Hg Species Research Articles

Dynamics of mercury stable isotope compounds in Arctic seals: New insights from a controlled feeding trial on hooded seals Cystophora cristata

Accurate interpretation of mercury (Hg) isotopic data requires the consideration of several biotic factors such as age, diet, geographical range, and tissue metabolic turnover. A priori knowledge of prey-predator isotopic incorporation rates and Hg biomagnification is essential. This study aims to assess Hg stable isotopes incorporation in an Arctic species of Phocidae, the hooded seal Cystophora cristata, kept in human care for 24 months (2012–2014) and fed on a constant diet of Norwegian Spring Spawning herring Clupea harengus. We measured THg, MMHg and iHg levels, as well as Hg stable isotope composition with both mass dependent (MDF) and mass independent (MIF) fractionation (e.g. δ202Hg and Δ199,200,201,204Hg) in hooded seal kidney, liver, hair and muscle, in addition to herring muscle. We then calculated Hg MDF and MIF isotopic fractionation between hooded seals and their prey. We found a significant shift in δ202Hg between hooded seal hair (+0.80‰) and kidney (−0.78‰), and herring muscle. In hooded seals tissues δ202Hg correlated positively with MMHg percentage. These findings suggest that tissue-specific Hg speciation is the major driver of changes in Hg isotopic fractionation rates in this Arctic predator. Δ199Hg, Δ200Hg, Δ201Hg and Δ204Hg values did not vary between herring and hooded seal tissues, confirming their utility as tracers of Hg marine and atmospheric sources in top predators. To our knowledge, this represents the first attempt to assess complex Hg isotope dynamics in the internal system of Arctic Phocidae, controlling the effects of age, diet, and distribution. Our results confirm the validity of Hg stable isotopes as tracers of environmental Hg sources even in top predators, but emphasize the importance of animal age and tissue selection for inter-study and inter-species comparisons.

Mercury Accumulation Pathways in a Model Marine Microalgae: Sorption, Uptake, and Partition Kinetics.

The accumulation of dissolved mercury (Hg) by phytoplankton is the largest concentration step along aquatic food chains. However, the cell uptake mechanisms remain unclear. In this study, the marine haptophyteTisochrysis lutea, a model phytoplankton species, was examined for its interactions with picomolar levels of dissolved inorganic divalent Hg (iHg) and monomethyl Hg (MMHg). For both these Hg species, the study observed their successive sorption and internalization over time, yielding Hg partition coefficients as well as sorption, uptake, and release rates. These results were integrated into a time-dependent, three-compartment model for marine cellular Hg accumulation that included exposure medium, phycosphere, and internalized mercury. Assuming equilibria and pseudo-first-order kinetics between compartments, this study obtained transfer rates of Hg between compartments. The results provide insight into the phycosphere as an intermediate compartment for Hg species accumulation and quantify its role in the internalization of Hg. Ultimately, the new model and its parametrization were successfully applied to literature data showing Hg cellular accumulation in different groups of marine phytoplankton, lending confidence in its robustness and potential contributions to help model the uptake of Hg in the aquatic food web.

Traceable Calibration of Atmospheric Oxidized Mercury Measurements.

Most previous measurements of oxidized mercury were collected using a method now known to be biased low. In this study, a dual-channel system with an oxidized mercury detection limit of 6-12 pg m-3 was deployed alongside a permeation tube-based automated calibrator at a mountain top site in Steamboat Springs Colorado, USA, in 2021 and 2022. Permeation tubes containing elemental mercury and mercury halides were characterized via an International System of Units (SI)-traceable gravimetric method and gas chromatography/mass spectrometry before deployment in the calibrator. The dual-channel system recovered 97 ± 4 and 100 ± 8% (±standard deviation) of injected elemental mercury and HgBr2, respectively. Total Hg permeation rates and Hg speciation from the gravimetric method, the chromatography system, the dual-channel system, and an independent SI-traceable measurement method performed at the Jožef Stefan Institute laboratory were all comparable within the respective uncertainties of each method. These are the first measurements of oxidized mercury at low environmental concentrations that have been verified against an SI-traceable calibration system in field conditions while sampling ambient air, and they show that accurate, routinely calibrated oxidized mercury measurements are achievable.

Alternating adsorption of gaseous Hg0 in smelting flue gas and aqueous Hg2+ in waste acid using FeSx/Fe2TiO5: Full utilization of active S resource and centralized control of Hg pollution

Gaseous Hg0 adsorption by metal sulfides is considered as a surface reaction, and most active S species may not be fully utilized during this process, causing the wastage of these valuable resources. To maximize the utilization of active S resource in FeSx/Fe2TiO5 after gaseous Hg0 adsorption, FeSx/Fe2TiO5 was exploited as a bifunctional sorbent to alternately adsorb gaseous Hg0in smelting flue gas and aqueous Hg2+in waste acid. FeSx/Fe2TiO5 demonstrated exceptional performance in adsorbing both gaseous Hg0 and aqueous Hg2+. The utilization of active S resource in FeSx/Fe2TiO5 was significantly improved after the alternating adsorption of gaseous Hg0 and aqueous Hg2+. FeSx/Fe2TiO5 showed strong super-paramagnetism, enabling it to be recovered via magnetic separation for recycle and regeneration. The spent FeSx/Fe2TiO5 can be effectively regenerated by re-reacting it with gaseous H2S for recycle. Hg species adsorbed on FeSx/Fe2TiO5 were primarily desorbed as extremely high levels of gaseous Hg0, which was afterwards recovered via a condensing unit as liquid Hg0 for centralized control. Therefore, the alternating adsorption of gaseous Hg0 in smelting flue gas and aqueous Hg2+ in waste acid using FeSx/Fe2TiO5 offered significant advantages in the centralized control of Hg pollution in smelters, double as fully utilizing its active S resource.

The binding effects and mechanisms of dissolved organic matter (DOM) on the fate of mercury in sludge anaerobic digestion combined with thermal hydrolysis

Dissolved organic matter (DOM) plays an important role in regulating the fate of mercury (Hg), e.g., mobility, bioavailability, and toxicity. Clarifying the role of DOM in binding Hg in the treatment processes of sewage sludge is important for relieving Hg contamination risks in land applications. However, the impacts of DOM on Hg binding in sewage sludge are still unclear. In this study, we investigated the evolution of Hg and its speciation in full-scale sludge anaerobic digestion (AD) with thermal hydrolysis. The role of DOM in binding Hg(II) was further analyzed. The results showed that AD with thermal hydrolysis led to an increase in the Hg content in the sludge (from 3.72 ± 0.47 mg/kg to 10.75 ± 0.16 mg/kg) but a decrease in Hg mobility (the mercury sulfide fraction increased from 60.56 % to 79.78 %). Further adsorption experiments revealed that at equivalent DOM concentrations, DOM with a low molecular weight (MW<1 kDa) in activated sludge, DOM with a medium molecular weight (1 kDa<MW<5 kDa) in thermally hydrolyzed sludge, and DOM with a high molecular weight (MW> 5 kDa) in both anaerobically digested sludge and conditioned sludge showed high binding amounts of Hg(II), with 1372.54, 535.28, 942.09 and 801.51 mg Hg/g DOM, respectively. Parallel factor analysis (PARAFAC) and fluorescence quotient (FQ) results showed that tryptophan-like and tyrosine-like substances had high binding affinities for Hg(II). Furthermore, X-ray photoelectron spectroscopy (XPS) indicated that the reduced organic sulfur contained in the DOM was potentially bound to Hg through the interactions of Hg-S and Hg-O. These results indicated that DOM may play special roles in regulating Hg speciation. The association between DOM and Hg(II), such as the significant positive correlation (p < 0.05) between the dissolution rate of Hg(II) and release of tryptophan-like substances during thermal hydrolysis, suggested the potential way for removing Hg from sludge.

Use of Metallic Mercury in Artisanal Gold Mining by Amalgamation: A Review of Temporal and Spatial Trends and Environmental Pollution

The introduction of mercury (Hg) into the environment by anthropogenic activities has resulted in negative implications for ecosystem functions and human health. Unlike the legacy of huge environmental pollution left by historic gold rushes in several developed countries, gold-rich nations in the developing world are currently witnessing what could qualify as a “new gold rush”, conducted primarily by small-scale mining operators and characterized by the use of metallic Hg (Hg0) in the amalgamation process to extract gold from crude ores. Once introduced into the environment, Hg0 can undergo biogeochemical transformations to produce Hg species such as methyl-Hg, with well-established adverse impacts on living organisms. This review summarizes published data on both historical and recent trends of the use of Hg0 in artisanal gold mining (AGM) on a global scale and emphasizes the impacts of AGM on the environment. To achieve this, we used citations from research conducted in North and South America, Europe, Asia, Africa, Australia, and New Zealand, obtained from several search engines and databases. Our findings show that, in addition to the well-known environmental and human health adverse effects of gold mining with Hg0, gold extraction by the Hg amalgamation technique is boosting the economy in parts of Africa, South America, and Asia. Unfortunately, this appealing aspect of AGM may not be easily halted, pending the creation of alternative employment. Therefore, there is a clear need for the development of safe and affordable gold extraction and purification technologies. Ultimately, the growth of this specific economic sector should be regulated to help protect both the environment and human health. Information compiled in this review should help to (i) improve the mapping of AGM-impacted soil and aquatic systems on a global scale and (ii) stimulate discussions and research on how to take down current barriers to the development and implementation of safe AGM methods.

Organ-specific mercury stable isotopes, speciation and particle measurements reveal methylmercury detoxification processes in Atlantic Bluefin Tuna

Identifying metabolism and detoxification mechanisms of Hg in biota has important implications for biomonitoring, ecotoxicology, and food safety. Compared to marine mammals and waterbirds, detoxification of MeHg in fish is understudied. Here, we investigated Hg detoxification in Atlantic bluefin tuna Thunnus thynnus using organ-specific Hg and Se speciation data, stable Hg isotope signatures, and Hg and Se particle measurements in multiple tissues. Our results provide evidence for in vivo demethylation and biomineralization of HgSe particles, particularly in spleen and kidney. We observed a maximum range of 1.83‰ for δ202Hg between spleen and lean muscle, whereas Δ199Hg values were similar across all tissues. Mean percent methylmercury ranged from 8% in spleen to 90% in lean muscle. The particulate masses of Hg and Se were higher in spleen and kidney (Hg: 61% and 59%, Se: 12% and 6%, respectively) compared to muscle (Hg: 2%, Se: 0.05%). Our data supports the hypothesis of an organ-specific, two-step detoxification of methylmercury in wild marine fish, consisting of demethylation and biomineralization, like reported for waterbirds. While mass dependent fractionation signatures were highly organ specific, stable mass independent fractionation signatures across all tissues make them potential candidates for source apportionment studies of Hg using ABFT.

Comparison of mercury (Hg) bioaccumulation with mono- and mixed Lemna minor and Spirodela polyrhiza cultures.

Mercury (Hg) is a prevalent and harmful contaminant that persists in the environment. For phytoremediation, it is important to discover which plants can bioaccumulate meaningful amounts of Hg while also tolerating its toxicity. Additionally, increasing biodiversity could create a more resilient and self-sustaining system for remediation. This study explores whether mixed populations of Lemna minor and Spirodela polyrhiza can better bioaccumulate and tolerate Hg than monocultures. Mono- and mixed cultures of L. minor and S. polyrhiza were grown in mesocosms of 0.5µg/L or 100µg/L Hg (HgCl2) spiked water for 96h. Change in weight of duckweed was used to assess Hg tolerance. Diffusive gradients in thin-films (DGTs) were used as surrogate monitoring devices for bioavailable levels of Hg. For biomass growth, the mixed culture of the L. minor was greater than the monoculture at the high dose. The L. minor accumulated more Hg in the mixed culture at the low dose while the S. polyrhiza was higher in the mixed at the high dose. Hg speciation in water was modeled using Windermere Humic Aqueous Model 7 (WHAM7) to compare the bioavailable species indicated by the DGTs. Potentially due to the controlled conditions, the WHAM7 output of bioavailable Hg was almost 1:1 to that estimated by the DGTs, indicating good predictive capability of geochemical modeling and passive sampler DGT on metal bioavailability. Overall, the mixed cultures statistically performed as well as or better than the monocultures when tolerating and bioaccumulating Hg. However, there needs to be further work to see if the significant differences translate into practical differences worth the extra resources to maintain multiple species.

Enhanced reductive removal of aqueous Hg(II) by a novel Pd-Cu-BTC catalyst

The reusability of catalytic materials is crucial for their practical applications to environmental water treatment technologies. In this study, we synthesized a novel catalytic metal–organic framework, Pd impregnated Cu-BTC (1,3,5-benzenetricarboxylate), and investigated its performance in the reductive removal of Hg(II). Our analysis of adsorbed Hg species and valence change of metals on the catalyst surface provided valuable insights into the reaction mechanism. Experimental findings revealed that the reactivity and the transformed Hg(0) adsorbed on the catalyst surface were significantly increased following the metal order of Pd > Ru > Pt. Reduced Pd-Cu-BTC exhibited a remarkable Hg(II) removal of 99.9 % within 2.5 min, with the highest adsorption capacity (4.43 mg·g−1) and pseudo-second-order rate constant (k2 = 0.343 g·mg−1·min−1). Increasing the Pd content significantly enhanced Hg(0) adsorption, from 40 % with 1 % Pd to 96 % with 6 % Pd. Moreover, the catalyst maintained its reactivity throughout nine consecutive cycles, effectively removing all aqueous Hg species. The catalyst shows promising potential for recovery through thermal desorption due to the highest adsorbed Hg(0) from Hg(II) reduction reaction. Hence, the reduced Pd-Cu-BTC is an effective and sustainable catalyst for application in the removal of Hg(II) in water and wastewater treatment technologies, highlighting its long-term usability.

Tracing anthropogenic mercury in soils from Fe–Hg mining/smelting area: Isotopic and speciation insights

Mercury (Hg) stable isotope ratios supplemented by Hg solid speciation data were determined in soils in a former Fe–Hg mining/smelting area (Jedová hora, Czech Republic, Central Europe). The dominant Hg phase in the studied soils was found to be cinnabar (HgS). A secondary form of soil Hg(II) was represented by Hg weakly and strongly bound to mineral (micro)particles, as revealed by thermo-desorption analysis. These Hg species probably play a key role in local soil Hg processes and biogeochemical cycling. The Hg isotopic data generally showed small differences between HgS (−1.1 to −0.8‰; δ202Hg) and the soil samples (−1.4 to −0.9‰; δ202Hg), as well as limited isotopic variability within the two studied soil profiles. On the other hand, the detected negative δ202Hg shift (∼0.4‰) in organic horizons compared to mineral soils in the highly contaminated profile suggests the presence of secondary post-depositional Hg processes, such as sorption or redox changes. For the less contaminated profile, the observed Hg isotopic variation (∼0.3‰; δ202Hg) in the subsurface mineral soil compared to both overlying and underlying horizons is likely due to cyclic redox reactions associated with Hg isotopic fractionation. We assume that the adsorption of Hg(II) to secondary Fe(III)/Mn(III,IV)-oxides could be of major importance in such cases.

Imaging gastrointestinal damage due to acute mercury poisoning using a mitochondria-targeted dual near-infrared fluorescent probe

Mercury (Hg) is one of the most widespread pollutants that pose serious threats to public health and the environment. People are inevitably exposed to Hg via different routes, such as respiration, dermal contact, drinking or diet. Hg poisoning could cause gingivitis, inflammation, vomiting and diarrhea, respiratory distress or even death. Especially during the developmental stage, there is considerable harm to the brain development of young children, causing serious symptoms such as intellectual disability and motor impairments, and delayed neural development. Therefore, it’s of great significance to develop a specific, quick, practical and labor-saving assay for monitoring Hg2+. Herein, a mitochondria-targeted dual (excitation 700 nm and emission 728 nm) near-infrared (NIR) fluorescent probe JZ-1 was synthesized to detect Hg2+, which is a turn-on fluorescent probe designed based on the rhodamine fluorophore thiolactone, with advantages of swift response, great selectivity, and robust anti-interference capability. Cell fluorescence imaging results showed that JZ-1 could selectively target mitochondria in HeLa cells and monitor exogenous Hg2+. More importantly, JZ-1 has been successfully used to monitor gastrointestinal damage of acute mercury poisoning in a drug-induced mouse model, which provided a great method for sensing Hg species in living subjects, as well as for prenatal diagnosis.

Assessment of mobile mercury concentration in soils of an abandoned coalfield waste pile in Douro region: the Fojo waste pile (Portugal) study case

PurposePejão Mining Complex locates in Castelo de Paiva municipality and, until its closure in 1994, was one of the most important coal mines in the Douro Coalfield. This work aims to study the presence, quantify, and evaluate the dissemination of mercury (Hg), a potentially toxic element (PTE) of major public health concern by the World Health Organization (WHO), from a waste pile affected by coal fires.Materials and methodsSamples from areas affected and unaffected by the combustion and from surrounding soil were collected from Fojo waste pile region. First, the Hg pseudo-total concentration was estimated for all collected samples by soil microwave–assisted digestion with aqua regia (USEPA 3051A). Then, a sequential extraction procedure (SEP), the USEPA 3200, was applied for Hg fractionation and speciation aiming to evaluate Hg mobility and bioavailability to surrounding ecosystems.Results and discussionThe results obtained showed a Hg enrichment in soil samples when compared to Portuguese and international reference values for soils. Relatively to the Hg availability and mobility, although it predominates in the semi-mobile fraction, the waste pile materials exposed to combustion showed a concerning increase of Hg levels in the mobile fraction that contains the more labile Hg species, being a major source of environmental contamination by Hg.ConclusionsThis study allowed to conclude that combustion of mining residues increased Hg mobility, toxicity, and bioavailability, increasing the contamination potential of the coal waste pile. The methodology applied in this work can be replicated in other abandoned mines to monitor, control, and/or mitigate the Hg environmental impact in the surrounding soils and waters.

Assessment of Hg Speciation Changes in the Sedimentary Rock Record From Thermal Desorption Characteristics

AbstractSedimentary mercury (Hg) has become a widely used proxy for paleo‐volcanic activity. However, scavenging and drawdown of Hg by organic‐matter (OM) and sulfides are important non‐volcanic factors determining variability in such records. Most studies, therefore, normalize total Hg (HgT) to a Hg “host‐phase” proxy (e.g., HgT/TOC for OM, HgT/TS for sulfides), with the dominant host‐phase determined based on the strongest observed (linear) correlations. This approach suffers from various non‐linearities in Hg‐host‐phase behavior and does not account for succession‐level, let alone sample‐level, Hg speciation changes. Thermal desorption characteristics or “profiles” (TDPs) for many Hg species during pyrolysis analysis are well‐established with applications including distinguishing between OM‐bound Hg and different Hg sulfides and oxides in (sub‐)recent sediments. We explore the use of TDPs for geological sediment (rock) samples and illustrate the presence of multiple release phases (Hg species)—correlated to geochemical host‐phase—in (almost) all the 65 analyzed Tithonian (146–145 Ma) silt and mudrock samples. By quantifying the Hg in each release phase for every sample, we find TOC concentration may determine ∼60% of the variability in the first (lower temperature) Hg TDP release phase: a stark difference with the total Hg released from these samples, where ∼20% of variation is explained by TOC variability. TDPs provide insight on sample‐level Hg speciation and demonstrate that, while the common assumption of single‐phase Hg speciation in sedimentary rocks is problematic, differences in Hg speciation can be detected, quantified, and accounted for using commonly applied techniques—opening potential for routine assessment.

Soil organic matter degradation and methylmercury dynamics in Hg-contaminated soils: Relationships and driving factors

Biodegradation of soil organic matter (SOM), which involves greenhouse gas (GHG) emissions, plays an essential role in the global carbon cycle. Over the past few decades, this has become an important research focus, particularly in natural ecosystems. SOM biodegradation significantly affects contaminants in the environment, such as mercury (Hg) methylation, producing highly toxic methylmercury (MeHg). However, the potential link between GHG production from SOM turnover in contaminated soils and biogeochemical processes involving contaminants remains unclear. In this study, we investigated the dynamics of GHG, MeHg production, and the relationship between biogeochemical processes in soils from two typical Hg mining sites. The two contaminated soils have different pathways, explaining the significant variations in GHG and MeHg production. The divergence of the microbial communities in these two biogeochemical processes is essential. In addition to the microbial role, abiotic factors such as Hg species can significantly affect MeHg production. On the other hand, we found an inverse relationship between CH4 and MeHg, suggesting that carbon emission reduction policies and management could inadvertently increase the MeHg levels. This highlights the need for an eclectic approach to organic carbon sequestration and contaminant containment. These findings suggest that it is difficult to establish a general pattern to describe and explain the SOM degradation and MeHg production in contaminated soils within the specific scenarios. However, this study provides a case study and helpful insights for further understanding the links between environmental risks and carbon turnover in Hg mining areas.

Legacy Mercury Re-emission and Subsurface Migration at Contaminated Sites Constrained by Hg Isotopes and Chemical Speciation.

The re-emission and subsurface migration of legacy mercury (Hg) are not well understood due to limited knowledge of the driving processes. To investigate these processes at a decommissioned chlor-alkali plant, we used mercury stable isotopes and chemical speciation analysis. The isotopic composition of volatilized Hg(0) was lighter compared to the bulk total Hg (THg) pool in salt-sludge and adjacent surface soil with mean ε202HgHg(0)-THg values of -3.29 and -2.35‰, respectively. Hg(0) exhibited dichotomous directions (E199HgHg(0)-THg = 0.17 and -0.16‰) of mass-independent fractionation (MIF) depending on the substrate from which it was emitted. We suggest that the positive MIF enrichment during Hg(0) re-emission from salt-sludge was overall controlled by the photoreduction of Hg(II) primarily ligated by Cl- and/or the evaporation of liquid Hg(0). In contrast, O-bonded Hg(II) species were more important in the adjacent surface soils. The migration of Hg from salt-sludge to subsurface soil associated with selective Hg(II) partitioning and speciation transformation resulted in deep soils depleted in heavy isotopes (δ202Hg = -2.5‰) and slightly enriched in odd isotopes (Δ199Hg = 0.1‰). When tracing sources using Hg isotopes, it is important to exercise caution, particularly when dealing with mobilized Hg, as this fraction represents only a small portion of the sources.

One-step synthesis of a core-shell structured biochar using algae (Chlorella) powder and ferric sulfate for immobilizing Hg(II)

Mercury (Hg) pollution poses a significant environmental challenge. One promising method for its removal is the sorption of mercuric ions using biochar. FeS-doped biochar (FBC) exhibits effective mercury adsorption, however may release excess iron into the surrounding water. To address this issue, a novel magnetic pyrrhotite/magnetite-doped biochar with a core-shell structure was synthesized for the adsorption of 2-valent mercury (Hg(II)). The proposed synthesis process involved the use of algae powder and ferric sulfate in a one-step method. By varying the ratio of ferric sulfate and alga powder (within the range of 0.18 - 2.5) had a notable impact on the composition of FBC. As the ferric sulfate content increased, the FBC exhibited a higher concentration of oxygen-containing groups. To assess the adsorption capacity, Langmuir and Freundlich adsorption models were applied to the experimental data. The most effective adsorption was achieved with FBC-4, reaching a maximum capacity (Qm) of 95.51 mg/g. In particular, at low Hg(II) concentrations, FBC-5 demonstrated the ability to reduce Hg(II) concentrations to less than 0.05 mg/L within 30 min. Additionally, the stability of FBC was confirmed within the pH range of 3.8 - 7.2. The study also introduced a model to analyze the adsorption preference for different Hg(II) species. Calomel was identified in the mercury saturated FBC, whereas the core-shell structure exhibited excellent conductivity, which most likely contributed to the minimal release of iron. In summary, this research presents a novel and promising method for synthesizing core-shell structured biochar and provides a novel approach to explore the adsorption contribution of different metal species.

Assessment of dietary Selenium and its role in Mercury fate in cultured fish rainbow trout with two sustainable aquafeeds

This study enhances the current limited understanding of the interaction between mercury (Hg) and selenium (Se) species in fish. Rainbow trout (Oncorhynchus mykiss), a model aquaculture fish, was exposed to Hg and Se species through controlled dietary conditions. Over a 6-month feeding trial, the impact of dietary Se on Hg bioaccumulation in fish, including flesh, brain, and liver, was tracked. Twelve dietary conditions were tested, including plant-based diets (0.25 µgSe g−1) and tuna byproduct diets (0.25 µgHg g−1, 8.0 µgSe g−1) enriched with methylmercury and/or Se as selenite or selenomethionine. The tuna byproduct diet resulted in lower Hg levels than the plant-based diets, with muscle Hg content below the European Commission's safe threshold. This study highlights the significant impact of specific Se compounds in the diet, particularly from tuna-based aquafeed, on Hg bioaccumulation. These promising results provide a strong recommendation for future use of fisheries byproducts in sustainable aquafeeds.

Optimized mercury speciation analysis using LC-ICP-MS and microwave assisted extraction for precise determination of methylmercury in fish, rice and soil

Mercury (Hg) is a toxic element that exists in various forms, each with its characteristics and impacts on the environment. Methylmercury (MeHg) bioaccumulates in the food chain and identifying mercury species is crucial to assessing risks to ecology and health. Therefore, accurate, sensitive, and broad-range analytical methods are essential for the determination of methylmercury. This study optimized and validated a procedure for Hg speciation analysis in rice, fish, and soil using different extractants, followed by liquid chromatography inductively-coupled plasma mass spectrometry (LC ICP-MS) using certified references. Microwave-assisted extraction (MAE) parameters were optimized using 25 % KOH, resulting in improved sensitivity, accuracy and processing time. The validated method achieved a limit of quantitation (LOQ) of 12 µg kg−1 and showed acceptable percentage recoveries (75.3–98.1 %) in all matrices, enabling precise determination of MeHg (%RSDr; 3.76–5.78, %RSDR; 2.34–6.75) and Hg in a large number of samples within a short time frame. The validated method is particularly well-suited for rice, followed by fish and then soil. Therefore, the method utilizing microwave-assisted extraction and LC ICP-MS ensures precise methylmercury determination in rice, fish, and soil, crucial for evaluating environmental and health risks associated with mercury bioaccumulation.

Organic matters, but inorganic matters too: column examination of elevated mercury sorption on low organic matter aquifer material using concentrations and stable isotope ratios

Abstract. Sorption of mercury (Hg) in soils is suggested to be predominantly associated with organic matter (OM). However, there is a growing collection of research that suggests that clay minerals and Fe/Mn oxides are also important solid phases for the sorption of soluble Hg in soil–groundwater systems. We use a series of (60 mL syringe based) column experiments to examine sorption and subsequent desorption of HgCl2 solutions (experiment 1 (EXP1): 46.1 ± 1.1 mg L−1; experiment 2 (EXP2): 144 ± 6 mg L−1) in low-OM (0.16 ± 0.02 %) solid-phase aquifer materials. Analyses of total Hg concentrations, Hg speciation (i.e. pyrolytic thermal desorption (PTD)), and Hg stable isotopes are performed on both solid- and liquid-phase samples across sorption and desorption phases of the experiments. The sorption breakthrough curve best fitted a Freundlich model. Despite the very low-OM content, the Hg equilibrium sorptive capacity in these columns is very high: 1510 ± 100 and 2320 ± 60 mg kg−1 for EXP1 and EXP2, respectively, and it is similar to those determined for high-OM soils. Data from the experiments on mass-dependent Hg stable isotope fractionation data from these experiments (described by δ202Hg) support preferential sorption of lighter isotopes to the solid-phase materials with results indicating an isotopically heavier liquid phase and an isotopically lighter solid phase. Desorption fits exponential decay models, and 46 ± 6 % and 58 ± 10 % of the sorbed Hg is removed from the solid-phase materials at the termination of desorption in EXP1 and EXP2, respectively. The divergence of δ202Hg values between liquid and solid phases also continues into desorption. This desorption profile is linked to the initial release of easily exchangeable Hg(II) species physically sorbed to Fe/Mn oxides and clay mineral surfaces (liquid phase enriched in heavy isotopes) and then slower release of Hg(II) species that have undergone secondary reaction to more stable/less-soluble Hg(II) species and/or diffusion/transport into the mineral matrices (processes favouring lighter isotopes; solid phase enriched in lighter isotopes). The secondary production of Hg(0) within the columns is confirmed by PTD analyses that indicate distinct Hg(0) release peaks in solid-phase samples at &lt;175 ∘C, which again agrees with field observations. Retardation (RD) and distribution (KD) coefficients are 77.9 ± 5.5 and 26.1 ± 3.0 mL g−1 in EXP1, respectively, and 38.4 ± 2.7 and 12.4 ± 0.6 mL g−1 in EXP2, respectively. These values are similar to values derived from column experiments on high-OM soil and provide the basis for future Hg fate and transport modelling in soil–groundwater systems.

Mercury Mobility in Epibenthic Waters of a Deltaic Environment

AbstractMercury (Hg) cycling at the sediment‐water interfaces (SWI) encompasses multiple homogeneous and heterogeneous biogeochemical reactions whose result is not yet elucidated. Estuarine SWIs, where the organic matter mineralization is active, constitute experimental sites particularly suitable for scrutinizing Hg speciation and mobilization. Here, we present high‐resolution vertical concentration profiles of Hg species, including inorganic divalent Hg () and monomethyl Hg (MMHg) in solid and dissolved (&lt;0.22 μm) phases, on both sides of the SWI of the proximal part of the Rhône prodelta (northwestern Mediterranean Sea) using sediment cores and dialyzers implemented for a 67‐day‐long period. Concentrations of the dissolved species were &lt;0.10 nM in the sediment pore waters but reached up to 0.58 nM in the epibenthic water zone, a concentration level that is ∼200 times higher than that of the water column. Conversely, MMHg concentrations were low (&lt;0.5 pM) above the SWI and increased to up to 4.6 pM in the sulfate‐reducing zones of the sediment. The dynamic of the Hg species interconversions was explored using one‐dimensional transport‐reaction equations. This model allowed us to constrain the depth intervals where various species are produced or consumed and to approximate the reaction rates. We conclude that the epibenthic zone of the Rhône prodelta is a location of intense mobilization of inorganic HgII associated with organic matter mineralization and MMHg distribution in pore water is controlled by microbiological in situ reactions, but sedimentary MMHg does not diffuse in the overlying water column.