Seawater Samples Research Articles

Novel Technique for Ultra‐Trace Determination of Lead in Seawater Samples Using Gold Coated Tungsten Coil Atom Trap Hydride Generation Atomic Absorption Spectrometry

AbstractA novel and simple trap technique combining a gold‐coated tungsten coil with hydride generation atomic absorption spectrometry (HGAAS) were developed for ultra‐trace lead determination. The technique was based on first transporting the plumbane produced by the HG system, together with H2, to a trap externally heated to 92 °C, where it was collected for in‐situ preconcentration and then volatilized by raising the trap temperature to 510 °C. For a 120 s trapping time, the limit of detection (LOD) was 2.9 ng L−1, the limit of quantification (LOQ) was 9.7 ng L−1 and the relative standard deviation was 3.1 % (at 0.02 μg L−1). The analytical performance of the technique was contrasted against the classical HGAAS method and a 39.2‐fold increase in sensitivity was obtained when comparing the characteristic concentrations of both methodologies. The morphology of the trap surface was also studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The accuracy of the proposed method was verified by analyzing the Pb concentration in the certified reference materials and the results agreed well with the certified values. Finally, the developed procedure was successfully applied to seawater samples and the recoveries of standard addition were between 102.4 % and 105.2 %.

Plutonium in the coastal seawater around Chinese nuclear power plants: Sources, distribution, and environmental implications

Coastal surface seawater samples within 30 km around ten Chinese nuclear power plants (NPPs) were systematically investigated. The 239+240Pu activity concentration in the samples varied from 0.226 mBq/m3 to 3.098 mBq/m3, meanwhile the 240Pu/239Pu atom ratios ranged from 0.151 to 0.353. Besides, the Pacific Proving Ground (PPG) close-in fallout and the global fallout were recognized as two primary sources of Pu in these samples. The 239+240Pu activity concentration as well as the PPG contribution showed similar trends as the Kuroshio intrusion path and the coastal currents in the China Seas, illustrating long-range transport and consuming of PPG derived Pu in the coastal China Seas. Moreover, accumulation of PPG sourced Pu in the Beibu Gulf were observed and was attributed to the continuous invasion of the high isotopic Pu that remobilized from the South China Sea (SCS).

Radioecological perspective: The concentration of natural radionuclides around the coast of PLTU Labuan

The utilization of coal in Power Plants (PLTUs) can lead to the generation of fly ash waste, which may contain natural radionuclides that can potentially contaminate the surrounding environment. Despite Labuan PLTU's land-coastal location, marine environment monitoring remains minimal. A recent study conducted sediment and seawater sampling, revealing varying levels of natural radionuclides 226Ra, 232Th, and 40K ranging from 3.4 to 27.5 Bq kg−1, 3.9 to 34.9 Bq kg−1, and 64.0 to 275.0 Bq kg−1 in sediments, respectively. Meanwhile, the activity concentration of natural radionuclides 226Ra and 232Th in seawater ranges from 0.5 to 1.1 Bq L−1 to 0.7–1.5 Bq L−1, respectively. These findings provide baseline data for marine radiation levels around PLTU Labuan. Additionally, risk assessments were conducted, indicating Raeq, Hin, and Hex ranges of 13.80–91.00 Bq kg−1, 0.04–0.25, and 0.05–0.31, respectively. The study concludes that Labuan's radiation levels are within safe limits for exposure.

Graphene Incorporated Sugar Derived Carbon Aerogel for Pyridine Adsorption and Oil-Water Separation.

Herein, we have synthesized a three-dimensional and hydrophobic graphene incorporated carbon aerogel (G-SCA) derived from sugar. G-SCA is being used as a multifunctional sorbent material for removing various advanced water-soluble and insoluble pollutants. Initially, G-SCA is being explored for the adsorption of nitroarenes (nitrophenols, 3-nitroaniline), an insecticide (Phoskill), an antibiotic (ciprofloxacin), and a pharmaceutical drug precursor (pyridine). Later, the same G-SCA is also explored in the absorption of various protic and aprotic organic solvents, and oils (including crude oil, waste cooking oil, and waste engine oil), with excellent recyclability checked up to 10 cycles. Moreover, oil-water separation experiments are also being done in various industrial wastewater and seawater samples to support the real-life accessibility of the present approach. Large-scale applicability of G-SCA is also checked by performing crude oil-seawater separation experiments using a laboratory-scale prototype demonstrating the successful continuous recovery of crude oil.

Full-length 16S rRNA gene sequencing combined with adequate database selection improves the description of Arctic marine prokaryotic communities

BackgroundHigh-throughput sequencing of the full-length 16S rRNA gene has improved the taxonomic classification of prokaryotes found in natural environments. However, sequencing of shorter regions from the same gene, like the V4-V5 region, can provide more cost-effective high throughput. It is unclear which approach best describes prokaryotic communities from underexplored environments. In this study, we hypothesize that high-throughput full-length 16S rRNA gene sequencing combined with adequate taxonomic databases improves the taxonomic description of prokaryotic communities from underexplored environments in comparison with high-throughput sequencing of a short region of the 16S rRNA gene.ResultsTo test our hypothesis, we compared taxonomic profiles of seawater samples from the Arctic Ocean using: full-length and V4-V5 16S rRNA gene sequencing in combination with either the Genome Taxonomy Database (GTDB) or the Silva taxonomy database. Our results show that all combinations of sequencing strategies and taxonomic databases present similar results at higher taxonomic levels. However, at lower taxonomic levels, namely family, genus, and most notably species level, the full-length approach led to higher proportions of Amplicon Sequence Variants (ASVs) assigned to formally valid taxa. Hence, the best taxonomic description was obtained by the full-length and GTDB combination, which in some cases allowed for the identification of intraspecific diversity of ASVs.ConclusionsWe conclude that coupling high-throughput full-length 16S rRNA gene sequencing with GTDB improves the description of microbiome profiling at lower taxonomic ranks. The improvements reported here provide more context for scientists to discuss microbial community dynamics within a solid taxonomic framework in environments like the Arctic Ocean with still underrepresented microbiome sequences in public databases.

Integrated multi-omics analyses reveal microbial community resilience to fluctuating low oxygen in the East China sea

Climate change and eutrophication are accelerating ocean deoxygenation, leading to a global decline in oxygen levels. The East China Sea, frequently experiencing deoxygenation events, harbors diverse microbial communities. However, the response of these communities to the changing deoxygenation dynamics remains poorly understood. Here, we explored the composition and function of microbial communities inhabiting seawaters of the Changjiang Estuary and offshore areas. Our findings suggested that neutral processes significantly influenced the assembly of these communities. The overall bacterial composition demonstrated remarkable high stability across the oxygen gradient. Salinity exhibited a significantly stronger correlation with bacterial community structure than dissolved oxygen. Both metagenomics and metaproteomics revealed that all of the samples exhibited similar functional community structures. Heterotrophic metabolism dominated these sites, as evidenced by a diverse array of transporters and metabolic enzymes for organic matter uptake and utilization, which constituted a significant portion of the expressed proteins. O2 was the primary electron acceptor in bacteria even under hypoxic conditions, evidenced by expression of low- and high-affinity cytochrome oxidases. Proteins associated with anaerobic processes, such as dissimilatory sulfite reductases, were virtually undetectable. Untargeted liquid chromatography with tandem mass spectrometry analysis of seawater samples revealed a diverse range of dissolved organic matter (DOM) components in amino acids, lipids, organic acids, peptides, and carbohydrates, potentially fueling dominant taxa growth. Despite fluctuations in the abundance of specific genera, the remarkable similarity in community structure, function, and DOM suggests that this ecosystem possesses robust adaptive mechanisms that buffer against abrupt changes, even below the well-defined hypoxic threshold in marine ecosystem.

Distinct diversity, assembly, and co-occurrence patterns of the prokaryotic microbiome in coral ecosystems of the South China Sea

Coral reefs are among the most energetic marine ecosystems, taking a place in ecological balance. Microbes participate in the energy exchange in coral ecosystems, which may affect coral resistance and resilience. However, there is still a lack of understanding regarding the microbial structure between corals and seawater. In this study, microbial structure and interactions in coral and seawater were studied using quantitative PCR and high-throughput sequencing. We found that the abundance and diversity of microbes in corals were higher than those in seawater. Corals, as nonfluidic ecosystems, limited the dispersal of microbes, causing broader stochasticity in the ecological shaping process, whereas ecological drift and homogeneous selection were the most important assembly mechanisms in seawater. The microbial niche width was larger in the coral group than in the seawater group, indicating strong adaptability. A group of microbes (e.g., Caldilineaceae, Burkholderiaceae, and Nitrosopumilaceae) may become microbial indicators which differentiate seawater samples (e.g., SAR11 and SAR86 clades, Cryomorphaceae), which may be due to separated habitats and nutrition. Coral microbes may participate in nitrogen-metabolism to maintain a nitrogen limited microenvironment. Nodes linked in the coral co-occurrence network showed coexisting interactions and higher complexity based on the comparison of topological values. Collectively, significant differences in microbial fractions were demonstrated observed in terms of diversity, composition, co-occurrence patterns, assembly processes and predicted functions between coral and seawater samples, showing potential microbial interactions and providing in-depth insights into the metacommunity diversity in coral reef ecosystems.

Isolation of seawater microplastics from biologically rich samples using an alkaline K2S2O8 method

In recent years, microplastics, especially marine microplastic pollution, have received global attention as a new type of environmental problem. The establishment of accurate and efficient methods for the detection of microplastics is the basis for in-depth research on the transport, transformation, fate, and ecotoxicological effects of microplastics in the environment. Microplastics in seawater frequently mix with biological tissues, resulting in challenges when identifying samples. However, commonly used pretreatment protocols for microplastics often suffer from long digestion times, inadequate digestion, and the risk of potentially damaging microplastics. This study compared the digestion efficiencies of five digestion reagents and provided further insights into two advanced oxidation methods involving Fenton’s reagent and an innovative alkaline K2S2O8 protocol based on sulfate and hydroxyl radicals. Using Raman spectroscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM−EDS), and carbonyl index (CI) analyses, the status of microplastics after pretreatment was evaluated. The results revealed that the alkaline K2S2O8 method could enhance the reaction efficiency while reducing the potential for functional group damage during microplastic pretreatment. Moreover, the proposed K2S2O8 method was applied to the pretreatment of field seawater samples, and field microplastics were effectively separated from biologically rich samples. Thus, a digestion protocol based on alkaline K2S2O8 provides an effective way to isolate seawater microplastics from biologically rich samples. This study contributes to the development of efficiently microplastic monitoring and provides valuable insights into access to reliable data for fate and inventory of oceanic microplastics.

Variability in Paralytic Shellfish Toxin Profiles and Dinoflagellate Diversity in Mussels and Seawater Collected during Spring in Korean Coastal Seawater.

Paralytic shellfish toxins (PSTs) are potent neurotoxins produced by certain microalgae, particularly dinoflagellates, and they can accumulate in shellfish in coastal seawater and thus pose significant health risks to humans. To explore the relationship between toxicity and PST profiles in seawater and mussels, the spatiotemporal variations in PST concentrations and profiles were investigated along the southern coast of Korea under peak PST levels during spring. Seawater and mussel samples were collected biweekly from multiple stations, and the toxin concentrations in the samples were measured. Moreover, the dinoflagellate community composition was analyzed using next-generation sequencing to identify potential PST-producing species. The PST concentrations and toxin profiles showed substantial spatiotemporal variability, with GTX1 and GTX4 representing the dominant toxins in both samples, and C1/2 tending to be higher in seawater. Alexandrium species were identified as the primary sources of PSTs. Environmental factors such as water temperature and salinity influenced PST production. This study demonstrates that variability in the amount and composition of PSTs is due to intricate ecological interactions. To mitigate shellfish poisoning, continuous monitoring must be conducted to gain a deeper understanding of these interactions.

Polyethylene terephthalate (PET) microplastics as radionuclide (U-232) carriers: Surface alteration matters the most

Polyethylene terephthalate (PET) plastics find widespread use in various aspects of our daily lives but often end up in the environment as (micro)plastic waste. In this study, the adsorption efficiency of PET microplastics for U-232 has been investigated prior and after surface alteration (e.g. oxidation (PET-ox), MnO2-coating (PET/MnO2) and biofilm-formation (PET/Biofilm)) in the laboratory (at pH 4, 7 and 9) and seawater samples under ambient conditions and as a function of temperature. The results revealed a significant increase in the adsorption efficiency upon surface alteration, particularly after biofilm development on the MP's surface. Specifically, the Kd values evaluated for the adsorption of U-232 by PET, PET-ox, PET/MnO2 and PET/Biofilm are 12, 27, 73 and 363, respectively, at pH 7 and under ambient conditions. The significantly higher adsorption efficiency of the altered and particularly biofilm-coated PET, emphasizes the significance of surface alteration, which may occur under environmental conditions. In addition, according to the thermodynamic investigations the adsorption of U-232 by PET-MPs (both non-treated and modified), the adsorption is an endothermic and entropy-driven reaction. A similar behavior has been also observed using seawater solutions and assumes that surface alteration is expected to enhance the radionuclide, stability, mobility and bioavailability in environmental water systems.

Microbial communities on microplastics from seawater and mussels: Insights from the northern Adriatic Sea

Microplastics, synthetic solid particles of different sizes (< 5 mm), pose a major challenge to marine ecosystems. Introducing microplastics into the marine environment leads to the formation of complex microbial communities, a topic of growing interest in environmental research. For this study, we selected an area in the northern Adriatic Sea, less affected by human activities, to understand how pristine environmental conditions influence microbial colonization of microplastics. Samples of coastal seawater and Mediterranean mussels (Mytilus galloprovincialis) were collected in a mussel farm near Debeli rtič of the Slovenian coast. Microplastics were isolated, visually and chemically analyzed and DNA was extracted for metagenomics. In the marine water column, 12.7 microplastics per m3 water column and 0.58 microplastics per individual mussel were found. Sufficient DNA was available to analyze six particles, five originating from seawater, and one from a mussel. This was the first-ever sequenced microplastic particle from a mussel. Genera of Pseudomonas and Serratia were identified in all samples. In one of the samples, the most abundant was a marine genus Pseudoalteromonas, while in another sample Campylobacter was present with >30 % abundance. The microbiomes of the mussel- and seawater-isolated particles were similar, suggesting a common microbial colonization pattern, which may have implications for the transfer of microplastic-associated microbes, including potential pathogens, through the food web to the consumers. Microplastic pollution is a complex issue requiring further research, especially regarding microbial biofilms, pathogen colonization and the potential of pathogen transmission via microplastic particles. Our findings enhance the understanding of microplastic pollution in the Adriatic Sea and stress the necessity for comprehensive strategies to mitigate the impact on marine ecosystems.

Fluorescence based visual sensing of cesium ions enabled by space-confined converting enriched cesium ions to CsPbBr3 nanocrystals in crown ether functionalized mesoporous silica

Portable fluorescence-based Cs+ radionuclide sensing has received great concerns yet challenged by interference in complex sample matrices. Herein, a reliable method was established by in situ converting the preconcentrated Cs+ to CsPbBr3 perovskite nanocrystals in mesoporous silica modified with dibenzo 24-crown-8 ethers (DB24C8E-SiO2), which combined the selective extraction of Cs+ with in situ fluorescence derivatization to achieve good anti-interference ability. The high adsorption capacity (49.5 mg g−1) of DB24C8E-SiO2 for Cs+ and elution-free operation enabled enrichment factor up to 4500, which was conducive to reducing the limit of detection (LOD) for Cs+. By this method, the fluorescence intensity linearly increased with the Cs+ concentration from 0.050 μg mL−1 to 100 μg mL−1 with an LOD of 0.017 μg mL−1 (S/N = 3). The concentration of Cs+ in seawater sample was detected to be 0.056 μg mL−1. The recoveries of Cs+ in spiked samples remained above 88.90 % and the relative standard deviations were less than 12.06 %. In addition, the relative errors of this method were within ±13.2 % compared with the result from atomic absorption spectrometry. The study demonstrated the high potential of the method for removal and portable detection of Cs+.

Diversity, virulence and antibiotic resistance of Vibrio Harveyi clade species associated with bivalve aquaculture within marine protected areas

The aim of the present study was to investigate the diversity, distribution of virulence factor genes and antimicrobial resistance phenotypes of Vibrio Harveyi clade species from two distinct and spatially distant near-shore bivalve farming environments located in protected marine reserves of the eastern Adriatic. Tissues of farmed Mediterranean mussel Mytilus galloprovincialis and European flat oyster Ostrea edulis, seawater and sediment samples were collected during six bi-monthly sampling events conducted over one year from farming locations in Lim Bay and Mali Ston Bay, Croatia. Eight distinctive Harveyi subclades, namely, V. harveyi, V. alginolyticus, V. diabolicus, V. jasicida, V. parahaemolyticus, V. rotiferianus, V. campbellii and V. communis, were detected by Phylogenetic Multilocus Sequence Analysis (MLSA) based on rpoD, toxR and rctB concatenated genes sequences. Genomic fingerprinting of MLSA-classified samples revealed substantial diversity of environmental isolates. The virulence-related genes considered typical for the Harveyi clade and their homologues were represented in all subclades with varying frequencies. Of twelve antibiotics commonly used in human and veterinary medicine, the most frequent resistance phenotypes were resistance to ampicillin (90%), erythromycin (39%), imipenem (29%) and streptomycin (22%). >60% of isolates were resistant to at least two classes of antibiotics. Seasonal or site-specific differences were found in the proportion of isolates carrying virulence genes and displaying specific antibiotic resistance phenotype.This study is the first to provide a broader perspective on the properties of Vibrio Harveyi clade species associated with ecosystems under presumably low anthropogenic pressures, such as marine protected areas. New data on virulence and antibiotic resistance are presented of Harveyi clade species coexisting in different environmental compartments, including those that have been largely overlooked or understudied in the context of bivalve aquaculture. Taken together, these results highlight the importance of monitoring the presence of potentially pathogenic strains in the natural Vibrio population of bivalve farming areas to reduce the risk to seafood consumers.

Development of spherical bismuth nanoparticles modified electrode for analysis of heavy metal ions in seawater samples using SWASV technique

Development of spherical bismuth nanoparticles modified electrode for analysis of heavy metal ions in seawater samples using SWASV technique

SMMP: A Deep-Coverage Marine Metaproteome Method for Microbial Community Analysis throughout the Water Column Using 1 L of Seawater.

Marine microbes drive pivotal transformations in planetary-scale elemental cycles and have crucial impacts on global biogeochemical processes. Metaproteomics is a powerful tool for assessing the metabolic diversity and function of marine microbes. However, hundreds of liters of seawater are required for normal metaproteomic analysis due to the sparsity of microbial populations in seawater, which poses a substantial challenge to the widespread application of marine metaproteomics, particularly for deep seawater. Herein, a sensitive marine metaproteomics workflow, named sensitive marine metaproteome analysis (SMMP), was developed by integrating polycarbonate filter-assisted microbial enrichment, solid-phase alkylation-based anti-interference sample preparation, and narrow-bore nanoLC column for trace peptide separation and characterization. The method provided more than 8500 proteins from 1 L of bathypelagic seawater samples, which covered diverse microorganisms and crucial functions, e.g., the detection of key enzymes associated with the Wood-Ljungdahl pathway. Then, we applied SMMP to investigate vertical variations in the metabolic expression patterns of marine microorganisms from the euphotic zone to the bathypelagic zone. Methane oxidation and carbon monoxide (CO) oxidation were active processes, especially in the bathypelagic zone, which provided a remarkable energy supply for the growth and proliferation of heterotrophic microorganisms. In addition, marker protein profiles detected related to ammonia transport, ammonia oxidation, and carbon fixation highlighted that Thaumarchaeota played a critical role in primary production based on the coupled carbon-nitrogen process, contributing to the storage of carbon and nitrogen in the bathypelagic regions. SMMP has low microbial input requirements and yields in-depth metaproteome analysis, making it a prospective approach for comprehensive marine metaproteomic investigations.

Spatiotemporal changes of pelagic food webs investigated by environmental DNA metabarcoding and connectivity analysis.

Environmental DNA metabarcoding (eDNA metaB) is fundamental for monitoring marine biodiversity and its spread in coastal ecosystems. We applied eDNA metaB to seawater samples to investigate the spatiotemporal variability of plankton and small pelagic fish, comparing sites with different environmental conditions across a coast-to-offshore gradient at river mouths along the Campania coast (Italy) over 2 years (2020-2021). We found a marked seasonality in the planktonic community at the regional scale, likely owing to the hydrodynamic connection among sampling sites, which was derived from numerical simulations. Nonetheless, spatial variability among plankton communities was detected during summer. Overall, slight changes in plankton and fish composition resulted in the potential reorganization of the pelagic food web at the local scale. This work supports the utility of eDNA metaB in combination with hydrodynamic modelling to study marine biodiversity in the water column of coastal systems. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Nitrogen are the main factors driving the structure and function of the marine archaeal community in Yongle Blue Hole, Sansha

To study the vertical distribution of archaea in the world’s deepest blue hole Yongle Blue Hole (YLLD), and its distribution characters driven by nitrogen, as well as, to predict the ecological functions of archaea, we collected 12 seawater samples from depths of 2 m to 170 m. Illumina high-throughput sequencing was performed, and the results indicated that the abundance of Thaumarchaeota (44.34 %) was the highest, and the dominant community of archaea at different water depths (surface, middle, and bottom) was different. The diversity of archaeal communities was greater in the surface and deep layers of the YLLD than in the middle layer, with significantly higher diversity in the deep layer than in the middle layer (P < 0.05). The results of the redundancy analysis showed that nitrate and ammonia nitrogen significantly influenced the structure of the seawater archaeal community at different depths (P < 0.05). By means of bioinformatics predicted that archaea play an important role in the aerobic ammonia oxidation in the ecosystem found within YLLD. The findings of this study showed that nitrate and ammonia were the main environmental factors affecting archaeal communities in different water layers of YLLD, Aerobic ammonia oxidation and nitrification were their primary ecological functions. These findings laid the theoretical foundation for further research on microbial biogeochemical processes in extreme environments, such as blue holes.

Occurrence of pharmaceuticals in Latin America: case study on hazard assessment and prioritization in Costa Rica.

Pharmaceuticals are considered as contaminants of emerging concern, and their occurrence in diverse environmental matrices has been described during the last 25years. Nonetheless, pharmaceutical occurrence has not been evenly described worldwide, and reports from some geographical areas such as most parts of Latin America are scarce. This work aims to address the situation of water pollution due to pharmaceuticals in Latin America by means of two main goals: i. First, reviewing the monitoring studies performed in Latin America on this topic (period 2009-2024), which were conducted in Brazil, Mexico, Colombia, Ecuador, Peru and Argentina, to highlight the most frequently detected compounds from each therapeutic group in the region. ii. Second, analyzing the case of Costa Rica through the hazard assessment and prioritization of pharmaceuticals based on the monitoring performed in this country (years 2011; 2018-2019). The monitoring in Costa Rica comprised a total of 163 sampling points: wastewater treatment plants (WWTPs) (14 urban WWTPs plus two landfill WWTPs; total samples n = 44 influents and n = 34 effluents), nine hospital effluents (n = 32), wastewater from livestock farms (six swine farms and seven dairy farms; n = 23 influents and n = 37 effluents), 64 continental surface water sampling points (n = 137), and 61 coastal seawater sampling points (n = 61). Risk assessment of detected concentrations by the hazard quotient (HQ) approach (period 2018-2019) revealed a total of 25 mediumorhigh-hazard compounds (out of 37 detected compounds). The prioritization approach (which included the Frequency of Appearance (FoA), the Frequency of PNEC exceedance (FoE), and the Extent of predicted no-effect concentration (PNEC) exceedance (EoE)), showed a critical list of nine pharmaceuticals: caffeine, diphenhydramine, acetaminophen, lovastatin, gemfibrozil, ciprofloxacin, ibuprofen, doxycycline and norfloxacin. These compounds should be taken into account as a first concern during the implementation of environmental policies related to pharmaceutical products in the region.

Measurement Error Analysis of Seawater Refractive Index: A Measurement Sensor Based on a Position-Sensitive Detector.

The seawater refractive index is an essential parameter in ocean observation, making its high-precision measurement necessary. This can be effectively achieved using a position-sensitive detector-based measurement system. However, in the actual measurement process, the impact of the jitter signal measurement error on the results cannot be ignored. In this study, we theoretically analysed the causes of long jitter signals during seawater refractive index measurements and quantified the influencing factors. Through this analysis, it can be seen that the angle between the two windows in the seawater refractive index measurement area caused a large error in the results, which could be effectively reduced by controlling the angle to within 2.06°. At the same time, the factors affecting the position-sensitive detector's measurement accuracy were analysed, with changes to the background light, the photosensitive surface's size, and the working environment's temperature leading to its reduction. To address the above factors, we first added a 0.9 nm bandwidth, narrow-band filter in front of the detector's photosensitive surface during system construction to filter out any light other than that from the signal light source. To ensure the seawater refractive index's measuring range, a position-sensitive detector with a photosensitive surface size of 4 mm × 4 mm was selected; whereas, to reduce the working environment's temperature variation, we partitioned the measurement system. To validate the testing error range of the optimised test system, standard seawater samples were measured under the same conditions, showing a reduction in the measurement system's jitter signal from 0.0022 mm to 0.0011 mm, before and after optimisation, respectively, as well as a reduction in the refractive index's deviation. The experimental results show that the refractive index of seawater was effectively reduced by adjusting the measurement system's optical path and structure.

Utilization of industrial waste sodium sulfate for calcined clay-based sustainable binder

This study explored the utilization of industrial waste Na2SO4 to develop a calcined clay-based sustainable cementitious composite inspired by ancient Roman concrete. Na2SO4 with or without the addition of NaCl was utilized, keeping the total Na2O quantity constant, and their performances at the macro and micro scale were compared. A separate set of samples was prepared using seawater. A medium-grade calcined clay, along with lime, was utilized as the binder. The salts were first dissolved in water and then used as the mixing water for sample preparation. A diverse array of characterization methods was utilized, encompassing thermogravimetric analysis, chemical extraction, X-ray diffraction (XRD), and Backscattered Scanning electron microscopy (SEM). It was observed that the salt-containing batches achieved compressive strength faster than the seawater samples. However, the strength remained in a comparable range (∼30 MPa) for all the samples after 28 days of curing. The initial strength of salt-containing samples was attributed to the formation of gypsum, ettringite, and hydrocalumite. Additionally, the geopolymer gel and calcium aluminum silicate hydrate (C-A-S-H) gel phases were present in all samples. Finally, this study also showed that lime-clay mortars can achieve a reduction in carbon footprint of up to 50 % compared to ordinary portland cement (OPC) mortars.