Specific UV Research Articles

Development and Validation of the UV Spectrophotometric Method for Simultaneous Determination of Paracetamol and Pseudoephedrine in Bulk and Combined Tablet Dosage Form

Paracetamol (PARA) and Pseudoephedrine (PSE) are co-formulated drugs that and widely used over the world for the treatment of symptoms associated with common cold. In the present study a specific, rapid and simple UV spectrophotometric method with good sensitivity was developed and validated for the simultaneous quantification of PARA and PSE in bulk and tablet dosage form using methanol as diluent. This method is based on the direct measurement of absorbance at 248 nm wavelength for PARA solution, whereas dual-wavelength absorption measurement is applied for PSE solution (i.e. subtraction of absorbance at 217 nm from that at 201 nm, in which PARA absorbance subtraction is equal to zero). The calibration curves were linear (R2 = 0.9988 and 0.9976 for PARA and PSE, respectively) in a concentrations range of 2 – 10 μg/mL for both drugs. Limit of detection is LOD = 0.4159 μg/mL and 0.29679 μg/mL and the limit of quantification is LOQ = 1.26 μg/mL and 0.8994 μg/mL for PARA and PSE, respectively. The RSD% values for all levels of precision (repeatability, intra-day and inter-day) are within the specified limit for both drugs. The accuracy of PARA determination was ascertained by standard addition method, and the percentage recovery for 50, 100, and 150 % of standard were 97.93, 100, and 101.39%, respectively (RSD% = 1.7). The accuracy of PSE determination was studied by percentage recovery (n = 3), and the results were 100.7, 101.16, and 99.57% (RSD% = 0.6648). The proposed spectrophotometric method was successfully applied to the analysis of commercial tablets and the obtained results were satisfactory.

Classifying pole-skipping points

We clarify general mathematical and physical properties of pole-skipping points. For this purpose, we analyse scalar and vector fields in hyperbolic space. This setup is chosen because it is simple enough to allow us to obtain analytical expressions for the Green’s function and check everything explicitly, while it contains all the essential features of pole-skipping points. We classify pole-skipping points in three types (type-I, II, III). Type-I and Type-II are distinguished by the (limiting) behavior of the Green’s function near the pole-skipping points. Type-III can arise at non-integer iω values, which is due to a specific UV condition, contrary to the types I and II, which are related to a non-unique near horizon boundary condition. We also clarify the relation between the pole-skipping structure of the Green’s function and the near horizon analysis. We point out that there are subtle cases where the near horizon analysis alone may not be able to capture the existence and properties of the pole-skipping points.

Elucidating the optimum added dosage of Diatomite during co-composting of pig manure and sawdust: Carbon dynamics and microbial community.

Six dosages of DM (0%, 2.5%, 5.0%, 10%, 15% and 20%) were added into initial mixtures for 42days of aerobic composting to investigate the optimum added dosage of Diatomite (DM) during co-composting of pig manure and sawdust. The results showed that adding DM was beneficial for reducing CH4 emissions and greenhouse gas emission equivalent (GHGE) values by 15.63-24.25% and 14.33-69.08%, respectively. Meanwhile, the main contributor to the GHGE value was N2O (58.76-75.98%), followed by CH4 (17.22-29.16%) and NH3 (6.38-13.36%). Moreover, the maximum values in the degradation of total organic matter and the formation rate of humic acid were 20.46% and 82.19% in 10% DM added treatment (T3), respectively. Furthermore, the increase in spectral parameters, including the specific UV absorbance at 254nm (SUVA254), the specific UV absorbance at 280nm (SUVA280) and Fourier transform - infrared parameters were facilitated by DM amendment. Additionally, the higher values of the relative abundances of Proteobacteria (50.98%) and Bacteroidetes (12.73%), and related metabolisms such as carbohydrate metabolism and amino acid metabolism, as well as the lower value of methane metabolism reported in T3, supported the difference in CH4 and humification of the two treatments. In conclusion, DM was determined to be an eco-practical additive to improve the quality of end products and reduce potential risks, and the best treatment in this study was 10% added treatment based on dry weight.

Research about Organic Matter Removal and Biofilms Development of Pilot-Scale UV/H2O2-BAC Process

As a green advanced process for drinking water treatment, the UV/hydrogen peroxide (UV/H2O2) process has been gradually applied in China. To study the effect and mechanism of organic matter removal and the development of microbial communities in the UV/H2O2-biological activated carbon (UV/H2O2-BAC) process, a pilot-scale UV/H2O2-BAC system was built and operated over one year. Low water temperature affects the UV/H2O2 process efficiency, the biofilms in the BAC system were mature and stable after 240 days, and the contribution rate of BAC adsorption to dissolved organic carbon (DOC) removal was approximately 14.2% after one year of operation. The liquid chromatography-organic carbon detection (LC-OCD) analysis shows that UV/H2O2 process can increase the amounts of Low Molecular Weight (LMW) neutrals, and the specific UV absorbance (SUVA254) value is not suitable for predicting Trihalomethanes (THMs) precursor contents in water after UV/H2O2 treatment. High-throughput sequencing results prove that microbial species in the middle section are the most abundant compared to those in the influent and effluent sections, hydrogen peroxide has lower inhibition on the development of microbial community than ozone and the low concentration of hydrogen peroxide (<0.25 mg/L) promotes the development of the microbial communities, hydrogen peroxide can reduce Proteobacteria abundance by inhibiting the growth of anaerobes. Acidobacteria may have a certain contribution to the degradation of soil organic matter (SOM), and the effluent section of BAC with low DOC concentration cannot form the dominant species of Rhodobacter.

Water- and Base-Extractable Organic Matter in Sediments From Lower Yangtze River–Estuary–East China Sea Continuum: Insight Into Accumulation of Organic Carbon in the River-Dominated Margin

The burial of organic carbon (OC) in the river-dominated margin plays an important role in global carbon cycle, but its accumulation mechanism is not well understood. Here, we examined the concentration and distribution of water-extractable organic matter (WEOM) and base-extractable organic matter (BEOM) in surface sediments from the lower Yangtze River, estuary, and the East China Sea. Chemical characteristics of the WEOM and BEOM were described by multiple ultraviolet-visible and fluorescence spectral indicators. Concentrations of both WEOM and BEOM showed significant correlations with sediment grain size, suggesting that mineral surface area is a key factor for OC loadings on sediments. Three components (C1, C2, and C3) extracted from fluorescence excitation emission matrices-parallel factor analysis were assigned as terrigenous humic-like substance, mixed terrigenous/aquatic humic-like substance, and microbial protein-like substance, respectively. From the lower Yangtze River to the East China Sea, the C1%, specific UV absorbance at 254 nm (SUVA254), and humification index (HIX) of the WEOM decreased, while the C3%, fluorescence index (FI), and biological index (BIX) of the WEOM increased. This suggested the loss of terrigenous OC and addition of microbial OC in the WEOM. While for BEOM, the overall increase of C1% and HIX and the decrease of C3% and FI suggested selective removal of microbial OC and preferential preservation of terrigenous OC. Our study demonstrates complex behaviors of sediment organic matter (OM) during the land-to-sea transport that is largely controlled by the binding strength of OM–sediment association, and that the formation of BEOM is an important pathway for accumulation of terrigenous OM in the river-dominated margin.

Persistence and photochemical transformation of water soluble constituents from industrial crude oil and natural seep oil in seawater

The persistence and transformation of water soluble chemical constituents derived from surface oil from the 2015 Refugio Oil Spill and from a nearby natural seep were evaluated under simulated sunlight conditions. Photoirradiation resulted in enhanced oil slick dissolution, which was more pronounced in spill oil compared to seep oil. Nontargeted analysis based on GC × GC/TOF-MS revealed that photoirradiation promoted oil slick dissolution, and more water soluble compounds were released from spill oil (500 compounds) than from seep oil (180 compounds), most of them (488 in spill oil and 150 in seep oil) still persisting in solution after 67 days of photoirradiation. First-order degradation rate coefficients of humic-like water soluble constituents were found to be 0.26 day−1 and 0.29 day−1 for irradiated spill and seep samples, respectively. The decreases in humic-like fluorescence, specific UV absorbance, and aromatic compounds without corresponding decreases in DOC concentration support indirect photochemical transformation in addition to complete photomineralization.

Evaluation of the main active species involved in the TiO2 photocatalytic degradation of ametryn herbicide and its by-products

In this study, we investigated the effectiveness of photocatalysis using TiO2 as catalyst on the removal of ametryn. The evaluation of photocatalytic activity under simulated sunlight was discussed as evidence by numerous controlled trials and several operational parameters such as ametryn concentration, total organic carbon, chemical oxygen demand, specific UV absorbance, biochemical oxygen demand, toxicity and formed intermediates. Moreover, the roles of reactive species involved in the degradation of ametryn were examined by using different specific scavengers. Ametryn removed by photocatalysis using 0.4 g L−1 of TiO2 was 100% within 60 min, while only 30% was achieved by photolysis at the same time. Biodegradability index improved from 0.3 (raw solution) up to 0.8 while the acute toxicity measured by the inhibition percentage of bioluminescence from Vibro fischeri indicates that the photocatalytic treatment promotes 97% of toxicity reduction. The scavenger study shows different percentages of inhibition in ametryn degradation, which allowed to conclude that HO•, valence-band holes and O2•− could intervene in the degradation of ametryn, with predominance of HO•. Thirty-eight intermediates were identified from the photocatalytic degradation of ametryn. The comparison of the generation of those intermediates with and without the addition of scavengers showed that different by-products are generated depending on the predominance of the active species. For example, the presence of azide resulted in intermediates formed by condensation reactions. Based on the identified intermediates, reaction pathways and a degradation mechanism were proposed, including HO• radicals, O2•−, holes, and 1O2.

Coupling between increased lake color and iron in boreal lakes

Increasing evidence show that lake color has increased more than DOC in several boreal lakes, promoted by enhanced levels of light absorbing iron (Fe). Fe levels show great spatial and temporal variations in northern freshwaters, and processes regulating long-term Fe trends as well as differences among lakes are not fully understood. In a boreal lake district of SE-Norway, the coupling between lake color and Fe were investigated in 24 non-productive lakes during 1983–2017. The lakes showed significant increases in color, total organic carbon (TOC), specific UV absorption and Fe with time. Based on regression models, TOC and Fe together explained 89% of lake color. Fe averagely contributed to 12% of the lake color. The color contribution from Fe was better predicted by the Fe-to-TOC ratio than the absolute Fe concentration. The variability in Fe contribution to color was large - ranging from 0 to 65% based on 429 lake water samples. Variability in Fe levels and color contribution were related to differences in water retention time (WRT), pH and to the terrestrial input of Fe-organic matter complexes. Size fractionation analyses showed that Fe and colored TOC were mainly in a colloidal form (>10 kDa). Along with reduced acid rain, there has been a significant reduction in ionic strength in several boreal lakes since 1980s, which promote the stability of colloids. Negative correlation between the Fe-to-TOC ratio and WRT, might be due to a size selective removal of colloidal Fe complexes related to water flow, which is supported by a higher Fe-to-TOC ratio in wet years compared to dry years. Responses of Fe complexes to increased runoff are relatively higher in lakes with short compared to long WRT. In addition, increases in hydrological extremes, due to climate change, may enhance the Fe variability among lakes even further in a future climate.

Characterization of algal organic matter as precursors for carbonaceous and nitrogenous disinfection byproducts formation: Comparison with natural organic matter

Algal organic matter (AOM) and natural organic matter (NOM) from a typical eutrophic lake were comprehensively investigated in terms of their physico-chemical property, components and disinfection byproduct formation potentials (DBPFPs). The relationships between specific chemical properties of AOM and NOM with their corresponding DBPFPs were further evaluated during chlorination. Results indicated that AOM had lower specific UV absorbance (SUVA) but richer organic nitrogen contents than NOM. Fluorescence excitation emission matrix spectroscopy further demonstrated that AOM were chiefly composed of aromatic protein-like and soluble microbial byproduct-like matters, while NOM were mainly contributed from humic acid-like and soluble microbial byproduct-like substances. Although the molecular weight (MW) distribution of AOM and NOM showed no significant difference, size-exclusion chromatography with organic carbon as well as organic nitrogen detection (LC-OCD-OND) revealed that AOM were concentrated with the fraction of building blocks and NOM had higher concentrations of biopolymers and humics (HS). Moreover, AOM displayed higher DBPFPs than NOM, especially for nitrogenous DBPFP (N-DBPFP). MW < 1 kDa fractions both in AOM and NOM contributed the largest proportion to the formation of carbonaceous disinfection byproducts (C-DBPs). In addition, Pearson correlation analysis showed that bulk parameter SUVA was significantly relevant to the formation potentials of trihalomethane both in AOM and NOM, but was ineffective for carbonaceous DBPFP (C-DBPFP) prediction. Dissolved organic nitrogen contents in biopolymer and HS characterized by LC-OCD-OND had strong correlations with N-DBPFPs from AOM and NOM, indicating that LC-OCD-OND quantitative analysis could improve the prediction accuracy of the DBP formation than bulk parameters during NOM and AOM chlorination.

Metal binding by dissolved organic matter in hypersaline water: A size fractionation study using different isolation methods

The influence of dissolved organic matter (DOM) on mineral extraction from salt lake brines depend on DOM quality. This study contributes to our knowledge of DOM’s metal binding behavior in hypersaline environments by characterization of DOM from lakes in the Qaidam Basin, i.e., Qarhan Lake (LQDOM), Da Qaidam (DQDOM) and West Ginair Salt Lake (WGDOM). The DOM was fractionated based on solid phase extraction (SPE) and ultrafiltration (UF), and the spectral and metal binding behavior of these fractions were studied by absorption spectroscopy, Pb(II) titration techniques and fluorescence parallel factor (PARAFAC) analysis. The results showed that bulk DOM generally contained more dissolved organic carbon (DOC), lower specific UV absorbance (SUVA254), higher fluorescence and biological indices, comparable humification index, and lower condition stability constants compared to the other nature waters. Compared with UF, SPE-derived DOM exhibited higher DOC recovery and aromaticity and lower carbohydrate yield. It appeared that the SPE procedure used affects the spectral composition of bulk DOM to a larger extent than UF. Source and molecular weight (MW)-dependent differences in abundance and quality of brine DOM was indicated by higher SUVA254 in high MW DOM, for LQDOM and DQDOM, and humic-like fluorophores were mainly in high MW-DOM in each lake. Moreover, the high MW humic-like component exhibited higher metal binding potential than the bulk and low MW counterparts for LQDOM and DQDOM, while the inverse was observed for WGDOM. This study revealed the effects of isolation techniques on interpretation of DOM characteristics, and meanwhile highlighted the importance of origin- and MW-dependent DOM in manipulating the behavior, fate, and bioavailability of heavy metals in salt lake brine.

Development and validation of zero and first-order derivative area under curve spectrophotometric methods for the determination of aripiprazole in bulk material and tablets

The proposed experiments explain simple, precise, specific and accurate UV spectrophotometry methods for the estimation of Aripiprazole in bulk and pharmaceutical formulation. Aripiprazole is a recent second generation atypical anti-psychotic drug used for the treatment of schizophrenia; four simple UV spectrophotometric methods were established for estimation of Aripiprazole, using double beam UV spectrophotometer (UV-2450, Shimadzu, Japan). Aripiprazole showed maximum absorbance (λ max) at 255 nm in methanolic HCl as a solvent. The calibration curve obeyed Beer-Lambert law in the concentration range of 5 -30 μg/mL. The % recovery was found to be in the range of 98 - 100 %. Precision value less than 2 in terms of % RSD indicates precise nature of developed methods. Validation of developed methods was carried out as per ICH guidelines. It was concluded that the results and statistical analysis amongst all four methods, AUC method is most simple, accurate, precise, and specific. All four methods can be used for routine analysis of Aripiprazole in bulk and pharmaceutical formulations. Keywords: Aripiprazole, UV-Spectrophotometry, Derivatives Methods, Area Under Curve Method.

Source and drinking water organic and total iodine and correlation with water quality parameters

Iodinated disinfection by-products (I-DBPs) have recently emerged as part of the pool of DBPs of public health concern. Due to limitations in measuring individual I-DBPs in a water sample, the surrogate measure of total organic iodine (TOI) is often used to account for the sum of all I-DBPs. In this study, TOI and total iodine (TI) are quantified in raw and treated waters in treatment trains at three sites in the Northeast United States. The occurrence, magnitude, and seasonality of these species was investigated within each sampling train and across the different sites. A regression model was developed to explore how TOI occurrence varies with routinely measured physical and chemical parameters in a water sample. The TOI and TI concentration at the three sites ranged from below the method detection limit to 18 µg/L and from 3 and 18.9 µg/L, respectively. There was substantial inter-monthly variability in TOI without a clear seasonal signal, and the concentration of TOI did not increase upon treatment. The results of the multivariate regression model showed that dissolved organic carbon (DOC), specific UV254 absorbance (SUVA), combined chlorine residual (TCl2), and pH were all significantly related to TOI concentration to varying degrees. A Tobit model was fit to show TOI predictions against observed (measured) TOI values. The model could explain approximately 46% of the variance of TOI concentrations in the treated waters.

Removal of natural organic matter by ion exchange: Comparing regenerated and non-regenerated columns

Dissolved organic matter (DOM) in water has adverse impacts on the water treatment process and is effectively removed by ion exchange (IEX). Some researchers have proposed the term biological ion exchange (BIEX) for the process of continuous DOM removal by ion exchange without the need for chemical regeneration that results in brine waste. Surface water with moderate dissolved organic carbon (DOC) concentrations (4–6 mg/L) and high sulfate concentrations (80 – 120 mg/L) was fed to two regenerated and two non-regenerated columns for 12,500 bed volumes (9 months) with the goal of investigating the effects of chemical and possibly biological regeneration on long-term IEX operation. Chemically regenerated columns achieved between 60 and 80% DOC removal for the entirety of the experiment, while non-regenerated columns achieved steady DOC removal of ~50%. Inorganic ion analysis showed that biological activity had minimal impact on DOC removal, and the main mechanism of removal was secondary IEX between sulfate (SO42−) and fractions of DOC with high affinities for ion exchange. Fluorescence and specific UV absorbance at 254 nm (SUVA 254) data showed that fractions of DOC with higher SUVA 254 values (terrestrial-like fractions) were better removed by secondary IEX than those with lower SUVA 254 values (aquatic/microbial-like fractions). Scanning electron microscopy showed that biofilms on non-regenerated resins covered 5–15% of the resin surface and are composed of numerous species of bacteria with varying functions, with some protozoa present.

Anaerobic and aerobic biodegradation of soil-extracted dissolved organic matter from the water-level-fluctuation zone of the Three Gorges Reservoir region, China

The biodegradation of dissolved organic matter (DOM) in natural environments is determined by its molecular composition and reactivity. Redox oscillations are common in the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR). As a consequence, the soil DOM released is degraded under both anaerobic and aerobic conditions. The DOM compounds available for degradation under contrasting redox conditions and the resulting DOM composition still need to be elucidated. By combining laboratory experiments with an in-depth characterization of DOM optical properties, we show that different pathways controlled the depletion and enrichment of the DOM optical components under different oxygen regimes. In particular, 28-day dark biodegradation assays showed that up to 39.5 ± 4% DOM was degraded under anaerobic conditions, while 55.5 ± 6% DOM was biodegraded under aerobic conditions. Aerobic biodegradation resulted in a higher aromaticity and degree of humification of the DOM compared to anaerobic degradation. The specific UV absorbance at a wavelength of 254 (SUVA254) and biological index (BIX) could be used to track DOM biodegradation under anaerobic conditions. Under aerobic conditions, the SUVA254, BIX and concentration of coloured DOM (CDOM, reflected by a (355)) could track DOM biodegradation, and significant amounts of CDOM could be aerobically biodegraded.

Mercury concentrations and associations with dissolved organic matter are modified by water residence time in eastern Canadian lakes along a 30° latitudinal gradient

AbstractSurface water mercury (Hg) and dissolved organic carbon (DOC) concentrations and their ratios, which play a critical role in food chain bioaccumulation of Hg, were examined in lakes from southern boreal, sub‐Arctic taiga, Arctic tundra and polar desert landscapes of eastern and northern Canada. The study sites investigated span a 30° latitudinal gradient representing differences in climate, ecosystem productivity, and atmospheric mercury deposition. Lakes were selected to obtain a range of simple morphometrics such as area, depth, volume and catchment area, with corresponding differences in water residence times (WRT), ranging from 0.1 to 7.5 years. Total mercury (THg) and mono‐methylmercury (MMHg) concentrations correlated positively but weakly with DOC in lake surface waters along the climate gradient, consistent with lower ecosystem and organic matter productivity at higher latitudes. Specific UV absorbance, an indicator of terrestrial organic matter sources, was found to explain some residual variability in THg not explained by DOC. Concentrations of THg and MMHg and their ratios with DOC, particularly the MMHg : DOC ratio as well as %MMHg, were best explained by inverse associations with WRT. These relationships were apparent both within and between regions along the latitudinal gradient, suggesting a net‐negative effect of in‐lake processing on THg and MMHg concentrations associated with longer WRTs. Since the water MMHg : DOC ratio was previously shown to explain foodweb MMHg in the same study lakes, our results suggest that smaller lakes with shorter residence times are more susceptible to MMHg exposure even at low levels of inorganic Hg loading or MMHg production.

Rainstorm events shift the molecular composition and export of dissolved organic matter in a large drinking water reservoir in China: High frequency buoys and field observations

Rainstorm events can flush large amounts of terrestrial organic-rich material into lakes that are used for drinking water. To date, few studies have been carried out to investigate how rainstorm events change the molecular composition, bio-lability, and flux of upstream-imported dissolved organic matter (DOM), which can impact the odor and taste of drinking water as well as the efficiency of wastewater treatment. We undertook high-frequency buoy monitoring and point sample collection (n = 495), during high, moderate, and low inflow discharge, in Lake Qiandao, a key drinking water source for about 10 million people. Data from two online fluorescent DOM sensors deployed and field samples collected at the river site, Jiekou, and the lake site, Xiaojinshan, showed that rainstorm events increased the specific UV absorbance (SUVA254), humification index (HIX), humic-like components (C1-C2), and FT-ICR MS derived condensed aromatic and polyphenolic compounds (p < 0.001) and decreased the spectral slope of DOM (S275–295), spectral slope ratio (SR), biological index (BIX), and highly bio-degradable peptide-like and aliphatic substances (p < 0.001). Our results suggest that rainstorm events enhanced the export to the lake of colored, hydrophobic, and aromatic DOM. Upstream-derived dissolved organic carbon (DOC) concentrations decreased (p < 0.001), while DOC bio-availability (BDOC) increased only slightly (p < 0.05) during rainstorm events. The loss rate of DOC in Lake Qiandao is 0.82 × 104 t C yr−1, of which 0.30 × 104 t C yr−1 is highly bio-labile, and higher occurrences of both ≥ 25 mm d − 1 and ≥ 50 mm d − 1 rainfall events are anticipated by linear fittings for this region in the future. The application of in situ fluorescence sensors provides an early warning of DOC surge incidents caused by rainstorm events and may be useful in advising drinking water treatment plant managers of changes in raw water DOM quality and treatability.

Development and Validation of simple UV Spectrophotometric Method for the Determination of Racecodotril both in Bulk and Marketed Dosage Formulations

Racecodotril (RCT), (N-[2-[(acetylthio) methyl]-1- oxo- 3- phenyl propyl] -glycine phenylmethyl ester) is an enkephalinase inhibitor. A rapid, specific, and economic UV spectrophotometric two methods have been developed using a solvent composed of methanol to determine the RCT content in bulk and pharmaceutical dosage formulations. Method A is the absorbance maxima method, in which λmax is 231 nm, linearity was observed in the concentration range 10 to 100 μg/mL for all the two methods, and exhibited good correlation coefficient for method A (r2 = 0.9991) and excellent mean recovery (98.22–102.77%). Method B is the area under curve (AUC), in which λmax 226 to 236 nm was selected for estimation of RCT and exhibited a good correlation coefficient for method B (r2 = 0.9953). The method was validated statistically and by recovery studies for linearity, precision, repeatability, and reproducibility. The obtained results reveal that the method can be employed for the routine analysis of RCT in bulks, as well as, in the commercial formulations.

Concentration and biodegradability of dissolved organic carbon derived from soils: A global perspective

Dissolved organic carbon (DOC), as active and mobile carbon, plays a critical role in terrestrial and aquatic ecosystems. However, it remains unclear how the concentration and biodegradability of soil-derived DOC (extracted from pore water or soil leachates) vary over a global scale and what determines the variations in DOC concentration and biodegradability. Here we addressed this issue by synthesizing the dataset involved in 121 sites from 39 literatures worldwide, and analyzed the patterns and drivers of DOC concentration and biodegradability. Our results showed that the DOC concentration in either pore water or soil leachates varied considerably, with mean values of 33.2 mg L−1 in pore water and 213.5 mg kg−1 in soil leachates, respectively. Mean annual precipitation (MAP) was the dominant control on the variability in soil-derived DOC concentration. Our results also revealed that the biodegradability of DOC in pore water was significantly lower than that in soil leachates, with the means of 16.5% versus 28.7%, respectively. Specific UV absorbance (SUVA254, a parameter used for evaluating dissolved aromatic carbon content) was the primary indicator predicting the spatial variation in DOC biodegradability, whereas MAP exerted limited effects on DOC biodegradability. These results demonstrate the high biodegradability of soil-derived DOC, highlighting its crucial role in the global carbon cycle under climate change.

Microwave–assisted synthesis of nanoscale tungsten trioxide hydrate with excellent photocatalytic activity under visible irradiation

Tungsten trioxide hydrate (WO3⋅1/3H2O) nanoparticles (NPs) were prepared via a microwave–assisted synthetic pathway by using Na2WO4·2H2O and PdCl2 as precursors. Microstructure and morphology of as–prepared WO3⋅1/3H2O NPs were investigated through X–ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FT–IR) spectra, while porosity and bandgap through specific surface area and UV–vis absorption spectroscopy. It was found that Pd2+ ions played a crucial role in the formation of WO3⋅1/3H2O NPs, and thus a possible formation mechanism was proposed based on the growth processes. The photocatalytic property of WO3⋅1/3H2O NPs was evaluated on the basis of Rhodamine B (RhB) degradation in aqueous solutions under simulated visible irradiation. Photocatalytic experimental results indicated that as–prepared WO3⋅1/3H2O NPs exhibited much more superior photocatalytic activity by contrast to that of the commercial WO3.

Impact of conventional agriculture on the concentration and quality of water-extractable organic matter (WEOM) in the surface horizons of Retisols—A case study from the Carpathian Foothills in Poland

In spite of many studies focused on the impact of land use changes on soil organic carbon (SOC) and the total nitrogen (TN) and soil organic matter (SOM) budget, less is known about the fate of water-extractable organic matter (WEOM) after the conversion of forestland to conventional farmland. The main aims of this study were: 1) to determine the concentration of water-extractable organic carbon (WEOC) and water-extractable total nitrogen (WETN) in topsoil horizons of forestland soils and cropland soils in the Carpathian Foothills in southern Poland and 2) to determine the quality of WEOM in topsoil horizons of forestland soils and cropland soils. Soil samples from topsoil horizons of forestland soils (Oi and Ah horizons) and cropland soils (Ap horizons) were collected and the concentration of WEOC and WETN was determined. In addition, the quality of WEOM was determined using ultraviolet-visible (UV–vis) spectroscopy and Fourier-transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The results of this comparative study clearly indicate that conventional agriculture significantly affects the concentration and quality of WEOM in surface soil horizons of Retisols in the Carpathian Foothills in southern Poland. Surface horizons of arable soils (Ap horizons) are characterized by a significantly lower mean concentration of WEOC and WETN in comparison with surface horizons of forestland soils (Oi and Ah horizons), and reflect changes in the content of bulk SOC and TN due to soil tillage. Mean concentrations of WEOC and WETN in the studied Ap horizons of arable soils are 1.98 mg l−1 and 0.15 mg l−1, respectively while the mean concentrations of WEOC and WETN in the Ah horizons of forestland soils are 15.53 mg l−1 and 0.84 mg l−1, respectively. The studied Oi horizons of forestland soils are characterized by the highest mean concentration of WEOC (44.53 mg l−1) and WETN (6.22 mg l−1). Mean specific UV absorbance values at wavelength of 254 nm (SUVA254) was the highest for WEOM from Ap horizons indicating the highest transformation of WEOM in these horizons. Mean FTIR-ATR absorption bands of WEOM obtained from Oi and Ah horizons are much more intensive than the bands of WEOM from Ap horizons, which is related to significantly lower concentration of WEOM in the latter horizons in comparison with Oi and Ah horizons of forestland soils.