Photodegradation of sulfonamide antibiotics in simulated and natural sunlight: Implications for their environmental fate

The photochemical fate of seven sulfonamides was investigated in matrices representative of natural water bodies under various light sources. Fundamental photolysis parameters such as molar absorption coefficient, quantum yield (QY) and first-order rate constants were determined. The photolysis decay rate was dependent on the protonation state of the molecule, pH of the water sample and dissolved organic matter. Natural organic matter was the most significant factor in the indirect photolysis of sulfonamides. Half-lives were in the range of minutes at 254 nm to days under natural sunlight. Under natural sunlight, all sulfonamides showed higher removal rates in natural waters implying that indirect photolysis is the predominant mechanism.     

Influence of heavy organic pollutants of anthropic origin on PAH retention by kaolinite.

The adsorption of heavy fuel oil No. 2 (F2) on a reference kaolinite (Arvor kaolin, France), and the influence of this anthropic organic matter on the phenanthrene (PHEN) retention capacity of a kaolinite were investigated in the laboratory. The heaviest and most polar compounds of F2 are adsorbed on kaolinite preferentially to the other compounds and also partly irreversibly. The precoating of kaolinite by F2 significantly increases the sorption of PHEN in the range of concentrations studied (10-500 microg l(-1)). The partition coefficients normalized to organic carbon content (Koc) of kaolin precoated with fuel oil (5.2 < log Koc < 5.5) are one order of magnitude higher than those of the original kaolin (4.2 < logKoc < 4.5), and show very good agreement with the literature for polluted industrial soils. The Koc measured on the uncoated kaolin are in close agreement with the values determined for natural soils in which humic substances represent the organic component. This demonstrates that the composition of organic matter is the primary factor in PHEN retention by the soils. Therefore, in predicting the transport of PHEN, and other Polycyclic aromatic hydrocarbons (PAHs) in general, in soils of industrial sites containing heavy hydrocarbons or tars requires that the specific nature of the organic matter contained in these soils be taken into consideration.     

Light-induced transformations of aza-aromatic pollutants adsorbed on models of atmospheric particulate matter: Acridine and 9(10-H) acridone

The effect of the characteristics of the surface on the phototransformation of acridine, one of the most abundant azapolycyclic compounds encountered in urban atmospheres, and of one of its principal photoproducts, acridone, was studied when adsorbed onto models of the atmospherice particulate matter. For this purpose, relative photodegradation rates were determined from absorption or emission intensities as a function of irradiation times, and some products were isolated and characterized. The relative photodegradation rates of adsorbed acridine show the tendency (NH(4))(2) SO(4) > MgO > Al(2)O(3) >SiO(2). In general, the rates decrease as the fraction of protonated acridine species on the surface increases in MgO, Al(2)O(3), and SiO(2), except for (NH(4))(2) SO(4) where a fast surface reaction occurs. Oxygen reduces the photodestruction rates by as much as 40 to 60% when compared to an inert atmosphere, implying the participation of an acrideine triplet state in the transformation processes on all surfaces except on (NH(4))(2)SO(4). Acridone, a major product, undergoes a photoinduced tautomerization to 9-hydroxy acridine. The formation of a dihydrodiol, another photoproduct of acridine, is suggested by comparison to reported spectral properties of these compounds. This is formed through a singlet oxygen reaction. Photoproducts showing the absence of the narrow absorption band of 250 nm, characteristic of the pi -->pi* transition in tricyclic aromatics, were detected in small yields but not identified. These results suggest possible photochemical transformation pathways that could lead to the ultimate fate of these pollutants in the environment.     

Kinetic studies of endosulfan photochemical degradations by ultraviolet light irradiation in aqueous medium

Kinetic studies of endosulfan photochemical degradation in controlled aqueous systems were carried out by ultraviolet light irradiation at lambda = 254 nm. The photolysis of (alpha + beta: 2 + 1) endosulfan, alpha-endosulfan and beta-endosulfan were first-order kinetics. The observed rate constants obtained from linear least-squares analysis of the data were 1 x 10(-4) s(-1); 1 x 10(-4) s(-1); and 2 x 10(-5) s(-1), respectively, and the calculated quantum yields (phi) were 1, 1 and 1.6, respectively. Preliminary differential pulse polarographic (DPP) analysis allowed to observe the possible endosulfan photochemical degradation pathway. This degradation route involves the formation of the endosulfan diol, its transformation to endosulfan ether and finally the ether's complete degradation by observing the potential shifts.     

Acute toxicity of excess mercury on the photosynthetic performance of cyanobacterium, S. platensis--assessment by chlorophyll fluorescence analysis

Measurement of chlorophyll fluorescence has been shown to be a rapid, non-invasive, and reliable method to assess photosynthetic performance in a changing environment. In this study, acute toxicity of excess Hg on the photosynthetic performance of the cyanobacterium S. platensis, was investigated by use of chlorophyll fluorescence analysis after cells were exposed to excess Hg (up to 20 microM) for 2 h. The results determined from the fast fluorescence kinetics showed that Hg induced a significant increase in the proportion of the Q(B)-non-reducing PSII reaction centers. The fluorescence parameters measured under the steady state of photosynthesis demonstrated that the increase of Hg concentration led to a decrease in the maximal efficiency of PSII photochemistry, the efficiency of excitation energy capture by the open PSII reaction centers, and the quantum yield of PSII electron transport. Mercury also resulted in a decrease in the coefficients of photochemical and non-photochemical quenching. Mercury may have an acute toxicity on cyanobacteria by inhibiting the quantum yield of photosynthesis sensitively and rapidly. Such changes occurred before any other visible damages that may be evaluated by other conventional measurements. Our results also demonstrated that chlorophyll fluorescence analysis can be used as a useful physiological tool to assess early stages of change in photosynthetic performance of algae in response to heavy metal pollution.     

Chemically catalyzed uptake of 2,4,6-trinitrotoluene by Vetiveria zizanioides

The efficiency of vetiver grass (Vetiveria zizanioides) in removing 2,4,6-trinitrotoluene (TNT) from aqueous media was explored in the presence of a common agrochemical, urea, used as a chaotropic agent. Chaotropic agents disrupt water structure, increasing solubilization of hydrophobic compounds (TNT), thus, enhancing plant TNT uptake. The primary objectives of this study were to: (i) characterize TNT absorption by vetiver in hydroponic media, and (ii) determine the effect of urea on chemically catalyzing TNT uptake by vetiver grass in hydroponic media. Results showed that vetiver exhibited a high TNT uptake capacity (1.026 mgg(-1)), but kinetics were slow. Uptake was considerably enhanced in the presence of urea, which significantly (p<0.001) increased the 2nd-order reaction rate constant over that of the untreated (no urea) control. Three major TNT metabolites were detected in the roots, but not in the shoot, namely 1,3,5-trinitrobenzene, 4-amino 2,6-dinitrotoluene, and 2-amino 4,6-dinitrotoluene, indicating TNT degradation by vetiver grass.     

Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments

Aqueous-phase photooxidation of glyoxal, a ubiquitous water-soluble gas-phase oxidation product of many compounds, is a potentially important global and regional source of oxalic acid and secondary organic aerosol (SOA). Reaction kinetics and product analysis are needed to validate and refine current aqueous-phase mechanisms to facilitate prediction of in-cloud oxalic acid and SOA formation from glyoxal. In this work, aqueous-phase photochemical reactions of glyoxal and hydrogen peroxide were conducted at pH values typical of clouds and fogs (i.e., pH=4–5). Experimental time series concentrations were compared to values obtained using a published kinetic model and reaction rate constants from the literature. Experimental results demonstrate the formation of oxalic acid, as predicted by the published aqueous phase mechanism. However, the published mechanism did not reproduce the glyoxylic and oxalic acid concentration dynamics. Formic acid and larger multifunctional compounds, which were not previously predicted, were also formed. An expanded aqueous-phase oxidation mechanism for glyoxal is proposed that reasonably explains the concentration dynamics of formic and oxalic acids and includes larger multifunctional compounds. The coefficient of determination for oxalic acid prediction was improved from 0.001 to >0.8 using the expanded mechanism. The model predicts that less than 1% of oxalic acid is formed through the glyoxylic acid pathway. This work supports the hypothesis that SOA forms through cloud processing of glyoxal and other water-soluble products of alkenes and aromatics of anthropogenic, biogenic and marine origin and provides reaction kinetics needed for oxalic acid prediction.     

Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide and UV radiation

A kinetic model for the decolorization of C.I. Reactive Black 5 by the combination of hydrogen peroxide and UV radiation was developed based on experimental results and known chemical and photochemical reactions. The observed kinetic reaction coefficient was determined and correlated as a function of hydrogen peroxide concentration and UV intensity. The validity of the rate expression was tested experimentally in a parameterization study. The decolorization rate follows pseudo-first order kinetics with respect to dye concentration. The rate increases linearly with UV intensity and nonlinearly with increasing hydrogen peroxide concentration, going from a linear relationship at low H(2)O(2) concentrations to a maximum as hydrogen peroxide concentration continues to increase. The decolorization rate expression derived from the proposed reaction mechanism was reconciled with that used for correlating the experimental data.     

LP/LIF study of the formation and consumption of mercury (I) chloride: kinetics of mercury chlorination

The laser photolysis/laser induced fluorescence (LP/LIF) technique has been applied to studies of gas-phase mercury (Hg) chlorination. Mercury (I) chloride (HgCl) was been detected via LIF at 272 nm from reactions of elemental Hg with Cl atoms generated from the 193 nm photolysis of carbon tetrachloride. While the formation of HgCl was too fast to be observed on millisecond time scales, the kinetics of the consumption of HgCl have been determined at temperatures characteristic of post-combustion conditions. Rate coefficients and Arrhenius parameters for the reaction of HgCl with Cl2, HCl and Cl atoms were determined. The reaction of HgCl with Cl2 was the fastest reaction studied, while the reaction of HgCl with HCl was the only reaction to show any measurable temperature dependence. Estimates of the rate coefficient for the reaction Hg + Cl --> HgCl were determined using a modeling approach. Comparisons of these new measurements with model predictions are discussed.     

Photochemical behaviour of carbendazim in aqueous solution

To elucidate the photochemical behaviour of carbendazim (or MBC) in superficial waters, photolysis studies have been carried out in aqueous solutions at several pH using a UV light source (high pressure mercury arc lamp) or a solar light simulator (xenon arc lamp). The kinetics of photodecomposition of carbendazim was determined using HPLC-DAD and the identification of photoproducts was carried out with HPLC-MS (ESI negative and positive mode). According to the experimental results carbendazim is a rather stable molecule in the dark or in environmental conditions. The pH influence of the environmental medium on the photodegradation rate has been confirmed. The photochemical process can be considerably accelerated in alkaline solutions using HPK-quartz irradiation (quantum efficiency at pH 9 phi = 3.1 x 10(-3) degraded molecule per absorbed photon) while the photodegradation is not as efficient under a simulated sun irradiation (quantum efficiency in the suntest phi = 10(-4) at pH 7). Three photoproducts have been tentatively identified in pure water: 2-aminobenzimidazole, benzimidazole isocyanate and monocarbomethoxy-guanidine (issued from the cleavage of the benzimidazole ring). The last one seems very stable and could be accumulated in the environment.     

Photolytic degradation of quinalphos in natural waters and on soil matrices under simulated solar irradiation

The photochemical persistence of quinalphos, one of the most widely used organophosphorous insecticides, was investigated in a variety of environmental matrices such as natural waters and soils of different composition. Simulated solar irradiation was obtained using a xenon arc lamp (Suntest CPS+ apparatus) giving an irradiation intensity of 750 W m(-2) equivalent to a light dose per hour of irradiation of 2,700 kJ m(-2). The phototransformation rates were determined using solid-phase microextraction (SPME) and ultrasonic extraction (USE) coupled to GC-FTD, while the identification of photoproducts was carried out by GC-MS. In water samples, the degradation kinetics followed a pseudo-first-order reaction and photolysis half-lives ranged between 11.6 and 19.0 h depending on the constitution of the irradiated media. Dissolved organic matter (DOM) has a predominant retarding effect, while nitrate ions accelerated the photodegradation kinetics. In soil samples, the degradation kinetics was monitored on 1mm soil layer prepared on glass TLC plates. The kinetic behaviour of quinalphos was complex and characterized by a double step photoreaction, fast in the first 4h of irradiation followed by a slow degradation rate up to 64 h. The photolysis half-life of quinalphos was shorter in sandy soil compared to the rest of the soil samples, varying between 16.9 and 47.5 h, and showing a strong dependence on the composition of the irradiated media. Among the transformation products formed mainly through photohydrolysis and photoisomerization processes, some photoproduct structures were proposed according to their mass spectral information.     

Transformation of carbon tetrachloride by bisulfide treated goethite, hematite, magnetite, and kaolinite

This study investigated the transformation of carbon tetrachloride (CT) by goethite, hematite, magnetite, and kaolinite treated with bisulfide to form coatings of iron monosulfide (FeS) and other Fe(II) species. These coatings contribute to abiotic natural attenuation in anaerobic environments. Batch kinetic experiments were performed under anoxic conditions at pH 8.0. Surface-area-normalized pseudo-first-order rate constants for CT transformation did not differ significantly for the three HS- treated iron oxides, but the rate of CT transformation by bisulfide-treated kaolinite was significantly lower, most likely due to kaolinite's lower iron content. The yield of chloroform (CF) from CT transformation was typically approximately 1%. There was negligible or only slight adsorption of several natural organic matter (NOM) model compounds to the surface of HS- treated goethite, and these compounds had no influence on CT transformation rate constants or CF yields. Juglone, on the other hand, adsorbed to a greater extent, and also significantly influenced the CF yield, increasing it by a factor of approximately 20 for HS- treated hematite. We speculate that juglone or its HS- addition product adsorbed to the mineral surface and acted as a hydrogen atom donor that reacted with the trichloromethyl radical intermediate, increasing the CF yield.     

Comparison of photochemical behavior of various humic substances in water: III. Spectroscopic properties of humic substances

Spectral absorption coefficients and fluorescence quantum efficiencies were determined for humic substances from a variety of sources. Specific absorption coefficients k_h, for humic substances at wavelengths λ from 300 to 500 nm can be closely described by the relation Ae^B(450-λ), where A and B are constants. When the k_h values are in units of liter (mg organic carbon)^?1meter^?1 and wavelength λ is in nanometers, mean values of A and B for aquatic humus in the 12 water bodies studied were 0.6±0.3 and 0.014±0.001, respectively. Spectral absorption coefficients of dissolved organic matter in blackwater rivers, of the “yellow substance” in the sea, and of fulvic acids extracted from soils are very similar. Fluorescence quantum yields of humic substances were low and more variable than the absorption coefficients, ranging from 0.0005 to 0.012 with excitation at 350 nm (average of 0.0045±0.0038 for 6 waters). Fluorescence spectra for the humic substances were remarkably similar with maximum emission at 430 to 470 nm. Results of this study can be used to compute photolysis rates of pollutants as a function of depth in natural water bodies.     

Cosolvent flushing for the remediation of PAHs from former manufactured gas plants

Cosolvent flushing is a technique that has been proposed for the removal of hydrophobic organic contaminants in the subsurface. Cosolvents have been shown to dramatically increase the solubility of such compounds compared to the aqueous solubility; however, limited data are available on the effectiveness of cosolvents for field-contaminated media. In this work, we examine cosolvent flushing for the removal of polycyclic aromatic hydrocarbons (PAHs) in soil from a former manufactured gas plant (FMGP). Batch studies confirmed that the relationship between the soil-cosolvent partitioning coefficient (K(i)) and the volume fraction of cosolvent (f(c)) followed a standard log-linear equation. Using methanol at an fc of 0.95, column studies were conducted at varying length scales, ranging from 11.9 to 110 cm. Removal of PAH compounds was determined as a function of pore volumes (PVs) of cosolvent flushed. Despite using a high f(c), rate and chromatographic effects were observed in all the columns. PAH effluent concentrations were modeled using a common two-site sorption model. Model fits were improved by using MeOH breakthrough curves to determine fitted dispersion coefficients. Fitted mass-transfer rates were two to three orders of magnitude lower than predicted values based on published data using artificially contaminated sands.     

Washing of marine coastal sand in a batch reactor: sorption and desorption of BTEX

This study addresses the issues related to decontamination of marine beach sand accidentally contaminated by petroleum products. Sorption and desorption of BTEX (i.e., benzene, toluene, ethylbenzene, and xylene) onto the sand from Uran Beach, located near the city of Mumbai, India, were studied, and isotherms were determined using the bottle point method to estimate sorption coefficients. Alternatively, QSARs (i.e., quantitative structure activity relationships) were developed and used to estimate the sorption coefficients. Experiments for kinetics of volatilization as well as for kinetics of sorption and desorption in the presence of volatilization were conducted in a fabricated laboratory batch reactor. A mathematical model describing the fate of volatile hydrophobic organic pollutants like BTEX (via sorption and desorption in presence of volatilization) in a batch sediment-washing reactor was proposed. The experimental kinetic data were compared with the values predicted using the proposed models for sorption and desorption, and the optimum values of overall mass transfer coefficients for sorption (K(s)a(s)) and desorption (K(d)a(d)) were estimated. This was achieved by minimization of errors while using the sorption coefficients (Kp) obtained from either laboratory isotherm studies or the QSARs developed in the present study. Independent experimental data were also collected and used for calibration of the model for volatilization, and the values of the overall mass transfer coefficient for volatilization (K(g)a(g)) were estimated for BTEX. In these exercises of minimization of errors, comparable cumulative errors were obtained from the use of Kp values derived from experimental isotherms and QSARs.     

Adsorption of arsenic (V) on kaolinite and on kaolinite-humic acid complexes. Role of humic acid nitrogen groups

In order to investigate the influence of organic matter on arsenic retention, we used batch experiments at pH 7 to determine the adsorption of As(V) on three different solids: a crude, purified, Ca-exchanged kaolinite and two kaolinites coated with humic acids (HAs) having different nitrogen contents. We first examined the adsorption of each HA onto kaolinite, and then used the HA-kaolinite complexes to study As(V) adsorption. The results clearly show an influence of the HA coating on As adsorption. For example, with low initial As concentrations the solid/liquid partition coefficient (R(d)) for both HA complexes is greater than that for the crude kaolinite. We found that increasing the initial As concentrations decreased the R(d) values of the HA-coated kaolinites until finally they were the same as the crude kaolinite R(d) values. This suggests that adsorption occurs first on the HA sites and then, once the HA sites are saturated, on the remaining kaolinite sites. We also noted that the more reactive HA-kaolinite complex was the one with the highest N/C ratio. Comparing the amount of amine groups in the HA-kaolinite complexes with the total amount of adsorbed As indicates that the HA amine groups, due to their positive charge at pH 7, play a key role in the adsorption of As onto organic matter.     

Estimation of K(OA) values of 209 polychlorinated trans-azobenzenes by PM6 and DFT methods

The octanol-air partition coefficients (K(OA)) of all 209 PCt-ABs were determined computationally to fill gaps on their environmentally relevant physical and chemical properties. These properties have been determined using two computational approaches: the semi-empirical quantum chemistry method for property parameterization (PM6) of the molecular orbital package (MOPAC) and density functional theory (DFT) method using B3LYP functional and 6-311++G** basis set in Gaussian 03 software and artificial neural network (ANN) predicting abilities. Both computational methods enabled estimation of log K(OA) partition coefficients of PCt-ABs with a similar accuracy and precision. The PM6 method compared to DFT was highly superior because it requires much less time, manpower and cost of hardware. The determined log K(OA) values of the investigated PCt-ABs for standard condition (25 °C) varied between 8.30 and 8.75 for Mono-; 8.71 and 9.92 for Di-; 9.58 and 10.72 for Tri-; 10.11 and 11.34 for Tetra-, 10.83 and 11.85 for Penta-; 11.24 and 12.36 for Hexa-; 11.87 and 12.66 for Hepta-; 12.31 and 12.97 for Octa-; 12.89 and 13.21 for Nona-Ct-ABs; and 13.17- and 13.49 for Deca-Ct-AB. PCt-ABs, in view of these log K(OA) values, can be classified as compounds of relatively low (Mono-, Di- and some of Tri- Ct-ABs with values of log K(OA) around 8 to 10) environmental mobility (most of Tri- to Nona-Ct-ABs and Deca-Ct-AB homologues with values of log K(OA) >10), and with a potential to be adsorbed by soil particles.     

Scattering cross-section emission factors for visibility and radiative transfer applications: military vehicles traveling on unpaved roads

Emission factors for particulate matter (PM) are generally reported as mass emission factors (PM mass emitted per time or activity) as appropriate for air quality standards based on mass concentration. However, for visibility and radiative transfer applications, scattering, absorption, and extinction coefficients are the parameters of interest, with visibility standards based on extinction coefficients. These coefficients (dimension of inverse distance) equal cross-section concentrations, and, therefore, cross-section emission factors are appropriate. Scattering cross-section emission factors were determined for dust entrainment by nine vehicles, ranging from light passenger vehicles to heavy military vehicles, traveling on an unpaved road. Each vehicle made multiple passes at multiple speeds while scattering and absorption coefficients, wind velocity and dust plume profiles, and additional parameters were measured downwind of the road. Light absorption of the entrained PM was negligible, and the light extinction was primarily caused by scattering. The resulting scattering cross-section emission factors per vehicle kilometer traveled (vkt) range from 12.5 m2/vkt for a slow (16 km/ hr), light (1176 kg) vehicle to 3724 m2/vkt for a fast (64 km/hr), heavy (17,727 kg) vehicle and generally increase with vehicle speed and mass. The increase is approximately linear with speed, yielding emission factors per vkt and speed ranging from 4.2 m2/(vkt km/hr) to 53 m2/(vkt km/hr). These emission factors depend approximately linearly on vehicle mass within the groups of light (vehicle mass < or =3100 kg) and heavy (vehicle mass >8000 kg) vehicles yielding emission factors per vkt, speed, and mass of 0.0056 m2/(vkt km/hr kg) and 0.0024 m2/(vkt km/hr kg), respectively. Comparison of the scattering cross-section and PM mass emission factors yields average mass scattering efficiencies of 1.5 m2/g for the light vehicles and of 0.8 m2/g for the heavy vehicles indicating that the heavy vehicles entrain larger particles than the light vehicles.     

Nonequilibrium sorption of phenols onto geosorbents: the impact of pH on intraparticle mass transfer

While the pH effect on sorption equilibrium of weak acids on natural sorbents was investigated in a number of studies, less is known about the pH dependence of sorption kinetics. This paper investigates the impact of pH on sorption kinetics during the transport of some selected phenols through a sandy aquifer material. Breakthrough curves measured in column experiments were analyzed using a mass transfer based nonequilibrium model designated as dispersed flow, film and particle diffusion model (DF-FPDM). In this model, the rate limiting intraparticle diffusion is characterized by the mass transfer coefficient, kSaV, which can be determined from breakthrough curves by curve fitting. The experimental results indicate that the kSaV is pH-dependent and inversely correlated with the pH-dependent distribution coefficient, K(d,app). Regression equations are presented that may be used to estimate approximate values of intraparticle mass transfer coefficients on the basis of experimentally determined or LFER predicted distribution coefficients.     

Low to negligible photoactivity of lake-water matter in the size range from 0.1 to 5 μm

We found that the photochemical generation of reactive transients such as singlet oxygen and triplet states upon irradiation of different lake water samples is mostly accounted for by components smaller than 0.10 μm. Larger components often showed a much lower absorption and/or scattering of radiation compared with the smaller ones, with one exception where the minor to negligible photochemical activity of larger species was associated with significant radiation absorption/scattering. It is also shown that filtration of the lake water samples at 0.10 μm was able to effectively remove the suspended particles, differently from the usually suggested filtration at 0.45 μm.