Numerical Study on the Homogeneous Reactions of Mercury in a 600 MW Coal-Fired Utility Boiler

The homogeneous oxidation of elemental mercury (Hg0) can promote Hg pollution control in coal-fired power plants, while the mechanisms and quantitative contributions of homogeneous reactions in Hg0 oxidation, especially the reactions between Hg and chlorine (Cl), are still unclear. Here, a numerical study on the homogeneous reactions of Hg was conducted within a 600 MW tangentially fired boiler for the first time. A novel Hg sub-model was established by coupling the thermodynamics, reaction kinetics and fluid dynamics. The results showed that the higher Cl content in coal was beneficial to the oxidation of Hg0. The homogeneous reactions of Hg mainly occurred in the vertical flue pass at low temperature. Hg0 was still the dominant Hg-containing species at the boiler exit, and the concentration of mercury chloride (HgCl2) was the highest among the oxidized mercury. When low-Cl coal was fired, the addition of a small amount of chlorine species into the boiler at the burnout area increased the ratio of HgCl2 by over 16 times without causing serious chlorine corrosion problems.

Experimental evidence for recovery of mercury-contaminated fish populations

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

Histopathological Biomarkers as Indicators of the Environmental Quality of Two Estuaries in Northeastern Brazil

The present study aimed at evaluating the environment quality of the Santa Cruz Channel estuary (area 1) and Sirinhaém river estuary (area 2), Northeastern Brazil, using histopathological biomarkers of liver and gills of fish species with different trophic levels as indicators. It was collected liver and gills from five species: Bairdiella ronchus (n=24) and Gobionellus stomatus (n=34) in the area 1; Caranx latus (n=35), Centropomus undecimalis (n=24) and Centropomus parallelus (n=29) from area 2. The liver showed several damages, such as, hepatic steatosis, necrosis, vacuolar degeneration, and infiltration. Centropomus undecimalis had the highest Histopathological Index of Liver (HIL). Gills exhibited moderate to severe alterations for all species, such as the lifting of epithelial cells, lamellar aneurysm, and rupture of the lamellar epithelium. Centropomus undecimalis in area 2 and G. stomatus in area 1 had the higher number of alterations in their organs. Both areas have been historically affected by mercury (Hg) pollution in área 1 and by the sugarcane industry in area 2 and the species used as biomarkers has been proven to be severely damaged in both estuaries. Species chosen in this study were considered good bioindicators of pollution and the combination of biomarkers methodologies in two organs, pioneering in the Northeastern of Brazil, was efficient in diagnosing the health status of the area using fish as bioindicator.

Distribution Characteristics and Risk Assessment of Mercury in Sediments From Taihu Lake

Persistent pollutants are easily accumulated in sediments, which can cause toxicity to benthos and secondary pollution to water. Mercury (Hg), as one kind of bioaccumulative and persistent pollutant, could cause great harm to water ecology and health, and has been widely concerned. The distribution characteristics and ecological risk of Hg in sediments from Taihu Lake were studied. In addition, the sediment quality criterion (SQC) of Hg was derived using tissue-based toxicity data combined with the phase-equilibrium partitioning (EqP) approach, and the ecological risk level of Hg in Taihu Lake sediment was evaluated. The results showed that Hg was detected in all the 30 sediment samples, and the concentrations of Hg ranged from 9.7 ng/g to 237.0 ng/g, with an average of 76.3 ng/g. The SQC of Hg was calculated to be 108.9 ng/g, and the ecological risk of Hg in the sediments of Taihu Lake is in the middle level, indicating that Hg pollution needs to be paid more attention. The results provide support for environmental management and risk assessment of Hg.

Particulate bound mercury pollution in the Central Italian Herbarium (Firenze, Italy)

<p>The attention devoted to air quality is particularly important in workplaces, such as museums, where the health of visitors and workers must couple with the safeguard of collections. This especially holds for herbaria where, until the middle of the last century, the collections were protected using a solution of mercury dichloride (HgCl<sub>2</sub>) to prevent cryptogamic or animal infestations. The decomposition of HgCl<sub>2</sub> causes the Hg reduction through a reaction pathway that is still poorly known, and the consequent release of Hg<sup>0</sup> in the indoor atmosphere. Besides Hg<sup>0</sup>, Hg in air exists also as bound to particulate (PBM). In the museums’ atmosphere, this fraction may represent a non-negligible proportion of total atmospheric Hg and should be monitored.</p><p>This study aims to characterize the PBM in the <em>Central Italian Herbarium</em> of Firenze (University of Firenze, Italy), one of the largest herbaria worldwide. Here recent studies proved high levels of Hg<sup>0</sup>.</p><p>PBM sampling has been carried twice (2018 and 2020 soon after the lockdown period caused by the Covid-19), collecting the dust on a SEM-EDS stub from different surfaces (furniture, wall cornice, sample cabinet). Samples were roughly divided according to their deposition time between old (<em>OD</em>), almost-new (<em>AD</em>) and new dust (<em>ND</em>). The samples were analyzed using SEM-EDS to characterize the dimension and the chemical speciation of Hg particulate.</p><p>Hg-particles were detected in all the three types of dust collected in both the years: the mean dimension is 0.80±0.01 µm (3σ). The highest number of Hg-particles has been always reached in the <em>AD</em>, i.e. the dust collected directly on the packages containing herbarium specimens, with a strong increase in the 2020 sample. Additionally, the EDS microanalysis revealed that Hg-particles are now mainly associated with S (sometimes with O), suggesting the presence of sulphate or sulphide.</p><p>The above evidences show that PBM constitutes a fraction of Hg pollution in the <em>Herbarium</em> that cannot be ignored. The number of particles strongly increased in a period of low attendance of the <em>Herbarium</em> rooms and consequently cleaning, due to the COVID-19 pandemic: despite this, almost all are still classifiable as fine particulate (i.e. ECD< 2.5 µm) particularly harmful for human health. The presence of sulphate/sulphide indicated the change of Hg speciation with time and its reaction with S and O. These compounds, although less bioavailable than Hg<sup>0</sup>, still represent a risk for both herbarium workers and visitors.</p><p>The results of the present study offer preliminary information on the abatement system to be installed in the museum halls, which should be supplied with filters to retain very fine particles (< 1 µm).</p>

Biomarker Responses of Spanish Moss Tillandsia usneoides to Atmospheric Hg and Hormesis in This Species

Hg is an environmental pollutant with severe biotoxicity. Epiphytic Tillandsia species, especially Spanish moss T. usneoides, are widely used as the bioindicator of Hg pollution. However, the effects of different Hg concentrations on Tillandsia have been rarely studied and the occurrence of hormesis in Tillandsia species has not been determined. In this study, T. usneoides was subjected to stress induced by 15 concentrations of gaseous Hg ranging from 0 to 1.8 μg m–3 through a misting system and then Hg content and eight common biomarkers in leaves were measured. The results showed that leaf Hg content significantly increased with Hg concentration, showing a linear relationship. However, there were no obvious mortality symptoms, indicating that T. usneoides showed strong resistance to Hg. Conversely, there were no simple linear relationships between changes in various biomarkers following Hg treatment of T. usneoides and Hg concentration. With increasing Hg concentration, malondialdehyde (MDA) content did not change significantly, superoxide anion radical content decreased gradually, superoxide dismutase (SOD) content decreased to the bottom and then bounced back, electrical conductivity increased, and glutathione (GSH) and metallothionein (MT) content increased to the peak and then dropped. The coefficient of determination of the dose-effect curves between SOD, GSH, and MT contents and Hg concentration was high, and the dose-effect relationship varied with hormesis. The present study is first to confirm hormesis induced by heavy metal pollution in Tillandsia species.

Outstanding performance of CuO/Fe–Ti spinel for Hg0 oxidation as a co-benefit of NO abatement: significant promotion of Hg0 oxidation by CuO loading

Conversion of gaseous Hg0 to soluble Hg2+ using selective catalytic reduction (SCR) catalysts with gaseous HCl as an oxidant as a co-benefit of NO abatement is widely used for resolving Hg pollution from coal-burning power plants.

Mercury Content Transported from Atmosphere and Land to Jiaozhou Bay

According to the data of May, August and October 1992, the range of Hg content in Jiaozhou Bay waters was 0.009-0.050 μg /L, which met the water quality standard of class I sea water. This showed that in terms of Hg content, in May, August and October, the water of Jiaozhou Bay was clean and free from any Hg pollution. In May, the range of Hg content in Jiaozhou Bay waters was 0.009-0.038 μg /L. In August, the range of Hg content in Jiaozhou Bay waters was 0.021-0.050 μg/L. In October, the range of Hg content in Jiaozhou Bay waters was 0.011-0.040 μg /L. There were two sources of Hg content in Jiaozhou Bay waters, surface runoff and atmospheric deposition. The Hg content from surface runoffwas 0.038-0.040 μg /L, and that from atmospheric deposition was 0.050 μg /L. The model diagram was established to show the different paths and contents of Hg content in the process of input into Jiaozhou Bay. In May and October, the surface runoff was not polluted by any Hg content. In August, atmospheric deposition was not contaminated by any Hg content. That revealed that Hg, humans issued to land and atmosphere, finally got to the ocean. There were two paths. One is that human beings discharge Hg into the atmosphere, and the Hg content reached into the ocean through atmospheric sedimentation. The Hg content from atmospheric sedimentation was relatively high, but the transportation time was relatively short. The other is that human beings discharge Hg content to the land. Through surface runoff, the Hg content reached into the ocean, and the Hg content from surface runoff was relatively low, but the transportation time was relatively short. With more and more paths, Hg content was decreasing.