An insight into PANI-TiO2 photocatalysis of refractory organic matter through molecular size fractionation.

Refractory organic matter (RfOM) is ubiquitous in aquatic environment and plays various roles in regulating the fate, transport, toxicity, and bioavailability of chemical species, such as metals, emerging organic contaminants, and nanomaterials. RfOM is mainly represented by humic acids (HA) as the acid insoluble fraction of organic matrix. Considering the complex and multicomponent characteristic of HA, a detailed study was designed to elucidate the fate of molecular size fractions (MSFrs) of humic under solar irradiation in the presence of polyaniline (PANI)-modified TiO2 composites. Humic acid as a consortium of diverse molecular size fractions with different tendencies towards oxidation requires further assessment by UV-vis and fluorescence spectroscopic parameters complementary to previous studies on the photocatalytic degradation of RfOM by using TiO2 and PANI-TiO2 composites. Absorbance-based removal efficiencies under initial and post-photocatalytic conditions showed a re-formation trend during photocatalysis in the presence of PANI and TiO2 where higher MSFrs were transformed to lower MSFrs that was apparent for < 3 kDa fraction. Completely different profiles were observed for PT-41 and PT-81 indicating similar degradation pathways independent of PANI ratio in the composite. As confirmed by the investigated parameters, formation of both 450 kDa and 220 kDa MSFrs were evident under all conditions indicating in situ generation of higher MSFrs. The eligibility of coupled absorbance-fluorescence measurements to discern molecular size distribution of humic acid via oxidative degradation was also investigated. Excitation-emission matrix (EEM) contour plots emphasized the ratio dependency of PANI modification of TiO2 and revealed sample specific variations that were more pronounced in terms of the emergence of tyrosine- and tryptophan-like aromatic proteins.

Do nanoparticles and colloids replenish soil phosphorus in the rhizosphere of winter wheat?

The rhizosphere is generally depleted in nutrients, but as a hotspot of microbial activity it fosters crop P uptake. We hypothesized that P contents of water extractable nanoparticles (<0.1 µm) and small sized colloids (<0.45 µm) differ between non-rhizosphere and rhizosphere soil. To test this hypothesis, rhizosphere and non-rhizosphere soils (Luvisol and Cambisol) were sampled at harvest period of winter wheat near Selhausen (Germany). Microaggregate and colloidal fractions in the size range of 53-250 µm, 20-53 µm, 0.45-20 µm, and <0.45 µm were separated by wet-sieving and centrifugation. Subsequently, the colloids <0.45 µm were further isolated in 0.66-20 nm, 20-100 nm and 100-450 nm fractions using asymmetric flow field flow fractionation (AF4) and directly analyzed by online coupled organic carbon detector (OCD) and inductively coupled plasma mass spectrometry (ICP-MS) for element composition. No significant differences (p > 0.05) were measured between rhizosphere and non-rhizosphere soil P contents of microaggregate fractions. The rhizosphere soil, however, showed ∼26 % depletion of average P content in the 0.66-20 nm fraction, which went along with an enrichment of P content of the 100-450 nm fraction by a factor of two. Apparently, P uptake by plants results in a redistribution of P in the rhizosphere, with small nanoparticles providing available P to plants while excess residual P is bound to fine colloids.

Size and polarity fractions of mobile organic matter from manure affect the sorption of sulfadiazine, caffeine and atenolol in soil.

Waste-derived organics introduced to soils along with pharmaceutical active compounds (PhAC) are a crude mixture of compounds occurring in various size and polarity fractions. They affect the sorption of PhACs to soil; however, the relevant knowledge is still insufficient. The effects of different size and polarity fractions of manure-derived mobile organic matter (<63 µm) on the sorption of sulfadiazine, caffeine and atenolol to five topsoils were investigated. Mobilization of the PhACs was strongest in the presence of dissolved organic matter (mDOM, <0.45 µm), with a reduction of Kd of sulfadiazine, caffeine and atenolol by mean factors of 0.66, 0.57 and 0.41, respectively. The mobilizing effects of colloidal organic matter (0.45-10 µm) were slightly smaller. Fine particulate organic matter (10-63 µm) reduced the sorption of the PhACs in slightly acidic soils (pH 6.0), but increased it in strongly acidic soil (pH 4.3). Furthermore, hydrophobic (HO-mDOM) and hydrophilic (HI-mDOM) fractions of mDOM reduced the sorption capacity but increased the sorption nonlinearity of PhACs in soils. Effects of HO-mDOM and HI-mDOM were PhAC specific. It is suggested to consider the varying impacts of mobile fractions in animal manure and/or treated wastewater in evaluating the fate and environmental relevance of associated PhACs.

Thermal Studies of Fractionated Lignite and Brown Coal Fly Ashes.

Coal fly ash (CFA), a by-product of coal combustion, is a valuable raw material for various applications. However, the heterogeneous nature of the composition and properties of CFA provides challenges to its effective usage and utilisation. This study investigates the thermal behaviour of the fly ashes of lignite (FA1) and brown coal (FA2) and their fractions obtained by dry aerodynamic separation. Thermal analysis techniques, including thermogravimetry (TG), differential scanning calorimetry (DSC), and evolved gas analysis (EGA), were used to characterise the behaviour of the fly ash fractions while heating up to 1250 °C. The results reveal distinct differences in the thermal behaviour between ash types and among their different size fractions. For the FA1 ashes, the concentration of calcium-rich compounds and the level of recrystallisation at 950 °C increased with the decrease in particle size. The most abundant detected newly formed minerals were anhydrite, gehlenite, and anorthite, while coarser fractions were rich in quartz and mullite. For the FA2 ashes, the temperature of the onset of melting and agglomeration decreased with decreasing particle size and was already observed at 995 °C. Coarser fractions mostly remain unchanged, with a slight increase in quartz, mullite, and hematite content. Recrystallisation takes place in less extension compared to the FA1 ashes. The findings demonstrate that the aerodynamic separation of fly ashes into different size fractions can produce materials with varied thermal properties and reactivity, which can be used for specific applications. This study highlights the importance of thermal analysis in characterising fly ash properties and understanding their potential for utilisation in various applications involving thermal treatment or exposure to high-temperature conditions. Further research on advanced separation techniques and the in-depth characterisation of fly ash fractions is necessary to obtain materials with desired thermal properties and identify their most beneficial applications.

Seasonal variation of arsenic in PM10 and PMx in an urban park: The influence of vegetation-related biomethylation on the distribution of its organic species and air quality.

Arsenic (As) levels in particulate matter (PM) are routinely monitored in cities of developed countries. Despite advances in the knowledge of its inorganic species in PM in urban areas, organic species are often overlooked with no information on their behaviour in urban parks - areas with increased potential for As biomethylation. Therefore, the aim of this study was to characterize As distribution, bioaccessibility, seasonal variation and speciation (AsIII, AsV, MMA, DMA and TMAO) in PMx-PM10 of an urban park. Two sites with different distance from the road were selected for winter and summer sampling. From the PM samples, we gravimetrically determined PM10 concentrations in the air and via ICP-MS the total As content there. To assess the portion of bioaccessible As, water extractable As content was analysed. Simultaneously, the As species in PM10 water extracts were analysed via coupling of HPLC with ICP-MS method. There was no seasonal difference in PM10 concentration in the park, probably due to the increased summer PM load related to recreational activities in the park and park design. Spatial distribution of total As in PM10 and As fractional distribution in PMx suggested that As mostly didn't originate from traffic although highest As content was observed in the fine fraction (PM2.5) related to combustion processes. However, significant winter increase of As (determined by AsIII and AsV) despite the unchanged concentration of PM10 indicated a decisive influence of household heating-related combustion and possibly influence of reduced vegetation density. As present in the PM10 was mostly in bioaccessible form. Seasonal influence of As biomethylation was clearly demonstrated on the TMAO specie during the summer campaign. Except the significant summer TMAO increase, the results also indicated the biomethylation influence on DMA. Therefore, an increased risk of exposure to organic As species in urban parks can be expected during summer.

Heavy metal migration dynamics and solid-liquid distribution strategy in abandoned tailing soils.

The tailings soil originating from an abandoned sulfur-iron mine in Sichuan Province, China, exhibits elevated concentrations of heavy metals (HMs) and possesses limited soil conservation capacity. Variability soil particle size fractions (PSFs) contributes to an increased risk of HMs ion migration. Existing research on HMs behavior has focused on the bulk soil scale, resulting in a dearth of comprehensive information concerning different particle sizes and colloid scales. We collected soil samples from upstream source (XWA), migration path (XWB), and downstream farmland (XWC) of an abandoned tailing and categorized into sand, silt, clay, colloid and dissolved, respectively. The investigation primarily aimed to elucidate the solid-liquid distribution trade-off strategies of soil HMs along migration pathway. Results show that PSFs composition predominantly influences HMs solid-liquid distribution. In the mining area, large particles serve as the principal component for HMs enrichment. However, along the migration pathway, the proportion of highly mobile fine particles increases, shifting HMs from solid to liquid phase. Furthermore, inorganic elements such as Mg, Al, and Fe influence on HMs distribution within PSFs through various reactions, whereas organic matter and glomalin-related soil protein (GRSP) also exert regulatory roles. Increasing the proportion of large particles can reduce the risk of HMs migration.

Abundance and biomass of copepods and cladocerans in Atlantic and Arctic domains of the Barents Sea ecosystem.

Zooplankton in the Barents Sea have been monitored annually with a standard procedure with determination of size-fractioned biomass since the mid-1980s. Biomass of copepods and cladocerans was estimated based on measured abundance and individual weights taken from literature. Calanus species were dominant, making up ~85% of the estimated biomass of copepods. The second most important taxon was Oithona spp. (~0.5 g dry weight (dw) m-2, ~10%), followed by Metridia spp. (~0.15 g dw m-2, 2-3%) and Pseudocalanus spp. (0.10-0.15 g dw m-2, 1-5%). Estimated biomass of cladoceran taxa (Evadne and Podon) was low (0.01 g dw m-2). Calanus spp. contributed most of the biomass of the medium size fraction (1-2 mm), whereas small copepod species (Oithona, Pseudocalanus and others) contributed to the small size fraction (<1 mm). Estimated biomass of Calanus spp. and of the sum of small copepod species were both positively correlated with measured total zooplankton biomass (R2 = 0.72 and 0.34, respectively). The biomass ratio of small copepod species to Calanus was similar in Atlantic and Arctic water masses (~0.15-0.2) but tended to increase with decreasing total biomass. This suggests a shift to relatively larger roles of small copepods as Calanus and total biomass decrease.

Effects of Road Dust Particle Size on Mineralogy, Chemical Bulk Content, Pollution and Health Risk Analyses.

Because of the rising environmental and health concerns associated with atmospheric pollution caused by potentially toxic elements (PTEs), several road dust studies have been performed across the world in recent decades. This paper illustrates the effects of particle size on the PTE contents, mineralogical composition, environmental pollution and health risk assessments in road dust from Barcelona (Spain). The samples were sieved into five size fractions ranging from <45 to 500-800 µm. Although the major mineral contents (tectosilicates, phyllosilicates, and carbonates) were profuse in all fractions, the identified inhalable PTE particles (e.g., Fe, Cr, Cu, Zn, Ni, and REE), with size < 10 µm, were more pervasive in the finest fraction (<45 µm). This is consistent with the concentrations measured: the finest fractions were richer in PTEs than the coarser ones, resulting in a direct correlation with the enrichment factor (EFx), geo-accumulation (Igeo), and non-carcinogenic (HI) and carcinogenic (CRI) values. Igeo and EFx values can be appropriate tracers for some common elements (e.g., Zn, Sb, Sn, Cu, and Cr), but they do not seem adequate for anthropogenic particles accumulated at concentrations similar to the geogenic background. Overall, the HI and CRI values obtained in Barcelona were acceptable, reflecting no serious health impacts in the study area, except for Cr. Our results suggest that fine dust particles are a more suitable fraction to conduct pollution and health risk assessments than coarser ones, although the EFx, Igeo, HI, and CRI threshold values should be redefined in the future to include all emergent pollutants as well. In summary, monitoring programs should include at least the road dust evaluation of <45 µm particles, which can be performed with a simple sieving method, which is both time- and cost-effective.

Hydrocarbons in size-fractionated plankton of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign).

Aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs, respectively) were analyzed in the dissolved fraction (<0.7 µm) of surface water and in various particulate/planktonic size fractions (0.7-60, 60-200, 200-500 and 500-1000 µm) collected at the deep chlorophyll maximum, along a North-South transect in the Mediterranean Sea in spring 2019 (MERITE-HIPPOCAMPE campaign). Suspended particulate matter, biomass, total chlorophyll a, particulate organic carbon, C and N isotopic ratios, and lipid biomarkers were also determined to help characterizing the size-fractionated plankton and highlight the potential link with the content in AHs and PAHs in these size fractions. Æ©28AH concentrations ranged 18-489 ng L-1 for water, 3.9-72 µg g-1 dry weight (dw) for the size fraction 0.7-60 µm, and 3.4-55 µg g-1 dw for the fractions 60-200, 200-500 and 500-1000 µm. AH molecular profiles revealed that they were mainly of biogenic origin. Æ©14PAH concentrations were 0.9-16 ng L-1 for water, and Æ©27PAH concentrations were 53-220 ng g-1 dw for the fraction 0.7-60 µm and 35-255 ng g-1 dw for the three higher fractions, phenanthrene being the most abundant compound in planktonic compartment. Two processes were evidenced concerning the PAH patterns, the bioreduction, i.e., the decrease in concentrations from the small size fractions (0.7-60 and 60-200 µm) to the higher ones (200-500 µm and 500-1000 µm), and the biodilution, i.e., the decrease in concentrations in plankton at higher suspended matter or biomass, especially for the 0.7-60 and 60-200-µm size fractions. We estimated the biological pump fluxes of Æ©27PAHs below 100-m depth in the Western Mediterranean Sea at 15 ± 10 ng m-2 day-1, which is comparable to those previously reported in the South Pacific and Indian Ocean.

Fate of Cd during mineral transformation by sulfate-reducing bacteria in clay-size fractions from soils with high geochemical background.

Sulfate-reducing bacteria (SRB) can immobilize heavy metals in soils through biomineralization, and the parent rock and minerals in the soil are critical to the immobilization efficiency of SRB. To date, there is little knowledge about the fate of Cd associated with the parent rocks and minerals of soil during Cd immobilized by SRB. In this study, we created a model system using clay-size fraction of soil and SRB to explore the role of SRB in immobilizing Cd in soils from stratigraphic successions with high geochemical background. In the system, clay-size fractions (particle size < 2 µm) with concentration of Cd (0.24-2.84 mg/kg) were extracted from soils for bacteria inoculation. After SRB reaction for 10 days, the Cd fraction tended to transform into iron-manganese bound. Further, two clay-size fractions, i.e., the non-crystalline iron oxide (Fe-OX) and the crystalline iron oxide (Fe-CBD), were separated by extraction. The reaction of SRB with them verified the transformation of primary iron-bearing minerals into secondary iron-bearing minerals, which contributed to Cd redistribution. This study shows that SRB could exploit the composition and structure of minerals to induce mineral recrystallization, thereby aggravating Cd redistribution and immobilization in clay-size fractions from stratigraphic successions with high geochemical background.

Quantification of microplastic by particle size down to 1.1 µm in surface road dust in an urban city, Japan.

The impact of microplastics (MPs, plastic particles ≤5 mm) on ecosystems is of great concern. Road surfaces represent a significant source of MPs where plastic fragments are physically and chemically reduced to MPs. However, the literature lacks information on fragmentation tendencies below 11 µm. This study aimed to characterize the occurrence of MPs in road dust in different size fractions down to 1.1 µm. Road dust was collected at five sites near a major road in Kusatsu city, Japan, and partitioned by size into 13 fractions (1.1-850 µm). The coarser fractions accounted for a greater proportion of the dust. The percentage of organic matter, determined by loss on ignition, increased as the fractions became finer. Pyrolysis-gas chromatography-mass spectrometry was used to quantify 12 types of polymers in each fraction. The dust was found to contain nine types of MP, namely, polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polystyrene (PS), styrene/butadiene rubber (SBR), acrylonitrile/butadiene/styrene resin (ABS), polycarbonate (PC), polymethylmethacrylate (PMMA), and polyamide 66 (PA66). The total MP concentration in road dust particles by particle size fraction (concentrationf) began to increase from the 125-250 µm fraction and remained elevated in finer fractions down to 1.1 µm, indicating that MPs in the road dust micronized to at least 1.1 µm. However, for individual polymer types, the tendency for concentrationf to increase or decrease with particle size fraction varied: the concentrationf of some polymers, such as PE and PVC, remained elevated in fractions down to 1.1 µm; the concentrationf of SBR, a rubber-MP, showed a stable or decreasing trend in fractions of 7.0-11 µm and finer. Particles of PE, PVC, and some other plastics might become increasingly finer, even down to 1.1 µm. Further research is needed to understand the comminution limits of these polymers under pertinent environmental conditions.

Modification of Saharan dust size distribution during its transport over the Anatolian Plateau.

Particle number size distribution in dust plumes and its modification as the plume travels over the Anatolia were investigated by measuring particle number size distributions at two stations: one located on the Mediterranean coast of Turkey and the other on the Anatolian plateau. Clustering of backtrajectories revealed six trajectory clusters at the Marmaris station and nine clusters at the Ankara station. Cluster 6 in Marmaris and clusters 6, 7 and 9 in Ankara stations had the potential to transport Saharan dust to stations. Concentration of particles with D ≤ 1 µm increased during dust events in the Ankara station, but decreased at the Marmaris station. Higher PM1 concentrations during the non-dust period at the Marmaris station were attributed to the dominance of secondary particle formation on PM1 concentrations. Occurrence of sea salt episodes at the Marmaris station and anthropogenic episodes at the Ankara station affects the distribution of episodes. If different types of episodes are not differentiated and all episodes are considered as dust, it can lead to misleadingly high dust episodes in winter. Six Saharan dust episodes were sequentially intercepted first at the Marmaris and then at the Ankara stations. These episodes were used to study how dust size distribution is modified as the plume travels from the Mediterranean coast to central Anatolia. On the average, travel time between the two stations is 1-2 days. Particle number concentrations in 1 µm ≤ D ≤ 110 µm size range were consistently high at the Ankara station, indicating that local sources play a role in modifying the number size distribution as the plume travels over the Anatolian plateau.

Competitive adsorption and desorption of three antibiotics in distinct soil aggregate size fractions.

Multiple antibiotics that are used in veterinary medicine coexist in soils, but their interaction and the effects on adsorption and desorption in soils have not been extensively studied. In this study, using batch experiments, we evaluated the adsorption and desorption of sulfadiazine (SDZ), tetracycline (TC), and norfloxacin (NFX) using four different soil aggregate size fractions and discovered that: (1) TC had the highest adsorption (76-98 %) and the lowest desorption in each tested system, whereas SDZ showed opposite adsorption and desorption ability, (2) the highest adsorption and the lowest desorption of all three tested antibiotics were observed with soil macroaggregates (250-2000 µm) in all the cases; in contrast, opposite adsorption and desorption ability were observed for soil clay (<53 µm), and (3) adsorption of each antibiotic was in the following order: single system (71-89 %) > binary system (56-84 %) > ternary system (50-78 %); however, desorption were in the reverse order. The Freundlich equation fitting and Brunauer-Emmett-Teller (BET) analysis further demonstrated that the adsorption competition between the tested antibiotics depended mainly on the specific surface area of each soil aggregate size fractions and its chemical properties. In conclusion, soil macroaggregates play a key role in the retention of antibiotics in soils, and the coexistence of multiple antibiotics greatly increases leaching risk.

Contamination of planktonic food webs in the Mediterranean Sea: Setting the frame for the MERITE-HIPPOCAMPE oceanographic cruise (spring 2019).

This paper looks at experiential feedback and the technical and scientific challenges tied to the MERITE-HIPPOCAMPE cruise that took place in the Mediterranean Sea in spring 2019. This cruise proposes an innovative approach to investigate the accumulation and transfer of inorganic and organic contaminants within the planktonic food webs. We present detailed information on how the cruise worked, including 1) the cruise track and sampling stations, 2) the overall strategy, based mainly on the collection of plankton, suspended particles and water at the deep chlorophyll maximum, and the separation of these particles and planktonic organisms into various size fractions, as well as the collection of atmospheric deposition, 3) the operations performed and material used at each station, and 4) the sequence of operations and main parameters analysed. The paper also provides the main environmental conditions that were prevailing during the campaign. Lastly, we present the types of articles produced based on work completed by the cruise that are part of this special issue.

Contamination levels and source apportionment of potentially toxic elements in size-fractionated road dust of Moscow.

The distributions of potentially toxic elements (PTEs) among PM1, PM1-10, PM10-50, and PM50-1000 fractions of the road dust were studied in the western and eastern parts of Moscow, impacted mainly by the road transport and the industrial sector, respectively. The partitioning of PTEs in road dust can provide more precise information on pollution sources and its further interpretation regarding human health risks. The concentrations of PTEs were analyzed by mass and atomic emission inductively coupled plasma spectrometry. Differences in the results between the western and eastern parts of the city were caused by the dissimilarity between traffic and industrial emissions. The source apportionment of the PTEs was carried out using absolute principal component analysis with multiple linear regressions (PCA/APCS-MLR). The contribution from anthropogenic sources was significant to PM1 and PM1-10 particles. In coarser fractions (PM10-50, PM50-1000), it decreased due to the input with the wind-induced resuspension of soil and rock particles. In the eastern part of the city, the accumulation of PTEs (especially Mo, Sb, Cd, Sn, Bi, Co, and As) is the most active in PM1-10, while in the western part, it is most pronounced in PM1 (especially Pb, Cu, Cr, and W) which is associated with differences in the size of particles coming from traffic and industrial sources. In the eastern part of Moscow, in comparison with the western part, the contribution from industrial sources to the accumulation of PTEs in all particle size fractions was higher by 10-30%. In the western part of Moscow, the finest particles PM1 and PM1-10 demonstrate the trend of rising pollution levels with the increase in road size, while in the eastern part of the city, only coarse particles PM50-1000 show the same trend. In the fractions PM1 and PM1-10 of road dust, a significant contribution was made by anthropogenic sources; however, its role decreased in the coarse fractions-PM10-50 and especially in PM50-1000- due to the influence of roadside soils and their parent material.

Soil particle size fractions affect arsenic (As) release and speciation: Insights into dissolved organic matter and functional genes.

Soil particle size fractions (PSFs) are important for arsenic (As) partitioning, migration, and speciation transformation. However, information is lacking about the environmental fate of As and its distribution on different PSFs. In the present study, two types of soils from mining areas were divided into four PSFs, including coarse sand (2-0.25 mm), fine sand (0.25-0.05 mm), silt (0.05-0.002 mm), and clay (< 0.002 mm) fractions. The results showed that As was enriched in the coarse sand, which was primarily affected by the content of organic carbon (OC), followed by iron (Fe), aluminum (Al), and manganese (Mn) (hydr)oxides. The elevated total As (TAs), As(III), organic As, Fe(II), and dissolved organic carbon (DOC) concentrations were mainly originated from the clay fraction. The intensified humification degree of DOM and promoted bacterial metabolism related to As/iron bioreduction were also exhibited in the clay fractions. The dynamics of As fractions in soils indicated the potential formation of secondary minerals and re-adsorption of As in the PSFs. The highest abundances of arrA, arsC, arsM, and Geo genes were found in the clay fraction, implying that the clay fraction potentially released more As, including As(III) and organic As. Results from the correlation analysis showed that elevated DOC concentrations promoted the catabolic responses of iron-reducing microorganisms and triggered microbial As detoxification. Overall, this study provides valuable information and guidance for the remediation of As-contaminated soils.

Metabolic activity and community structure of prokaryotes associated with particles in the twilight zone of the South China Sea.

The twilight zone is an important depth of the ocean where particulate organic matter (POM) remineralization takes place, and prokaryotes contribute to more than 70% of the estimated remineralization. However, little is known about the microbial community and metabolic activity associated with different particles in the twilight zone. The composition and distribution of particle-attached prokaryotes in the twilight zone of the South China Sea (SCS) were investigated using high-throughput sequencing and quantitative PCR, together with the Biolog Ecoplate™ microplates culture to analyze the microbial metabolic activity. We found that α- and γ-Proteobacteria dominating at the lower and upper boundary of the twilight zone, respectively; Methanosarcinales and Halobacteriales of the Euyarchaeota occupied in the larger particles at the upper boundary. Similar microbial community existed between euphotic layer and the upper boundary. Higher amount of shared Operational Taxonomic Units (OTUs) in the larger particles along the water depths, might be due to the fast sinking and major contribution of carbon flux of the larger particles from the euphotic layer. In addition to polymers as the major carbon source, carbohydrates and amino acids were preferentially used by microbial community at the upper and lower boundary, respectively. This could potentially be attributed to the metabolic capabilities of attached microbial groups in different particles, and reflected the initial preference of the carbon source by the natural microbes in the twilight zone as well. The microbial structure and carbon metabolic profiles could be complemented with metatranscriptomic analysis in future studies to augment the understanding of the complex carbon cycling pathways in the twilight zone.

Phytoplankton Sources and Sinks of Dimethylsulphoniopropionate (DMSP) in Temperate Coastal Waters of Australia.

The ecologically important organic sulfur compound, dimethylsulfoniopropionate (DMSP), is ubiquitous in marine environments. Produced by some species of phytoplankton and bacteria, it plays a key role in cellular responses to environmental change. Recently, uptake of DMSP by non-DMSP-producing phytoplankton species has been demonstrated, highlighting knowledge gaps concerning DMSP distribution through the marine microbial food web. In this study, we traced the uptake and distribution of DMSP through a natural marine microbial community collected from off the eastern coastline Australia. We found a diverse phytoplankton community representing six major taxonomic groups and conducted DMSP-enrichment experiments both on the whole community, and the community separated into large (≥8.0 µm), medium (3.0−8.0 µm), and small (0.2−3.0 µm) size fractions. Our results revealed active uptake of DMSP in all three size fractions of the community, with the largest fraction (>8 µm) forming the major DMSP sink, where enrichment resulted in an increase of DMSPp by 144%. We observed evidence for DMSP catabolism in all size fractions with DMSP enrichment, highlighting loss from the system via MeSH or DMS production. Based on taxonomic diversity, we postulate the sources of DMSP were the dinoflagellates, Phaeocystis sp., and Trichodesmium sp., which were present in a relatively high abundance, and the sinks for DMSP were the diatoms and picoeucaryotes in this temperate community. These findings corroborate the role of hitherto disregarded phytoplankton taxa as potentially important players in the cycling of DMSP in coastal waters of Australia and emphasize the need to better understand the fate of accumulated DMSP and its significance in cellular metabolism of non-DMSP producers.

Effect of oxidative and non-oxidative conditions on molecular size fractionation of humic acids: TiO2 and Cu-doped TiO2 photocatalysis.

Natural waters contain some carbonaceous materials referred to as dissolved organic matter, which is mainly composed of humic acids (HA). Owing to its polydispersed character related to the presence of diverse molecular size fractions (< 450 kDa to even < 1 kDa), HA displays curious reactivity in natural waters and during water treatment train. In this study, a system-based stepwise approach was tracked by characterizing HA following photolysis, adsorptive interactions, and solar photocatalysis using bare TiO2, sol-gel prepared TiO2, and their respective Cu-doped specimens complementary to kinetic evaluation on this respect. For this purpose, prior to and following each treatment, HA was monitored by dissolved organic carbon content, UV-vis parameters, and fluorescence features. Attenuated total reflection Fourier transform infrared (FTIR), surface-enhanced Raman scattering spectroscopy (SERS), XRD, SEM, EDAX XPS, and DRS were used to characterize the materials and solutions reported in this study. Most significant quantitative variations were attained in UV-vis spectroscopic parameters along with fluorescence characteristics; however, infrared and Raman profiles displayed slight deviations in qualitative measures. Differentiation between the selected photocatalyst specimens could be visualized through molecular size effects pointing out the significance of HA 10 kDa fraction. For the first time, this study reports the degradation of specific fractions of HA as a function of their molecular size fraction. Cu-TiO2 seems to photocatalyze more effectively the degradation of the diverse HA fractions due to their more extended absorption of solar light by this photocatalyst.

Kinetic modeling of As release from contaminated soils: Consideration of particle size and co-contamination of Cu.

Prediction on the release kinetics of metalloids from soils is challenging due to the physio-chemical heterogeneity of soil and the varying binding abilities of metalloid contaminants on soil. In this study, the kinetics of As(V), together with Cu(II), release from two typical field contaminated soils were investigated by the stirred-flow experiments. We formulated the quantitative models to describe the release kinetics of As(V) from the contaminated soils with consideration of varying soil particle size and presence of Cu(II). The results showed that the release kinetics of As(V) and Cu(II) from different particle size fractions and at different reaction pH was well described by the model. The models also indicated that the bidentate binding sites on goethite were the major contributor for As(V) release, while soil organic matter (SOM) mainly controlled the Cu(II) release. Finer particle size fractions had more significant contributions to As(V) and Cu(II) release due to higher concentrations of reactive metal(loid)s and more reactive adsorbents. Moreover, the models also showed applicability for predicting metal(loid) release from the bulk soils by considering the contribution of each soil particle size fraction, and the kinetic behaviors of two individual contaminants, As(V) and Cu(II), can be modeled independently. Our results provided a modeling framework to predict the release kinetics of metal(loid)s from soils co-contaminated with different cation and anion pollutants with consideration on the effects of physical and chemical heterogeneity of soils.