Transport Vectors Research Articles

Ocean mover's distance: using optimal transport for analysing oceanographic data.

Remote sensing observations from satellites and global biogeochemical models have combined to revolutionize the study of ocean biogeochemical cycling, but comparing the two data streams to each other and across time remains challenging due to the strong spatial-temporal structuring of the ocean. Here, we show that the Wasserstein distance provides a powerful metric for harnessing these structured datasets for better marine ecosystem and climate predictions. The Wasserstein distance complements commonly used point-wise difference methods such as the root-mean-squared error, by quantifying differences in terms of spatial displacement in addition to magnitude. As a test case, we consider chlorophyll (a key indicator of phytoplankton biomass) in the northeast Pacific Ocean, obtained from model simulations, in situ measurements, and satellite observations. We focus on two main applications: (i) comparing model predictions with satellite observations, and (ii) temporal evolution of chlorophyll both seasonally and over longer time frames. The Wasserstein distance successfully isolates temporal and depth variability and quantifies shifts in biogeochemical province boundaries. It also exposes relevant temporal trends in satellite chlorophyll consistent with climate change predictions. Our study shows that optimal transport vectors underlying the Wasserstein distance provide a novel visualization tool for testing models and better understanding temporal dynamics in the ocean.

Proposal for an index of roads and structures for the mapping of non-vegetated urban surfaces using OSM and Sentinel-2 data

The use of volunteered geographic information (VGI), such as OpenStreetMap (OSM), to assist in mapping land use and coverage together with remote sensing images is relatively recent. Most studies have used OSM to assist in sample collection for image classification or aggregated vectors of buildings, transport, and land-use and coverage as ancillary data to support mapping refinements. This study proposes a metric called the “index of roads and structures” (IRS) created on the basis of OSM data with the intention of assisting in the mapping of non-vegetated and non-aquatic urban surfaces. IRS thresholds were defined and supplemented with information derived from the Normalized Difference Vegetation Index (NDVI) and the Modified Normalized Difference Water Index (MNDWI) as a way of extending the restriction between urban and non-urban classes and thus achieving better mapping accuracy. To implement this study, multispectral Sentinel-2 images resampled to 10 m on the ground were processed in the Google Earth Engine (GEE). The IRS is a raster file, in which each pixel is associated with the possibility of being inserted in an urban context; thus, the importance of this index as an aid in mapping urban areas is clear. We have demonstrated the possibility of using the IRS to map non-vegetated urban surfaces in Brazil (8.5 million square kilometers) and obtained a very high accuracy of 91.2%.

Modeling Clothing as a Vector for Transporting Airborne Particles and Pathogens across Indoor Microenvironments.

Evidence suggests that human exposure to airborne particles and associated contaminants, including respiratory pathogens, can persist beyond a single microenvironment. By accumulating such contaminants from air, clothing may function as a transport vector and source of “secondary exposure”. To investigate this function, a novel microenvironmental exposure modeling framework (ABICAM) was developed. This framework was applied to a para-occupational exposure scenario involving the deposition of viable SARS-CoV-2 in respiratory particles (0.5–20 μm) from a primary source onto clothing in a nonhealthcare setting and subsequent resuspension and secondary exposure in a car and home. Variability was assessed through Monte Carlo simulations. The total volume of infectious particles on the occupant’s clothing immediately after work was 4800 μm3 (5th–95th percentiles: 870–32 000 μm3). This value was 61% (5–95%: 17–300%) of the occupant’s primary inhalation exposure in the workplace while unmasked. By arrival at the occupant’s home after a car commute, relatively rapid viral inactivation on cotton clothing had reduced the infectious volume on clothing by 80% (5–95%: 26–99%). Secondary inhalation exposure (after work) was low in the absence of close proximity and physical contact with contaminated clothing. In comparison, the average primary inhalation exposure in the workplace was higher by about 2–3 orders of magnitude. It remains theoretically possible that resuspension and physical contact with contaminated clothing can occasionally transmit SARS-CoV-2 between humans.

The travelling particles: community dynamics of biofilms on microplastics transferred along a salinity gradient

Microplastics (MP), as novel substrata for microbial colonization within aquatic ecosystems, are a matter of growing concern due to their potential to propagate foreign or invasive species across different environments. MP are known to harbour a diversity of microorganisms, yet little is understood of the dynamics of their biofilms and their capacity to successfully displace these microorganisms across different aquatic ecosystems typically marked by steep salinity gradients. To address this, we performed an in situ sequential incubation experiment to simulate MP transport from riverine to coastal seawaters using synthetic (high-density polyethylene, HDPE and tyre wear, TW) and natural (Wood) substrata. Bacterial communities on incubated particles were compared to each other as well as to those in surrounding waters, and their dynamics along the gradient investigated. All communities differed significantly from each other in their overall structure along the salinity gradient and were shaped by different ecological processes. While HDPE communities were governed by environmental selection, those on TW and Wood were dominated by stochastic events of dispersal and drift. Upon transfer into coastal seawaters, an almost complete turnover was observed among HDPE and TW communities. While synthetic particles displaced a minor proportion of communities across the salinity gradient, some of these comprised putatively pathogenic and resistant taxa. Our findings present an extensive assessment of MP biofilms and their dynamics upon displacement across different aquatic systems, presenting new insights into the role of MP as transport vectors.

MicroRNA-631 deriving from bone marrow mesenchymal stem cell exosomes facilitates the malignant behavior of non-small cell lung cancer via modulating the E2F family of transcription factor 2/phosphatidylinositol 3‐kinase/Akt signaling pathway

ABSTRACT The exosomes (Exo) had always been considered as transport vectors for microRNA (miRNA). An increasing number of data had clarified the influence of Exo on the cell progression of non-small cell lung cancer (NSCLC). Nevertheless, its specific mechanism had not yet been verified. This work was to explore the potential mechanism of Exo-derived miR-631 targeting and regulating E2F family of transcription factor 2 (E2F2) to repress the malignant behavior of NSCLC cells. Test of microRNA (miR)-631 and E2F2 in NSCLC was performed. BMSCs-Exo that altered miR-631 was co-cultured with NSCLC cells. Detection of the cloning and progression of NSCLC cells was performed. Testification of the targeting of miR-631 with E2F2 was conducted. In vivo experiments were performed to verify the results in vitro. In short, elevation of miR-631 Exo repressed the advancement and phosphatidylinositol 3‐kinase/Akt activation of NSCLC cells, while silence of miR-631 was in the opposite. In terms of mechanism, miR-631 exerted the influence via targeting E2F2. The coincident results were obtained in animal models. In brief, BMSC-Exo mediated E2F2 via delivering miR-631 to NSCLC cells to modulate the malignant behavior of NSCLC.

Large-Scale Maritime Transport of Hydrogen: Economic Comparison of Liquid Hydrogen and Methanol

For the first time, a comparative economic study between liquid hydrogen and methanol as hydrogen vectors for the bulk transport of hydrogen at sea has been performed. The objective of this study is to gain insight on whether it is cost-effective to produce green hydrogen locally or, instead, import it from another location overseas featuring lower costs of renewable energy. In addition, this study aims to determine the break-even point at which the hydrogen transport alternatives, covered in this study, become more inexpensive. The alternatives covered include the seaborne transport of liquid hydrogen or methanol with the reconversion to hydrogen at the destination through methanol electrolysis or a steam-reforming process. Three different production mass flow rates of hydrogen at the origin are explored, 100 kt/y, 1 Mt/y, and 10 Mt/y, in regard to three representative routes: Brazil–Spain, Brazil–The Netherlands, and Australia–Japan. The findings of this study suggest that for the production of hydrogen at 1 Mt/y with an electricity cost of 40 USD/MWh, liquid hydrogen is the cheapest alternative with a levelized cost of hydrogen at the destination of approximately 2 USD/kg for all of the explored routes. If the synthesized e-methanol reaching the import destination is directly used as an energy vector, the levelized cost of energy contained in this e-methanol practically coincides with that of liquid hydrogen at a mass flow rate of 10 Mt/y at the origin.

The role of nanoplastics on the toxicity of the herbicide phenmedipham, using Danio rerio embryos as model organisms

Once in the aquatic ecosystems, nanoplastics (NPls) can interact with other contaminants acting as vectors of transport and altering their toxicological effects towards organisms. Thus, the present study aims to investigate how polystyrene NPls (44 nm) interact with the herbicide phenmedipham (PHE) and affect its toxicity to zebrafish embryos. Single exposures to 0, 0.015, 0.15, 1.5, 15 and 150 mg/L NPls and 0.02, 0.2, 2 and 20 mg/L PHE were performed. Embryos were also exposed to the binominal combinations: 0.015 mg/L NPls + 2 mg/L PHE, 0.015 mg/L NPls + 20 mg/L PHE, 1.5 mg/L NPls + 2 mg/L PHE and 1.5 mg/L NPls + 20 mg/L PHE. Due to the low solubility of PHE in water, a solvent control was performed (0.01% acetone). PHE was quantified. Mortality, heartbeat and hatching rate, malformations appearance, locomotor behavior and biomarkers related to oxidative stress, neurotransmission and energy budgets were analyzed. During 96 h, NPls and PHE single and combined exposures did not affect embryos development. After 120 h, NPls induced hyperactivity and PHE induced hypoactivity. After 96 h, NPls increased catalase activity and PHE increased glutathione S-transferases activity. On the combination 0.015 mg/L NPls + 20 mg/L PHE, hyperactivity behavior was found, similar to 0.015 mg/L NPls, and cholinesterase activity was inhibited. Additionally, the combination 1.5 mg/L NPls + 20 mg/L PHE increased both catalase and glutathione S-transferases activities. The combination NPls with PHE affected more biochemical endpoints than the single exposures, showing the higher effect of the binominal combinations. Dissimilar interactions effects – no interaction, synergism and antagonism – between NPls and PHE were found. The current study shows that the effects of NPls on bioavailability and toxicity of other contaminants (e.g. PHE) cannot be ignored during the assessment of NPls environmental behavior and risks.

Viral diversity and potential environmental risk in microplastic at watershed scale: Evidence from metagenomic analysis of plastisphere.

Microplastics (MPs) have been considered as a new vector for the long-distance transport of pathogens in aquatic ecosystems. However, the composition of viral communities attached on MPs and their environmental risk are largely unknown. Here, we profiled the viral diversity and potential risk in five different MPs collected from the Beilun River based on metagenomic analysis. Nearly 2863 million raw reads were produced and assembled, and annotation resulted in the identification of 1719 different species of viruses in MPs. Viruses in polypropylene (PP) displayed the highest diversity, with about 250 specific viruses detected. Source tracking of viruses in MPs by the fast expectation-maximization microbial source tracking method (FEAST) demonstrated that viruses in upstream and downstream MPs are two major sources of viruses in estuary. Furthermore, the MP-type-dependent potential environmental risk of viruses was significant based on both antibiotic resistance genes (ARGs) and virulence factors (VFs) detected in viral metagenomes, and PP was confirmed with the highest potential environmental risk. This study reveals the high diversity and potential environmental risk of viruses in different MPs, and provides an important guidance for future environmental monitoring and understanding the potential risks associated with both viral transmission and MPs pollution.

Environmental Racism and the COVID-19 Pandemic

Exposure to air pollutants like ground-level ozone and particulate matter is closely associated with rates of COVID-19 mortality and transmission. Potential biological mechanisms connecting pollution with COVID-19 severity include overexpression of the ACE2 receptor, pollutants’ role as a carrier or transport vector for COVID-19, destruction of the cilia, and compromised immune response of the lungs. Thus, individuals with more long-term exposure to air pollution are much more susceptible to severe symptoms from COVID-19. Social disparities dramatically affect which populations are regularly exposed to air pollutants and therefore incur disproportionate rates of respiratory diseases. Environmental racism and racial segregation have been shown to be significantly and positively associated with exposure to air pollution from sources like car engines and power plants. This results in individuals of low socioeconomic status, people of color, and those living in low-income areas being often exposed to increased levels of air pollution, making them more likely to suffer greater tragedies from COVID-19 and respiratory diseases. The results of this study provide insight into the public policy work necessary to ameliorate health inequities resulting from environmental racism and to prevent worse outcomes from future pandemics.

Hydrotalcite Colloidal Stability and Interactions with Uranium(VI) at Neutral to Alkaline pH.

In the United Kingdom, decommissioning of legacy spent fuel storage facilities involves the retrieval of radioactive sludges that have formed as a result of corrosion of Magnox nuclear fuel. Retrieval of sludges may re-suspend a colloidal fraction of the sludge, thereby potentially enhancing the mobility of radionuclides including uranium. The colloidal properties of the layered double hydroxide (LDH) phase hydrotalcite, a key product of Magnox fuel corrosion, and its interactions with U(VI) are of interest. This is because colloidal hydrotalcite is a potential transport vector for U(VI) under the neutral-to-alkaline conditions characteristic of the legacy storage facilities and other nuclear decommissioning scenarios. Here, a multi-technique approach was used to investigate the colloidal stability of hydrotalcite and the U(VI) sorption mechanism(s) across pH 7–11.5 and with variable U(VI) surface loadings (0.01–1 wt %). Overall, hydrotalcite was found to form stable colloidal suspensions between pH 7 and 11.5, with some evidence for Mg2+ leaching from hydrotalcite colloids at pH ≤ 9. For systems with U present, >98% of U(VI) was removed from the solution in the presence of hydrotalcite, regardless of pH and U loading, although the sorption mode was affected by both pH and U concentrations. Under alkaline conditions, U(VI) surface precipitates formed on the colloidal hydrotalcite nanoparticle surface. Under more circumneutral conditions, Mg2+ leaching from hydrotalcite and more facile exchange of interlayer carbonate with the surrounding solution led to the formation of uranyl carbonate species (e.g., Mg(UO2(CO3)3)2–(aq)). Both X-ray absorption spectroscopy (XAS) and luminescence analysis confirmed that these negatively charged species sorbed as both outer- and inner-sphere tertiary complexes on the hydrotalcite surface. These results demonstrate that hydrotalcite can form pseudo-colloids with U(VI) under a wide range of pH conditions and have clear implications for understanding the uranium behavior in environments where hydrotalcite and other LDHs may be present.

The role of inherited Pb in controlling the quality of speleothem U-Pb ages

Over two decades of technical and application-based advances to the speleothem U-Pb chronometer have cemented this terrestrial archive at the forefront of landscape reconstruction, palaeoclimatology, and palaeoanthropology. The ability to access speleothem palaeoclimate records beyond the 650 ka limit of the U-Th system has opened many avenues to such ‘deep-time’ considerations. Yet still this chronometer remains a challenging analytical exercise, more-so as the technique becomes routinely applied to carbonates with less-than-ideal U/Pb ratios. In this contribution, we review the vadose speleothem U-Pb system, as revealed by 68 previously published isochrons produced from 474 solution-mode analyses across three separate geographical regions. We develop a new statistical parameter of ‘average distance’ to quantify the dispersion or ‘spread’ along the previously published isochrons and compare this with available U and Pb elemental concentrations. Our findings highlight the importance of regional geology and karst morphology in controlling the speleothem's overall U/Pb ratio. Furthermore, we show that variability in the amount of inherited Pb across the sampling layer (average variability of 63% relative to sample average) – not uranium (23% variability) or by extension radiogenic Pb – is a main factor controlling the resulting isochron's quality. This is demonstrated using Z-score distributions of the U and Pb concentrations and isochron average distance values. By making this distinction we hope to initiate further research into Pb-specific transportation vectors through the karst, in addition to physical/chemical processes that fractionate inherited Pb at the speleothem precipitation site. We go on to extend the use of Tera-Wasserburg common Pb anchors to the ‘classical’ U-Pb isochrons as an example of the utility gained by considering the role of inherited Pb within speleothems. Finally we argue that an improved theoretical understanding of inherited Pb distributions within speleothems would greatly benefit solution mode sampling strategies, especially for poor-to-moderate U/Pb speleothems.

Seasonal influence of surface and underground continental runoff over a reef system in a tropical marine protected area

Continental runoff is an important source of solutes and nutrients to coastal coral reefs. Nevertheless, they can also act as local stressors due to high coastal urbanization and the associated release of untreated effluents. Here we aimed to qualitatively evaluate the effects of seasonality over reefs from the Costa dos Corais Marine Protected Area (Brazil) and to identify the influence of rivers and submarine groundwater discharge (SGD) on the reefs' environmental status. Surface waters from the reef lagoon, local rivers and shoreline porewaters were sampled monthly during a year and abiotic parameters were determined. The results showed that the reef lagoon is oligotrophic throughout most of the year, with conditions that generally favor biological activities, such as calcification. Chlorophyll-a, with an average of 0.78 ± 0.43 mg m−3, was significantly correlated with salinity and radon in excess. This indicates the influence of rivers and SGD over the reefs, especially during the rainy season. These are important sources of nutrients, regulating primary production. However, signs of anthropogenic pressure were found in the local rivers. In addition, porewaters had a N:P ratio (27.68 ± 24.45) which could potentially impact surface waters through SGD by increasing the local trophic status. In summary, the studied reefs still present good water quality conditions, although continental runoff is a significant transport vector of anthropogenic solutes to the area.

Do microplastics impair male dominance interactions in fish? A test of the vector hypothesis.

Microplastics (MPs) are widespread in aquatic environments and have become a critical environmental issue in recent years due to their adverse impacts on the physiology, reproduction, and survival of aquatic animals. Exposure to MPs also has the potential to induce sub‐lethal behavioral changes that can affect individual fitness, but these effects are understudied. Many plastic additives introduced during the manufacture of MPs are known endocrine‐disrupting chemicals (EDCs) that mimic the action of natural hormones, alter sexual and competitive behavior, and impair reproductive success in fish. In addition, EDCs and other aquatic contaminants may adhere to MPs in the environment, the latter of which may serve as transport vectors for these compounds (i.e., the vector hypothesis). In this study, we staged territorial contests between control males, and males exposed to virgin MP particles or to MPs previously immersed in one of two environmentally relevant concentrations of 17‐alpha ethinyl estradiol (EE2; 5 ng/L and 25 ng/L) to evaluate the independent and synergistic effects of exposure to MPs and a common environmental estrogen on male–male aggression and competitive territory acquisition in a freshwater fish, Pimephales promelas. Short‐term (30 days) dietary exposure to MPs did not impair the ability of males to successfully compete for and obtain a breeding territory. Overall levels of aggression in control and exposed males were also similar across trial series. These results help to fill a critical knowledge gap regarding the direct and indirect (vector‐borne) effects of MPs on the reproductive behavior of aquatic vertebrates in freshwater systems.

Poly(butyl cyanoacrylate) nanoparticles-delivered β-nerve growth factor promotes the neurite outgrowth and reduces the mortality in the rat after traumatic brain injury

Several transport vectors, including nanoparticles, have been reported to be used for the delivery of therapeutic medicines crossing the impermeable blood-brain barrier (BBB) to treat the diseases in the central nerve system (CNS), such as traumatic brain injury (TBI). Poly(n-butyl-2-cyanoacrylate) (PBCA) nanoparticles, made from biocompatible material, are regarded as a better potential delivery tool than others such as gold nanoparticles due to their degradability in vivo. However, little is known whether PBCA nanoparticles can be used to deliver neurotrophic factors into the brain to treat TBI. In this study, we first synthesized PBCA-carried β-nerve growth factor, a neurotrophic agent with a large molecular weight, and then intravenously injected the compound into TBI rats. We found that despite undergoing several synthesis steps and host circulation, β-NGF was able to be successfully delivered into the injured brain by PBCA nanoparticles, still maintain its neurotrophic activity for neurite outgrowth, and reduce the mortality of TBI rats. Our findings indicate that PBCA nanoparticles, with Tween 80, are an efficient delivery vector and a protective reservoir for large molecular therapeutic agents to treat TBI intravenously.

ЄВРОПЕЙСЬКИЙ ВИМІР РОЗВИТКУ ЗАЛІЗНИЧНОГО ТРАНСПОРТУ УКРАЇНИ ЯК ОБ’ЄКТУ КРИТИЧНОЇ ІНФРАСТРУКТУРИ

In the article, the authors analyze the main components of the European integration directions of railway transport of Ukraine, the feature of which is the activation of armed aggression against our state by the Russian Federation. The methodological basis of the research is the current works of domestic scientists, as well as analytical materials on the problems of the European integration of railway transport of Ukraine. To solve the set goal, we used the following forms, methods and methods of research: as historical – for researching the processes of the European integration of railway transport of Ukraine into the transport system of the European Union, methods of analyzing scientific literature regarding the disclosure of the features of the European integration of domestic railway transport, an abstract-logical method for theoretical generalization and formulation of research conclusions, etc. The authors prove that the intensification of armed aggression against Ukraine by the Russian Federation on February 24, 2022 forced both our state and the European Union to update the directions of cooperation. This is due to the fact that railway transport is of strategic importance, because it is thanks to its round-the-clock clear operation that evacuation and military transports are carried out. In addition, Russian armed aggression substantiated the need to rebuild the domestic track to the European standard, which, on the one hand, will make it impossible for the enemy to use railway com- munication routes, and on the other hand, will increase the carrying capacity for the cooperation of our state with European countries. Also, the authors emphasize that railway transport is an object of critical infrastructure, which requires special ap- proaches to its protection. In general, the authors consider such directions of European integration directions of railway transport as legal, economic, technological and safety. Taking into account the experience of the member states of the European Union, rail transport is a component of increasing the country’s military mobility, which consists in simplifying and standardizing the procedures of cross-border military transport. According to the authors, it is the European vector of railway transport develop- ment in Ukraine that will not only improve the economic situation of the industry, but also contribute to the improvement of the defense capability of both our country and the member states of the European Union.

Can Aged Microplastics Be Transport Vectors for Organic Micropollutants? – Sorption and Phytotoxicity Tests

Can Aged Microplastics Be Transport Vectors for Organic Micropollutants? – Sorption and Phytotoxicity Tests

BALLAST WATER: A POLYPHASIC APPROACH IN THE EVALUATION OF POTENTIAL PHYTOPLANKTONIC BIOINVASION

The main transport vector for exotic-invasive species around the world is ballast water in merchant ships, crossing natural biogeographic barriers. This is one of the main factors responsible for the reduction and homogenization of the global biota. As phytoplankton is the main group transported by these vessels, this study assesses the risk of bioinvasion in the port complex of Itajaí and Navegantes (southern Brazil), using a polyphasic approach, mixing classical taxonomy with molecular biology. Ballast water collections were carried out to analyze the traditional taxonomy and for clonal cultivation in the laboratory. A successful cultivation of 12 local strains and 10-ballast water was successful. In the latter case, some fresh water, contrary to the statement by the commanders of the exchange of water in the deep ocean (> 200 m). Molecular identification was performed by sequencing the complete ITS region, confirming the presence of Thalassiosira minuscula Krasske, 1941, harmful and of public health interest, previously not mentioned for the region. The species Pleurosigma W. Smith, 1852; Asterionellopsis glacialis (Castracane) Round, 1990; Trieres mobiliensis (Bailey) Ashworth and E.C. Theriot, 2013; Thalassiosira minima Gaarder, 1951; Skeletonema pseudocostatum Medlin, 1991; Pectinodesmus holtmannii E. Hegewald, C. Bock and Krienitz, 2013; Neodesmus Hindák, 1976; and Pseudopediastrum boryanum (Turpin) E. Hegewald, 2005, were identified. The results indicate the possibility of growth of the species found in the ballast environment, which may negatively alter the disposal environment.
 Keywords: exotic species, molecular identification, marine phytoplankton, port complex of Itajaí and Navegantes.

The Influence of Marina Characteristics on Non-native Colonisation

The marina properties, such as; salinity range, tidal fluctuations, depth, and ascidian presence in-fluence the distribution of invasive non-natives. Transport vectors, aquaculture and fishery practic-es also have an important role in the distribution of invasive non-native species during the bioinva-sion process. We focused on 10 invasive non-native species of marine invertebrates in the UK. This study explained the distribution and ecology of five invasive non-native species (Styela clava (As-cidia), Didemnum vexillum (Ascidia), Caprella mutica (Crustacea), Crepidula fornicata (Gastropo-da), Watersipora subtorquata (Bryozoa)) and the marina characteristics of five invasive non-native species colonization (Austrominius modestus (Arthropoda), Ciona intestinalis (Ascidia), Botrylloides violaceus (Ascidia), Tricellaria inopinata (Bryozoa), Bugula neritina (Bryozoa)) in Wales coasts. The study site deployed settlement tiles in the inner and the outer tile as two positions in each marina: An equal number of vertical and horizontal tiles was deployed at each site with half-sampled at two weeks (very early colonization) and at eight weeks (later colonization). The results showed that some variations in marina characteristics affected the distribution of invasive non-native species. Invasive non-native species abundance, diversity and multivariate structure of the assemblages were very high. The colonization of tiles varied between locations at the entrance and within the marina, but not in any way, and the effect of tile orientation was surprisingly low.

Tracking Microplastics Across the Streambed Interface: Using Laser‐Induced‐Fluorescence to Quantitatively Analyze Microplastic Transport in an Experimental Flume

AbstractRivers and streams are a primary transport vector for microplastics (MPs), connecting terrestrial sources to marine environments. While previous studies indicated that pore‐scale MPs can accumulate in streambed sediments, the specific MPs transport and retention mechanisms in fluvial systems remain poorly understood. As part of this technical note, we present a novel method for a quantitative analysis of the spatiotemporal transport and retention of pore‐scale MPs in an experimental flume. A continuous mass balance for MPs in surface water was achieved using two online fluorometers, while a laser‐induced Fluorescence‐Imaging‐System was developed to track and quantify the spatial migration of MPs through the streambed sediments. The detection limit was <1 μg/L for 1 μm polystyrene microbeads with the fluorometers and 3 μg/L for the Fluorescence‐Imaging‐System. The system was able to quantitatively track the advective transfer of MPs into the streambed sediments: a process that has yet not been observed experimentally. Results showed that MPs infiltrated into the streambed sediments up to a depth twice the bedform amplitude. This work provides a novel experimental method to quantitatively monitor MP transport through porous media and advective exchange of MP across the streambed interface.

Mineral characterization and composition of Fe-rich flocs from wetlands of Iceland: Implications for Fe, C and trace element export

In freshwater wetlands, redox interfaces characterized by circumneutral pH, steep gradients in O2, and a continual supply of Fe(II) form ecological niches favorable to microaerophilic iron(II) oxidizing bacteria (FeOB) and the formation of flocs; associations of (a)biotic mineral phases, microorganisms, and (microbially-derived) organic matter. On the volcanic island of Iceland, wetlands are replenished with Fe-rich surface-, ground- and springwater. Combined with extensive drainage of lowland wetlands, which forms artificial redox gradients, accumulations of bright orange (a)biotically-derived Fe-rich flocs are common features of Icelandic wetlands. These loosely consolidated flocs are easily mobilized, and, considering the proximity of Iceland's lowland wetlands to the coast, are likely to contribute to the suspended sediment load transported to coastal waters. To date, however, little is known regarding (Fe) mineral and elemental composition of the flocs. In this study, flocs from wetlands (n = 16) across Iceland were analyzed using X-ray diffraction and spectroscopic techniques (X-ray absorption and 57Fe Mössbauer) combined with chemical extractions and (electron) microscopy to comprehensively characterize floc mineral, elemental, and structural composition. All flocs were rich in Fe (229–414 mg/g), and floc Fe minerals comprised primarily ferrihydrite and nano-crystalline lepidocrocite, with a single floc sample containing nano-crystalline goethite. Floc mineralogy also included Fe in clay minerals and appreciable poorly-crystalline aluminosilicates, most likely allophane and/or imogolite. Microscopy images revealed that floc (bio)organics largely comprised mineral encrusted microbially-derived components (i.e. sheaths, stalks, and EPS) indicative of common FeOB Leptothrix spp. and Gallionella spp. Trace element contents in the flocs were in the low μg/g range, however nearly all trace elements were extracted with hydroxylamine hydrochloride. This finding suggests that the (a)biotic reductive dissolution of floc Fe minerals, plausibly driven by exposure to the varied geochemical conditions of coastal waters following floc mobilization, could lead to the release of associated trace elements. Thus, the flocs should be considered vectors for transport of Fe, organic carbon, and trace elements from Icelandic wetlands to coastal waters.