Hg Ratio Research Articles

The spotted ratfish Hydrolagus colliei as a potential biomonitor of mercury and selenium from deep-waters of the northern Gulf of California

The purpose of this work was to use the deep-water chimaera Hydrolagus colliei to examine the bioaccumulation and availability of Hg and Se in its deep-water habitat; the Se:Hg molar ratio was calculated to establish baseline information of the species and its associated ecosystem. The organisms were collected from northern Gulf of California. Hg levels in muscle were higher than liver and the opposite pattern happened with Se concentrations. Female had total lengths and weights higher than male but there were not found differences between elements concentrations by sex. Hg in muscle was correlated with weight. Molar Se:Hg ratio in muscle was the lowest compared to the liver. It was hypothesized that Hg and Se uptake to H. colliei were by its feeding habits because is a dominant species component of the demersal ecosystem and that play and important functional role in the control of oceanic ecosystem structure and function.

Significant mercury efflux from a Karst region in Southwest China - Results from mass balance studies in two catchments

Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg0 exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg0 exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m−2 yr−1 and 4.8 ± 98.2 μg m−2 yr−1. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg0 exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.

Evaluating the transport of Hg(II) in the presence of natural organic matter through a diffusive gradient in a thin-film passive sampler

The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (Kd) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg—NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements.

Mercury and its form in a dammed reservoir ecosystem during the charging phase.

Throughout continents, reservoirs tend to have elevated methylmercury (MeHg) concentration transformed from mercury (Hg/total Hg). This impact may be pronounced in the reservoir with less velocity of water during the charging period resulted in the deposition of sediments. In sediments on favorable conditions, methylation may be enhanced by the decomposition of flood organic material, which can release Hg and enhance microbial activity. However, much less is known about the transfer ratio of Hg and its form MeHg from sediment to biota in the hydrological reservoir during the dam charging phase. The objective of our study was to understand the interrelationship between total Hg and MeHg in two key components sediment and fish in the reservoir ecosystem. This study was performed at the Three Gorges Reservoir (TGR) located on upstream of the Yangtze River in China. At the TGR charging phase, during winter time, the water level was high due to blockade of water by Three Gorges Dam (TGD). Sediment and fish samples were collected in winter season for total Hg, MeHg, and several ancillary parameters. The results showed that total Hg in sediment samples of the winter season were ranged from 6.2 ± 0.001 to 193.3 ± 0.001 × 10-3mg/kg, with an average value of 53.76 ± 51.80 × 10-3mg/kg, and for MeHg was ranged from 12.1 ± 0.04 to 348.7 ± 0.16 × 10-2ng/g, with an average value of 98.96 ± 93.07 × 10-2ng/g. Total Hg and MeHg in fish samples of the winter season were from 42.48 ± 6.71 to 166 ± 52.56ng/g, with an average value of 76.22 ± 31.23ng/g, and from 21.09 ± 2.31 to 61.60 ± 13.30ng/g, with an average value of 37.89 ± 11.96ng/g. The relationship of total Hg and MeHg concentrations in fish to those of sediments from corresponding sites showed a negative relationship. This might include a strong association of total Hg with an inorganic component of sediment (e.g., bound to sulfides or coprecipitated with other metal oxides such as manganese and iron). The average concentration of fish MeHg found in this study, at rates greater than 1.72g/day, was estimated hazardous to human health. This study concludes sediment was acting as sequestrate for total Hg and MeHg in TGR. The bioaccumulation of total Hg and MeHg in fish was not controlled by sediment further investigation about pathological routes and dietary habits of fish needed to be identified for total Hg and MeHg study in TGR.

European eels and heavy metals from the Mar Menor lagoon (SE Spain)

Heavy metal pollution is related to the fall in European eel (Anguilla anguilla) populations. The Mar Menor lagoon (SE Spain) is home to an endangered population of this species, which is still caught for human consumption. The presence of Pb, Cd and Hg in the livers and muscles and the Se:Hg ratio in muscle of 150 eels from this lagoon were determined. Pb concentrations were higher than those reported from other populations in the world, while Cd and Hg concentrations in the tissues analysed were lower. In terms of food safety, Se concentrations play an important role in sequestering Hg in eels from this lagoon.

Potato (Solanum tuberosum L.) can be grown safety on human consumption in slight Hg-contaminated soils across China mainland

Mercury (Hg) exposure poses serious health risks to humans, resulting in extensive investigations examining Hg accumulation, biotransformation and uptake in crops. In this investigation, Hg accumulation in potato tubers due to bioaccumulation processes was determined and bioconcentration factors affecting bioaccumulation were identified using a greenhouse experiment. Our results showed that the percentage of available Hg concentrations from total Hg in soil samples were less than 1.2%, indicating that soils used in our experiment exhibited a high binding strength for Hg, with alkaline soil recording the lowest available Hg/total Hg ratio. Results indicated that soil type and Hg treatment, as well as their interactions, significantly affected Hg accumulation in potato tubers (P < 0.01). Importantly, our results also indicated that potatoes grown in soil with a Hg concentration two times higher than the Chinese Environmental Quality Standard exhibited no obvious toxic effects on humans; Bioconcentration factors (BCF) values (<0.04) suggested that potatoes can be considered as a low Hg accumulating species and suitable for human consumption. Potato yields in acidic soil were lower than those in neutral or alkaline soils, making this medium unsuitable for growth.

Mercury (Hg) and selenium (Se) content in the shark Mustelus henlei (Triakidae) in the northern Mexican Pacific.

Mercury and selenium were assessed in Mustelus henlei, which is a carnivorous predatory shark that is important for the coastal communities of the northern Mexican Pacific (NMP). Sixty-two individuals were sampled; muscle and liver were isolated and analyzed by atomic absorption spectrophotometry. The mean Hg concentrations (wet weight) obtained for muscle (0.08 ± 0.10μgg-1) and liver (0.09 ± 0.26μgg-1) were below the allowed limits (< 1.0μgg-1 Hg). The average Se concentration was 0.03 ± 0.01μgg-1 in muscle and 0.13 ± 0.05μgg-1 in liver. The Se/Hg molar ratio of muscle was 1.83; however, the selenium health benefit value (HBVSe) was of 0.08. We calculated that an adult man (70kg), an adult woman (60kg), and a child (16kg) could consume 1595, 838, and 223g/week of M. henlei muscle, respectively, without risks to health. In conclusion, the concentrations and molar ratio of Hg and Se in M. henlei muscle mean that consumption of this shark's meat does not represent neither a benefit nor a public health risk.

Mercury methylation and demethylation potentials in Arctic lake sediments

Mercury (Hg) transformations in sediments are key factors in the Hg exposure pathway for wildlife and humans yet are poorly characterized in Arctic lakes. As the Arctic is rapidly warming, it is important to understand how the rates of Hg methylation and demethylation (wich determine Hg bioavailability) change with temperature in lake sediments. Methylation and demethylation potentials were determined for littoral sediments (2.5 m water depth) in two deep and two shallow lakes in the Canadian Arctic using Hg stable isotope tracers at incubation temperatures of 4, 8, or 16 °C for 24 h. Compared to sediments from other regions, Hg methylation and demethylation potentials in these sediments are low. The maximum depth of the lake from which sediment was collected exerted a stronger influence over methylation potential than sediment Hg concentration or organic matter content; the shallowest lake had the highest Hg methylation potential. Sediments from the shallowest lake also demonstrated the greatest response to the temperature treatments, with significantly higher methylation potentials in the 8 and 16 °C treatments. Sediments from the deep lakes demonstrated greater demethylation potentials than shallow lakes. The methylmercury to total Hg ratio in sediments supported the measured transformation potentials as the lake with the greatest methylation potential had the highest ratio. This study supports previous works indicating that Hg methylation potential may increase as the Arctic warms, but demethylation potential does not respond to warming to the same degree, indicating that Hg methylation may predominate in warming Arctic sediments.

Mercury and Alzheimer's Disease: Hg(II) Ions Display Specific Binding to the Amyloid-β Peptide and Hinder Its Fibrillization.

Brains and blood of Alzheimer’s disease (AD) patients have shown elevated mercury concentrations, but potential involvement of mercury exposure in AD pathogenesis has not been studied at the molecular level. The pathological hallmark of AD brains is deposition of amyloid plaques, consisting mainly of amyloid-β (Aβ) peptides aggregated into amyloid fibrils. Aβ peptide fibrillization is known to be modulated by metal ions such as Cu(II) and Zn(II). Here, we study in vitro the interactions between Aβ peptides and Hg(II) ions by multiple biophysical techniques. Fluorescence spectroscopy and atomic force microscopy (AFM) show that Hg(II) ions have a concentration-dependent inhibiting effect on Aβ fibrillization: at a 1:1 Aβ·Hg(II) ratio only non-fibrillar Aβ aggregates are formed. NMR spectroscopy shows that Hg(II) ions interact with the N-terminal region of Aβ(1–40) with a micromolar affinity, likely via a binding mode similar to that for Cu(II) and Zn(II) ions, i.e., mainly via the histidine residues His6, His13, and His14. Thus, together with Cu(II), Fe(II), Mn(II), Pb(IV), and Zn(II) ions, Hg(II) belongs to a family of metal ions that display residue-specific binding interactions with Aβ peptides and modulate their aggregation processes.

Transformation of Heavy Metals during Pyrolysis of Predried Dyeing Sludge

Heavy metals in sludge may cause serious pollution and restrict the industrial application of sludge heat treatment. In this paper, predried dyeing sludge (PDS) char samples were prepared on a fixed bed in a pure nitrogen atmosphere. X-ray diffractometry, microwave digestion, and inductively coupled plasma-atomic emission spectrometry were used to measure the content, speciation occurrence, and the transformation of heavy metals during heat treatment of PDS samples. The results show that heavy metal elements such as Cr, Cu, Hg, Ni, and Pb in PDS both in raw PDS and derived char samples are mainly dominated by hydrochloric acid soluble speciation and insoluble speciation, while the ammonium acetate soluble speciation is very little and the water soluble speciation is negligible. Part of the hydrochloric acid soluble Cr is volatilized when pyrolyzed at 400–600 °C. Cr is mainly fixed in the PDS char as the insoluble speciation and hydrochloric acid soluble speciation above 600 °C. One part of the hydrochloric acid soluble Cu is volatilized and the other part transforms to the insoluble speciation at 400–500 °C. Cu is mainly fixed in the PDS char in the insoluble state above 600 °C. A small amount of Hg transforms from the hydrochloric acid soluble speciation to the gaseous speciation. Ni is observed to transform from the hydrochloric acid soluble speciation to the insoluble speciation below 700 °C, while it transforms from the insoluble speciation to the hydrochloric acid soluble speciation above 700 °C. The higher the temperature is, the more the ammonium acetate soluble Pb and the hydrochloric acid soluble Pb released to by volatilization as gaseous Pb. The fixing ratio of Cr, Cu, and Ni is proportional to the pyrolysis temperature, and the fixing ratio of Hg and Pb is inversely proportional to the pyrolysis temperature. PDS has a high fixing ratio of heavy metals at 700–800 °C, which indicates the best temperature window for heavy metal fixing. The present results may be helpful for the prevention and control of heavy metals in PDS.

New colorimetric and fluorometric chemosensor for selective Hg2+ sensing in a near-perfect aqueous solution and bio-imaging

We report a new 7-nitrobenzo-2-oxa-1, 3-diazolyl (NBD)-based chemosensor containing a piperazine derivative, NBDP, for detection of mercury ions in almost 100% aqueous medium. The chemosensor shows sensing exclusively toward Hg2+ with a switch-on fluorescence response at 543 nm, which could be attributed to the blocking of PET (photo-induced electron transfer) process upon complexation with mercury ions. The molar ratio of Hg(Ⅱ) to NBDP in the complex is 1:1 based on the Job’s plot and HRMS studies. Optimized configurations of NBDP and NBDP-Hg2+ complexes were simulated by means of DFT calculations. The reversible fluorescence response with low detection limit (19.2 nM) in the pH range of 6.0–7.5 renders NBDP a promising candidate for Hg2+ detection in neutral aqueous environments. For the practical application of the chemosensor, test strips were successfully fabricated for rapid detection of Hg2+ ions. Moreover, the utility of NBDP showing the mercury recognition in Human liver cancer cells (SMMC-7721) and zebrafish as well as in live tissues of Arabidopsis thaliana has been demonstrated as monitored by fluorescence imaging.

Geochemical Factors Controlling Dissolved Elemental Mercury and Methylmercury Formation in Alaskan Wetlands of Varying Trophic Status.

The transformations of aqueous inorganic divalent mercury (Hg(II)i) to volatile dissolved gaseous mercury (Hg(0)(aq)) and toxic methylmercury (MeHg) govern mercury bioavailability and fate in northern ecosystems. This study quantified concentrations of aqueous mercury species (Hg(II)i, Hg(0)(aq), MeHg) and relevant geochemical constituents in pore waters of eight Alaskan wetlands that differ in trophic status (i.e., bog-to-fen gradient) to gain insight on processes controlling dark Hg(II)i reduction and Hg(II)i methylation. Regardless of wetland trophic status, positive correlations were observed between pore water Hg(II)i and dissolved organic carbon (DOC) concentrations. The concentration ratio of Hg(0)(aq) to Hg(II)i exhibited an inverse relationship to Hg(II)i concentration. A ubiquitous pathway for Hg(0)(aq) formation was not identified based on geochemical data, but we surmise that dissolved organic matter (DOM) influences mercury retention in wetland pore waters by complexing Hg(II)i and decreasing the concentration of volatile Hg(0)(aq) relative to Hg(II)i. There was no evidence of Hg(0)(aq) abundance directly limiting mercury methylation. The concentration of MeHg relative to Hg(II)i was greatest in wetlands of intermediate trophic status, and geochemical data suggest mercury methylation pathways vary between wetlands. Our insights on geochemical factors influencing aqueous mercury speciation should be considered in context of the long-term fate of mercury in northern wetlands.

Stratigraphic variations in the δ201Hg/δ199Hg ratio of mercury in sediment cores as historical records of methylmercury production in lakes

Total mercury (Hg) profiles of sediment cores from lakes serve as historical records of Hg pollution. They do not, however, provide information about temporal variations in the abundance of the toxic, preferentially bioaccumulated species methylmercury (CH3Hg+), whose production rate is largely a function of environmental variables that control the growth and activities of Hg-methylating and Hg-demethylating bacteria and the bioavailability of the inorganic Hg(II) from which CH3Hg+ is formed. Earlier studies showed that CH3Hg+ in freshwater food webs had anomalously high δ201Hg/δ199Hg ratios and, similarly, that the δ201Hg/δ199Hg ratio of Hg in a core from a severely Hg-polluted lake paralleled temporal changes in CH3Hg+ production. The present study was undertaken to test the hypothesis that variations in the δ201Hg/δ199Hg ratios of sediment cores from lakes reflect historical variations in CH3Hg+ production in the lakes. Core profiles of δ201Hg/δ199Hg ratios and total Hg concentrations from three widely separated, environmentally distinct temperate lakes polluted with Hg from different industrial sources, and one practically pristine Arctic lake, were examined, and changes attributable to known historical events were noted. Hg pollution led to increases in the δ201Hg/δ199Hg ratio, suggesting enhanced production of CH3Hg+, but the lakes showed different patterns of variation over time, implying the influence of site-specific environmental and biotic factors. In one lake the δ201Hg/δ199Hg ratio increased at the onset of each of three pollution episodes but peaked and then declined, suggesting a surge in methylation that was reversed by demethylation. In another lake, mercury pollution initiated a long-term upward trend in the isotope ratio, with secondary maxima and minima superimposed on it, implying a progressive increase in CH3Hg+, with successive shorter-term changes caused by fluctuations in methylation and demethylation rates. In the third lake, moderately elevated isotope ratios and one large maximum were associated with Hg contamination, but the maximum is attributable to accelerated eutrophication that intensified CH3Hg+ production. In the Arctic lake, the isotope ratio varied with climate change, decreasing during warming trends and increasing during cooling phases. These results constitute evidence that δ201Hg/δ199Hg ratios of sediment cores from lakes record historical variations in the net rate of CH3Hg+ production.

Source relationships between streambank soils and streambed sediments in a mercury-contaminated stream

PurposeIn contaminated streams, understanding the role of streambank and streambed source contributions is essential to developing robust remedial solutions. However, identifying relationships can be difficult because of the lack of identifying signatures in source and receptor pools. East Fork Poplar Creek (EFPC) in Oak Ridge, TN, USA received historical industrial releases of mercury that contaminated streambank soils and sediments. Here, we determined relationships between the contaminated streambank soils and sand-sized streambed sediments.Materials and methodsField surveys revealed the spatial trends of the concentrations of inorganic total mercury (Hg) and methyl mercury (MeHg), Hg lability as inferred by sequential extraction, particle size distribution, and total organic carbon. Statistical tests were applied to determine relationships between streambank soil and streambed sediment properties.Results and discussionConcentrations of Hg in streambank soils in the upper reaches averaged 206 mg kg−1 (all as dry weight) (n = 457), and 13 mg kg−1 in lower reaches (n = 321), while sand-sized streambed sediments were approximately 16 mg kg−1 (n = 57). Two areas of much higher Hg and MeHg concentrations in streambank soils were identified and related to localized higher Hg concentrations in the streambed sediments; however, most of the streambank soils have similar Hg concentrations to the streambed sediments. The molar ratio of Hg to organic carbon, correlation between MeHg and Hg, and particle size distributions suggested similarity between the streambank soils and the fine sand-sized fraction (125–250 μm) collected from the streambed sediments. Mercury in the fine sand-sized streambed sediments, however, was more labile than Hg in the streambank soils, suggesting an in-stream environment that altered the geochemistry of sediment-bound Hg.ConclusionsThis study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments. This work will guide future remedial decision making in EFPC and will aid other researchers in identifying source–sink linkages in contaminated fluvial systems.

High-density element concentrations in fish from subtidal to hadal zones of the Pacific Ocean

Anthropogenic use of high density, toxic elements results in marine pollution which is bio-accumulating throughout marine food webs. While there have been several studies in various locations analyzing such elements in fish, few have investigated patterns in these elements and their isotopes in terms of ocean depth, and none have studied the greatest depth zones. We used a flame atomic absorption spectrophotometer-hydride system and an inductively coupled plasma-mass spectrometer to determine concentrations of the high-density elements arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), plus the light-metal barium (Ba), in fish ranging from bathyal (1000 m in Monterey Bay) to upper hadal zones (6500–7626 m in the Kermadec and Mariana Trenches) in the Pacific Ocean. Five species of fish—including the Mariana Trench snailfish, the world's deepest known fish newly discovered—were analyzed for patterns in total element concentration, depth of occurrence, Se:Hg ratio, plus mercury isotopes in the deepest species. Co and As levels decreased with depth. In the Mariana Trench, Pb, Hg, Cd, and Cu were higher than in all other samples, and higher in those plus Ba than in the Kermadec Trench. The latter samples had far higher Ni and Cr levels than all others. Mercury relative isotope analysis showed no depth trends in the deepest species. Se:Hg showed a large molar excess of Se in bathyal flatfish species. These patterns indicate that exposures to pollutants differ greatly between habitats including trenches of similar depths.

Biomarkers of the cholinergic and dopaminergic signaling pathways in Arctic beluga whales (Delphinapterus leucas): relationship to methylmercury and selenium

There are increasing concerns about potential neurotoxicity of chronic methylmercury (MeHg) exposure in Arctic wildlife and human populations. The relationships between mercury (Hg), MeHg, inorganic Hg (iHg), and selenium (Se) exposure, and neurochemical and molecular biomarkers in beluga whales (Delphinapterus leucas (Pallas, 1776)) were characterized. Samples were collected in 2008 (n = 20) and 2010 (n = 15) in the Canadian Arctic from hunter-harvested beluga whales. Total Hg concentrations in the temporal cortex and cerebellum were 21.0 ± 22.6 mg kg−1 dry weight (dw) and 14.9 ± 18.9 mg kg−1 dw, respectively. Monoamine oxidase (MAO) activity was predicted by MeHg and the molar ratio of total Hg to Se (Hg:Se, p < 0.05); MAO-A mRNA transcription levels were predicted by iHg and Se (p < 0.05). Muscarinic AChR binding was predicted by MeHg (p < 0.05) and Hg:Se molar ratio (p < 0.05), and mRNA transcription levels of mAChR m1 was predicted by the Hg:Se molar ratio (p < 0.05). These results suggest that the c...

Mercury and Alzheimers Disease: HG(II) Ions Display Specific Binding to the Amyloid-Beta Peptide and Modulate its Aggregation

Increasing evidence connects Alzheimer's disease (AD) to metal exposure. Aberrant metal concentrations are observed in AD brains, but the role of metals in AD pathology remains unresolved. Animal models exposed to mercury display the typical pathological signs of AD, and many studies (but not all) indicate elevated mercury levels in brain tissue of AD patients. At a molecular level, however, no mechanisms have been described that would link mercury to AD pathogenesis. The pathological hallmark of AD brains is deposition of amyloid plaques, consisting mainly of amyloid-β (Aβ) peptides aggregated into amyloid fibrils. Previous research has shown that Aβ peptide aggregation and fibrillation can be modulated by specific binding between Aβ and metal ions such as Cu(II) and Zn(II). Here, we study in vitro the molecular interactions between Aβ(1-40) and Hg(II) ions. NMR spectroscopy results show that Hg(II) ions bind the N-terminal part of the Aβ(1-40) peptide, likely via the same ligands that bind Cu(II) and Zn(II) ions, i.e. histidines H6, H13, and H14. Fluorescence quenching of Aβ residue Y10 by Hg(II) ions indicates the apparent Hg(II)/Aβ dissociation constant to be around 1-3 µM. Fluorescence spectroscopy and solid state atomic force microscopy (AFM) show a concentration-dependent effect of Hg(II) ions on Aβ fibrillation, which is completely inhibited at a 1:1 Aβ:Hg(II) ratio. Thus, together with e.g. Cu(II), Fe(II), Mn(II), Pb(IV) and Zn(II), the Hg(II) ion belongs to a family of metal ions that modulate Aβ aggregation by binding to specific Aβ ligands. This indicates that AD metal chemistry is more complex than previously considered, and may have implications for AD pathology and pathogenesis, especially as in most countries mercury continues to be an important environmental contaminant.

The Shannon Entropy Trend of a Fish System Estimated by a Machine Vision Approach Seems to Reflect the Molar Se:Hg Ratio of Its Feed.

The present study investigates the suitability of a machine vision-based method to detect deviations in the Shannon entropy (SE) of a European seabass (Dicentrarchus labrax) biological system fed with different selenium:mercury (Se:Hg) molar ratios. Four groups of fish were fed during 14 days with commercial feed (control) and with the same feed spiked with 0.5, 5 and 10 mg of MeHg per kg, giving Se:Hg molar ratios of 29.5 (control-C1); 6.6, 0.8 and 0.4 (C2, C3 and C4). The basal SE of C1 and C2 (Se:Hg > 1) tended to increase during the experimental period, while that of C3 and C4 (Se:Hg < 1) tended to decrease. In addition, the differences in the SE of the four systems in response to a stochastic event minus that of the respective basal states were less pronounced in the systems fed with Se:Hg molar ratios lower than one (C3 and C4). These results indicate that the SE may be a suitable indicator for the prediction of seafood safety and fish health (i.e., the Se:Hg molar ratio and not the Hg concentration alone) prior to the displaying of pathological symptoms. We hope that this work can serve as a first step for further investigations to confirm and validate the present results prior to their potential implementation in practical settings.

Isotopic and chemical characteristics of mercury in organs and tissues of fish in a mercury-polluted lake: Evidence for fractionation of mercury isotopes by physiological processes.

Organs and tissues of whitefish and trout from mercury (Hg)-polluted Lake Ontario were analyzed for Hg isotopes, methylmercury (CH3 Hg+ ), and inorganic Hg to investigate possible mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes by physiological processes of the fish. Isotope signatures of different body parts were defined by δ-values of 198 Hg/202 Hg, 199 Hg/202 Hg, 200 Hg/202 Hg, and 201 Hg/202 Hg ratios and by Δ-values representing effects of MIF on 199 Hg/202 Hg and 201 Hg/202 Hg ratios. The research yielded the following evidence for MDF and MIF, including MIF of isotopes with even as well as odd mass numbers, by metabolic activities: 1) anomalously low δ-values for whitefish kidneys but not for trout kidneys; 2) widely varying differences between the δ-values of different body parts of whitefish but practically uniform differences for those of trout; 3) different relationships between Δ199 Hg and Δ201 Hg for whitefish than for trout; 4) nonlinear correlation between δ198 Hg and δ200 Hg for whitefish but linear correlation for trout; 5) an inverse correlation between the δ199 Hg values and CH3 Hg+ concentrations of whitefish and trout; 6) an inverse correlation between the δ201 Hg/δ199 Hg and CH3 Hg+ /inorganic Hg ratios of trout kidneys and gills (and lipids of trout near the sources of pollution) but a positive correlation for muscle, liver, and gut; and 7) inverse correlations between Δ199 Hg and the CH3 Hg+ /inorganic Hg ratio for trout liver, kidneys, and gut. Environ Toxicol Chem 2018;37:515-529. © 2017 SETAC.

Contrasting Effects of Dissolved Organic Matter on Mercury Methylation by Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132.

Natural dissolved organic matter (DOM) affects mercury (Hg) redox reactions and anaerobic microbial methylation in the environment. Several studies have shown that DOM can enhance Hg methylation, especially under sulfidic conditions, whereas others show that DOM inhibits Hg methylation due to strong Hg-DOM complexation. In this study, we investigated and compared the effects of DOM on Hg methylation by an iron-reducing bacterium Geobacter sulfurreducens PCA and a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under nonsulfidic conditions. The methylation experiment was performed with washed cells either in the absence or presence of DOM or glutathione, both of which form strong complexes with Hg via thiol-functional groups. DOM was found to greatly inhibit Hg methylation by G. Sulfurreducens PCA but enhance Hg methylation by D. desulfuricans ND132 cells with increasing DOM concentration. These strain-dependent opposing effects of DOM were also observed with glutathione, suggesting that thiols in DOM likely played an essential role in affecting microbial Hg uptake and methylation. Additionally, DOM and glutathione greatly decreased Hg sorption by G. sulfurreducens PCA but showed little effect on D. desulfuricans ND132 cells, demonstrating that ND132 has a higher affinity to sorb or take up Hg than the PCA strain. These observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.