Experimental evidence for recovery of mercury-contaminated fish populations.

Anthropogenic releases of mercury (Hg)1-3 are a human health issue4 because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans5,6. Predicting the efficacy of Hg pollution controls on fish MeHg concentrations is complex because many factors influence the production and bioaccumulation of MeHg7-9. Here we conducted a 15-year whole-ecosystem, single-factor experiment to determine the magnitude and timing of reductions in fish MeHg concentrations following reductions in Hg additions to a boreal lake and its watershed. During the seven-year addition phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from additions to the lake because most of those in the watershed remained there. Thereafter, isotopic additions were stopped, resulting in an approximately 100% reduction in Hg loading to the lake. The concentration of labelled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38-76% of MeHg concentration in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this experiment clearly demonstrates that any reduction in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.

Anthropogenic short-lived halogens increase human exposure to mercury contamination due to enhanced mercury oxidation over continents.

Mercury (Hg) is a contaminant of global concern, and an accurate understanding of its atmospheric fate is needed to assess its risks to humans and ecosystem health. Atmospheric oxidation of Hg is key to the deposition of this toxic metal to the Earth's surface. Short-lived halogens (SLHs) can provide halogen radicals to directly oxidize Hg and perturb the budget of other Hg oxidants (e.g., OH and O3). In addition to known ocean emissions of halogens, recent observational evidence has revealed abundant anthropogenic emissions of SLHs over continental areas. However, the impacts of anthropogenic SLHs emissions on the atmospheric fate of Hg and human exposure to Hg contamination remain unknown. Here, we show that the inclusion of anthropogenic SLHs substantially increased local Hg oxidation and, consequently, deposition in/near Hg continental source regions by up to 20%, thereby decreasing Hg export from source regions to clean environments. Our modeling results indicated that the inclusion of anthropogenic SLHs can lead to higher Hg exposure in/near Hg source regions than estimated in previous assessments, e.g., with increases of 8.7% and 7.5% in China and India, respectively, consequently leading to higher Hg-related human health risks. These results highlight the urgent need for policymakers to reduce local Hg and SLHs emissions. We conclude that the substantial impacts of anthropogenic SLHs emissions should be included in model assessments of the Hg budget and associated health risks at local and global scales.

Seabirds reveal mercury distribution across the North Atlantic.

Mercury (Hg) is a heterogeneously distributed toxicant affecting wildlife and human health. Yet, the spatial distribution of Hg remains poorly documented, especially in food webs, even though this knowledge is essential to assess large-scale risk of toxicity for the biota and human populations. Here, we used seabirds to assess, at an unprecedented population and geographic magnitude and high resolution, the spatial distribution of Hg in North Atlantic marine food webs. To this end, we combined tracking data of 837 seabirds from seven different species and 27 breeding colonies located across the North Atlantic and Atlantic Arctic together with Hg analyses in feathers representing individual seabird contamination based on their winter distribution. Our results highlight an east-west gradient in Hg concentrations with hot spots around southern Greenland and the east coast of Canada and a cold spot in the Barents and Kara Seas. We hypothesize that those gradients are influenced by eastern (Norwegian Atlantic Current and West Spitsbergen Current) and western (East Greenland Current) oceanic currents and melting of the Greenland Ice Sheet. By tracking spatial Hg contamination in marine ecosystems and through the identification of areas at risk of Hg toxicity, this study provides essential knowledge for international decisions about where the regulation of pollutants should be prioritized.

Climate-driven changes of global marine mercury cycles in 2100.

Human exposure to monomethylmercury (CH3Hg), a potent neurotoxin, is principally through the consumption of seafood. The formation of CH3Hg and its bioaccumulation in marine food webs experience ongoing impacts of global climate warming and ocean biogeochemistry alterations. Employing a series of sensitivity experiments, here we explicitly consider the effects of climate change on marine mercury (Hg) cycling within a global ocean model in the hypothesized twenty-first century under the business-as-usual scenario. Even though the overall prediction is subjected to significant uncertainty, we identify several important climate change impact pathways. Elevated seawater temperature exacerbates elemental Hg (Hg0) evasion, while decreased surface wind speed reduces air-sea exchange rates. The reduced export of particulate organic carbon shrinks the pool of potentially bioavailable divalent Hg (HgII) that can be methylated in the subsurface ocean, where shallower remineralization depth associated with lower productivity causes impairment of methylation activity. We also simulate an increase in CH3Hg photodemethylation potential caused by increased incident shortwave radiation and less attenuation by decreased sea ice and chlorophyll. The model suggests that these impacts can also be propagated to the CH3Hg concentration in the base of the marine food web. Our results offer insight into synergisms/antagonisms in the marine Hg cycling among different climate change stressors.

An aggregation-induced emission-based ratiometric fluorescent chemosensor for Hg(II) and its application in Caenorhabditis elegans imaging.

A chromone-based ratiometric fluorescent probe L2 was developed for the selective detection of Hg(II) in a semi-aqueous solution based on aggregation-induced emission (AIE) and chelation-enhanced fluorescence (CHEF) effect. The probe L2 fluoresced significantly at 498 nm in its aggregated state, and when chelated with Hg(II), the soluble state fluoresced 1-fold higher. In addition, Job's plot reveals that the probe forms a 1:1 stoichiometry complex with Hg(II) with an association constant of 9.10 × 103M-1 estimated by the BH plot. The probe L2 detects Hg(II) down to 22.47 nM without interference from other interfering ions. The FTIR, ESI mass, and DFT-based computational studies investigated the binding mechanism of probe L2 with Hg(II). Taking advantage of its AIE characteristics, the probe L2 was successfully applied for bio-capability analysis in Caenorhabditis elegans (a nematode worm) imaging of Hg(II) in a living model.

Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs.

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

Mercury isotopic evidence for the importance of particles as a source of mercury to marine organisms.

The origin of methylmercury in pelagic fish remains unclear, with many unanswered questions regarding the production and degradation of this neurotoxin in the water column. We used mercury (Hg) stable isotope ratios of marine particles and biota to elucidate the cycling of methylmercury prior to incorporation into the marine food web. The Hg isotopic composition of particles, zooplankton, and fish reveals preferential methylation of Hg within small (< 53 µm) marine particles in the upper 400 m of the North Pacific Ocean. Mass-dependent Hg isotope ratios (δ202Hg) recorded in small particles overlap with previously estimated δ202Hg values for methylmercury sources to Pacific and Atlantic Ocean food webs. Particulate compound specific isotope analysis of amino acids (CSIA-AA) yield δ15N values that indicate more-significant microbial decomposition in small particles compared to larger particles. CSIA-AA and Hg isotope data also suggest that large particles (> 53 µm) collected in the equatorial ocean are distinct from small particles and resemble fecal pellets. Additional evidence for Hg methylation within small particles is provided by a statistical mixing model of even mass-independent (Δ200Hg and Δ204Hg) isotope values, which demonstrates that Hg within near-surface marine organisms (0-150 m) originates from a combination of rainfall and marine particles. In contrast, in meso- and upper bathypelagic organisms (200-1,400 m), the majority of Hg originates from marine particles with little input from wet deposition. The occurrence of methylation within marine particles is supported further by a correlation between Δ200Hg and Δ199Hg values, demonstrating greater overlap in the Hg isotopic composition of marine organisms with marine particles than with total gaseous Hg or wet deposition.

Extended-Gate FET Biosensor Based on GaN Micropillar Array and Polycrystalline Layer: Application to Hg2+ Detection in Human Urine.

Owing to the separation of field-effect transistor (FET) devices from sensing environments, extended-gate FET (EGFET) biosensor features high stability and low cost. Herein, a highly sensitive EGFET biosensor based on a GaN micropillar array and polycrystalline layer (GMP) was fabricated, which was prepared by using simple one-step low-temperature MOCVD growth. In order to improve the sensitivity and detection limit of EGFET biosensor, the surface area and the electrical conductivity of extended-gate electrode can be increased by the micropillar array and the polycrystalline layer, respectively. The designed GMP-EGFET biosensor was modified with l-cysteine and applied for Hg2+ detection with a low limit of detection (LOD) of 1 ng/L, a high sensitivity of -16.3 mV/lg(µg/L) and a wide linear range (1 ng/L-24.5 µg/L). In addition, the detection of Hg2+ in human urine was realized with an LOD of 10 ng/L, which was more than 30 times lower than that of reported sensors. To our knowledge, it is the first time that GMP was used as extended-gate of EGFET biosensor.

Novel Nucleic Acid-Assisted Ion-Responsive ECL Biosensor Based on Hollow AuAg Nanoboxes with Excellent SPR and Effective Coreaction Acceleration.

Novel hollow AuAg nanoboxes (AuAg NBs) were designed for an innovative electrochemiluminescence (ECL) sensor to ultrasensitively detect Pb2+ and Hg2+ with the aid of DNAzyme and "thymine-Hg2+-thymine" ("T-Hg2+-T") structure. AuAg NBs are employed as an excellent surface plasma resonance (SPR) source, as well as an effective coreaction accelerator for the CoNi NFs/S2O82- system to greatly improve ECL performance. To detect Pb2+, the DNAzyme catalyzes the cleavage of ribonucleic acid targets into numerous small nucleic acid fragments, leading to an ECL signal. When Hg2+ is added, the thymine-thymine (T-T) mismatches of the Hg2+ aptamer bind Hg2+ to form the "T-Hg2+-T" structure, which not only inhibits the SPR process but also produces a large steric hindrance, thus quenching the ECL signal and allowing quantification of Hg2+. The novel ECL sensor quantifies Pb2+ in the range of 0.1 fM to 0.1 µM with a limit of detection of 0.07 fM and Hg2+ in the range of 10 pM to 1 µM with a LOD of 4.07 pM.

A selective colorimetric and efficient removal strategy for mercury(II) in aquatic systems using mesoporous Fe3O4-loaded silver probes.

Mesoporous Fe3O4-loaded silver nanocomposites (Fe3O4@Ag) were simply fabricated as bi-functional nanozymes for the catalysis-based detection and removal of Hg2+ ions. It was found that the as-prepared magnetic Fe3O4@Ag could display peroxidase-like catalysis activity that could be rationally enhanced in the presence of Hg2+ ions. To our surprise, the shell of the Ag element may decrease the catalysis of the Fe3O4 to some degree. However, the Ag particles could serve as the probes for specifically recognizing Hg2+ ions and trigger increased catalysis through the formation of Ag-Hg alloys, with a decreased signal background. A high-throughput colorimetric analytical method was thereby developed based on the Fe3O4@Ag catalysis for probing Hg2+ ions in the muscles of fish by using 96-well plates, at linear Hg2+ concentrations ranging from 0.010 to 2.5 mg kg-1. Moreover, the developed colorimetric analytical method was applied to evaluate Hg2+ levels in muscle samples of different kinds of fish. Unexpectedly, an obvious difference of Hg2+ levels in muscles of four kinds of fish was discovered, with the order of snakehead (Ophicephalus argus) > largemouth bass (Micropterus salmoides) > crucian carp (Carassius auratus) > silver carp (Hypophthalmichthys molitrix), where the carnivorous fish showed higher Hg2+ levels than the omnivorous or plant-based ones. Moreover, the as-fabricated Fe3O4@Ag adsorbents with their large specific surface area and high environmental robustness could exhibit efficient Hg2+ adsorption with capacities of up to 397.60 mg g-1. A removal efficiency of 99.40% can also be expected for Hg2+ ions from wastewater, with the magnet-aided recycling of Fe3O4@Ag adsorbents. Such an Fe3O4@Ag-based colorimetric analysis and removal strategy for Hg2+ ions should find wide applications in the fields of aquatic food safety, environmental monitoring, and clinical diagnostics of Hg-poisoning diseases.

Can Mercury Influence Carbon Dioxide Levels? Implications for the Implementation of the Minamata Convention on Mercury.

The Paris Agreement and the Minamata Convention on Mercury are two of the most important environmental conventions being implemented concurrently, with a focus on reducing carbon and mercury emissions, respectively. The relation between mercury and carbon influences the interactions and outcomes of these two conventions. This perspective investigates the link between mercury and CO2, assessing the consequences and exploring the policy implications of this link. We present scientific evidence showing that mercury and CO2 levels are negatively correlated under natural conditions. As a result of this negative correlation, the CO2 level under the current mercury reduction scenario is predicted to be 2.4-10.1 ppm higher than the no action scenario by 2050, equivalent to 1.0-4.8 years of CO2 increase due to human activity. The underlying causations of this negative correlation are complex and need further research. Economic analysis indicates that there is a trade-off between the benefits and costs of mercury reduction actions. As reducing mercury emission may inadvertently undermine efforts to achieve climate goals, we advocate for devising a coordinated implementation strategy for carbon and mercury conventions to maximize synergies and reduce trade-offs.

Fate and Transport of Mercury through Waterflows in a Tropical Rainforest.

Knowledge gaps of mercury (Hg) biogeochemical processes in the tropical rainforest limit our understanding of the global Hg mass budget. In this study, we applied Hg stable isotope tracing techniques to quantitatively understand the Hg fate and transport during the waterflows in a tropical rainforest including open-field precipitation, throughfall, and runoff. Hg concentrations in throughfall are 1.5-2 times of the levels in open-field rainfall. However, Hg deposition contributed by throughfall and open-field rainfall is comparable due to the water interception by vegetative biomasses. Runoff from the forest shows nearly one order of magnitude lower Hg concentration than those in throughfall. In contrast to the positive Δ199Hg and Δ200Hg signatures in open-field rainfall, throughfall water exhibits nearly zero signals of Δ199Hg and Δ200Hg, while runoff shows negative Δ199Hg and Δ200Hg signals. Using a binary mixing model, Hg in throughfall and runoff is primarily derived from atmospheric Hg0 inputs, with average contributions of 65 ± 18 and 91 ± 6%, respectively. The combination of flux and isotopic modeling suggests that two-thirds of atmospheric Hg2+ input is intercepted by vegetative biomass, with the remaining atmospheric Hg2+ input captured by the forest floor. Overall, these findings shed light on simulation of Hg cycle in tropical forests.

Interspecific Variations in the Internal Mercury Isotope Dynamics of Antarctic Penguins: Implications for Biomonitoring.

Mercury (Hg) biomonitoring requires a precise understanding of the internal processes contributing to disparities between the Hg sources in the environment and the Hg measured in the biota. In this study, we investigated the use of Hg stable isotopes to trace Hg accumulation in Adélie and emperor penguin chicks from four breeding colonies in Antarctica. Interspecific variation of Δ199Hg in penguin chicks reflects the distinct foraging habitats and Hg exposures in adults. Chicks at breeding sites where adult penguins predominantly consumed mesopelagic prey showed relatively lower Δ199Hg values than chicks that were primarily fed epipelagic krill. Substantial δ202Hg variations in chick tissues were observed in both species (Adélie: -0.11 to 1.13‰, emperor: -0.27 to 1.15‰), whereas only emperor penguins exhibited the lowest δ202Hg in the liver and the highest in the feathers. Our results indicate that tissue-specific δ202Hg variations and their positive correlations with % MeHg resulted from MeHg demethylation in the liver and kidneys of emperor penguin chicks, whereas Adélie penguin chicks showed different internal responses depending on their exposure to dietary MeHg. This study highlights the importance of considering intra- and interspecific variations in adult foraging ecology and MeHg demethylation when selecting penguin chicks for Hg biomonitoring.

Transformation of Mercurous [Hg(I)] Species during Laboratory Standard Preparation and Analysis: Implication for Environmental Analysis.

Hg(I) may control Hg redox kinetics; however, its metastable nature hinders analysis. Herein, the stability of Hg(I) during standard preparation and analysis was studied. Gravimetric analysis showed that Hg(I) was stable in its stock solution (1000 mg L-1), yet completely disproportionated when its dilute solution (10 µg L-1) was analyzed using liquid chromatography (LC)-ICPMS. The Hg(I) dimer can form through an energetically favorable comproportionation between Hg(0) and Hg(II), as supported by density functional theory calculation and traced by the rapid isotope exchange between 199Hg(0)aq and 202Hg(II). However, the separation of Hg(0) and Hg(II) (e.g., LC process) triggered its further disproportionation. Polypropylene container, increasing headspace, decreasing pH, and increasing dissolved oxygen significantly enhanced the disproportionation or redox transformations of Hg(I). Thus, using a glass container without headspace and maintaining a slightly alkaline solution are recommended for the dilute Hg(I) stabilization. Notably, we detected elevated concentrations of Hg(I) (4.4-6.1 µg L-1) in creek waters from a heavily Hg-polluted area, accounting for 54-70% of total dissolved Hg. We also verified the reductive formation of Hg(I) in Hg(II)-spiked environmental water samples, where Hg(I) can stably exist in aquatic environments for at least 24 h, especially in seawater. These findings provide mechanistic insights into the transformation of Hg(I), which are indicative of its further environmental identification.

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.

Multi-Emission Carbon Dots Combining Turn-On Sensing and Fluorescence Quenching Exhibit Ultrahigh Selectivity for Mercury in Real Water Samples.

Mercury is a ubiquitous heavy-metal pollutant and poses serious ecological and human-health risks. There is an ever-growing demand for rapid, sensitive, and selective detection of mercury in natural waters, particularly for regions lacking infrastructure specialized for mercury analysis. Here, we show that a sensor based on multi-emission carbon dots (M-CDs) exhibits ultrahigh sensing selectivity toward Hg(II) in complex environmental matrices, tested in the presence of a range of environmentally relevant metal/metalloid ions as well as natural and artificial ligands, using various real water samples. By incorporating structural features of calcein and folic acid that enable tunable emissions, the M-CDs couple an emission enhancement at 432 nm and a simultaneous reduction at 521 nm, with the intensity ratio linearly related to the Hg(II) concentration up to 1200 µg/L, independent of matrix compositions. The M-CDs have a detection limit of 5.6 µg/L, a response time of 1 min, and a spike recovery of 94 ± 3.7%. The intensified emission is attributed to proton transfer and aggregation-induced emission enhancement, whereas the quenching is due to proton and electron transfer. These findings also have important implications for mercury identification in other complex matrices for routine, screening-level food safety and health management practices.

Dimethylmercury as a Source of Monomethylmercury in a Highly Productive Upwelling System.

Monomethylmercury (MMHg) is a neurotoxicant that biomagnifies in marine food webs, reaching high concentrations in apex predators. To predict changes in oceanic MMHg concentrations, it is important to quantify the sources and sinks of MMHg. Here, we study mercury speciation in the California Current System through cruise sampling and modeling. Previous work in the California Current System has found that upwelling transports mercury-enriched deep waters to productive surface waters. These upwelled waters originate within the California Undercurrent water mass and are subsequently advected as a surface water parcel to the California Current. Between the two major water masses, we find that compared to the California Current, the California Undercurrent contains elevated dissolved total mercury (THg) and dimethylmercury (DMHg) concentrations by 59 and 69%, respectively. We explain that these differences result from losses during advection, specifically scavenging of THg and DMHg demethylation. We calculate a net DMHg demethylation rate of 2.0 ± 1.1% d-1 and build an empirically constrained mass budget model to demonstrate that net DMHg demethylation accounts for 61% of surface MMHg sources. These findings illustrate that DMHg is a significant source of MMHg in this region, challenging the current understanding of the major sources of marine MMHg.

A Meta-analysis Reveals Global Change Stressors Potentially Aggravate Mercury Toxicity in Marine Biota.

Growing evidence demonstrates that global change can modulate mercury (Hg) toxicity in marine organisms; however, the consensus on such effect is lacking. Here, we conducted a meta-analysis to evaluate the effects of global change stressors on Hg biotoxicity according to the IPCC projections (RCP 8.5) for 2100, including ocean acidification (-0.4 units), warming (+4 °C), and their combination (acidification-warming). The results indicated an overall aggravating effect (ln RRΔ = -0.219) of global change on Hg toxicity in marine organisms, while the effect varied with different stressors; namely, acidification potentially alleviates Hg biotoxicity (ln RRΔ = 0.117) while warming and acidification-warming have an aggravating effect (ln RRΔ = -0.328 and -0.097, respectively). Moreover, warming increases Hg toxicity in different trophic levels, i.e., primary producers (ln RRΔ = -0.198) < herbivores (ln RRΔ = -0.320) < carnivores (ln RRΔ = -0.379), implying increasing trends of Hg biomagnification through the food web. Notably, ocean hypoxia appears to boost Hg biotoxicity, although it was not considered in our meta-analysis because of the small sample size. Given the persistent global change and combined effects of these stressors in marine environments, multigeneration and multistressor research is urgently needed to fully disclose the impacts of global change on Hg pollution and its risk.

New Insights into MeHg Accumulation in Rice (Oryza sativa L.): Evidence from Cysteine.

The intake of methylmercury (MeHg)-contaminated rice poses immense health risks to rice consumers. However, the mechanisms of MeHg accumulation in rice plants are not entirely understood. The knowledge that the MeHg-Cysteine complex was dominant in polished rice proposed a hypothesis of co-transportation of MeHg and cysteine inside rice plants. This study was therefore designed to explore the MeHg accumulation processes in rice plants by investigating biogeochemical associations between MeHg and amino acids. Rice plants and underlying soils were collected from different Hg-contaminated sites in the Wanshan Hg mining area. The concentrations of both MeHg and cysteine in polished rice were higher than those in other rice tissues. A significant positive correlation between MeHg and cysteine in rice plants was found, especially in polished rice, indicating a close geochemical association between cysteine and MeHg. The translocation factor (TF) of cysteine showed behavior similar to that of the TF of MeHg, demonstrating that these two chemical species might share a similar transportation mechanism in rice plants. The accumulation of MeHg in rice plants may vary due to differences in the molar ratios of MeHg to cysteine and the presence of specific amino acid transporters. Our results suggest that cysteine plays a vital role in MeHg accumulation and transportation inside rice plants.

Unveiling the Sources and Transfer of Mercury in Forest Bird Food Chains Using Techniques of Vivo-Nest Video Recording and Stable Isotopes.

Knowledge gaps in mercury (Hg) biomagnification in forest birds, especially in the most species-rich tropical and subtropical forests, limit our understanding of the ecological risks of Hg deposition to forest birds. This study aimed to quantify Hg bioaccumulation and transfer in the food chains of forest birds in a subtropical montane forest using a bird diet recorded by video and stable Hg isotope signals of biological and environmental samples. Results show that inorganic mercury (IHg) does not biomagnify along food chains, whereas methylmercury (MeHg) has trophic magnification factors of 7.4-8.1 for the basal resource-invertebrate-bird food chain. The video observations and MeHg mass balance model suggest that Niltava (Niltava sundara) nestlings ingest 78% of their MeHg from forest floor invertebrates, while Flycatcher (Eumyias thalassinus) nestlings ingest 59% from emergent aquatic invertebrates (which fly onto the canopy) and 40% from canopy invertebrates. The diet of Niltava nestlings contains 40% more MeHg than that of Flycatcher nestlings, resulting in a 60% higher MeHg concentration in their feather. Hg isotopic model shows that atmospheric Hg0 is the main Hg source in the forest bird food chains and contributes >68% in most organisms. However, three categories of canopy invertebrates receive ∼50% Hg from atmospheric Hg2+. Overall, we highlight the ecological risk of MeHg exposure for understory insectivorous birds caused by atmospheric Hg0 deposition and methylation on the forest floor.