Sequestration Of Hg Research Articles

Predicting Behavior and Fate of Atmospheric Mercury in Soils: Age-Dating METAALICUS Hg Isotope Spikes with Fallout Radionuclide Chronometry.

Soils accumulate anthropogenic mercury (Hg) from atmospheric deposition to terrestrial ecosystems. However, possible reemission of gaseous elemental mercury (GEM) back to the atmosphere as well as downward migration of Hg with soil leachate influence soil sequestration of Hg in ways not sufficiently understood in global biogeochemical models. Here, we apply fallout radionuclide (FRN) chronometry to understand soil Hg dynamics by revisiting the METAALICUS experiments 20 years after enriched isotope tracers (198Hg, 200Hg, 201Hg, and 202Hg) were applied to two boreal watersheds in northwestern Ontario, Canada. Hg spikes formed well-defined peaks in organic horizons of both watersheds at depths of 3-6 cm and were accurately dated to the year of spike application in 6 of 7 cases (error = -0.8 ± 1.2 years). A seventh site was depleted by ca. 90% of both the 200Hg spike and background Hg, and the spike was dated 16 years older than its application. Robust FRN age models and mass balances demonstrate that loss of Hg is attributable to its specific physicochemical behavior at this site, but more work is required to attribute this to reemission or leaching. This study demonstrates the potential of FRN chronometry to provide insights into Hg accumulation, mobilization, and fate in forest soils.

Organic matter is a predominant control on total mercury concentration of near-surface lake sediments across a boreal to low Arctic tundra transect in northern Canada

Mercury (Hg) is a bioavailable and toxic element with concentrations that are persistently high or rising in some Arctic and subarctic lakes despite reduced atmospheric emissions in North America. This is due to rising Hg emissions to the atmosphere outside of North America, enhanced sequestration of Hg to sediments by climate-mediated increases in primary production, and ongoing release of Hg from terrestrial reservoirs. To evaluate the influence of organic matter and other parameters on Hg accumulation in northern lakes, near-surface sediments were sampled from 60 lakes across a boreal to shrub tundra gradient in the central Northwest Territories, Canada. The organic matter of the lake sediments, assessed using programmed pyrolysis and petrology, is composed of a mixture of terrestrial, aquatic, and inert organic matter. The proportion of algal-derived organic matter is higher in sediments of lakes below treeline relative to shrub tundra sites. Total sedimentary Hg concentration is correlated to all organic matter constituents but is unrelated to latitude or lake position below or above treeline. The concentrations of Ag, Ca, P, S, U, Ti, Y, Cd, and Zn are also strong predictors of total sedimentary Hg concentration, indicating input from a common geogenic source and/or common sequestration pathways associated with organic matter. Catchment area is a strong negative predictor of total sedimentary Hg concentration, particularly in lakes above treeline, possibly due to retention capacity of Hg and other elements in local sinks. This research highlights the complexity of controls on Hg sequestration in sediment and shows that while organic matter is a strong predictor of total sedimentary Hg concentration on a landscape scale and across extreme gradients in climate and associated vegetation and permafrost, other factors such as catchment area and sources from mineralized bedrock are also important.

Radiation grafting mediated tailoring of a mercury (Hg(II)) selective adsorbent “RAdMer”: Mechanistic insights, uptake performance and reusability evaluation in artificially contaminated groundwater

The presence of mercury (Hg(II)) in water bodies poses a pressing threat not only to aquatic life forms but also human health. This work proposes the fabrication of a novel thiol (-SH), amine (–NH–) and carboxylic (-COOH) group containing trifunctional adsorbent based on a radiolytically surface engineered biodegradable platform for selective sequestration of Hg(II) from aqueous media. Polyacrylonitrile (PAN) was gamma radiolytically incorporated onto cotton fabric via Radiation Induced Graft Polymerization (RIGP) process, followed by chemical conversion of the nitrile groups using dl-Cysteine as the trifunctional agent. The developed adsorbent RAdMer was characterized by FTIR, TGA, SEM-EDX, EDXRF, XRD, CHNS, 13C NMR and XPS techniques, and tested for Hg(II) removal in batch and continuous flow adsorption modes. Adsorption kinetics and equilibrium characteristics were validated using various theoretical models as well column adsorption models. Density Functional Theory (DFT) calculations performed to determine the complexation mechanism revealed the binding to be occurring predominantly in a 1:2 metal to ligand ratio with calculated binding affinity of −19.63 kcal.mol−1. RAdMer demonstrated fast uptake kinetics with over 60 % of total Hg(II) adsorption occurring within the first 30 min, while peak adsorption capacity was calculated at 174.3 mg.g−1. Moreover, RAdMer could be reused for >5 iterative cycles using an optimized HCl-Thiourea eluent system. Acting upon the UNOs SDG6 principle of providing “clean water and sanitation for all”, RAdMer efficiency was demonstrated with Hg(II) spiked ground water samples to successfully achieve the WHO permissible limit of <1.0 μg.L−1, and can therefore be potentially upscaled as an efficient methodology for remediation of Hg(II) ions in contaminated water.

Nano-mineral assemblages in mercury- and silver-contaminated soils: records of sequestration, transformation, and release of mercury- and silver-bearing nanoparticles.

Mercury-bearing nano-mineral assemblages (Hg-NMAs) are chemically and mineralogically heterogeneous, micrometer-sized aggregates of nanoparticles (NPs) found in contaminated soils and sediments. Although these NMAs control sequestration and release of Hg that is a global contaminant, our understanding is limited with respect to the conditions of different types of Hg-NMAs, the diversity of its minerals, the size distribution of its NPs and whether mineral replacement and alteration reactions in these NMAs result in the release of Hg-bearing NPs. For this purpose, Hg-NMAs in four sediment samples from the Guanajuato Mining District (GMD) in Mexico, a region that was polluted by Hg and silver (Ag) due to historical mining involving Hg amalgamation, are characterized at the micro- and nanoscale. Microscale examinations with SEM show that the majority of Hg-NMAs occurs in mineral surface coatings (MSC) and fillings in fractures within quartz grains and are enriched in Hg and sulfur (S) relative to Ag, and in S and selenium (Se) relative to chloride (Cl). Examinations at the nanoscale show that Hg-NMAs contain (a) residuals of the patio process such as amalgam phases and elemental Ag; (b) associations of Hg- and Ag-sulfide NPs with pyrite and marcasite; (c) associations of Hg- and Ag-sulfide NPs with goethite and clay minerals along the rims of the MSC. The latter minerals replaced the Fe-Si-rich matrix at high-water rock ratios most likely due to an increase in porosity during flooding of the Pastita River. Consequently, the rims are depleted in Hg-Ag-sulfide NPs relative to the unaltered Fe-Si-rich matrices indicating that changes in the physiochemical conditions of soils and sediments in the GMD can result in the release of Hg-Ag-bearing NPs. In this context, this study discusses whether release and dissolution of Hg-Ag-bearing NPs contribute to the recently observed elevated gaseous elemental Hg concentrations in the soil, interstitial air and ambient air, and to the fate and effects of Hg in local aquatic environments.

Wettability tunable conjugated microporous poly(aniline)s for long-term, rapid and ppb level sequestration of Hg(II)

Wettability tunable conjugated microporous poly(aniline)s for long-term, rapid and ppb level sequestration of Hg(II)

Highly fractionated Hg isotope evidence for dynamic euxinia in shallow waters of the Mesoproterozoic ocean

Studies of Mesoproterozoic ocean chemistry have converged on a widely accepted scenario where a stable shallow layer of oxic waters occurred over deeper anoxic ferruginous waters, with mid-depth euxinic waters restricted to continental margins. However, several lines of evidence suggest shallow waters may not always have remained oxic, but fluctuated between oxic, anoxic, and euxinic conditions. Here, we present new Hg-C-S geochemistry data of ca. 1.5–1.4 Ga sediments in the Yanliao Basin to better understand the redox structure of shallow water environments, especially for the photic zone. In this study, positive Δ199Hg values suggest atmospheric Hg(II) deposition into oxic surface waters, whereas abnormally negative Δ199Hg values indicate enhanced sequestration of gaseous Hg(0) and photo-reduction of reduced sulfur-bound Hg(II) in response to photic zone euxinia. Our highly fractionated Δ199Hg values reveal a new scenario, in which the extent of euxinia is more dynamic than generally thought, and may expand from the mid-depth to the photic zone, likely linked to the superimposed operation of enhanced oxidative weathering input of SO42− and high OM flux in the water column. Given that euxinic waters may accelerate the sequestration of bio-essential elements, it is suggested that the dynamic euxinia of shallow water played a significant role in delaying the diversification of eukaryotes in the Mesoproterozoic oceans. Our study also highlights that Hg isotopes may act as a promising new proxy to trace redox changes in the surface ocean over geological time.

Buffering effect of global vegetation on the air-land exchange of mercury: Insights from a novel terrestrial mercury model based on CESM2-CLM5

The vegetation uptake of atmospheric elemental mercury [Hg(0)] and its subsequent littering are critical processes of the terrestrial Hg cycles. There is a large uncertainty in the estimated global fluxes of these processes due to the knowledge gap in the underlying mechanisms and their relationship with environmental factors. Here, we develop a new global model based on the Community Land Model Version 5 (CLM5-Hg) as an independent component of the Community Earth System Model 2 (CESM2). We explore the global pattern of gaseous elemental Hg [Hg(0)] uptake by vegetation and the spatial distribution of litter Hg concentration constrained by observed datasets as well as its driving mechanism. The annual vegetation uptake of Hg(0) is estimated as 3132 Mg yr−1, which is considerably higher than previous global models. The scheme of dynamic plant growth including stomatal activities substantially improves the estimation for global terrestrial distribution of Hg, compared to the leaf area index (LAI) based scheme that is often used by previous models. We find the global distribution of litter Hg concentrations driven by vegetation uptake of atmospheric Hg(0), which are simulated to be higher in East Asia (87 ng/g) than in the Amazon region (63 ng/g). Meanwhile, as a significant source for litter Hg, the formation of structural litter (cellulose litter + lignin litter) results in a lagging effect between Hg(0) deposition and litter Hg concentration, implying the buffering effect of vegetation on the air-land exchange of Hg. This work highlights the importance of vegetation physiology and environmental factors in understanding the vegetation sequestration of atmospheric Hg globally, and calls for greater efforts to protect forests and afforestation.

Efficient removal of Hg(II) from dental effluents by thio-functionalized biochar derived from cape gooseberry (Physalis peruviana L.) leaves

Mercury is well known to be highly toxic to humans and aquatic life. Wastewater discharges from dental clinics are the predominant source of mercury species in the environment. Innovative biochar was fabricated by the thio-functionalization of cape gooseberry (Physalis peruviana L.) leaves to produce thio-modified biochar for the sequestration of Hg (II) ions. The removal Hg(II) efficiency for the native and thio-functionalized cape gooseberry biochars were compared. Sulfur impregnation improved the affinity of biochar for Hg(II) uptake via –SH exchange and complexation mechanisms by 54%. The applicability of the novel thio-modified biochars for Hg(II) removal from dental effluents below five ppb levels was tested. The Hg(II) removal efficiency was 96.4% for 3BHS at pH = 5.0 and 25 min of contact time. The results of the present study indicated that thio-modified biochar from cape gooseberry could be a potential low-cost material for the sequestration of Hg(II) ions from acidic wastewater.

Impacts of Extreme Weather on Mercury Uptake and Storage in Subtropical Forest Ecosystems

AbstractAs climate change accelerates, extreme weather events become more severe and frequent. We analyzed the datasets of decade‐long observation (2005–2020) of mercury (Hg) stored in two subtropical evergreen forests to understand the impacts of extreme weather on the sequestration of atmospheric Hg in forest ecosystems. Results show a weak correlation between litterfall Hg and atmospheric Hg0 concentration. Droughts and snowstorms significantly disturb Hg accumulation in litterfall and soils. Litterfall Hg concentration and deposition both display an increasing trend during the period of extended droughts in 2011–2014, but a decreasing trend after droughts. This is caused by the water stress that influences the change of tree physiology and processes of foliage Hg0 uptake. Snowstorm damages large areas of canopy, which leads to substantial canopy epiphyte cover mixed into the forest floor, thus considerably increasing soil Hg concentrations. Over a decadal timescale, soil Hg variabilities are shaped by the combined effects of atmospheric Hg inputs and processes of organic soil mineralization mediated climatic factors. Our study highlights that the accelerated climate change increases the unpredictability of Hg accumulation in terrestrial ecosystems. Future studies are needed for better understanding the response of Hg biogeochemical cycling to climate change among different terrestrial biomes.

Shale weathering profiles show Hg sequestration along a New York-Tennessee transect.

Shale-derived soils have higher clay, organic matter, and secondary Fe oxide content than other bedrock types, all of which can sequester Hg. However, shales also can be Hg-rich due to their marine formation. The objectives of this study were to determine the concentration and phase partitioning of Hg in seven upland weathering profiles from New York to Tennessee USA and use geochemical normalization techniques to estimate the extent of Hg inheritance from weathering of shale bedrock or sequestration of atmospheric Hg. Total Hg concentrations in unweathered shale ranged from 3 to 94ng/g. Total Hg concentrations decreased with depth in the Ultisols and Alfisols, with total Hg concentrations ranging from 18 to 265ng/g. Across all shale soils and rocks, the oxidizable fraction of Hg (15% H2O2 extraction) comprised a large portion of the total Hg at 68% ± 8%. This fraction was dominated by organic matter as confirmed with positive correlations between Hg and %LOI, but could also be impacted by Hg sulfides. Across all sites, the reducible fraction of Hg (citrate-bicarbonate-dithionite extraction) was only 10% ± 4% of the total Hg on average. Thus, secondary Fe oxides did not contain a significant portion of Hg, as commonly observed in tropical soils. Although colder sites had a higher organic matter and sequestered more Hg, τ values for Hg indexed to Ti suggest that atmospheric deposition, such as pollution sources in Ohio River Valley, drove the highest enrichment of Hg along the transect. These results demonstrate that shale-derived soils have a net accumulation and retention of atmospheric Hg, primarily through stabilization by organic matter.

Mercury mobility, colloid formation and methylation in a polluted Fluvisol as affected by manure application and flooding–draining cycle

Abstract. Floodplain soils polluted with high levels of mercury (Hg) are potential point sources to downstream ecosystems. Repeated flooding (e.g., redox cycling) and agricultural activities (e.g., organic matter addition) may influence the fate and speciation of Hg in these soil systems. The formation and aggregation of colloids and particles influence both Hg mobility and its bioavailability to microbes that form methylmercury (MeHg). In this study, we conducted a microcosm flooding–draining experiment on Hg-polluted floodplain soils originating from an agriculturally used area situated in the Rhone Valley (Valais, Switzerland). The experiment comprised two 14 d flooding periods separated by one 14 d draining period. The effect of freshly added natural organic matter on Hg dynamics was assessed by adding liquid cow manure (+MNR) to two soils characterized by different Hg (47.3±0.5 or 2.38±0.01 mg kg−1) and organic carbon (OC: 1.92 wt % or 3.45 wt %) contents. During the experiment, the release, colloid formation of Hg in soil solution and net MeHg production in the soil were monitored. Upon manure addition in the highly polluted soil (lower OC), an accelerated release of Hg to the soil solution could be linked to a fast reductive dissolution of Mn oxides. The manure treatments showed a fast sequestration of Hg and a higher percentage of Hg bound by particulate (0.02–10 µm). Also, analyses of soil solutions by asymmetrical flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (AF4–ICP–MS) revealed a relative increase in colloidal Hg bound to dissolved organic matter (Hg–DOM) and inorganic colloidal Hg (70 %–100 %) upon manure addition. Our experiment shows a net MeHg production the first flooding and draining period and a subsequent decrease in absolute MeHg concentrations after the second flooding period. Manure addition did not change net MeHg production significantly in the incubated soils. The results of this study suggest that manure addition may promote Hg sequestration by Hg complexation on large organic matter components and the formation and aggregation of inorganic HgS(s) colloids in Hg-polluted Fluvisols with low levels of natural organic matter.

Phytoremediation and Microorganisms-Assisted Phytoremediation of Mercury-Contaminated Soils: Challenges and Perspectives.

Mercury (Hg) pollution is a global threat to human and environmental health because of its toxicity, mobility and long-term persistence. Although costly engineering-based technologies can be used to treat heavily Hg-contaminated areas, they are not suitable for decontaminating agricultural or extensively-polluted soils. Emerging phyto- and bioremediation strategies for decontaminating Hg-polluted soils generally involve low investment, simple operation, and in situ application, and they are less destructive for the ecosystem. Current understanding of the uptake, translocation and sequestration of Hg in plants is reviewed to highlight new avenues for exploration in phytoremediation research, and different phytoremediation strategies (phytostabilization, phytoextraction and phytovolatilization) are discussed. Research aimed at identifying suitable plant species and associated-microorganisms for use in phytoremediation of Hg-contaminated soils is also surveyed. Investigation into the potential use of transgenic plants in Hg-phytoremediation is described. Recent research on exploiting the beneficial interactions between plants and microorganisms (bacteria and fungi) that are Hg-resistant and secrete plant growth promoting compounds is reviewed. We highlight areas where more research is required into the effective use of phytoremediation on Hg-contaminated sites, and conclude that the approaches it offers provide considerable potential for the future.

Integration of CuS nanoparticles and cellulose fibers towards fast, selective and efficient capture and separation of mercury ions

This work demonstrates a novel nanomaterial for rapid, efficient and selective enrichment as well as portable separation of Hg(II) ions, which integrates the advantages of hydrophilic porous cellulose fibers and specific Hg(II) recognizing CuS nanoparticles. The optimal CuS/cellulose fibers nanomaterial (CC-60) exhibits a markedly faster adsorption rate, reaching adsorption equilibrium within 30 s, and a large Hg(II) uptake capacity as high as 1040 mg g−1 in 2 min. The distribution coefficient (Kd) of CC-60 for Hg(II) ions is four orders of magnitude higher than those for other common metal ions, thus giving unique selectivity for Hg(II) ions in the presence of other common metal ions. CC-60 can be used in portable column devices for the sequestration of Hg(II) ions from practical water samples, rapidly lowering the Hg(II) concentration from 16.6 mg L−1 to 9 μg L−1 in 5 s, which surpasses all those sulfur-based materials reported thus far. Such exciting properties are closely related to the synergistic effects arising from the porous structure and hydrophilicity of cellulose fibers, the unique recognition capability of CuS towards Hg(II), and the readily accessible CuS sites on cellulose fibers. This work would open up a new avenue to materials and devices for fast recognition, sequestration, enrichment and detection of Hg(II) as well as other toxic heavy metal ions.

Botanic Metallomics of Mercury and Selenium: Current Understanding of Mercury-Selenium Antagonism in Plant with the Traditional and Advanced Technology.

The antagonistic effect between mercury (Hg) and selenium (Se) is conclusively established in animals and human beings in the past decades. However, the underlying mechanisms of the interactions between Hg and Se in plants, as well as the metabolism of Hg-Se compounds in crops are still far from being understood. The botanic metallomics of Hg and Se mainly focuses on the translocation, transformation, and metabolism of Hg and Se in the environmental and botanic systems employing metallomics methods. An adequate understanding of the biological behavior of Hg and Se in plant is beneficial for sequestration of Hg and Se in soil-plant systems with high Hg and Se contamination. It can also provide a molecular mechanistic basis for Se supplementation in Se-deficient areas. Here, the key developments in current understanding of Hg and Se interactions in plants are reviewed. The metabolism and antagonism of Hg and Se in various plants, as well as the advanced analytical methods commonly used in this field, are summarized and discussed. As suggested, plant Hg and Se uptake, metabolism, and antagonism can be taken into account for detoxification and remediation strategies for the reduction of Hg and Se in the food chain.

Sequestration of Gaseous Hg0 by Sphalerite with Fe Substitution: Performance, Mechanism, and Structure–Activity Relationship

The enrichment of mercury in sphalerite plays an important role in the migration and accumulation of Hg in the earth system. Despite Fe being the most common foreign ion in natural sphalerite, the ...

Mercury speciation and retention in a salt marsh undergoing long-term fertilization

Experimental plots in Great Sippewissett Marsh (Falmouth, MA USA) have been undergoing long-term (>48 years) fertilization through the application of commercial sewage sludge-based fertilizer. The experimental treatment focuses on the effect of added nitrogen on the salt marsh plots, but also supplies mercury (Hg) and other metals. This experiment provides a unique opportunity to test hypotheses regarding the Hg-related response of coastal marine ecosystems to eutrophication as well as assess the efficacy of salt marshes as sinks for increased loadings of Hg to the coastal zone. Hg inventories in sediments of control plots were similar to loadings from atmospheric deposition and inventories in the fertilized plots closely reflected the estimated loadings of Hg contained in the added fertilizer. In both the control and fertilized plots, distribution of Hg appeared somewhat different than the history of loadings, implying some level of Hg mobility. The relative abundance of monomethylmercury (CH3Hg+) within the plots varied with the amount of fertilizer applied with the highest percentage of Hg as CH3Hg+ found in the control plots, and the lowest percentages of CH3Hg+ and S were measured in plots fertilized at the highest dose. The results from this marsh suggest that eutrophication indirectly lowers CH3Hg+ production in this particular ecosystem, but perhaps not as a result of the sequestration of Hg(II) with S.

Mercury sequestration and transformation in chemically enhanced treatment wetlands

Mercury (Hg) pollution is a concern to human and wildlife health worldwide, and management strategies that reduce Hg inputs to aquatic systems are of broad interest. Using a replicated field-scale study in California's Sacramento-San Joaquin Delta, we tested the effectiveness of chemically enhanced treatment wetlands (CETWs) under two coagulation treatments, polyaluminum chloride (Al treatment) and ferric sulfate (Fe treatment), in their initial removal and longer-term sequestration of Hg compared to untreated control wetlands. The primary mechanism for Hg removal by CETWs was the transfer of Hg from filtered forms to insoluble particulate forms and enhanced settling of particles. CETWs resulted in total Hg annual load removals of 63 ng m−2 yr−1 (71%) and 54 ng m−2 yr−1 (54%) for the Al and Fe treatments, respectively. Control wetlands removed significantly less at 13 ng m−2 yr−1 (14%). Load removals indicate that Fe treatment wetlands more effectively reduced filtered and total methylmercury (MeHg) exports, while Al treatment wetlands more effectively reduced particulate MeHg and total Hg exports. These differences in Hg species load reductions possibly indicate different mechanisms of Hg sequestration; current data suggest more effective floc formation and particle settling was likely responsible for the Al treatment behavior, while either preferential MeHg sequestration or methylation suppression was potentially responsible for Fe treatment behavior. Differences in Hg sequestration behavior post-coagulation between the flocs formed by different coagulants indicate the importance of in-situ studies and the need for careful selection of coagulant treatment depending on the Hg species requiring remediation.

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Photic zone euxinia (PZE) is a condition where anoxic, H2S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life.

Toxic Metal Sequestration Exploiting a Unprecedented Low-Molecular-Weight Hydrogel-to-Metallogel Transformation.

We report herein the development of a unique low-molecular-weight gelator-induced technique for environmental remediation. The motive of this work is wastewater purification using a gel-based toxic heavy metal sequestration. The essence of this technique was to bring two different functionalities, one capable of multiple coordination and another with gel-forming ability, arranged in tandem within a single ligand molecule. Naturally, the success of the approach depends on whether the two tandem-arrayed functionalities are indeed working in tandem. Our results show that the ligand molecule is an excellent example of concomitant hydrogelator and metallogelator. The most interesting aspects of this study involve the toxic metal sequestration of Pb, Cd, and Hg which was further studied in detail with spectroscopic, microscopic, and diffraction techniques. We also report here a rare property of pure organic hydrogel-to-metallogel transformation which could open up a new avenue on wastewater purification. In essence, the hydrogels can be envisaged as a unique class of metal-free zeolite analogue for environmental remediation not by just absorbance but through absorbance cum coordination, which are further corroborated by the inductively coupled plasma-optical emission spectroscopy results.

Effect of mercury on the polyphosphate level of alga Chlamydomonas reinhardtii

In this study, the accumulation and toxicity effect of 1–7 μM of Hg was determined during 24–72 h on two strains of Chlamydomonas reinhardtii, CC-125 and CC-503 as a cell wall-deficient mutant, by monitoring the growth rate and the maximum quantum yield of Photosystem II. In addition, the level of extracytoplasmic polyphosphates (polyP related to the cell wall) was determined to understand the polyP physiological role in Hg-treated algal cells. The results showed that the polyP level was higher in the strain CC-125 compared to CC-503. When algal cells were exposed to 1 and 3 μM of Hg, the accumulation of Hg was correlated with the degradation of polyP for both strains. These results suggested that the degradation of polyP participated in the sequestration of Hg. In fact, this mechanism might explain at 72 h the recovery of the polyP level, the efficiency of maximum PSII quantum yield, the low inhibition of growth rate, and the low accumulated Hg in algal biomass. Under the effect of 5 and 7 μM of Hg, the degradation of polyP was complete and could not be recovered, which was caused by a high accumulation and toxicity of Hg already at 24 h. Our results demonstrated that the change of polyP level was correlated with the accumulation and effect of Hg on algal cells during 24–72 h, which can be used as a biomarker of Hg toxicity. Therefore, this study suggested that extracytoplasmic polyP in C. reinhardtii contributed to the cellular tolerance for Hg.