed to occur by a rotation about the distal alkene of the ketodiene functionality. Concurrent forward (quantum yield = 0.39 +/- 0.09) and back (quantum yield = 0.32 +/- 0.08) reactions lead to a photochemical equilibrium near a tylosin/photoisomer ratio of 50:50, completed in less than 2 min under a spectrum equivalent to noontime, summer sunlight. The activity of the isomer for the inhibition of Escherichia coli DH5alpha growth was observed to be less than that of tylosin. On a longer time scale than that of isomerization, the isomer mixture undergoes photolysis with a quantum yield of (1.4 +/- 0.3) x 10(-3). The observed quantum yields and UV-vis absorbance data allow for the prediction of the photochemical behavior of tylosin in most environmental systems. Indirect photosensitization was not a significant loss process in solutions of Suwannee River fulvic acid with concentrations from 1 to 20 mg L(-1).

Disinfection byproducts (DBPs) in drinking water flowing through corroded iron or steel pipes may encounter carbonate green rust (GR(CO32-)), a mixed Fe(II)/Fe(lll) hydroxide mineral and potent reductant. This research was performed to investigate the kinetics and pathways of the degradation of selected halogenated DBPs in the presence of GR(C032-). Trichloronitromethane was rapidly degraded to methylamine via sequential hydrogenolysis followed by nitro-reduction. Haloacetic acids reacted solely via sequential hydrogenolysis. Trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldehyde hydrate were transformed via hydrolysis and hydrogenolysis. Chloroform was unreactive over 300 h. The buffer identity affected reductive dehalogenation rates of DBPs, with faster rates in MOPS buffer than in carbonate buffer, the latter being representative of the buffer in drinking water systems. GR(CO32-) was unstable in both buffers and transformed to magnetite within 48 h. Thus, slower reacting compounds (half life >3 hours) were transformed by a combination of minerals. Reductive dehalogenation kinetics were influenced by DBP chemical structure and correlated with one-electron reduction potential.

Iron metal (Fe(0)) is a potent reductant capable of reducing a wide variety of halogenated organic compounds including disinfection byproducts (DBPs). These reduction reactions may play a role in DBP fate in iron water mains and potentially could be exploited to remove DBPs from drinking water or wastewater in a packed-bed configuration. Oxidants (i.e., dissolved oxygen (DO) and chlorine) present in the water, however, may decrease the DBP degradation rate by competing for reactive sites and rapidly aging or corroding the iron surface. Thus, batch experiments were performed to investigate the effect of DO on the degradation rates of selected DBPs by Fe(0). Experiments were performed under anaerobic conditions, in initially oxygen saturated buffer without DO control, and under controlled DO (approximately 4.0 or 8.0 mg l(-1)) conditions. The effect of short-term (25-105 min) iron aging in DO-containing buffer on DBP degradation rate also was investigated in separate experiments. For fresh Fe(0), the degradation rates of trichloronitromethane (TCNM) and trichloroacetonitrile (TCAN) in initially oxygen saturated buffer were similar to their respective rates under anaerobic conditions. The degradation rate of 1,1,1-trichloropropanone (1,1,1-TCP), however, decreased significantly in the presence of DO and the effect was proportional to DO concentration in the controlled DO experiments. For a DO concentration of 4 mg l(-1), the degradation rate of the three DBPs was greater for longer aging times as compared to their respective rates after 25 min, suggesting the formation of a mineral phase that increased reactivity. For a DO concentration of 8 mg l(-1), the effects of increasing aging time were mixed. TCNM degradation rates were stable for all aging times and comparable to that under anaerobic conditions. The TCAN and 1,1,1-TCP degradation rates, however, tended to decrease with increasing aging time. These results suggest that the reduction of highly reactive DBPs by Fe(0) will not be affected by the presence of DO but that the reaction rates will be slowed by DO for DBPs with slower degradation kinetics.

The environmental photochemical kinetics of the antibiotic compound tetracycline were investigated. The aqueous speciation of tetracycline over a range of natural pH and water hardness values is dominated by association with Ca2+ and Mg2+ ions. The association constants necessary to calculate tetracycline aqueous speciation given knowledge of pH, [Ca2+], and [Mg2+] were measured by spectrophotometric titrations and matrix deconvolution of a series of UV-vis absorption spectra into individual component species. A series of photolysis experiments was performed under simulated sunlight, and quantum yields for the solar photolysis of each environmentally relevant species were calculated. The results indicate that the pseudo-first-order rate constant for tetracycline photolysis at varied Mg2+ and Ca2+ concentrations relevant to natural conditions can vary by up to an order of magnitude. A self-sensitization effect was observed and was accounted for by varying the initial tetracycline concentration under each set of photolysis conditions.

The aquatic photochemical degradation of a class of pharmaceuticals known as the nitrofuran antibiotics (furaltadone, furazolidone, and nitrofurantoin) was investigated. Direct photolysis is the dominant photodegradation pathway for these compounds with the formation of a photostationary state between the syn and the anti isomers occurring during the first minutes of photolysis. The direct photolysis rate constant and quantum yield were calculated for each of the three nitrofurans. Reaction rate constants with reactive oxygen species (ROS), 102 and *OH, were also measured, and half-lives were calculated using environmentally relevant ROS concentrations. Half-lives calculated for reaction with 1O2 and *OH are in the ranges of 120-1900 and 74-82 h, respectively. When compared to the direct photolysis half-lives, 0.080-0.44 h in mid-summer at 45 degrees N latitude, it is clear that indirect photochemical processes cannot compete with direct photolysis. The major photodegradation product of the nitrofurans was found to be nitrofuraldehyde, which is also photolabile. Upon photolysis, nitrofuraldehyde produces NO, which is easily oxidized to nitrous acid. The acid produced further catalyzes the photodegradation of the parent nitrofuran antibiotics, leading to autocatalytic behavior. Natural waters were found to buffer the acid formation.

Cross-correlations of rate constants between a system of interest and a better-defined one have become popular as a tool in studying transformations of organic pollutants. A slope of unity (if the correlation is conducted on a log-log basis) in such plots has been invoked as evidence of a common mechanism. To explore this notion, benzotrichloride and several of its substituted analogues were reacted with Cr(H2O)6(2+), an iron(II) porphyrin (iron meso-tetra(4-carboxyphenyl)porphine chloride, Fe(II)TCP), and granular iron. The first two reductants react with organohalides by dissociative inner sphere single-electron transfer, while mechanism(s) for organohalide reduction by granular iron are still debated. Apartfrom sterically hindered compounds, good correlations were obtained in comparing any two systems, although slopes (on a log-log basis) deviated from unity. We argue that a slope of unity is neither necessary nor sufficient evidence of a common mechanism. Overall rate constants may be composite entities, consisting in part of rate or equilibrium constants for adsorption onto surfaces or for precursor formation in solution; these components may differ between systems in their susceptibility to substituent effects. Cross-correlations may prove useful in predicting reactivity in the absence of steric effects, but additional evidence is required in deducing reaction mechanisms.

Sulfa drugs and triclosan represent two classes of antibacterials that have been found in natural waters and for which photodegradation is anticipated to be a significant loss process. Parent antibacterial compounds and the products of photolysis reactions were compared for three sulfa drugs and triclosan to determine the extent to which photolysis affects their antibacterial potency on Escherichia coli DH5alpha. Sulfathiazole (median effective concentration [EC50] = 20.0 microM), sulfamethoxazole (EC50 = 12.3 microM), and sulfachloropyridazine (EC50 = 6.9 microM) inhibited bacterial growth but did not affect respiratory activity. Photolysis products of these sulfa drugs did not retain any measurable ability to inhibit growth. Triclosan inhibited both the growth (EC50 = 0.24 microM) and respiratory activity of E. coli DH5alpha. Triclosan photolysis products also exhibited no measurable effect on growth or respiratory activity. These experiments indicate that the products of triclosan and sulfa drug photolysis are unlikely to possess antibacterial activity in natural waters. The rapid screening method used for these two classes of compounds will be useful for helping to identify photolabile antibacterial compounds, for which photoproducts could require further investigation.

Reactions mediated by iron mineral surfaces play an important role in the fate of organic contaminants in both natural and engineered systems. As such reactions proceed, the size, morphology, and even the phase of iron oxide minerals can change, leading to altered reactivity. The reductive degradation of 4-chloronitrobenzene and trichloronitromethane by Fe(II) associated with goethite (alpha-FeOOH) was examined by performing sequential-spike batch experiments. The particle size and size distribution of the pre- and postreaction particles were quantified using transmission electron microscopy (TEM). Results demonstrate that the degradation reactions result in goethite growth in the c-direction. Furthermore, pseudo-first-order reaction rate constants for the degradation of 4-chloronitrobenzene and trichloronitromethane and for the loss of aqueous Fe(II) decrease dramatically with each subsequent injection of organic compound and Fe(II). This result indicates that the newly formed material, which TEM and X-ray diffraction results confirm is goethite, is progressively less reactive than the original goethite. These results represent an important step toward elucidating the link between mineral surface changes and the evolving kinetics of contaminant degradation at the mineral-water interface.

In diaphragm cell experiments, a permeable model reactive barrier for the containment of cesium is tested. Primary targets for cesium containment are former plutonium processing sites (e.g., Hanford, WA and Savannah River, SC), which are currently contaminated with cesium-137. Adding up to 10 wt % crystalline silicotitanate, a sacrificial reagent, to poly(vinyl alcohol) films increases the time before cesium can cross the film by a factor of 30. The increased lag times are consistent with theories developed for this type of reactive membrane. Theory also correctly predicts the effects of cesium concentration and membrane thickness on membrane performance. Because the relative improvements of the model barrier are expected to be independent of the polymer used, these increased lags should hold for less permeable polymers that are more resistant to radiation, although these polymers have not been tested.

Halonitromethanes (HNMs) are a class of halogenated disinfection byproducts formed upon the addition of chlorine to water containing organic matter. Batch experiments were performed to investigate the reaction pathways and kinetics of three HNMs (chloropicrin or trichloronitromethane [TCNM], dichloronitromethane [DCNM], and chloronitromethane [CNM]) with zero-valent iron (Fe0). All three compounds reacted rapidly in the presence of Fe0 (1.8-4.4 g/L) with methylamine (MA) as the final product. The geometric surface area-normalized rate constants decreased with decreasing halogenation: TCNM (301 L/[h-m2]) > DCNM (153 L/(h-m2)) > CNM (45.9 L/[h-m2]). Nitromethane, an intermediate species, rapidly reacted to form MA (302 L/[h-m2]). These reactions all experienced some degree of mass transfer limitation (9-73%). The average carbon and chlorine mass balances for TCNM were >85%, indicating that the major reaction products were recovered. The degradation of TCNM and DCNM proceeded via the parallel reaction pathways of hydrogenolysis and alpha-elimination. For TCNM, 60.7 +/- 8.7% of reaction proceeded via hydrogenolysis and 39.3 +/- 6.4% via alpha-elimination. Knowledge of HNM reaction pathways and kinetics in the presence of Fe0 may be useful for predicting the fate of these compounds in drinking water distribution systems containing cast or ductile iron pipe and for developing treatment systems for HNM removal from water.

Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface. Fe(II), a potent reductant when associated with iron oxide surfaces, can mediate the reduction of halogenated organic compounds. Batch experiments were performed to investigate the kinetics and pathways of the degradation of selected chlorinated disinfection byproducts (OBPs) by Fe(II) in the presence of synthetic goethite and magnetite. Trichloronitromethane was degraded via reduction, while trichloroacetonitrile, 1,1,1-trichloropropanone, and trichloroacetaldyde hydrate were transformed via both hydrolysis and reduction. Chloroform and trichloroacetic acid were unreactive. Observed pseudo-first-order reductive dehalogenation rates were influenced by DBP chemical structure and identity of the reductant. Fe(II) bound to iron minerals had greater reactivity than either aqueous Fe(II) or structural Fe(II) present in magnetite. For DBPs of structure Cl3C-R, reductive dehalogenation rate constants normalized by the surface density of Fe(II) on both goethite and magnetite correlated with the electronegativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1-trichloropropanone.

The aquatic photochemical behavior of a class of sulfa drugs containing six-membered heterocyclic substituents (sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine, and sulfadimethoxine) was investigated. Photodegradation of the sulfa drugs in a natural water sample was significantly enhanced relative to the degradation in deionized water, with the exception of sulfadimethoxine. This indicated an indirect photochemical process that was identified through the use of quenchers to be attributable to interaction with triplet excited-state dissolved organic matter (3DOM). The direct photolysis rate constant and quantum yield for both the neutral and anionic species of each sulfa drug were calculated using matrix deconvolution methods. The quantum yield values range from 0.01 x 10(-3) for the neutral form of sulfadimethoxine to 5 x 10(-3) for the anionic form of sulfamethazine and are significantly lower than those observed in a previous study for sulfa drugs containing five-membered heterocyclic substituents, although the rate constants are of similar magnitude. The primary product formed in both direct and indirect photodegradation for all five compounds was identified as a sulfur dioxide extrusion product. The predicted environmental half-lives solely attributable to direct photolysis range from 8.6 h in midsummer at 30 degrees latitude in pH 7 surface water for sulfachloropyridazine to 420 h in midwinter at 45 degrees in pH 7 surface water for sulfadimethoxine. These half-lives, except for sulfadimethoxine, will be decreased by interaction with 3DOM.

The photochemical fate of the antimicrobial agent triclosan is presented. Experiments performed in both natural and buffered deionized water show that triclosan rapidly photodegrades by direct photolysis (t(1/2) = 5 h, pH 8, noon summer sunlight, 45 degrees N latitude). Both 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) and 2,4-dichlorophenol (2,4-DCP) are produced. The 2,8-DCDD and 2,4-DCP also are photolabile and, thus, are intermediates. The yields for 2,8-DCDD and 2,4-DCP ranged from 3 to 12% depending on the conditions employed. When triclosan is photolyzed in the presence of Suwannee River (GA, USA) fulvic acid, a portion of the initial mass is recovered as insoluble material. Based on experiments in which the formation of insoluble material was monitored with photolysis time, it is postulated that photolysis in natural waters leads to some of the triclosan being coupled to humic matter. Triclosan also reacts rapidly with both singlet oxygen (k(rxn) = 1.07 +/- 0.03 x 10(8) M(-1) s(-1) in water of pH 10) and hydroxyl radical (k(*OH) = 5.4 +/- 0.3 X 10(9) M(-1)(s-1). Indirect photolysis pathways, however, are not expected to be important because of low steady-state concentrations of reactive oxygen species in natural waters and the efficiency of the direct photolysis of triclosan.

Pharmaceuticals and personal care products are an emerging class of environmental pollutants. Photolysis is expected to be a major loss process for many of these compounds in surface waters, including the common non-steroidal anti-inflammatory drug mefenamic acid. The direct photolysis solar quantum yield of mefenamic acid was observed to be 1.5+/-0.3x10(-4). Significant photosensitization was observed in solutions of Suwanee River fulvic acid and Mississippi River water, as well as for the model photosensitization compounds 3'-methoxyacetophenone, 2-acetonaphthone and perinaphthenone. Quenching, sparging and light-filtering experiments suggested a direct reaction of mefenamic acid with excited triplet-state dissolved organic matter as the major photosensitization process. The persistence of the model photosensitizer suggests that the photosensitization by perinaphthenone occurs either by triplet-energy transfer or an electron transfer followed by rapid regeneration of the sensitizer. Due to its low quantum yield, the loss of mefenamic acid in sunlit natural waters is expected to depend on both direct and indirect photodegradation processes.

Detailed kinetic studies of the reactions of haloacetic acids (HAAs) with Fe(0) were performed in longitudinally mixed batch reactors. The reactions of tribromoacetic acid (TBAA), bromodichloroacetic acid, and chlorodibromoacetic acid were mass transfer limited, with corrected mass transfer coefficients of 3.7-3.9 x 10(-4) m/s. The reactions of trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), chloroacetic acid (CAA), and bromoacetic acid (BAA) were reaction limited. Bromochloroacetic acid (BCAA) and dibromoacetic acid (DBAA) were partially reaction limited. For the reaction limited species and partially reaction limited species, intra- and interspecies competition effects were observed. A Langmuir-Hinshelwood-Hougen-Watson kinetic model incorporating a mass transfer term was adopted to account for these effects. The lumped kinetic parameters for the HAAs ranged from 0.04 to 248 microM min(-1) for an iron loading of 0.3 g of Fe/125 mL and followed the trend DBAA > BCAA > TCAA > BAA > DCAA. The adsorption parameters ranged from 0.0007 to 0.0065 microM(-1). The effect of dissolved oxygen (DO) on the reaction of TBAA or BAA with Fe(0) was also investigated. No significant effect of DO on the reaction rate of TBAA, which is a mass transfer limited species, was observed. A lag phase, however, was observed for the reaction of BAA, which is a reaction limited species, until the DO was depleted. Simulations were performed to investigate the potential significance of the reactions of HAAs with Fe(0) in water distribution systems.

The photochemical fate of five sulfa drugs with varying five-membered heterocyclic substituents (sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, and sulfamoxole) was investigated in aqueous solution. The rate of direct photolysis of these compounds is dependent upon the identity of the heterocyclic R group as well as the pH of the solution. Matrix deconvolution methods were employed to determine the absorption spectrum and photolysis rate of each protonation state (cationic, neutral, and anionic). From these data, quantum yields for direct photodegradation were calculated for each protonation state of the sulfa drugs. The quantum yields calculated range from <0.005 for the neutral state of sulfamethizole to 0.7 +/- 0.3 for the protonated state of sulfisoxazole. The protonation state that is most photoreactive varies among the sulfa drugs and cannot be attributed to the rate of photon absorption. Products arising from the direct photolysis of the sulfa drugs were also investigated. For all the compounds, sulfanilic acid was observed as a common product. The singlet oxygen quenching rates of the sulfa drugs were determined by laser flash photolysis and range from (2 +/- 1) x 10(4) M(-1) s(-1) for sulfamethoxazole to (3.0 +/- 0.7) x 10(8) M(-1) s(-1) for sulfamoxole. Reaction of the sulfa drugs with hydroxyl radical is not modulated by the R group, and the rate constants are all near the bimolecular diffusion-controlled limit of 10(10) M(-1) s(-1). The photodegradation of the sulfa drugs in natural water samples of Lake Josephine (St. Paul, MN) and Lake Superior was attributed solely to direct photolysis. This study indicates thatthese similarly structured antibiotics will be subject to a wide range of photodegradation rates with sulfathiazole degrading relatively quickly, sulfisoxazole and sulfamethizole degrading moderately, and sulfamethoxazole degrading much more slowly.

A poly(vinyl alcohol) (PVA) membrane containing iron (Fe(0)) particles was developed and tested as a model barrier for contaminant containment. Carbon tetrachloride, copper (Cu2+), nitrobenzene, 4-nitroacetophenone, and chromate (Cr04(2-)) were selected as model contaminants. Compared with a pure PVA membrane, the Fe(0)/PVA membrane can increase the breakthrough lag time for Cu2+ and carbon tetrachloride by more than 100-fold. The increase in the lag time was smaller for nitrobenzene and 4-nitroacetophenone, which stoichiometrically require more iron and for which the PVA membrane has a higher permeability. The effect of Fe(0) was even smaller for CrO4(2-) because of its slow reaction. Forty-five percent of the iron, based on the content in the dry membrane prior to hydration, was consumed by reaction with Cu2+ and 15% by reaction with carbon tetrachloride. Similarly, 25%, 17%, and 6% of the iron was consumed by nitrobenzene, 4-nitroacetophenone, and CrO4(2-), respectively. These percentages approximately double when the loss of iron during membrane hydration is considered. The permeability of the Fe(0)/PVA membrane after breakthrough was within a factor of 3 for that of pure PVA, consistent with theory. These results suggest that polymer membranes with embedded Fe(0) have potential as practical contaminant barriers.

The importance of abiotic reductive transformations as a sink for four dinitroaniline herbicides (trifluralin, pendimethalin, nitralin, and isopropalin) has been evaluated. Using reductants representative of abiotic reductants found in natural systems, the results of this study indicate that nitro groups present on the dinitroaniline herbicides can be reduced by surface-bound Fe(II) species in goethite suspensions or by hydroquinone moieties such as (mercapto)juglone in a hydrogen sulfide solution. Aqueous iron species are also effective at pH values above 7.0. The reaction in aqueous Fe(II) and in Fe(II)/goethite systems is strongly pH dependent, with rates increasing with increasing pH. Montmorillonite clay, however, is not effective in mediating the reduction of dinitroaniline herbicides in the presence of Fe(II). Because the selected dinitroaniline herbicides have a mixture of electron withdrawing and electron donating groups, linear free energy relationships were developed for the H(2)S/(mercapto)juglone and Fe(II)/goethite systems. Anilines resulting from reduction of the nitro group as well as cyclization products (benzimidazoles) were observed in the degradation of trifluralin. Only one aniline product was observed for pendimethalin.

The photochemical fates of the histamine H2-receptor antagonists cimetidine and ranitidine were studied. Each of the two environmentally relevant pharmaceuticals displayed high rates of reaction with both singlet oxygen (1O2, O2(1delta(g))) and hydroxyl radical (*OH), two transient oxidants formed in sunlit natural waters. For cimetidine, the bimolecular rate constant for reaction with *OH in water is 6.5 +/- 0.5 x 10(9) M(-1) s(-1). Over the pH range 4-10, cimetidine reacts with 1O2 with bimolecular rate constants ranging from 3.3 +/- 0.3 x 10(6) M(-1) s(-1) at low pH to 2.5 +/- 0.2 x 10(8) M(-1) s(-1) in alkaline solutions. The bimolecular rate constants for ranitidine reacting with 1O2 in water ranges from 1.6 +/- 0.2 x 10(7) M(-1) s(-1) at pH 6-6.4 +/- 0.2 x 10(7) M(-1) s(-1) at pH 10. Reaction of ranitidine hydrochloride with *OH proceeds with a rate constant of 1.5 +/- 0.2 x 10(10) M(-1) s(-1). Ranitidine was also degraded in direct photolysis experiments with a half-life of 35 min under noon summertime sunlight at 45 degrees latitude, while cimetidine was shown to be resistant to direct photolysis. The results of these experiments, combined with the expected steady-state near surface concentrations of 1O2 and *OH, indicate that photooxidation mediated by 1O2 is the likely degradation pathway for cimetidine in most natural waters, and photodegradation by direct photolysis is expected to be the major pathway for ranitidine, with some degradation caused by 1O2. These predictions were verified in studies using Mississippi River water. Model compounds were analyzed by laser flash photolysis experiments to assess which functionalities within ranitidine and cimetidine are most susceptible to singlet-oxygenation and direct photolysis. The heterocyclic moieties of the pharmaceuticals were clearly implicated as the sites of reaction with 1O2, as evidenced by the high relative rate constants of the furan and imidazole models. The nitroacetamidine portion of ranitidine has been shown to be the moiety active in direct photolysis.

Products of the transformation of organic pollutants in the environment are often predicted based on the structure of the parent compounds. In some cases, however, multiple products may result from the same reaction pathway. In this study, the reduction of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) is investigated both experimentally and computationally. Experimental results and data available in the literature reveal that the ratio of Z-1,2-dichloroethylene (Z-DCE) to E-1,2-dichloroethylene (E-DCE) produced from the reductive beta-elimination of 1,1,2,2-TeCA is approximately 2:1, and this ratio is independent of the reductant used. The exception is iron metal, which results in a ratio of 4.5:1. Computational results reveal that the 1,2,2-trichloroethyl radicals (1,1,2-TCA*) formed upon the transfer of the first electron are nearly isoenergetic and are in rapid equilibrium. Thus, the conformer population of the 1,1,2,2-TeCA does not dictate the product distribution. Using Marcus theory, it is demonstrated that the Z:E ratio of 2:1 reflects the relative rates of the two possible electron transfer steps to the two radical conformers. Further analysis of the thermochemistry of the reaction reveals that this ratio of rate constants should be essentially independent of the thermodynamic driving force, which is consistent with the experimental results. The different observed product distribution when iron metal is the reductant is hypothesized to result from an organometallic intermediate. The reduction of the 1,1,2,2-TeCA is an overall two-electron process, but the fact that the radicals equilibrate at a rate more rapid than the transfer of the second electron suggests that reductants employed act as decoupled single electron-transfer agents.

To predict the fate of haloacetic acids (HAAs) in natural or engineered systems, information is needed concerning the types of reactions that these compounds undergo, the rates of those reactions, and the products that are formed. Given that many drinking water distribution systems consist of unlined cast iron pipe, reactions of HAAs with elemental iron (Fe0) may play a role in determining the fate of HAAs in these systems. In addition, zerovalent iron may prove to be an effective treatment technology for the removal of HAAs from chlorinated drinking water and wastewater. Thus, batch experiments were used to investigate reactions of four trihaloacetic acids, trichloroacetic acid (TCAA), tribromoacetic acid (TBAA), chlorodibromoacetic acid (CDBAA), and bromodichloroacetic acid (BDCAA), with Fe0. All compounds readily reacted with Fe0, and investigation of product formation and subsequent disappearance revealed that the reactions proceeded via sequential hydrogenolysis. Bromine was preferentially removed over chlorine, and TBAA was the only compound completely dehalogenated to acetic acid. In compounds containing chlorine, the final product of reactions with Fe0 was monochloroacetic acid. Halogen mass balances were 95-112%, and carbon mass balances were 62.6-112%. The pseudo-first-order rate constants for trihaloacetic acid degradation were as follows: BDCAA (10.6 +/- 3.1 h-1) > CDBAA (1.43 +/- 0.32 h-1) approximately TBAA (1.41 +/- 0.28 h-1) >> TCAA (0.08 +/- 0.02 h-1).

In this article, I have provided a brief history of my life. After tracing my family background and my early interest in physical sciences, I discuss how I entered biology under the influence of Robert Emerson. I have always enjoyed doing experiments and this led to new measurements and analyses of 'chlorophyll unit', efficiency of photosynthesis, excitation energy transfer, delayed light emission, thermoluminescence and electroluminescence in photosynthetic organisms. It is my view that discoveries are made because we follow our scientific curiosities.

An electrical field across a suspension of Chenopodium chloroplasts stimulates the emission of delayed light during the time the field is on. This stimulation can be used to calculate the distance over which the electron moves in the untrapping process that gives the delayed light. An electrical field applied at the time of illumination gives a polarization to the suspension of chloroplasts that lasts for some seconds. This polarization is a new way to study delayed light and fluorescence from chloroplasts.

Data obtained on yeast irradiated with monochromatic ultra-violet radiation has been analyzed for the number of quantum hits involved in the production of different degrees of inhibition of cell division, according to the method proposed by Mme. Curie (1929). Sufficient data are not available for a rigorous determination, but the calculated results tend to indicate that a multiple hit to kill relation is followed, that different numbers of hits are involved in the production of different degrees of inhibition, and that this number increases with increase in the degree of damage sustained.

1. The kinetics of the inactivation of photosynthesis by 2537 A in Chlorella pyrenoidosa and Scenedesmus D(1) indicate that, while the destruction process is largely a first order effect, higher order effects also occur, which become evident at low exposures. In agreement with previous observations, endogenous respiration is insensitive to exposures which inactivate photosynthesis. 2. In Scenedesmus D(1) a solid dose of ultraviolet has no more effect on the photosynthetic apparatus than a dose of equal total duration interrupted by periods of photosynthesis. Nor is any difference noted if the cells are in a different buffer, e.g. 0.05 M KH(2)PO(4), or carbonate-bicarbonate buffer 9. 3. In C. pyrenoidosa, a solid dose and an interrupted dose cause equal effects on photosynthesis when neutral phosphate buffer is used. If the ultraviolet exposure schedules are identical, equal effects are also noted in cells suspended in buffer 9, and in 0.05 M phosphate (pH 6.2). Solid exposures are, however, much more effective than interrupted exposures, when buffer 9 is used. 4. Oxygen evolution (Hill reaction), photosynthesis, and photoreduction in Scenedesmus D(1) are equally sensitive to a given dose of ultraviolet. The mechanism responsible for adaptation to hydrogen metabolism is not more sensitive to ultraviolet than is the photosynthetic mechanism. The O(2)/H(2)/CO(2) reaction in darkness is less sensitive to ultraviolet than any of the above reactions. 5. Glucose oxidation by C. pyrenoidosa, and colony formation in Scenedesmus D(1) are far more sensitive to a given dose of ultraviolet than photosynthesis in these organisms. 6. The photosynthetic apparatus of C. pyrenoidosa is more sensitive to ultraviolet than that of Scenedesmus D(1). 7. The Hill reaction in chloroplast fragments is also inactivated by 2537 A by a first order process. Exposures which inactivate this reaction completely have no effect on polyphenol oxidase, cytochrome oxidase, or catalase in the same chloroplast preparation. 8. After irradiation, the survival of photosynthesis in Scenedesmus D(1) and of the Hill reaction in chloroplast fragments are independent of the light intensity used to measure these processes. 9. No significant changes occur in the ultraviolet absorption of chloroplasts after an exposure to 2537 A, which completely inactivates the Hill reaction.