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The Shandong Peninsula (SP) is the largest peninsula in China hosting rich economic and agricultural activities. In this study, we investigated the behavior of dissolved Mn, Fe, Cu, Zn, Cd, and Pb and their colloidal phases in the coastal and estuarine areas of SP. Pb and Zn had the highest contamination factors of 0.22-10.15 and 0.90-4.41, respectively. The <1 kDa accounted for 23-57 % of the total dissolved phase. Mn, Fe, Cu, Zn, Cd, and Pb were more likely to bind to 100 kDa-0.45 μm colloids (21-57 %). For colloidal Fe and Cu, the adsorption-release behavior had more significant effects on their dynamics. In contrast, the changes in colloidal Mn, Cd, and Pb were mainly controlled by the combined influence of temperature, dissolved oxygen, and microbial activity. However, the 1-3 kDa Zn exhibited a greater pH-dependent dispersion and was significantly positively correlated with it., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Considering the impact of the high salinity and high turbidity of coastal seawater on phosphorus forms, a new method was proposed to determine bioavailable inorganic phosphorus (BIP). The phosphorus most relevant to eutrophication is BIP, and traditional analysis methods may underestimate the degree of eutrophication. In this study, a microelectrode of multigold (AuμE) was fabricated for direct voltammetric determination of BIP without filtration, and BIP environmental characteristics including distribution and correlation relationships with environmental factors in typical coastal seawater of Northern China were analyzed. The proposed AuμE showed a low detection limit of 0.03 μM. The surface and bottom BIP concentrations ranged from 1.00 to 2.13 and from 0.88 to 2.05 μM, respectively. BIP dominated the total P (TP) accounting for 48.5-67.5 % in the surface layer samples, and 32.6-92.7 % in the bottom layer samples, respectively. The concentrations of BIP were obviously higher than those of DIP, indicating that DIP may underestimate the probability of eutrophication occurring. And BIP was positively correlated with dissolved oxygen (DO) (P < 0.05). BIP may be a promising indicator of eutrophication potential in coastal areas with high salinity and high turbidity. The proposed reliable voltammetry method provides a new indicator for environmental assessment and represents a significant step in the comprehensive analysis of P species., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Different species of trace heavy metals (HMs) in seawater samples were simultaneously analyzed by anodic stripping voltammetric method, an analytical technique that does not require sample pre-concentration or the addition of reagents. The effects of the crucial parameters, deposition potential and time, on the determination of HMs were investigated. Concentrations of the total dissolved, dissolved active, and dissolved inert HMs were obtained through different analysis processes. The three species of Cu, Pb, Cd and Zn in seawater samples collected in different locations across Sishili Bay, North Yellow Sea, China were studied. The relative concentration of the dissolved active Cu, Pb, Cd and Zn in the total dissolved concentrations is 59.0%, 69.6%, 87.3% and 84.1%, respectively. The concentrations of different HMs species in Sishili Bay could be affected by the discharged effluent, sea current, and uptake of marine organism.

Field determination and ecological risk assessment of dissolved lead (Pb) were performed at two Yellow Sea sites in China using a continuous automated electrochemical system (CAEDS). This CAEDS instrument includes an automatic triple filter sampler and an electrochemical detection water quality analyzer, which might be operated automatically four times daily. The dissolved Pb concentrations varied from 0.29 to 1.57 μg/L in the South Yellow Sea over 16 days and from 0.32 to 2.28 μg/L in the North Yellow Sea over 13 days. During the typhoon and algal bloom periods, the Pb concentration was as high as ten times greater than usual. According to the calculation of contamination factors (Cf) and subsequent analysis, seawater quality was classified as Grade II. Through species sensitivity distribution (SSD) method experiments and ecological risk analysis, an average risk quotient (RQ) below 1 for both areas was obtained, indicating a low-to-moderate ecological risk. This system will be helpful for Pb monitoring and assessment in seawater and contribute to the biogeochemical cycling study of Pb. [ABSTRACT FROM AUTHOR]

A portable electrochemical system based on rGO/AuNPs/Nafion was constructed for selenium (IV) field determination in coastal seawater of the North Yellow Sea, East China Sea and South China Sea. This system demonstrated a low determination limit (0.03 μg/L), a wide linear range of concentration (0.1–30 μg/L), exceptional reproducibility and repeatability, and excellent selectivity. Each individual, entire test could be accomplished within 8 min. In Yantai Sishili Bay, the Se (IV) concentrations ranged from 0.16–3.59 μg/L (average 1.43 μg/L). In Shengshan Island, the Se (IV) concentrations ranged from 0.20–5.18 μg/L (average 2.06 μg/L). In Zhelin Bay, the Se (IV) concentrations ranged from 0.87–4.87 μg/L (average 3.13 μg/L). The average concentrations of Se (IV) in surface seawater showcased an increasing trend from the north to the south of China, suggesting Zhelin Bay > Shengshan Island > Sishili Bay. The system develops a new, competitive method for water quality assessment, and contributes to the accurate study of the biogeochemical cycles of selenium. [ABSTRACT FROM AUTHOR]

The concentrations of total dissolved iron (TdFe) and dissolved reactive iron (DrFe) in the Northern coastal China seawater (Yantai Sishili Bay) in 2018 were determined using cathodic stripping voltammetry (CSV). It was found that while the concentrations of TdFe ranged from 27.8 to 82.0 nM, DrFe concentrations changed in a much narrower range from 6.8 to 13.3 nM. The annual mean concentrations of DrFe also ranged from 7.1 to 12.6 nM at the 12 sites monitored over the 4 years of the study (2017–2020). Considering the obvious changes in temperature (T), chlorophyll a (Chl a) concentrations (Chl a contents were higher in May, July and September than in March and November), and nutrients over a year in this zone, the consumption of DrFe was expected; the supplement of DrFe observed may have resulted from the transformation of strong organically complexed iron by photoreduction and cell surface reduction. Additionally, a pre-liminary conclusion was drawn based on the theoretical calculation of Fe* that the concentration of DrFe was sufficient to meet the phytoplankton demand. [ABSTRACT FROM AUTHOR]

Considering that zinc (Zn) is essential for marine phytoplankton growth and cadmium (Cd) can replace Zn as a cofactor of mutual conversion and regulate the effect of carbonic anhydrase, we here presented the concentration, chemical speciation and relationship of Zn and Cd collected from three consecutive voyages (2019–2021) in summer coastal seawater of northern China. Dissolved Zn and Cd concentrations were determined using inductively coupled plasma mass–spectrometry (ICP–MS) and ranged from 0.37 to 3.09 μM and 1.88–13.66 nM, respectively. Natural labile Zn and Cd were determined using a highly automated electrochemical detection system and ranged from below detection limit-1.11 μM and below detection limit-5.23 nM, respectively. The speciation, distribution and interrelationships of Zn and Cd were compared with the distribution of the diatoms community, and studied by the correlation with pH and dissolved inorganic carbon (DIC). Finally, the Zn and Cd labile and inert chemical species concentrations were compared with those of the open sea and the coast. The results indicated that the dissolved Zn and Cd concentrations in surface seawater were higher than those in bottom seawater, possibly due to the dominance of exogenous inputs compared to phytoplankton uptake. Higher phytoplankton abundance was associated with lower natural labile Zn and Cd concentrations, but this was not the main factor affecting the distribution of natural labile Zn and Cd. Unlike the open ocean, there was no potential for Zn limitation of certain phytoplankton groups in this region, but both Zn and Cd played important roles in the fixation of carbon dioxide, and Cd might result in mitigating Zn uptake. Activities such as ocean currents, which bring limiting nutrient trace metals (e.g., Zn) from the coast into the open ocean, could regulate the structure of primary producers. This study has great potential for the investigation of the biogeochemical cycling of Zn and Cd and their role in marine carbon fixation in coastal seawater. • The concentration, chemical speciation and relationship of Zn and Cd were studied. • A highly automated electrochemical detection system detects natural labile Zn and Cd. • No potential for Zn limitation of certain phytoplankton groups in Yantai Coastal. • Both Zn and Cd played important roles in the fixation of carbon dioxide. • Cd might play a role in mitigating Zn consumption. [ABSTRACT FROM AUTHOR]

Different species of trace heavy metals (HMs) in seawater samples were simultaneously analyzed by anodic stripping voltammetric method, an analytical technique that does not require sample pre-concentration or the addition of reagents. The effects of the crucial parameters, deposition potential and time, on the determination of HMs were investigated. Concentrations of the total dissolved, dissolved active, and dissolved inert HMs were obtained through different analysis processes. The three species of Cu, Pb, Cd and Zn in seawater samples collected in different locations across Sishili Bay, North Yellow Sea, China were studied. The relative concentration of the dissolved active Cu, Pb, Cd and Zn in the total dissolved concentrations is 59.0%, 69.6%, 87.3% and 84.1%, respectively. The concentrations of different HMs species in Sishili Bay could be affected by the discharged effluent, sea current, and uptake of marine organism. [ABSTRACT FROM AUTHOR]

In this paper, reduced graphene oxide/gold nanoparticle/Nafion (rGO/AuNP/Nafion) modified electrode was fabricated through in-situ synthesis and used for determination of copper ions in strong salt electrolyte (0.5 M NaCl) by differential pulse anodic stripping voltammetry (DPASV). This in-situ synthesis procedure was based on the ion-exchange and electrochemical reduction. The use of rGO provided a larger electrode surface and the presence of more active sites, while electron transfer was accelerated by incorporating AuNPs. Nafion was utilized as a cation exchange polymer in which rGO and AuNPs could be tightly attached to the electrode surface. The physical and electrochemical characterizations of the as-prepared modified electrode were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. AuNPs with diameter of 5–10 nm on rGO decorated in the gold electrode surface were observed. Under the optimal conditions, the rGO/AuNP/Nafion electrode had a linear response to copper ions in the concentrations range from 20 nM to 1 μM (R 2 = 0.998), with the lowest detectable concentration of 8 nM and the detection limit of 4 nM (S/N = 3). Additionally, this electrode was successfully applied to the speciation analysis of copper (free, dissolved and total) in seawater. [ABSTRACT FROM AUTHOR]

Nanomaterial-functionalized voltammetric microsensors are promising tools for detecting trace metals at low concentrations in the complex environment of natural seawater. However, the sensitivity reduction caused by the loss of modified nanomaterials in the detection process has always been a major problem. Herein, to fabricate a highly stable sensing platform, a microneedle electrode with a hierarchical porous tip was prepared through electrochemical etching technology to firmly embed nanoparticles. Using copper (Cu) as a model trace metal, a micro-cluster needle sensor based on a gold nanoparticle (AuNP)-embedded tip-porous microneedle electrode (P-MNE) was fabricated for the direct voltammetric determination of labile Cu in natural seawater. The porous structure of P-MNE not only provided a larger specific surface area and active sites for AuNPs which had excellent electrocatalytic performance for Cu2+ determination, but also protected from their loss during the detection process in seawater. Therefore, this novel micro-cluster needle sensor exhibited significantly improved stability with a relative standard deviation (RSD) of 1.5% for 30 detections. The linear range of Cu2+ on this micro-cluster needle sensor was from 0.1 to 1000 nM with a detection limit of 0.03 nM. More importantly, this micro-cluster needle sensor was successfully used for directly detecting labile Cu in natural seawater samples without any preaccumulation treatment or reagent addition to obtain the contribution proportions of the labile fraction in total dissolved Cu. Furthermore, this sensing platform might also be extended to the reliable determination of other labile metals in seawater by changing the functional nanoparticles embedded in the nanopores. A highly stable sensing platform based on nanoparticle-embedded tip-porous microneedle sensor was developed for the direct determination of labile trace metal in natural seawater. [Display omitted] • The nanoparticle-embedded tip-porous microneedle electrode has been fabricated. • The micro-cluster needle sensor has a superior stability for metals detection. • The sensor has achieved the direct determination of labile copper in seawater. • The sensor has obtained the contribution of labile copper in total dissolved ones. • The sensor-based highly stable sensing platform has been developed for trace metals. [ABSTRACT FROM AUTHOR]

Monitoring the spatio-temporal distribution and concentration changes of nutrients in marine environments is significant for the protection of marine ecosystems. Electrochemical technologies are ideal candidates for marine nutrient monitoring systems with the advantage of miniaturization, low reagent consumption, and easy combination with automation devices. This review assesses nutrient determination (including nitrate, nitrite, ammonium, phosphate, and silicate) using electrochemical technologies, focusing on methods for analysis of coastal, estuarine and marine water, or with specific salinity effects. The research principles, laboratory methodology and in situ application of devices are summarized. In particular, this review focuses on the response mechanism, sensitivity and detection limit of the reported sensors, with reports on in situ instruments also reviewed. Overall, this review summarizes the advances in knowledge in terms of the modes of action of devices and deployment strategies, identifying the current limitations and future challenges for the electrochemical detection of nutrients in marine environments. [Display omitted] • Main parameters assessed in studies published in last five decades are reviewed. • Advantages of in situ electrochemical technology applications are summarized. • Challenges and perspectives of marine nutrient monitoring systems are presented. • This review aims to promote the development of marine monitoring systems. [ABSTRACT FROM AUTHOR]

In this work, the modified electrode based on composites of reduced graphene oxide/leucomethylene blue/platinum nanoparticles (rGO/LMB/PtNPs) was fabricated in-situ via an electron relay effect. Cationic dye of methylene blue (MB) was absorbed on the surface of graphene oxide (GO) with through π-π bond interactions. Then PtCl 6 2− ions were self-assembled on the surface of the composites of GO/MB through Coulomb interactions. Using NaBH 4 as the reducing agent, PtNPs were formed and GO was reduced to rGO. With the aid of PtNPs, MB was catalytically degraded to LMB and a rGO/LMB/PtNPs modified electrode was successfully prepared in situ. Due to the excellent electrochemical properties of rGO and the well-established assistant reductant of MB, as well as the catalytic amplifying effect of PtNPs, this as prepared rGO/LMB/PtNPs modified electrode showed excellent properties for the voltammetric determination of Fe(II) with the linear range of 0.01 to 2 μM and a detection limit of 3 nM. This modified electrode was successfully applied to detect the content of Fe(II) in seawater. • rGO/LMB/PtNPs were fabricated in-situ via an electron relay effect. • rGO/LMB/PtNPs modified GC electrode was successfully fabricated. • The contents of Fe(II) in seawater were detected by the functional modified electrode. • The functional modified electrode has a great potential in marine electroanalysis. [ABSTRACT FROM AUTHOR]

The marine biogeochemistry of iron plays a significant role in regulating climate change. Trace dissolved iron in oceanic surface water can limit phytoplankton growth which in turn limits the carbon dioxide flux at the air/sea interface. To better understand the relationship between iron and its different species with phytoplankton, as well as the biogeochemical cycle of iron in seawater, accurate, sensitive, and in situ methods are needed for iron determination. This paper reviews the methods for determining iron in seawater from the laboratory, shipboard to in situ measurements, including such strategies as atomic spectrometry, spectrophotometry, chemiluminescence, and voltammetry, which will provide the foundation for developing reliable long-term iron monitoring and sensing platforms in the future. [ABSTRACT FROM AUTHOR]

• A self-assembly method was developed for the fabrication of AgNPs-based micro-needle electrode. • The modified micro-needle electrode shows a superior performance for nitrate determination. • The direct determination of nitrate in seawater was conducted with the modified micro-needle electrode. • The modified micro-needle electrode has a great potential application in seawater analysis. In this work, silver nanoparticles (AgNPs) were self-assembled on the micro-needle electrode (MNE) with the help of chitosan (CTS) and polyvinylpyrrolidone (PVP) and used for the amperometric (i-t) determination of nitrate (NO 3 –) in seawater samples. CTS/PVP was electrodeposited on the MNE surface to improve the conductivity and specific surface area of the MNE, and to provide reduction conditions needed for Ag+ reduction and strong binding affinity for combination of AgNPs which had excellent catalytic activity for NO 3 –. AgNPs were self-assembled uniformly on the surface of MNE with the diameter of about 150–400 nm. Thanks to the unique aciform structure of MNE, the outstanding adhesion ability of CTS/PVP, and the excellent electrocatalytic ability of AgNPs, the so-prepared AgNPs/CTS/PVP/MNE showed significantly improved performance and stability for the amperometric determination of NO 3 –. Under the optimal conditions, the AgNPs/CTS/PVP/MNE was found to have a wide linear range (5–2000 μM) and a low limit of detection (1.2 μM). Furthermore, the AgNPs/CTS/PVP/MNE was successfully used for the direct determination of NO 3 – in coastal seawater samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A honeycomb-like micro-needle sensor with gold nanoparticles embedded for the determination of hexavalent chromium in seawater. [Display omitted] • A stainless steel micro-needle sensor with honeycomb-like structure was fabricated. • The honeycomb-like holes were embedded with gold nanoparticles. • The sensor showed high sensitivity and stability for the determination of Cr (VI). • The sensor was adopted for the determination of Cr (VI) in real seawater samples. As one of the most toxic heavy metals, hexavalent chromium (Cr(VI)) is a typical environmental pollutant that directly affects human health. In this work, a novel micro-needle sensor with honeycomb-like structure and embedded gold nanoparticles was proposed for the stable and sensitive determination of Cr(VI). The honeycomb-like structure provided larger specific surface area to support more gold nanoparticles which exhibited excellent catalytic activity towards the electrochemical reduction of Cr(VI) to Cr(Ⅲ). In addition, gold nanoparticles were embedded into the holes of the honeycomb-like structure, which can effectively prevent them from falling off from the electrode surface due to the protection of the holes. Combining the honeycomb-like structure of micro-needle electrode with the excellent catalytic activity of gold nanoparticles, the fabricated sensor exhibited outstanding stability and sensitivity for the cathodic stripping determination of Cr(VI). A linear range of Cr(VI) from 0.5 to 300 μmol/L was obtained, with the detection limit of 0.15 μmol/L. The recovery of the sensor for the determination of hexavalent chromium in seawater samples was also investigated. Moreover, the sensor might be further adapted for the determination of other heavy metals with different nanoparticles embedded. [ABSTRACT FROM AUTHOR]

Abstract Here, a needle-shaped electrode based on commercial acupuncture needle was fabricated and functionalized with dendritic gold nanostructures (AuNDs) and ion-exchange polymer (Nafion) for voltammetric speciation analysis of copper (Cu) in seawater. To achieve the enhanced performance for voltammetric determination of Cu in seawater, the acupuncture needle electrode (ANE) was functionalized with AuNDs via electrochemical deposition and covered with Nafion. AuNDs facilitate the electrochemical responses of Cu due to their excellent catalytic and electroconductive properties, whereas Nafion can stabilize the AuNDs deposited on the surface of the needle tip and enhance the voltammetric responses through its specific cation-exchange ability with Cu2+. The so-designed AuNDs/Nafion/ANE showed excellent performance for the determination of Cu in complex matrix like seawater. Under the optimal conditions, the response of Cu at this functional needle-shaped electrode was linear in the concentration range from 0.05 to 1 nmol L−1 with an ultralow detection limit of 15.4 pmol L−1. Additionally, the functional needle-shaped electrode has been successfully used for the direct determination of different Cu species in seawater via anodic stripping voltammetry. Graphical abstract Dendritic gold nanostructures/ion-exchange polymer based needle-shaped electrode was fabricated for the ultrasensitive determination of copper in seawater. Image 1 Highlights • The AuNDs/Nafion functionalized electrode has been successfully fabricated. • Ultralow detection limit of Cu2+ can be obtained at this functional needle-shaped electrode. • The different speciation of Cu in seawater has been analyzed by this electrode. • This needle-shaped electrode as a platform has a great potential in marine electrochemistry. [ABSTRACT FROM AUTHOR]

Copper (Cu), a natural micronutrient with ecotoxicological significance, is involved in the carbon and nitrogen cycles occurring in marine ecosystems. Here, we developed a novel, antifouling gel-protected iridium (Ir) needle electrode modified with gold nanoparticles (G-IrNS) for long-term continuous and steady Cu monitoring. The gel formed an efficient membrane that effectively prevented the fouling of the sensing surface and displayed anti-convective properties, ensuring that mass transport toward the sensor surface was wholly controlled via diffusion. The repeatability, reproducibility, and stability of G-IrNS showed that it was suitable for long-term and on-site monitoring of Cu in seawater. Cu concentrations were successfully measured via fixed-point continuous monitoring for >2 weeks and onboard continuous monitoring in Bohai Sea using one sensor. Moreover, the relationship between Cu concentrations measured on-site via G-IrNS and its dissolved concentration in Bohai Sea was evaluated. G-IrNS can be applied to other metal ions as well, especially for long-term automatic on-site monitoring, thereby providing a basis for further research. [Display omitted] • An agarose gel-based antifouling iridium needle sensor was fabricated. • The sensor showed excellent long-term repeatability, reproducibility, and stability. • The long-term, on-site detection of Cu in seawater was realized using the sensor. • The speciation analysis of Cu in Bohai Sea based on the sensor was achieved. [ABSTRACT FROM AUTHOR]