Hg Retention Research Articles

Impact of climatic seasons on the dynamics of carbon, nitrogen and mercury in soils of Brazilian biomes affected by gold mining

Land use change, especially mining activities, contributes to anthropic CO2 emissions, leading to decreased carbon (C) storage and loss of biodiversity. Artisanal gold mining associated with the use of mercury (Hg) for amalgamation may change soil organic matter (SOM) contents, and the release of Hg into the environment generates serious environmental problems. Changes in soil biogeochemistry due to C loss and seasonal climate fluctuations affect Hg dynamics and can either increase or decrease its availability. Therefore, our objective was to evaluate the impact of mining on SOM and Hg geochemistry in four Brazilian biomes. We evaluated the dynamics of C and Hg in the dry and rainy seasons of mining and pasture areas by combining spectroscopic, thermogravimetric, and chemical extraction. The critical role of SOM in Hg retention and the influence of climatic seasons on C and nitrogen (N) stocks were highlighted, along with the availability of Hg in solution. Key findings indicated a 50 % reduction in soil C stocks in mined areas, exacerbated during dry seasons, which also saw up to a 70 % increase in bioavailable Hg. SOM played a critical role in Hg retention, with Hg availability closely linked to soil C stability. These results highlight the environmental degradation linked to mining and suggest strategies to mitigate these impacts by increasing SOM and immobilizing Hg. Amalgamation of gold directly into ore, as in the Amazon, has generated great soil Hg stocks, while Hg availability appeared to be governed by soil C stability. This information can serve as a basis for choosing strategies to mitigate environmental degradation caused by changes in land use in mining activities to promote increase in SOM and to immobilize Hg contents.

Retention properties and mechanism of agricultural waste maize whisker on atmospheric mercury

Mercury (Hg) is a global pollutant transmitted mainly through the atmosphere, posing a serious threat to biological survival and human health. Porous materials, with high specific surface area, high porosity, and high adsorption, are particularly suitable for the purification of atmospheric Hg mixtures. However, plant porous materials are rarely directly used for atmospheric Hg purification. In this study, the properties and mechanism of maize whisker in removing atmospheric Hg were analyzed. The results show that the Hg content in the whiskers increases significantly as the initial Hg concentration increases, and 79.38% Hg can be removed by 0.2 g maize whiskers after 1 h exposure when the initial Hg concentration is 0.1 μg m−3, indicating that maize whiskers can accumulate atmospheric Hg rapidly and effectively. The hole diameter of the maize whisker is between 0.83 and 3.06 μm, which is suitable for the adsorption of small substances. Correlation analysis shows that maize whiskers have a significant correlation between atmospheric Hg retention and its specific surface area, pore size, medium pore ratio, and micropore ratio, suggesting that the maize whisker hole feature has a significant influence on its ability to retain atmospheric Hg. Compared with the energy profiles before and after Hg treatment, the peak of Mg decreased after Hg adsorption. Fourier infrared spectrometer analysis suggests that functional groups such as -OH, -COOH, and -O- are involved in the adsorption process. The change in pH value shows an obvious effect on the overall change in zeta potential in the adsorption process. Therefore, a variety of mechanisms, including physical adsorption, electrostatic adsorption, complexation, chelation, and ion exchange, are involved in Hg retention with the maize whisker. This study reveals the important potential value of agricultural waste maize whiskers in the purification of atmospheric heavy metal Hg.Graphical

Retention and transformation of exogenous Hg in acidic paddy soil under alternating anoxic and oxic conditions: Kinetic and mechanistic insights

To estimate the risks and developing remediation strategies for the mercury (Hg)-contaminated soils, it is crucial to understand the mechanisms of Hg transformation and migration in the redox-changing paddy fields. In present study, a Hg-spiked acidic paddy soil (pH 4.52) was incubated under anoxic conditions for 40 d and then under oxic conditions for 20 d. During anoxic incubation, the water-soluble, exchangeable, specifically adsorbed, and fulvic acid-complexed Hg decreased sharply, whereas the humic acid-complexed Hg, organic, and sulfide-bound Hg gradually increased, which were mainly ascribed to the enhanced adsorption on the surface of soil minerals with an increase in soil pH, complexation by organic matters, precipitation as HgS, and absorption by soil colloids triggered by reductive dissolution of Fe(III) oxides. By contrast, after oxygen was introduced into the system, a gradual increase in available Hg occurred with decreasing soil pH, decomposition of organic matters and formation of Fe(III) oxides. A kinetic model was established based on the key elementary reactions to quantitatively estimate transformation processes of Hg fractions. The model matched well with the modified Tessier sequential extraction data, and suggested that large molecular organic matter and humic acid dominated Hg complexation and immobilization in acidic paddy soils. The content of methylmercury increased and reached its peak on anoxic 20 d. Sulfate-reducing bacteria Desulfovibrio and Desulfomicrobium were the major Hg methylating bacteria in the anoxic stage whereas demethylating microorganisms Clostridium_sensu_stricto_1 and Clostridium_sensu_stricto_12 began to grow after oxygen was introduced. These new dynamic results provided new insights into the exogenous Hg transformation processes and the model could be used to predict Hg availability in periodically flooded acidic paddy fields.

Mercury (II) removal from aqueous solutions by iron nanoparticles synthesized from extract of Eucalyptus grandis

Artisanal mining is the main source of mercury emissions in South America, which generates a serious environmental impact due to this toxic metal, recent research is directed to minimize the impact, therefore this study focuses on the green synthesis of nanoparticles for the absorption of mercury in water. For the synthesis of iron nanoparticles, an extract of Eucalyptus grandis was used with iron chloride salts using water as solvent. The synthesized nanoparticles showed a specific surface area of 131.90 m2/g, determined by Brunauer-Emmett-Teller isotherm (BET). Nanoparticles were characterized by Fourier transformed infrared spectroscopy (FTIR) and transmission electron microscopy (MET). The behavior of nanoparticles synthesized during Hg (II) retention was evaluated measuring pH, temperature, nanoparticle dosing, presence of other ions and comparing with other adsorbents. All analyses measured by atomic absorption spectroscopy by the cold vapor technique (CVAAS), presenting a retention percentage for Hg (II) between 75.05 and 79.59% with pH between 4 and 7. The adsorption isothermal was adjusted to the Freundlich model and the percentage of retention of Hg by the synthesized nanoparticle was 79.26%. This work shows a method for obtaining an environmentally friendly mercury adsorbent from iron and E. grandis with a mercury retention capacity comparable to commercial adsorbents.

Climate change and mercury in the Arctic: Abiotic interactions

Dramatic environmental shifts are occuring throughout the Arctic from climate change, with consequences for the cycling of mercury (Hg). This review summarizes the latest science on how climate change is influencing Hg transport and biogeochemical cycling in Arctic terrestrial, freshwater and marine ecosystems. As environmental changes in the Arctic continue to accelerate, a clearer picture is emerging of the profound shifts in the climate and cryosphere, and their connections to Hg cycling. Modeling results suggest climate influences seasonal and interannual variability of atmospheric Hg deposition. The clearest evidence of current climate change effects is for Hg transport from terrestrial catchments, where widespread permafrost thaw, glacier melt and coastal erosion are increasing the export of Hg to downstream environments. Recent estimates suggest Arctic permafrost is a large global reservoir of Hg, which is vulnerable to degradation with climate warming, although the fate of permafrost soil Hg is unclear. The increasing development of thermokarst features, the formation and expansion of thaw lakes, and increased soil erosion in terrestrial landscapes are increasing river transport of particulate-bound Hg and altering conditions for aquatic Hg transformations. Greater organic matter transport may also be influencing the downstream transport and fate of Hg. More severe and frequent wildfires within the Arctic and across boreal regions may be contributing to the atmospheric pool of Hg. Climate change influences on Hg biogeochemical cycling remain poorly understood. Seasonal evasion and retention of inorganic Hg may be altered by reduced sea-ice cover and higher chloride content in snow. Experimental evidence indicates warmer temperatures enhance methylmercury production in ocean and lake sediments as well as in tundra soils. Improved geographic coverage of measurements and modeling approaches are needed to better evaluate net effects of climate change and long-term implications for Hg contamination in the Arctic.

Genesis of Coalbed Methane and Its Storage and Seepage Space in Baode Block, Eastern Ordos Basin

The Baode block on the eastern margin of the Ordos Basin is a key area for the development of low-rank coalbed methane (CBM) in China. In order to find out the genesis of CBM and its storage and seepage space in Baode block, the isotopic testing of gas samples was carried out to reveal the origin of CH4 and CO2, as well, mercury intrusion porosimetry, low temperature nitrogen adsorption, and X-ray CT tests were performed to characterize the pores and fractures in No. 4 + 5 and No. 8 + 9 coal seams. The results showed that the average volume fraction of CH4, N2, and CO2 is 88.31%, 4.73%, and 6.36%, respectively. No. 4 + 5 and No. 8 + 9 coal seams both have biogenic gas and thermogenic methane. Meanwhile, No. 4 + 5 and No. 8 + 9 coal seams both contain CO2 generated by coal pyrolysis, which belongs to organic genetic gas, while shallow CO2 is greatly affected by the action of microorganisms and belongs to biogenic gas. The average proportion of micropores, transition pores, mesopores, and macropores is 56.61%, 28.22%, 5.10%, and 10.07%, respectively. Samples collected from No. 4 + 5 coal seams have developed more sorption pores. Meanwhile, samples collected from No. 8 + 9 coal seams exhibited a relatively low degree of hysteresis (Hg retention), suggesting good pore connectivity and relatively high seepage ability, which is conducive to gas migration. The connected porosity of coal samples varies greatly, mainly depending on the relative mineral content and the proportion of connected pores.

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.

Synthesis of hybrid materials and application to the retention of some effluents

This present work is subdivided into two main parts: the first part consists in preparing the adsorbent: the double-layered hydroxide Mg/AL-CO3, which was prepared according to the co-precipitation method described by MIYATA and then grafting this LDH with Taurinyl-phosphonic acid (TPA) by anion exchange. The new synthesized material Mg/Al-TPA is applied to the retention of mercuric ions Hg+2. The characterization of this product was carried out by different methods such as Fourier transform infrared (FTIR), x-ray diffraction (DRX) and Brunauer–Emmett–Teller (BET) to explain the physical adsorption. In the second part, the material obtained was studied for the retention of Hg+2 ions and gave an extraction yield of 73% , with 0.1 g of adsorbent at pH = 5.8 and T = 25° C for a grafted LDH.

The human health risks assessment of mercury in soils and plantains from farms in selected artisanal and small-scale gold mining communities around Obuasi, Ghana.

Food consumption remains the commonest pathway through which humans ingest higher levels of mercury (Hg). Long-term exposure to Hg through Hg-contaminated food may result in acute or chronic Hg toxicity. Incessant discharge of Hg waste from ASGM facilities into nearby farms contaminates food crops. Ingestion of such food crops by residents may lead to detrimental human health effects. The human health risks upon exposure to total mercury (THg) and methylmercury (MeHg) in farmland soils and plantains from farms sited near ASGM facilities were studied in four communities around Obuasi, Ghana. The human health risk assessment was evaluated using hazard quotient (HQ), estimated average daily intake (e AvDI), hazard index (HI) and Hg elimination and retention kinetics. Tweapease, Nyamebekyere and Ahansonyewodea had HQ, e AvDI and HI for THg of plantains for both adults and children below the recommended USEPA limit of 1, 3 × 10-4 mg/kg/day and 1, respectively. Odumase had HQ, e AvDI and HI for THg of plantains for both adults and children, higher than the guideline values. This meant that only Odumase may cause non-carcinogenic human health effects upon repeated exposure. The HQ, e AvDI and HI values of MeHg for all the study areas were far below guideline values, hence may not pose any non-carcinogenic human health risks to residents even upon repeated exposure. Retention and elimination kinetics of Hg also showed that only plantains from Odumase may pose significant non-carcinogenic human health risks to residents because the final amount of inorganic mercury exceeded the extrapolated USEPA guideline value of 0.393 μg/kg/year.

Preparation and Characterization of the Sulfur-Impregnated Natural Zeolite Clinoptilolite for Hg(II) Removal from Aqueous Solutions

Sulfur-impregnated zeolite has been obtained from the natural zeolite clinoptilolite by chemical modification with Na2S at 150 °C. The purpose of zeolite impregnation was to enhance the sorption of Hg(II) from aqueous solutions. Chemical analysis, acid and basic properties determined by Bohem’s method, chemical behavior at different pHo values, zeta potential, cation-exchange capacity (CEC), specific surface area, X-ray powder diffraction (XRPD), scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), as well as thermogravimetry with derivative thermogravimetry (TG-DTG) were used for detailed comparative mineralogical and physico-chemical characterization of natural and sulfur-impregnated zeolites. Results revealed that the surface of the natural zeolite was successfully impregnated with sulfur species in the form of FeS and CaS. Chemical modification caused an increase in basicity and the net negative surface charge due to an increase in oxygen-containing functional groups as well as a decrease in specific surface area and crystallinity due to the formation of sulfur-containing clusters at the zeolite surface. The sorption of Hg(II) species onto the sulfur-impregnated zeolite was affected by the pH, solid/liquid ratio, initial Hg(II) concentration, and contact time. The optimal sorption conditions were determined as pH 2, a solid/liquid ratio of 10 g/L, and a contact time of 800 min. The maximum obtained sorption capacity of the sulfur-impregnated zeolite toward Hg(II) was 1.02 mmol/g. The sorption mechanism of Hg(II) onto the sulfur-impregnated zeolite involves electrostatic attraction, ion exchange, and surface complexation, accompanied by co-precipitation of Hg(II) in the form of HgS. It was found that sulfur-impregnation enhanced the sorption of Hg(II) by 3.6 times compared to the natural zeolite. The leaching test indicated the retention of Hg(II) in the zeolite structure over a wide pH range, making this sulfur-impregnated sorbent a promising material for the remediation of a mercury-polluted environment.

Modified clay mineral: A method for the remediation of the mercury-polluted paddy soil

Rice is easy to accumulate mercury (Hg), especially methylmercury (MeHg) with high toxicity, and this leads to a serious health risk for residents in some Hg-polluted areas of Asia. Thus, there is an urgent need to find soil remediation techniques that can both guarantee agricultural production and protect human health in these Hg-contaminated areas. In this study, montmorillonite (Mont) and medical stone (Med) were modified by a thiol-based material (-SH) and by chitosan to obtain modified clay mineral adsorbents. Pot experiments were then performed to explore their ability to reduce the levels of Hg and MeHg in rice and their reduction mechanisms. Compared with unmodified clay minerals, modified clay minerals had better Hg reduction efficiencies in rice. The amendment of SH-modified Med (Med-SH) had the highest THg and MeHg reduction efficiencies in rice, reaching up to 78% and 81%, respectively, and brought the THg concentration in the rice below China's health guidelines for rice (20 ng g−1). Not only did amendment of the SH-modified clay minerals reduce the exchangeable and specially adsorbed Hg in the soil, as did the other amendments, but they also significantly reduced the amount of oxide-bound Hg and MeHg in the soil, and greatly enhanced the retention of Hg and MeHg in soil, thus significantly reduced the concentration of Hg and MeHg in rice.

Binding of Hg to preformed ferrihydrite-humic acid composites synthesized via co-precipitation and adsorption with different morphologies

Iron (hydr)oxide-natural organic matter (NOM) colloids, the dominant components of soil, usually occur in varied circumstances and may affect Hg transport and fate in soil. This study aims to reveal the Hg binding to preformed composites rather than only focusing on Hg retention by iron (hydr)oxides in the presence of NOM. Ferrihydrite-humic acid (FH-HA) is chosen as a representative composite, and the effect of the complexation method and FH morphology on Hg binding to various composites is evaluated. Three types of composites are developed: a dense coprecipitated composite (p-d-f), a gel-like adsorbed composite (a-g-f) and a dense adsorbed (a-d-f) composite. Batch sorption and stirred-flow kinetic tests together with surface property analysis and modern spectral analyses are carried out to explore the binding behavior of Hg to the three composites and clarify the interactions in the ternary systems of FH-HA-Hg. The results show that the Hg sorption isotherms all fit well with the Langmuir model, and the maximum sorption capacities follow the order a-g-f> a-d-f > p-d-f, implying that the adsorbed composite is more favorable than the coprecipitated composite for Hg binding and a gel morphology is more beneficial than a dense morphology. The stirred-flow experiments show that the adsorbed composite has a small advantage in Hg sorption compared to the coprecipitated composite and that the gel-like composite can adsorb more Hg at a faster rate than the dense composite. Both FH and HA participate in Hg sorption, and FH-HA-Hg complexes are speculated to form. These findings are helpful to better understand the mobility and fate of Hg in soils, as well as the associated dynamic model for predicting Hg behavior in the environment where the iron (hydr) oxide-NOM composites are pre-existed.

Efficient Removal of Toxic mMetal Ions (Pb(II) and Hg(II) Ions in Single Component Systems by Adsorption on Romanian Clay Material

In this study, a local natural clay material was used for the efficient removal of Pb(II)ions and Hg(II) ions from aqueous media, in batch system. The adsorptive potential of clay material was testes at different initial solution pH, adsorbent dosage, contact time and initial heavy metal ions concentration and room temperature (20  2C). The highest adsorption efficiency of clay material was found at initial pH of 7.0 in case of Pb(II) ions, and 2.0 in case of Hg(II) ions, while the adsorbent dosage had the same value (4 g/L) for both metal ions. The adsorption equilibrium is very fast and was reach within 10 min. The modelling of experimental data showed that the adsorption processes followed the Freundlich isotherm model and pseudo-second order kinetic model. Detailed analysis of the experimental data indicate that the retention of Pb(II) and Hg(II) ions from aqueous solution on clay materials involves two processes, one of adsorption and the other of precipitation, whose succession depends on the speciation form of the metal ion in aqueous solution. However, the high adsorption capacity and short contact time are important characteristics which suggest the potential use of this clay material in environmental remediation processes.

Effect of additives on mercury partitioning in wet-limestone flue-gas desulfurization

AbstractThe wet-flue-gas desulfurization (FGD) process plays an important role in removing water-soluble flue-gas components such as sulphur dioxide (SO2) and oxidized mercury compounds. Under the reducing environment of the FGD, there is the possibility of re-emission of the already absorbed mercury (Hg) to the gas phase, which may be diminished by the utilization of specific additives. In this study, the effect of two different additives on Hg re-emission from the aqueous phase and Hg partitioning in gypsum and filtrate of a lab-scale wet-limestone FGD is investigated. Furthermore, the behaviour of additives in the presence of different halides is studied. The studied additives are TMT 15® as a sulphidic precipitating agent, which forms non-soluble mercury compounds, and activated lignite (AL) as a carbon-based sorbent, which adsorbs Hg compounds from the aqueous phase. TMT 15® has no significant effect on SO2 absorption; on the other hand, addition of AL improves the SO2-removal efficiency by up to 30%. Using both additives, Hg re-emission is suppressed in all the experimented cases except for AL in the absence of halides, in which Hg re-emission shows no change. Thus, the need to form nucleophilic oxidized mercury compounds in the slurry for the adsorption of oxidized mercury on AL can be concluded. Usage of both additives improves Hg retention in the slurry to different extents. It is shown that, for the additive-free slurries, the Hg-adsorption capacity of the solid fraction of the slurry is the limiting parameter. Moreover, the utilization of both additives results in a significant increase in the Hg concentration of solid fraction. The correlation between redox potential and partitioning of Hg in the slurry is presented by comparing the change in the redox potential of slurries when additives are used.

Subtropical Forests Act as Mercury Sinks but as Net Sources of Gaseous Elemental Mercury in South China.

Comprehensive mercury (Hg) budgets were constructed in two typical subtropical forests in southern China in 2014 to quantify Hg (gaseous elemental Hg, Hg0, and reactive Hg, HgII) input and output fluxes and Hg retention in forests, consequently exploring the roles of subtropical forests in the global Hg cycle. At site Qianyanzhou, representing a background region with an enhanced atmospheric Hg0 concentration, the total HgII deposition (67.7 μg·m-2·year-1, 73% as dry HgII deposition) was found to be slightly higher than the Hg0 emission above the canopy (58.5 μg·m-2·year-1), indicating that the forest is a minor Hg sink but a significant net Hg0 source on a yearly basis. In contrast, the forest in the moderately polluted region (site Huitong) acted as a significant Hg sink but a minor net Hg0 source with a higher HgII deposition (73.7 μg·m-2·year-1) and relatively negligible Hg0 emission (2.65 μg·m-2·year-1). The decreasing atmospheric Hg0 concentrations declined the total Hg sink based on the Hg budgets synthesized of this and previous studies and may promote forest Hg0 emissions. Consequently, it was expected that the re-emission of historically deposited Hg may be enhanced from subtropical forests by recent decreases in atmospheric Hg0 concentrations throughout China.

Carbon materials loaded with maghemite as regenerable sorbents for gaseous Hg0 removal

In a scenario where mercury emission regulations are becoming increasingly stringent, the use of regenerable sorbents is an attractive economic and ecological alternative for the elimination of gaseous mercury. This study attempts to develop cost-effective regenerable sorbents made up of carbon supports loaded with maghemite and evaluate their application for mercury capture in CO2 enriched atmospheres. To achieve this goal, an activated carbon (AC) and a carbon foam (CF) were impregnated with different concentrations of an iron salt and then subjected to thermal treatment to obtain the maghemite oxide. The Hg removal capacity of the prepared sorbents was evaluated at a laboratory-scale at 80 °C under different gas atmospheres. It was found that the characteristics of the carbon support as well as the iron concentration influence the distribution and morphology of the deposited maghemite particles. The CF-derived sorbents exhibited a better Hg0 removal performance than the AC-derived sorbents due to the presence of areas with a high concentration of iron oxide particles on the carbon support, which led to stronger interactions between the Hg and sorbent. The adsorption mechanism seems to occur via an adsorption/oxidation process involving the oxygen lattice of the metal oxide. Consequently, the sorbents lose their Hg retention capacity as the lattice oxygen is consumed. However, the deactivation can be counteracted by adding O2 to the gas stream to regenerate the sorbents. Carbon foams loaded with maghemite possess interesting properties which make them suitable for application at industrial scale. These include their low-cost, design versatility, and easy in-batch producibility. Hence, CF-derived sorbents are a versatile option for Hg capture in regenerable columns, capable of competing with the one-use sorbents, typically injected into flue gas.

Efflux behavior of inorganic mercury and methylmercury in the marine copepod Tigriopus japonicus

Marine copepods play an important role in transferring mercury to higher trophic levels in aquatic ecosystems. Exposure time is an important environmental parameter that potentially influences the bioaccumulation and biomagnification of Hg in copepods, which increases the uncertainty in risk assessments of Hg in food chains. In the present study, we employed the radiotracer technique to evaluate the efflux behavior of inorganic mercury [Hg(II)] and methylmercury (MeHg), and the effects of exposure time in a population of Tigriopus japonicus copepods. Exposure treatments were compared to understand the effects of exposure time (1 d, 3 d, and 7 d) on the release routes and efflux rate constants (ke) of Hg in copepods. During a depuration period of 5 d, the ke value of Hg(II) in the three exposure treatments ranged from 0.190–0.330 d−1, while the ke of MeHg was generally slower and ranged from 0.031–0.051 d−1. The exposure time significantly affected the efflux rates of Hg(II), i.e., a longer exposure time caused a higher retained Hg(II) burden in copepods, while no significant changes were observed in the MeHg treatments. The release routes of Hg in T. japonicus included excretion, feces production, and reproduction. In all the treatments, the excretion of Hg was the most important release route. The relative contribution of reproduction significantly increased in the MeHg exposure treatments, while the contribution of water excretion decreased with exposure time. Our study demonstrated that the retention of Hg(II) and the maternal transfer of MeHg were time-dependent and significantly affected by exposure time. Long-term exposure caused a decrease in the ke of Hg(II) and increase in the contribution of MeHg transfer to nauplii, thereby indicating an increasing risk of biological transmission of Hg under long-term exposure.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO2 condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO2-free condition. This work further evaluated SO2 influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl2 was found in a two-section CaO-AcS trap under SO2 conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO3. Hg0 release from CaO-AcS samples suggested potential reactions between Hg(II) and SO2. The detected HgO and Hg2SO4 species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO2 on surface-bound Hg(II) species were substantiated by DFT calculations. SO2 showed a stronger interaction with CaO than HgCl2 because SO2 has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg2SO4 under SO2-deficient condition, or directly reduced to Hg0 under SO2-rich condition. This work fully proposed the SO2 influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.

SPATIAL ANALYSIS OF MERCURY LEVELS AS INDICATOR OF ENVIRONMENTAL CHANGES AND SOIL QUALITY IN AGROFORESTRY SYSTEMS IN SOUTHERN AMAZON

An agroforestry system (AFS) describes the conjoint use of land for agricultural andforestry purposes. An AFS plays a strategic role in the mitigation of carbon dioxide(CO2) emissions, and stands as an alternative in land use that reduces mercury (Hg)remobilization in cultivated soils. This study evaluated the spatial variability of Hgconcentrations as indicators of environment changes and soil quality in different landcover and use systems in a rural settlement in southern Amazon, Brazil. Themethodological procedures were carried out as steps: the experimental units weredefined, physical and chemical characteristics of soil samples were analyzed, anddata were evaluated using conventional and spatial statistics. The AFS included hadbeen established 10 years before or more, and had high Hg retention capacity ,compared with Hg levels in soils on migratory agriculture or that are not fallowed .Therefore, due to low AFS improve soil quality due to the low intensity of harrowing,increasing retention of gaseous and particulate Hg in the soil.

Size Scaling of Contaminant Trace Metal Accumulation in the Infaunal Marine Clam Amiantis umbonella.

Size scaling of the accumulation of four trace metals was examined in the infaunal clam Amiantis umbonella in Kuwait Bay. In clams of varying shell length (2.5-5cm), soft tissue growth in A. umbonella from a contaminated site was inhibited compared with clams from a less contaminated reference site. Body burdens of all four metals were positively correlated with clam soft tissue wet weight, but forCd, Cu, and Pb, correlations were stronger in clams from the contaminated site (r2 = 0.6-0.9, p < 0.001) than the reference site (r2 = 0.2-0.3, p < 0.002). Scaling factors for the accumulation of Cd, Cu, and Pb in the soft tissues of A. umbonella from both sites were not significantly different than 1, indicating that clams accumulated these metals in proportion to growth with little regulation. The scaling factor of Hg in clams from the contaminated site also was 1 but was 0.5 and 2.4 for high and low Hg accumulating subpopulations of clams from the reference site, respectively. The greater retention of Hg with respect to growth in clams from the reference site than from the contaminated site requires further investigation to determine differences in Hg bioavailability at the two sites and the form of Hg these clams accumulate.