Seawater Cycling Research Articles

PVA-based Hydrogel Materials for Underwater Energy Storage and Underwater Sensing.

As human exploration of marine continues to expand, the demand for underwater devices is also increasing. The unique properties of hydrogel materials make them well-suited for underwater applications. We propose a multi-functional polyvinyl alcohol (PVA) - NaCl @ Polyaniline (PANI) (PNP) hydrogel, which is characterized by easy fabrication, integrated structure, and flexibility, and can be directly applied in the fields of underwater energy storage and underwater sensing. Solid-state supercapacitors fabricated by the PNP hydrogel, due to integrated and all-solid-state design, can be charged and discharged underwater without encapsulation. What's more, the PNP supercapacitor can maintain a capacitance retention rate of over 90% after 5,000 cycles in simulated seawater, eliminating concerns about the hydrogel's dehydration when used underwater. The PNP hydrogel with an integrated three-layer structure can also be applied to the capacitive pressure sensors, which can also be directly used in underwater environments without the need for encapsulation, significantly reducing the structural complexity and preparation steps of the device. Finally, we demonstrate a "supercapacitor module"with a voltage window greater than 1.6 V created by directly connecting multiple PNP supercapacitors in series, as well as an underwater intelligent glove, providing new solutions for underwater energy storage and underwater wearable sensing applications.

Rapid cycling and emission of volatile sulfur compounds in the eastern Indian Ocean: Impact of runoff inputs and implications for balancing atmospheric carbonyl sulfide budget

Volatile sulfur compounds, such as dimethyl sulfide (DMS), carbonyl sulfide (OCS), and carbon disulfide (CS2), significantly influence atmospheric chemistry and climate change. Despite the oceans being an important source of these sulfides, the limited understanding of their biogeochemical cycles in seawater introduces considerable uncertainties in quantifying their oceanic emissions and assessing atmospheric OCS budgets. To address this issue, we conducted a comprehensive field survey in the tropical eastern Indian Ocean (EIO) to examine the spatial distributions, source-sink dynamics, and sea-air exchange fluxes of marine DMS, OCS, and CS2. Our study indicates that nutrients, organic matter, and freshwater input from terrestrial runoff significantly affect most of the source-sink processes of these sulfides in the Bay of Bengal and even the tropical EIO. The resulting sulfide accumulation in seawater combined with high wind speeds establishes the tropical EIO as a considerable direct and indirect atmospheric OCS source. These insights underscore the potentially critical role of marine environments influenced by runoff in contributing to the atmospheric OCS budget. However, by integrating these results with previous field surveys, we believe that actual OCS emissions from tropical oceans exceed some bottom-up box-model simulations, yet fall significantly below those predicted by top-down models, still insufficient to bridge the atmospheric OCS source gap. Our detailed examination of source-sink dynamics offers deeper insights into the marine sulfur cycle and has potential implications for refining future box-models, thus mitigating uncertainties in estimating marine sulfur emissions.

Operando-XRD of Electrochemical Reactors for Selective Li+ Extraction from Brines and Seawater

In times of rising demand of Li for use in Li-ion batteries (LIBs), and ensuring its supply for aluminum electrolysis, ultralight alloys, optics, synthesis, nuclear research, and pharmaceuticals, it is essential to simplify the processing of Li sources in a sustainable manner. Current extraction from ores is complex and requires large energy input while generating high amounts of waste. This causes the danger of making Li a limited resource and even more expensive.[1] A new promising way is the electrochemical extraction of Li by desalination batteries (DBs) from brines or seawater[2]. Thereby, selective extraction of ions can be promoted by the chemistry of the electrode material, e.g., by using FePO4. To further enhance the selectivity, potentiostatic application proved to be useful[3]. DBs are superior to other extraction methods in terms of energy efficiency, and waste generation. Still, varying Li+ concentrations in brines[1b], competitive intercalation of other cations with similar size - especially Na+ [2] -, and degradative effects of anions[4], H2O, and O2 [5] are major challenges to overcome for DBs with FePO4.In this contribution, we focus on the selective extraction of Li+ using FePO4 electrodes by specifically-designed multi-step potentiostatic application. Results are shown for salt solutions containing a mixture of Na+/Li+, and artificial seawater. It is vital to understand the atomic-scale processes so that the electrodes, and electrochemical parameters can be optimized. Therefore, we used operando high-energy X-ray diffraction (HEXRD) microscopy to investigate the crystal structure of FePO4 during the electrochemical process. The experiments showed that the energy barrier for Na+ (de)intercalation was higher than that of Li+ during galvanostatic cycling, i.e., FePO4 is selective for Li+. Using a multi-step potentiostatic procedure, the (de)intercalation process could be enhanced, as evident from our HEXRD results and simultaneous conductivity measurements. Our tentative interpretation is that Li+ is highly selectively (de)intercalated, although electrochemical signatures hinted on a two-step process during deintercalation, which may indicate the intercalation of Na+. To selectively deintercalate the remaining Na+ over Li+, we further optimized the applied potentials. During galvanostatic cycling in artificial seawater, the (de)intercalation potentials were at more positive and more negative potentials, respectively, likely caused by the variety of cations. We expect that our results contribute to the design of high-performance DBs and inspire the exploration of further systems based on our proposed multi-step process.

Strong electronic coupling between Ni-based MOF and Ni2P enables high-efficiency oxygen evolution reaction for various application scenarios

The high overpotential and sluggish kinetics of oxygen evolution reaction (OER) severely hinder the widespread application of electrochemical water splitting, especially at industrial-level current densities. Herein, we report a novel heterostructural Ni-based metal organic framework (MOF)-Ni2P in-situ grown on iron foam (NiMOF-Ni2P/IF), which shows remarkable OER activity and stability. We demonstrate that the work function difference between NiMOF and Ni2P leads to the strong electron coupling effect by promoting electron transfer at the interface and results in a discernible upward shift of the d-band center of Ni sites for favorable OH− adsorption. The as-fabricated NiMOF-Ni2P/IF exhibits an ultralow overpotential of 330 mV and a small cell voltage of 1.796 V to drive NiMOF-Ni2P/IF‖Pt/C system at 1000 mA cm−2 in 1 M KOH, outperforming the majority of state-of-the-art non-noble-metal-based electrocatalysts. Furthermore, the catalyst shows remarkable performance even under harsh industrial conditions of 40, 60, and 80 °C in 6 M KOH. In addition, NiMOF-Ni2P/IF holds great promise with remarkable stability of 200 h and 600 cycles in simulated seawater and secondary zinc-air batteries (ZABs), respectively. This work offers a rational design strategy for low cost, high activity, and long durability OER electrocatalyst based on in-depth comprehension of the electronic coupling effect.

Assessment of Glass-Fiber-Reinforced Polymer (GFRP)–Concrete Interface Durability Subjected to Simulated Seawater Environment

Fiber-reinforced polymer (FRP)-retrofitted concrete structures are extensively utilized, and they have attracted growing research interest due to their combined performance in marine environments. To investigate the effect of seawater exposure, a total of 20 single-shear GFRP (glass-FRP)-bonded concrete structures were tested. Three corrosion conditions, i.e., exposure to single-salinity and triple-salinity seawater through wet–dry cycles as well as continuous immersion in triple-salinity seawater, were simulated and tested. The minimum shear strength (13,006 N) was tested using specimen B150-T-DW-90, which was cured in triple-salinity seawater with wet–dry cyclic exposure. The results of the shear strengths, load–displacement curves, interfacial shear stresses, and fracture energies indicated that seawater exposure degraded the bonding strength of the GFRP–concrete interface. Notably, the wet–dry cycles in triple-salinity seawater resulted in the most significant interface degradation, which could exacerbate with prolonged exposure. By introducing a parameter, the residual coefficient α, a new strength calculation model for GFRP–concrete exposed to a seawater environment was proposed and discussed.

CS2 Cycling in Seawater: Dark Production and UV Light Driven Consumption

AbstractCarbon disulfide (CS2) has recently gained attention as an important precursor for the atmospheric trace gas carbonyl sulfide (OCS), which delivers sulfur to the stratospheric sulfur layer and impacts the radiative budget of the Earth. CS2 is naturally produced in the ocean and emitted to the atmosphere. However, the magnitude of its marine emissions is only poorly constrained due to lacking understanding of its production and consumption processes. Here, we present incubation experiments with and without UV light treatment and provide evidence for a previously not considered UV‐light‐driven degradation process of CS2 in seawater, following first‐order kinetics. In addition to its already known photochemical production process, CS2 production is found in the dark, depending on the amount of dissolved organic sulfur present in seawater. We provide novel production and consumption rates of CS2 in seawater that pave the way toward mechanistically quantifying marine emissions of this important trace gas.

Revealing the Marine Cycles of Volatile Sulfur Compounds and Their Biogeochemical Controls: A Case of the Western North Pacific.

Volatile sulfur compounds, such as dimethyl sulfide (DMS), carbonyl sulfide (OCS), and carbon disulfide (CS2), have significant implications for both atmospheric chemistry and climate change. Despite the crucial role of oceans in regulating their atmospheric budgets, our comprehension of their cycles in seawater remains insufficient. To address this gap, a field investigation was conducted in the western North Pacific to clarify the sources, sinks, and biogeochemical controls of these gases in two different marine environments, including relatively eutrophic Kuroshio-Oyashio extension (KOE) and oligotrophic North Pacific subtropical gyre. Our findings revealed higher concentrations of these gases in both seawater and the atmosphere in the KOE compared to the subtropical gyre. In the KOE, nutrient-rich upwelling stimulated rapid DMS biological production, while reduced seawater temperatures hindered the removal of OCS and CS2, leading to their accumulation. Furthermore, we have quantitatively evaluated the relative contribution of each pathway to the source and sink of DMS, OCS, and CS2 within the mixed layer and identified vertical exchange as a potential sink in most cases, transporting substantial amounts of these gases from the mixed layer to deeper waters. This research advances our understanding of sulfur gas source-sink dynamics in seawater, contributing to the assessment of their marine emissions and atmospheric budgets.

Strategy to mitigate salinization of sulfide-autotrophic denitrification: Sodium ion uptake from the environment and mutualistic symbiosis among microorganisms

Sulfolithoautotrophic denitrification metabolic pathways are widely distributed in nitrogen cycling of seawater and saline lakes. Sulfide-autotrophic denitrification process (SAD) has been demonstrated a promising method for treating hypersaline nitrogenous wastewater. Meanwhile, the disposal of hypersaline nitrogenous wastewater has always been a problem to be solved. Therefore, it is urgent the clarification of the substrate removal performance of SAD under salinity stress. Furthermore, the response strategy and community interaction mechanism of SAD to salinity invasion are still unexplored. The present work aimed to unravel the salt tolerance of SAD at different substrate concentrations. It was found that the denitrification performance of SAD could reach 55.65 % when the salinity level was below 4.67 wt%, but the denitrification performance of SAD collapsed when the salinity level reached 6.64 wt%. Changes in the physicochemical characteristics of microbial communities in the sludge indicated that microorganisms resisted osmotic stress by taking up Sodium from the environment after salinity invasion, and the large concentration of accumulated Sodium inhibited the SAD behavior of functional microorganisms. However, the results of community succession showed that the functional microorganisms like Thauera and Sulfurimonas, showed resilience to salinity and restored SAD behavior through interactions with other microorganisms in the sludge.

Chloride-induced corrosion propagation of alkali-activated slag mortar with pulverized fuel ash and metakaolin replacements

Alkali-activated materials have great potential in reducing CO2 emissions in cement production industry. This study aims to investigate the corrosion propagation performance of alkali-activated slag mortars with various pulverized fuel ash (PFA) and metakaolin (MK) replacements subject to chloride-induced corrosion. The corrosion propagation performances including corrosion potential, corrosion rate and mortar electrical resistivity under wetting and drying cycles in seawater are studied. Scanning electron microscope (SEM), mercury intrusion porosimetry (MIP) and pH value measurement were conducted to analyze the effects of PFA and MK replacements on the relationship between reaction degree, pore structure, pH value and corrosion propagation performances. The results show that the MK replacement can enhance the corrosion propagation resistance of slag-based alkali-activated mortars under high activator concentration while the PFA replacement reduces the resistance to metallic corrosion of alkali-activated mortars. Mechanisms controlling the corrosion propagation are discussed.

Short-term durability of GFRP stirrups under wet-dry and freeze–thaw cycles

GFRP stirrups are a promising alternative to conventional steel stirrups due to their non-corrosive nature. However, their performance under cyclic exposure to wet-dry and freeze–thaw conditions in seawater needs to be evaluated to ensure their long-term durability and sustainability. This study investigates the tensile strength of glass fibre reinforced polymer (GFRP) stirrups under seawater wet-dry cycles and seawater and tap water freeze–thaw cycles. In total, 220stirrups in two different shapes, i.e. U and L shapes, and two different diameters, i.e. 6 mm and 8 mm were manufactured, conditioned, and tested under stirrup tensile test. Conditioned stirrups were subjected to 9 months and 18 months wet-dry cycles in seawater at 25 ℃, 40 ℃, and 60 ℃, and 9 months and 18 months freeze–thaw cycles in seawater and tap water. At first, the samples underwent a fast deterioration rate, which then decreased as the conditioning period progressed from 9 months to 18 months. The strength retention values of L-shaped stirrups were found to be higher than those of U-shaped stirrups, regardless of the environmental conditions or diameter. The maximum tensile strength reductions of 31%, 28% and 16% were observed, respectively after exposure to 18 months conditioning in seawater wet-dry cycles at 60 ℃, freeze–thaw in seawater, and freeze–thaw in tap water.

Microbial Dimethylsulfoniopropionate Cycling in Deep Sediment of the Mariana Trench.

Dimethylsulfoniopropionate (DMSP) and related organic sulfur compounds play key roles in global sulfur cycling. Bacteria have been found to be important DMSP producers in seawater and surface sediments of the aphotic Mariana Trench (MT). However, detailed bacterial DMSP cycling in the Mariana Trench subseafloor remains largely unknown. Here, the bacterial DMSP-cycling potential in a Mariana Trench sediment core (7.5 m in length) obtained at a 10,816-m water depth was investigated using culture-dependent and -independent methods. The DMSP content fluctuated along the sediment depth and reached the highest concentration at 15 to 18 cm below the seafloor (cmbsf). dsyB was the dominant known DMSP synthetic gene, existing in 0.36 to 1.19% of the bacteria, and was identified in the metagenome-assembled genomes (MAGs) of previously unknown bacterial DMSP synthetic groups such as Acidimicrobiia, Phycisphaerae, and Hydrogenedentia. dddP, dmdA, and dddX were the major DMSP catabolic genes. The DMSP catabolic activities of DddP and DddX retrieved from Anaerolineales MAGs were confirmed by heterologous expression, indicating that such anaerobic bacteria might participate in DMSP catabolism. Moreover, genes involved in methanethiol (MeSH) production from methylmercaptopropionate (MMPA) and dimethyl sulfide (DMS), MeSH oxidation, and DMS production were highly abundant, suggesting active conversions between different organic sulfur compounds. Finally, most culturable DMSP synthetic and catabolic isolates possessed no known DMSP synthetic and catabolic genes, and actinomycetes could be important groups involved in both DMSP synthesis and catabolism in Mariana Trench sediment. This study extends the current understanding of DMSP cycling in Mariana Trench sediment and highlights the need to uncover novel DMSP metabolic genes/pathways in extreme environments. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is an abundant organosulfur molecule in the ocean and is the precursor for the climate-active volatile gas dimethyl sulfide. Previous studies focused mainly on bacterial DMSP cycling in seawater, coastal sediment, and surface trench sediment samples, but DMSP metabolism in the Mariana Trench (MT) subseafloor sediments remains unknown. Here, we describe the DMSP content and metabolic bacterial groups in the subseafloor of the MT sediment. We found that the tendency for vertical variation of the DMSP content in the MT was distinct from that of the continent shelf sediment. Although dsyB and dddP were the dominant DMSP synthetic and catabolic genes in the MT sediment, respectively, both metagenomic and culture methods revealed multiple previously unknown DMSP metabolic bacterial groups, especially anaerobic bacteria and actinomycetes. The active conversion of DMSP, DMS, and methanethiol may also occur in the MT sediments. These results provide novel insights for understanding DMSP cycling in the MT.

Bond durability between anchored GFRP bar and seawater concrete under offshore environmental conditions

The lower bond strength of FRP bars to concrete compared to steel bars has remained an unsolved barrier to the widespread use of FRP-reinforced concrete under extreme loading. Additionally, the degradation of the bond between FRP reinforcement and concretes in aggressive environments adds to the existing concern. In this study, an innovative anchorage system comprised of polypropylene pipe was used to strengthen the bond between seawater concrete and GFRP bars after 250 days of exposure to offshore environmental conditions. As material factors, two types of GFRP bars (sand-coated and ribbed) and two types of concrete (normal and seawater concrete) were evaluated. Four distinct environmental conditions were used to assess the samples: (i) ambient environment (control), (ii) tap water, (iii) seawater, and (iv) wet-dry cycles in seawater. According to the findings of the direct pull-out tests, the suggested anchor system strengthens the bond and shifts the failure mode from bond failure to bar rupture. Additionally, after exposure to 250 days of seawater wet-dry cycles, GFRP-reinforced seawater concrete lost 5% of its maximum bond strength (developed bar tensile stress). All other samples exposed to different environmental conditions either increased or decreased in bond strength by less than 5% after 250 days, compared to the control samples.

Hierarchical Polyoxometallate Confined in Woven Thin Films for Single-Cluster Catalysis: Simplified Electrodes for Far-Fetched O2 Evolution from Seawater

The highly anticipated artificial conversion of water to oxygen for the imperishable growth of renewable energy requires efficient water oxidation catalysts (WOCs) to drive the exciting 4e– transformation at low driving potentials. Herein, we describe the freestanding thin film of P5Q7 (TFPQ), where Preyssler [P5W30O110]14– (P5) clusters are woven with [CH3(CH2)6]4N(Br) chains (Q7) to confine P5 clusters and maximize its catalytic exposure. The TFPQ-supported electrode shows OER at record-low overpotentials at 10 mAcm2 (η10 = 130 and 490 mV), rapid migration of electrons (Tafel, 35 and 56 mVdec–1), turnover frequency (TOF, 8.55 s–1), in alkaline water (1 M KOH), and natural seawater, respectively. Evenly dispersed and confined conducting P5 clusters with a delocalized charge cloud shows ∼3 times lower η10 and eventually high OER efficiency than nonconfined clusters. The TFPQ electrodes showed a prolonged stability of minimum 1000 cycles in alkaline water and seawater, without the leaching of true catalytic species P5.

Distribution and Environmental Impact Factors of Phytoplankton in the Bay of Bengal during Autumn

In order to better understand the effects of environmental factors and water mixing on the phytoplankton community structure in the Bay of Bengal, a field investigation was conducted from October to December 2016. A total of 276 species from 68 genera were identified, including Bacillariophyta (81 species), Miozoa (188 species), Cyanobacteria (four species), and Ochrophyta (three species). The abundance and distribution of dominant cyanobacteria gradually decreased along the latitude. This is evidenced in the vertical direction, which shows that cyanobacteria were affected by changes in environmental factors caused by the vertical mixing of seawater. The relationship between stratified N:P and phytoplankton also revealed that the changes in the vertical direction of the water deeply affected the phytoplankton community structure in the Bay of Bengal. The regions with strong vertical stratification were more favorable for the growth of cyanobacteria, while the regions with weak vertical stratification were more favorable for the growth of diatoms and dinoflagellates. According to the canonical correspondence analysis, nitrogen, silicates, phosphates, vertical stratification, and temperature were key control factors for phytoplankton communities. However, changes in these chemical parameters in the study area were also caused by the seawater cycle process.

Higher Levels of Soluble Reactive Phosphorus Promote Labile Organic Nitrogen Cycling in Subsurface Coastal Waters

AbstractRemineralization of labile organic nitrogen is a key part of nitrogen cycling in seawater, yet factors controlling this process remain poorly understood. The degradation and fate of amino acids in coastal waters were investigated with incubation experiments using 15N‐labeled alanine (Ala). The cycling of Ala, including the release of NH4+ through remineralization, the subsequent removal of NH4+ via assimilation and nitrification, and the formation of refractory dissolved organic nitrogen (DON), was more rapid in subsurface (mid‐depth 8 m and bottom 17 m) than in surface coastal waters (2 m) of the northern Gulf of Mexico in summer. This pattern is attributed to the different levels of soluble reactive phosphorus (SRP) observed at different depths of the water column. The addition of orthophosphate to the surface water with low SRP (<0.1 μmol L−1) significantly accelerated the remineralization of amino acid, nitrification, and the formation of refractory DON. The rapid remineralization of amino acid and further nitrification in SRP‐replete waters are linked to the rapid growth of heterotrophic bacteria and ammonia‐oxidizing archaea, respectively. Taken together, these results suggest that subsurface coastal waters enriched with SRP are pre‐primed for rapid organic N metabolisms, providing mechanistic insights into nitrogen cycling in marine waters.

Single-atom tungsten engineering of MOFs with biomimetic antibiofilm activity toward robust uranium extraction from seawater

Selective uranium extraction from seawater is challenging because of ubiquitous marine biofouling and poor reusability of adsorbents. A reusable atomic-scale tungsten nanozyme integrating uranium capture capacity and intrinsic haloperoxidase-like activity is constructed, resulting in strong antibiofouling ability and superb reusability for uranium extraction after consecutive multiple regeneration cycles in bio-aggressive seawater. • Atomically dispersed tungsten is anchored in metal organic frameworks (W-UiO). • The presence of atomic-scale tungsten endows W-UiO with haloperoxidase-mimicking activity. • W-UiO nanozyme exerts strong antibacterial activity and inhibition effect against marine microbial colonization. • Such nanozyme exhibits excellent reusability for uranium extraction from seawater. Uranium is the essential element for nuclear power industry. Selective uranium extraction from seawater is very attractive, but challenging because ubiquitous marine biofouling seriously impairs the uranium extraction capacity and reusability of absorbents in bio-aggressive seawater. Herein, we construct a reusable nanozyme for uranium recovery from seawater based on atomically dispersed tungsten anchored on metal organic frameworks (W-UiO). We illustrate that W-UiO nanozyme mimics naturally occurring vanadium haloperoxidase that catalytically converting halides to biocidal hypobromous acid, inducing strong antibiofouling activity against marine microbial colonization. As demonstrated, W-UiO nanozyme shows superb reusability in raw seawater simultaneously, preserving a 78.0% of its initial uranium capture capacity (6.8 times higher than its pristine counterpart) after five consecutive adsorption-desorption cycles. This study is anticipated to spur rationally realizing robust absorbents by mimicking the natural enzymes for practical application in uranium recovery from seawater.

Aging of recycled aggregates mortars by drying-wetting cycles

Due to the large amount of CO2 emissions produced nowadays by the construction sector, the scientific community is looking for measures that will bring constructions to the be as environmental-friendly as possible. One of the most popular lines of research is the use of construction waste as recycled aggregates for the production of recycled aggregates concrete. Regarding the use of coarse recycled aggregates, there are a large number of studies that validate their use at both a mechanical and durability levels. Regarding the use of fine particles, which are inherent to the existence of coarse particles, it is necessary to increase the existing knowledge before they can be widely used. In this paper, the authors have sought to isolate the weakest part of those concrete mixes with exclusively recycled aggregate, i.e. a mortar made exclusively with fine recycled aggregates, in order to analyse the effect of drying-wetting cycles on mixes with recycled aggregates only. Specifically, three types of fine aggregates were used, one natural silica aggregate, one aggregate from crushed ballast and one from crushed sleepers. The mortars made with these aggregates were subjected to 50 durability cycles in distilled water, seawater and water with sulphates. Mechanical, visual and microstructural tests were carried out to analyse the effect of each of these environments on each of the mortars.

Development of a novel rinse-off method for improved sunscreen exposure assessment.

Recent legislative measures restricting the sale of sunscreens containing certain ultraviolet light filtering ingredients (UVFs) have been based on a perception of risk to aquatic life despite the lack of a robust data set to support these decisions. Concerns were focused on the potential for recreational swimmers' and divers' sunscreen use to result in exposures to coral already stressed due to climate change, disease, and other local conditions. In published environmental risk assessments for UVFs, exposure estimates were based on episodic environmental monitoring or estimates of typical sunscreen use, arbitrarily assuming the portion rinsed off from skin in seawater. To improve the accuracy of exposure estimates and thereby develop more robust risk assessments, we measured the amount of the UVFs, avobenzone, homosalate, octisalate, octocrylene, and oxybenzone released to seawater from four sunscreen products (two lotions, one spray, one stick) in a novel porcine skin model of typical human sunscreen use. Sunscreen was applied to porcine skin, allowed to briefly dry, then exposed to four rinse cycles in artificial seawater. The mass of each UVF in seawater, partitioned from seawater onto glassware, and extractable from skin after rinsing were determined. The proportion rinsed from skin varied by UVF, by formula type, and by application rate. Less than 1.4% of applied octisalate, homosalate, and octocrylene was detected in seawater samples (independent of formula) increasing to an average of 4% and 8% for avobenzone in stick and lotion forms, and to 24% for oxybenzone in lotions. The initial data show substantial differences in rinse‐off among formulation types and sunscreen application rates, and stress the importance of using UVF‐specific rinse‐off values rather than a single value for all UVFs. This new method provides a tool for more robust exposure estimates, with initial data supporting lower rinse‐off values than adopted in published risk assessments. Integr Environ Assess Manag 2021;17:961–966. © 2021 Johnson & Johnson Consumer Companies Inc. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Thallium cycling in pore waters of intertidal beach sediments

Pore water data of thallium (Tl) in marine environments are scarce. It has been suggested that anoxic sediments are a sink for dissolved Tl likely due to its incorporation into Fe sulfides. However, recent studies indicated that Tl is removed from solution prior to the onset of sulfidic conditions and that Tl is involved in biological cycles in coastal seawater. To assess the Tl behavior in marine sediments, pore waters of a high energy beach (Spiekeroog Island, Germany) were sampled during different seasons and on different spatial scales. The study site provides a perfect set of samples to assess trace metal behavior under various redox conditions.Samples were analyzed for the dissolved trace metals Tl, molybdenum (Mo), uranium (U), and rhenium (Re). Additionally, sediments were incubated to monitor trace metal removal or release under controlled conditions. On-site redox conditions were characterized using dissolved oxygen (O2), manganese (Mn), and iron (Fe) concentrations.Our results indicated high enrichments of Tl in pore waters concurrently to aerobic organic matter (OM) degradation, exceeding seawater concentrations up to 6-fold. In contrast, Tl was completely removed in weakly reducing pore water characterized by more than 1 µM Mn or Fe. The spatial Tl distribution in intertidal pore waters responded to the present dissolved Mn and Fe level, which varied in space and with season. We suggest, Tl release to be attributed to OM degradation, particle desorption, or reoxidation, whereas Tl removal is likely related to the presence of trace amounts of dissolved sulfide.In conclusion, the fast reaction kinetics of Tl led to fast and complete removal in comparison to Mo, U, and Re and we suggest the following order of removal: Tl > Re > U > Mo. The removal behavior as well as the high enrichments of Tl in pore waters implicate that sinks and sources in the marine environment are not yet fully understood. Although the intertidal sediments form an overall sink for Tl (U and Re), especially under mostly anoxic conditions in summer, sediments turn into a Tl net source in winter, when sediments are more oxic.For global marine Tl balances, Tl fluxes have been estimated based on pore water Tl/Mn ratios. Contrastingly, Tl removal from pore waters at low threshold concentrations of Mn at our site indicated that these Tl flux estimations may not be applicable in permeable sandy beach sediments and in many other types of sediments, which host mildly sulfidic conditions.

Chemical archeoceanography

Elemental fluxes to the ocean are expected to increase with the surface area of continental exposure to weathering and atmospheric PCO2. The record of phosphorus in sediments, which has no notable source within the ocean, and the radiogenic strontium isotopes in Archean carbonates indicate that, prior to the Great Oxidation Event (GOE), subaerial expanses represented only about 20% of the modern continental surface area, i.e. 7% of the surface of the Earth. Because these simple first-order observations, in contrast to the low oxygen content of the pre-GOE atmosphere, have so far received only little attention in the appraisal of the marine chemistry of the early Earth, a reassessment of the chemistry of the pre-GOE ocean is warranted. Here we discuss some of the geochemical cycles of the Archean world, including protons, alkalinity, electrons, and other electrolytes, and attempt to build a first conceptual framework for Chemical Archeoceanography. The smaller subaerial exposures characterizing the Archean and the low abundance of Archean carbonates and mudstones imply that the flux of alkalinity to the ocean was much weaker than today and therefore that the capacity of the runoff to neutralize the high-temperature hydrothermal fluids was less important. Such a reduced flux in turn entails lower seawater pH and higher chlorinity. The lack of atmospheric O2 allowed iron to be in its soluble Fe(II) form and to reduce HCO3− to CH4 while liberating large amounts of protons. The low pH of the pre-GOE ocean and the reduced alkalinity input, reinforced by scant P supply, account for reduced carbonate precipitation. Ocean chemistry evolved under the control of two changing factors: (i) the balance between chemical weathering and hydrothermal fluxes and (ii) the oxygen pressure in the ocean and the atmosphere. Seawater iron concentration was controlled by high [Fe2+]/[H+]2 ratios. With the temperature of hydrothermal fluids at mid-ocean ridges and other active volcanic edifices being determined by the expansion properties of seawater, the chemistry of hydrothermal fluids is controlled by the chlorinity of the ocean. Of all the major element cycles in seawater, those of Na, Mg, and P seem to be unbalanced when runoff falls below the modern value. The very low P content of banded iron formations is inconsistent with a major role of biological activity in the oxidation of Fe2+ dissolved in the Archean ocean. Prior to the GOE, banded iron formations were the major sedimentary sink of seawater cations, a role now played by carbonates. The controls of seawater alkalinity, which today are exerted by the Ca2+–CaCO3 couple, was exerted by dissolved Fe2+-magnetite or Fe2+-ferrihydrite. Plain language summaryWe here evaluate the constraints on seawater chemistry before free oxygen was introduced into the atmosphere some 2.4 billion years ago. We suggest a simple conceptual framework which we validated on modern seawater and which is based on two so-far largely overlooked observations, namely that the phosphorus concentration and strontium isotopic records in ancient sediments require that emerged continental land masses were covering only ~7% of Earth's surface at the time of the Great Oxidation Event instead of 30% today. Atmospheric and seawater chemistry critically depend on this proportion as well as on the chlorinity of the ocean. The oxygen-free atmosphere allowed iron to remain in solution and to reduce atmospheric carbon dioxide to methane. The pH of the ancient oceans must have been lower because less river water was available to neutralize the acidic submarine high-temperature hydrothermal fluids emitted at mid-ocean ridges. Limited continental surface starved the sedimentary column for clays. The low pH and scant phosphorus drainage led to rare carbonate deposition. We conclude by proposing a new scheme for Archean marine chemistry and geochemical cycles that can explain the chemical and geological observations from the Archean and early Proterozoic rock record.