Multimedia fate simulation of mercury in a coastal urban area based on the fugacity/aquivalence method.

Due to intensive industrial production and living activities, urban areas are the main anthropogenic mercury (Hg) emission sources. After entering the environment through exhaust gases, wastewater or waste residues, Hg can migrate and transform among different environmental compartments in various species, such as elemental mercury (Hg0), divalent mercury (Hg2+) and methylmercury (MeHg). Studies have yet to report on the multimedia behaviors of Hg in urban areas due to the complexity of the processes involved. In this study, the atmospheric Hg emission in Dalian, a coastal city in Northeast China, was estimated by an anthropogenic emission inventory, and a Level III multimedia model was constructed based on the fugacity/aquivalence method to simulate the fate of Hg in air, water, soil, sediment, vegetation and film. The total annual atmospheric emission was 9.91 t, of which coal combustion and non-coal sources accounted for 70.1 % and 29.9 %, respectively. Atmospheric emission and advection were dominated by Hg0, and aquatic emission and advection were dominated by Hg2+. The migration of air-vegetation, vegetation-soil and soil-air were three important pathways of Hg in urban areas. The model was validated by collecting local soil and vegetation samples and regional air, seawater and sediment monitoring data. The scenario simulation indicated that the local load would decrease to different extents with a 21.0 % reduction in atmospheric Hg emission by implementing the "coal-to-gas" measures. Our developed model can characterize the fate of Hg in coastal urban areas and provide a reference for control strategies.

Efficient and stable N-heterocyclic ketone-Cu complex catalysts for acetylene hydrochlorination: the promotion effect of ligands revealed from DFT calculations.

Cu-based catalysts are a promising alternative to toxic mercury catalysts for acetylene hydrochlorination, but their effectiveness is limited due to the poor dispersion and deactivation caused by reduction, agglomeration, and carbon deposition. In this study, the activity and stability of carbon-supported CuCl2 catalysts were largely improved by introducing N-heterocyclic ketones. Remarkably, N-methyl-2-pyridone (NM2P) coordinated Cu-based catalysts exhibited over 95% acetylene conversion with better stability under the reaction conditions of T = 180 °C, GHSV (C2H2) of 80 h-1, and VHCl/VC2H2 = 1.2. The combined results of characterization and exhaustive density functional theory (DFT) calculations revealed that the O-Cu coordination between the NM2P ligand and Cu cation strengthened the combination of reactants and Cu active sites, lowering the key reaction energy barrier, thereby leading to high activity. Meanwhile, the addition of the NM2P ligand significantly inhibited the reduction of Cu2+ to Cu+/Cu0, avoiding the formation of CuCl aggregates and the coking caused by Cu0, enhancing the catalytic stability. Overall, our study provides important insights into the design and optimization of Cu-based catalysts for acetylene hydrochlorination.

Effects of accumulated straw residues on sorption of pesticides and antibiotics in soils with maize straw return.

Outspread straw return practice leads to accumulation of structurally diverse organic materials in soils, including raw straw and straw residues. This practice provides a supplementary source of organic sorbents for compounds released into soils. However, effects of accumulated straw materials on sorption of compounds in soils remain poorly understood. Here we report that straw materials accumulated in soils display changing chemical structure and properties during decomposition, the majority of which distribute in exponential growth or decay manners with decomposition extents of materials. Sorption of straw materials toward 40 commonly used pesticides and antibiotics takes a compromise of decreasing crystalline index and increasing water absorption capacity of the sorbent materials during decomposition. This tradeoff in sorption leads to case-specific sorption trends of organic compounds in soils with straw return practice, following a composite linear sorption model of mixed soils and straw materials. The predictive model shows that relatively hydrophobic, hydrogen bond acceptor-rich chemicals (about 22.5% of the 40 compounds) display decreasing sorption capacity in organic matter-rich and/or relatively acidic soils with straw return. This finding may contradict the notion that crop straw return usually increases sorption and decreases leaching of compounds in soils.

Interrelated effects of soils and compounds on persulfate oxidation of petroleum hydrocarbons in soils.

Persulfate-based chemical oxidation of petroleum hydrocarbons (TPHs) in soils usually varies drastically with soil sites. Complex effects of soil components on persulfate oxidation of TPHs remains poorly understood, impeding the understanding of persulfate oxidation in practical systems. Here we provided empirical evidence for the interrelated effects of natural soils components and target TPHs on persulfate oxidation of TPHs. Inputs of TPHs led to notable alterations of organic matter, minerals and pH of soils, which in turn influenced distributions and availability of TPHs in soils. These soil/TPH properties and oxidant dose constituted five interrelated terms that were used to develop a predictive model of persulfate oxidation of TPHs. Such interrelation accounted for ilmenite-base coupling activation of persulfate oxidation, Fe/Mn mineral activation of persulfate oxidation, chemical oxidant demand of soils, mass transfer-reactivity limiting of TPHs, and applicable parameters of persulfate oxidation, respectively. The interrelation-based model of persulfate oxidation of TPHs displayed high predictive accuracy of 43% for a factor of 0.3 above and below the ideal fit, despite large differences in contaminated sites and applicable parameters. This finding may have practical interests in the optimization of persulfate oxidation.

CoMPARA: Collaborative Modeling Project for Androgen Receptor Activity.

BACKGROUND: Endocrine disrupting chemicals (EDCs) are xenobiotics that mimic the interaction of natural hormones and alter synthesis, transport, or metabolic pathways. The prospect of EDCs causing adverse health effects in humans and wildlife has led to the development of scientific and regulatory approaches for evaluating bioactivity. This need is being addressed using high-throughput screening (HTS) in vitro approaches and computational modeling. OBJECTIVES: In support of the Endocrine Disruptor Screening Program, the U.S. Environmental Protection Agency (EPA) led two worldwide consortiums to virtually screen chemicals for their potential estrogenic and androgenic activities. Here, we describe the Collaborative Modeling Project for Androgen Receptor Activity (CoMPARA) efforts, which follows the steps of the Collaborative Estrogen Receptor Activity Prediction Project (CERAPP). METHODS: The CoMPARA list of screened chemicals built on CERAPP's list of 32,464 chemicals to include additional chemicals of interest, as well as simulated ToxCast™ metabolites, totaling 55,450 chemical structures. Computational toxicology scientists from 25 international groups contributed 91 predictive models for binding, agonist, and antagonist activity predictions. Models were underpinned by a common training set of 1,746 chemicals compiled from a combined data set of 11 ToxCast™/Tox21 HTS in vitro assays. RESULTS: The resulting models were evaluated using curated literature data extracted from different sources. To overcome the limitations of single-model approaches, CoMPARA predictions were combined into consensus models that provided averaged predictive accuracy of approximately 80% for the evaluation set. DISCUSSION: The strengths and limitations of the consensus predictions were discussed with example chemicals; then, the models were implemented into the free and open-source OPERA application to enable screening of new chemicals with a defined applicability domain and accuracy assessment. This implementation was used to screen the entire EPA DSSTox database of ∼875,000 chemicals, and their predicted AR activities have been made available on the EPA CompTox Chemicals dashboard and National Toxicology Program's Integrated Chemical Environment. https://doi.org/10.1289/EHP5580.

Active centre and reactivity descriptor of a green single component imidazole catalyst for acetylene hydrochlorination.

A green catalyst for acetylene hydrochlorination yielding a VCM is presented using imidazole as a single component metal-free catalyst. The mechanisms and reactivities of imidazole-catalyzed acetylene hydrochlorination have been investigated by combined computational and experimental studies. The electronic effects of ortho-substituents on the reactivities have also been investigated. Through theoretical calculations and experimental studies, the nitrogen-atom including a lone pair active site of single component imidazole for metal-free acetylene hydrochlorination is proposed. It is suggested that the nitrogen-atom including a lone pair of imidazole adsorbs an HCl molecule to form an imidazole-HCl complex, which serves as the active catalyst to participate in the reaction process of acetylene hydrochlorination. Besides, the results show that C2H2 assists in the electrophilic addition of HCl, undergoing an almost planar six-membered ring transition state. Computational studies on the ortho-substitution of the active sites will have an important impact on the catalytic efficiency.

Insight into dynamics and bioavailability of antibiotics in paddy soils by in situ soil moisture sampler.

Plant-soil systems have complex regulatory mechanisms for xenobiotics uptake by plant, and these chemicals in soil pore water (SPW) are regarded as the bioavailable fraction. To date, little is known about the role of SPW in regard to the bioavailability of antibiotics for plant. In this study, in situ soil moisture sampler (SMS) was adopted to collect SPW from four paddy soils without disrupting the rhizosphere zone to evaluate antibiotic uptake in rice. The results show that SMS is applicable for antibiotics that have small molecular sizes and Log Kow values, e.g., sulfadiazine (SDZ), sulfamethoxazole (SMZ), trimethoprim (TRM), and florfenicol (FLR). However, SMS performance was not feasible for large size and medium hydrophobic clarithromycin (CLR). Antibiotics in SPW demonstrated differences among chemicals and soils. Relatively higher levels of SDZ, SMZ, and FLR were observed in SPW than TRM, and neutral Panjin soil had the highest levels of antibiotics in SPW among four soils. The levels of antibiotics in SPW were negatively correlated with their soil partition parameter, Kd. Rapid decreases of SMZ, FLR, and SDZ in the SPW were consistent with their low residues in the final soils. All antibiotics were detectable in rice roots, followed by low detection levels in a few shoot samples, while no antibiotics were detectable in the grains of four soils. Relatively higher levels of SDZ, SMZ and FLR were observed in the roots of Panjin soil, consistent with their levels in SPW and Kd values. Furthermore, CLR and TRM were observed to have higher levels in roots, which was regarded as a consequence of their relatively longer persistence. Our study indicates that SMS is an applicable technique for in situ sampling of SPW, and level of antibiotics in SPW can work as a useful indicator to explore their bioavailability to plants.

Uptake and metabolism of clarithromycin and sulfadiazine in lettuce.

Antibiotics are introduced into agricultural fields by the application of manure or biosolids, or via irrigation using reclaimed wastewater. Antibiotics can enter the terrestrial food chains through plant uptake, which forms an alternative pathway for human exposure to antibiotics. However, previous studies mainly focused on detecting residues of the parent antibiotics, while ignoring the identification of antibiotics transformation products in plants. Here, we evaluated the uptake and metabolism of clarithromycin (CLA) and sulfadiazine (SDZ) in lettuce under controlled hydroponic conditions. The antibiotics and their metabolites were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-QToF-MS/MS) and ultra-performance liquid chromatograph Micromass triple quadrupole mass spectrometry (UPLC-QqQ-MS/MS). The structure of CLA, SDZ and N-acetylated SDZ were confirmed with synthesized standards, verifying the reliability of the identification method. Eight metabolites of CLA and two metabolites of SDZ were detected in both the leaves and roots of lettuce. The metabolites of CLA included phases I and II transformation products, while only phase II metabolites of SDZ were observed in lettuce. The proportion of CLA metabolites was estimated to be greater than 70%, indicating that most of the CLA was metabolized in plant tissues. The proportion of SDZ metabolites was lower than 12% in the leaves and 10% in the roots. Some metabolites might have the ability to increase or acquire antibacterial activity. Therefore, in addition to the parent compounds, metabolites of antibiotics in edible vegetables are also worthy of study for risk assessment and to determine the consequences of long-term exposure.

Development of cerium oxide-based diffusive gradients in thin films technique for in-situ measurement of dissolved inorganic arsenic in waters.

A diffusive gradients in thin films (DGT) method using a new high-capacity cerium oxide (CeO2) binding gel, for the first time, was developed for measuring dissolved inorganic arsenic in freshwater and seawater. The capacities of the new CeO2 binding gel were 682 µg and 375 µg for AsIII and AsV, respectively. The masses of AsIII and AsV accumulated by CeO2-DGT device increased linearly with time and agreed well with the theoretical value calculated by DGT equation. The arsenic accumulation by CeO2-DGT was independent of pH (4.05-9.04) and ionic strength (0.1-750 mM), and common anions including CO32-, SO42-, Cl- and PO43- had no obvious interference. CeO2-DGT showed excellent long-term deployment performance in freshwater and synthetic seawater. Field trials with CeO2-DGT achieved successfully the time-weighted-average concentrations of total inorganic arsenic in reservoir water (1.38 ±â€¯0.09 µg/L) and coastal seawater (0.45 ±â€¯0.06 µg/L). The results were comparable to those measured by grab sampling. The proposed method was reliable and robust for in-situ measurements of dissolved inorganic arsenic in environmental waters.

Disparate effects of DOM extracted from coastal seawaters and freshwaters on photodegradation of 2,4-Dihydroxybenzophenone.

Dissolved organic matter (DOM) plays an important role in degradation of organic pollutants by photochemically-produced reactive intermediates (RIs), such as excited triplet-states of DOM (3DOM*), singlet oxygen (1O2) and hydroxyl radical (·OH). However, it is not clear whether DOM extracted from coastal seawaters (CS-DOM) and DOM derived from freshwaters (FW-DOM) exhibit similar effects on photodegradation of organic micropollutants. Herein, 2,4-dihydroxybenzophenone (BP-1) was adopted as a model compound to probe the effects of different DOM on photodegradation kinetics of organic micropollutants. Results show that the CS-DOM promotes the photodegradation of BP-1 mainly via the pathway involving 3DOM*; while 3DOM*, 1O2 and ·OH are responsible for BP-1 photodegradation in the presence of the FW-DOM. Compared with the FW-DOM, the CS-DOM undergoes more photobleaching, and contains less aromatic C=C and C=O functional groups. Although 3DOM* formation quantum yields for the CS-DOM are relatively higher than those for the FW-DOM, the CS-DOM has lower rates of light absorption, leading to lower steady-state RI concentrations for the CS-DOM. BP-1 photodegradation in the presence of the CS-DOM is faster than in the presence of the FW-DOM, due to higher second-order reaction rate constants between BP-1 and CS-3DOM* and fewer antioxidants contained in the CS-DOM.

Bacterial community variations in paddy soils induced by application of veterinary antibiotics in plant-soil systems.

Soil bacterial communities have complex regulatory networks, which are mainly associated with soil fertility and ecological functions, and are likely to be disturbed due to antibiotics applications. The impact of antibiotics, particularly in mixtures form, on bacterial communities in different paddy soils is poorly understood. Using pyrosequencing techniques of 16 S rRNA genes, this study investigated the synergistic effects of veterinary antibiotics (sulfadiazine, sulfamethoxazole, trimethoprim, florfenicol, and clarithromycin) on bacterial communities in a soil-bacteria-plant system. Rice was grown under controlled greenhouse conditions where unplanted and planted treatments were doped with 200 µg kg-1 of combined antibiotics over a period of 3 months. Bacterial richness remained unaltered, while a significant decline was observed in bacterial diversity due to antibiotics in the four paddy soils. Bacteroidetes and Acidobacteria were increased, while Actinobacteria and Firmicutes decreased under antibiotics exposure. Despite antibiotics perturbation, compositional variations were mainly attributed to the different paddy soils which harbor distinct bacterial communities. Haliangium and Gaiella were among the sensitive genera that were negatively correlated to antibiotics perturbation. Additionally, electrical conductivity, total organic carbon, and total nitrogen of soil solution were the key physiochemical indices which significantly influenced the structure of bacterial communities in the paddy soils. These findings expanded our knowledge of effects from synergistic antibiotics application and variations in bacterial communities among different paddy soils.

Profile and source apportionment of volatile organic compounds from a complex industrial park.

Industrial emissions, mainly from industrial parks, are important sources of ambient volatile organic compounds (VOCs). Identification of the major sources of VOCs from industrial parks has practical significance in emission reduction. In this study, the major species of VOCs from a residential area located downwind of a complex industrial park were sampled with Tenax absorption tubes and analyzed by thermal desorption coupled with gas chromatography/mass spectrometry (TD-GC/MS). Receptor models of factor analysis with nonnegative constraints (FA-NNC) and positive matrix factorization (PMF) were employed to recognize the potential emission sources, which suggested an association with the production processes in the nearby industrial park. In order to validate the sources, the profiles of VOC emissions of related workshops under actual manufacturing processes were acquired. It was found that xylenes & amines, phenols and esters were the major species of VOCs for the workshops of foundry, refractory materials and printing, respectively. Similarity analysis indicated that the detected profiles of VOC emissions from the dominant industrial types had good correlations with the identified factors from receptor models. Source contributions to VOCs in the receptor region exhibited that foundry production was the primary contributor (56-64%), followed by refractory material production (22-26%) and printing (14-18%). This study provides a strategy for source apportionment of VOCs from a local complex industrial park, which is helpful in the development of targeted control strategies.

DOM from mariculture ponds exhibits higher reactivity on photodegradation of sulfonamide antibiotics than from offshore seawaters.

Mariculture activities and river inputs lead to coastal seawaters with DOM levels that are comparable to or even higher than those in terrestrial water bodies. However, effects of seawater DOM, and especially of DOM occurring in areas impacted by mariculture, on photodegradation of organic micropollutants, are largely unknown. In this study, simulated sunlight irradiation experiments were performed to probe the effects of DOM extracted from mariculture impacted seawaters and from offshore areas, on photodegradation of three sulfonamide antibiotics (SAs). Results show that the SAs are transformed mainly by indirect photodegradation induced by triplet excited DOM (3DOM*). Compared with DOM from the more pristine coastal waters, the DOM from mariculture impacted areas undergoes less photobleaching, contains higher percentage of humic-like materials and higher proportions of aromatic and carbonyl structures. Thus, the DOM from mariculture areas exhibits higher rates of light absorption, higher formation quantum yields of 3DOM*, higher 3DOM* steady-state concentrations and higher reactivity on photodegradation of the SAs. Photochemistry of the seawater DOM is different from that reported for freshwater lake DOM. This study highlights the importance of probing the effects of DOM from coastal seawaters on photodegradation of organic micropollutants since coastal seawaters are sinks of many aquatic pollutants.

Remediation of cadmium contaminated water and soil using vinegar residue biochar.

This study investigated a new biochar produced from vinegar residue that could be used to remediate cadmium (Cd)-contaminated water and soil. Aqueous solution adsorption and soil incubation experiments were performed to investigate whether a biochar prepared at 700 °C from vinegar residue could efficiently adsorb and/or stabilize Cd in water and soil. In the aqueous solution adsorption experiment, the Cd adsorption process was best fitted by the pseudo-second-order kinetic and Freundlich isotherm models. If the optimum parameters were used, i.e., pH 5 or higher, a biochar dosage of 12 g L-1, a 10 mg L-1 Cd initial concentration, and 15-min equilibrium time, at 25 °C, then Cd removal could reach about 100%. The soil incubation experiment evaluated the biochar effects at four different application rates (1, 2, 5, and 10% w/w) and three Cd contamination rates (0.5, 1, and 2.5 mg kg-1) on soil properties and Cd fractionation. Soil pH and organic matter increased after adding biochar, especially at the 10% application rate. At Cd pollution levels of 1.0 or 2.5 mg kg-1, a 10% biochar application rate was most effective. At 0.5 mg Cd kg-1 soil, a 5% biochar application rate was most efficient at transforming the acid extractable and easily reducible Cd fractions to oxidizable and residual Cd. The results from this study demonstrated that biochar made from vinegar residue could be a new and promising alternative biomass-derived material for Cd remediation in water and soil.

Different binding mechanisms of neutral and anionic poly-/perfluorinated chemicals to human transthyretin revealed by In silico models.

Chemical forms-dependent binding interactions between phenolic compounds and human transthyretin (hTTR) have been elaborated previously. However, it is not known whether the binding interactions between ionizable halogenated alphatic compounds and hTTR also have the same manner. In this study, poly-/perfluorinated chemicals (PFCs) were selected as model compounds and molecular dynamic simulation was performed to investigate the binding mechanisms between PFCs and hTTR. Results show the binding interactions between the halogenated aliphatic compounds and hTTR are related to the chemical forms. The ionized groups of PFCs can form electrostatic interactions with the -NH+3 groups of Lys 15 residues in hTTR and form hydrogen bonds with the residues of hTTR. By analyzing the molecular orbital energies of PFCs, we also found that the anionic groups (nucleophile) in PFCs could form electron donor - acceptor interactions with the -NH+3 groups (electrophile) in Lys 15. The aforementioned orientational interactions make the ionized groups of the PFCs point toward the entry port of the binding site. The roles of fluorine atoms in the binding interactions were also explored. The fluorine atoms can influence the binding interactions via inductive effects. Appropriate molecular descriptors were selected to characterize these interactions, and two quantitative structure-activity relationship models were developed.

Ligand-free nickel-catalyzed semihydrogenation of alkynes with sodium borohydride: a highly efficient and selective process for cis-alkenes under ambient conditions.

We report a low-cost and efficient catalytic system, involving in situ generated ligand-free Ni NPs, methanol and sodium borohydride, for the semihydrogenation of alkynes under ambient conditions. This catalytic system exhibits remarkably high activity, satisfactory cis-selectivity for internal alkynes, good stability and general applicability.

Effects of Atmospheric Water on ·OH-initiated Oxidation of Organophosphate Flame Retardants: A DFT Investigation on TCPP.

Tris(2-chloroisopropyl) phosphate (TCPP), a widely used organophosphate flame retardant, has been recognized as an important atmospheric pollutant. It is notable that TCPP has potential for long-range atmospheric transport. However, its atmospheric fate is unknown, restricting its environmental risk assessment. Herein we performed quantum chemical calculations to investigate the atmospheric transformation mechanisms and kinetics of TCPP initiated by ·OH in the presence of O2/NO/NO2, and the effects of ubiquitous water on these reactions. Results show the H-abstraction pathways are the most favorable for the titled reaction. The calculated gaseous rate constant and lifetime at 298 K are 1.7 × 10-10 cm3molecule-1 s-1 and 1.7 h, respectively. However, when considering atmospheric water, the corresponding lifetime is about 0.5-20.2 days. This study reveals for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transition states via forming hydrogen bonds, which unveils one underlying mechanism for the observed persistence of TCPP in the atmosphere. Water also influences secondary reaction pathways of selected TCPP radicals formed from the primary H-abstraction. These results demonstrate the importance of water in the evaluation of the atmospheric fate of newly synthesized chemicals and emerging pollutants.

Development of a QSAR model for predicting aqueous reaction rate constants of organic chemicals with hydroxyl radicals.

Reaction with hydroxyl radicals (˙OH) is an important removal pathway for organic pollutants in the aquatic environment. The aqueous reaction rate constant (kOH) is therefore an important parameter for fate assessment of aquatic pollutants. Since experimental determination fails to meet the requirement of being able to efficiently handle numerous organic chemicals at limited cost and within a relatively short period of time, in silico methods such as quantitative structure-activity relationship (QSAR) models are needed to predict kOH. In this study, a QSAR model with a larger and wider applicability domain as compared with existing models was developed. Following the guidelines for the development and validation of QSAR models proposed by the Organization for Economic Co-operation and Development (OECD), the model shows satisfactory performance. The applicability domain of the model has been extended and contained chemicals that have rarely been covered in most previous studies. The chemicals covered in the current model contain functional groups including [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right], -C[triple bond, length as m-dash]C-, -C6H5, -OH, -CHO, -O-, [double bond splayed left]C[double bond, length as m-dash]O, -C[double bond, length as m-dash]O(O)-, -COOH, -C[triple bond, length as m-dash]N, [double bond splayed left]N-, -NH2, -NH-C(O)-, -NO2, -N[double bond, length as m-dash]C-N[double bond splayed right], [double bond splayed left]N-N[double bond splayed right], -N[double bond, length as m-dash]N-, -S-, -S-S-, -SH, -SO3, -SO4, -PO4, and -X (F, Cl, Br, and I).

Effects of halide ions on photodegradation of sulfonamide antibiotics: Formation of halogenated intermediates.

The occurrence of sulfonamide antibiotics (SAs) in estuarine waters urges insights into their environmental fate for ecological risk assessment. Although many studies focused on the photochemical behavior of SAs, yet the effects of halide ions relevant to estuarine and marine environments on their photodegradation have been poorly understood. Here, we investigated the effects of halide ions on the photodegradation of SAs with sulfapyridine, sulfamethazine, and sulfamethoxazole as representative compounds. Results showed that halide ions did not significantly impact the photodegradation of sulfapyridine and sulfamethoxazole, while they significantly promoted the photodegradation of sulfamethazine. Further experiments found that ionic strength applied with NaClO4 significantly enhanced the photodegradation of the SAs, which was attributed to the decreased quenching rate constant of the triplet-excited SAs ((3)SA(∗)). Compared with ionic strength, specific Cl(-) effects retarded the photodegradation of the SAs. Our study found that triplet-excited sulfamethazine can oxidize halide ions to produce halogen radicals, subsequently leading to the halogenation of sulfamethazine, which was confirmed by the identification of both chlorinated and brominated intermediates. These results indicate that halide ions play an important role in the photochemical behavior of some SAs in estuarine waters and seawater. The occurrence of halogenation for certain organic pollutants can be predicted by comparing the oxidation potentials of triplet-excited contaminants with those of halogen radicals. Our findings are helpful in understanding the photochemical behavior and assessing the ecological risks of SAs and other organic pollutants in estuarine and marine environment.

Photochemical transformation of sunscreen agent benzophenone-3 and its metabolite in surface freshwater and seawater.

The occurrence of sunscreen agents and their metabolites in surface waters gives rise to public concerns. However, little is known about the environmental fate of these pollutants at present, especially for their metabolites. In this study, we investigated the photochemical of sunscreen agents and their metabolites in natural waters, adopting benzophenone-3 (BP-3) and its human metabolite 4-hydroxybenzophenone (4-OH-BP3) as examples. Results show that only anionic forms of both BP-3 and 4-OH-BP3 can undergo direct photodegradation. The photolytic rates of both compounds in natural waters are faster as compared to those in pure water. Radical scavenging experiments revealed that triplet-excited dissolved organic matter ((3)DOM(∗)) was responsible for the indirect photodegradation of BP-3 and 4-OH-BP3 in seawater, whereas in freshwater, the indirect photodegradation of these two compounds was attributed to (3)DOM(∗) and ·OH. (1)O2 plays a negligible role in their photodegradation because of the weak (1)O2 reactivity. Furthermore, we probed the contribution of ·OH and (3)DOM(∗) to the photodegradation of both compounds in freshwater, and the results revealed that ·OH accounted for 56% and 59% of the observed photodegradation for BP-3 and 4-OH-BP3, respectively, whereas (3)DOM(∗) accounted for 43% and 12% of the observed photodegradation for BP-3 and 4-OH-BP3, respectively. These results are helpful in assessing the ecological risk of BP-3 and its metabolite in the aquatic environment.