Legacy Mercury Re-emission and Subsurface Migration at Contaminated Sites Constrained by Hg Isotopes and Chemical Speciation

The re-emission and subsurface migration of legacy mercury (Hg) are not well understood due to limited knowledge of the driving processes. To investigate these processes at a decommissioned chlor-alkali plant, we used mercury stable isotopes and chemical speciation analysis. The isotopic composition of volatilized Hg(0) was lighter compared to the bulk total Hg (THg) pool in salt-sludge and adjacent surface soil with mean ε202HgHg(0)-THg values of -3.29 and -2.35‰, respectively. Hg(0) exhibited dichotomous directions (E199HgHg(0)-THg = 0.17 and -0.16‰) of mass-independent fractionation (MIF) depending on the substrate from which it was emitted. We suggest that the positive MIF enrichment during Hg(0) re-emission from salt-sludge was overall controlled by the photoreduction of Hg(II) primarily ligated by Cl- and/or the evaporation of liquid Hg(0). In contrast, O-bonded Hg(II) species were more important in the adjacent surface soils. The migration of Hg from salt-sludge to subsurface soil associated with selective Hg(II) partitioning and speciation transformation resulted in deep soils depleted in heavy isotopes (δ202Hg = -2.5‰) and slightly enriched in odd isotopes (Δ199Hg = 0.1‰). When tracing sources using Hg isotopes, it is important to exercise caution, particularly when dealing with mobilized Hg, as this fraction represents only a small portion of the sources.

Sources and Transformation Mechanisms of Atmospheric Particulate Bound Mercury Revealed by Mercury Stable Isotopes

This study examined the isotopic composition of particulate bound mercury (PBM) in 10 Chinese megacities and explored the associated sources and transformation mechanisms. PBM in these cities was characterized by negative δ²⁰²Hg (mean: -2.00 to -0.78‰), slightly negative to highly positive Δ¹⁹⁹Hg (mean: -0.04 to 0.47‰), and slightly positive Δ²⁰⁰Hg (mean: 0.02 to 0.06‰) values. The positive PBM Δ¹⁹⁹Hg signatures were likely caused by physiochemical reactions in aerosols. The Δ¹⁹⁹Hg/Δ²⁰¹Hg ratio varied from 0.94 to 1.39 in the cities and increased with the increase in the corresponding mean Δ¹⁹⁹Hg_PBM value. We speculate that, in addition to the photoreduction of oxidized Hg, other transformation mechanisms in aerosols (e.g., isotope exchange, complexation, and oxidation, which express nuclear volume effects) also shape the Δ¹⁹⁹Hg_PBM signatures in the present study. These processes are likely enhanced in the presence of strong gas-particle partitioning of gaseous oxidized Hg (GOM) and elevated levels of redox active metals (e.g., Fe), halides, and elemental carbon. Based on Δ²⁰⁰Hg_PBM data presented in this and previous studies, we estimate that large proportions (∼47 ± 22%) of PBM were sourced from the oxidation of gaseous elemental Hg followed by the partitioning of GOM onto aerosols globally, indicating the transformation of Hg(0) to PBM as an important sink of atmospheric Hg(0).

Mercury Isotope Fractionation during the Exchange of Hg(0) between the Atmosphere and Land Surfaces: Implications for Hg(0) Exchange Processes and Controls

Atmosphere-surface exchange of elemental mercury (Hg(0)) is a vital component in global Hg cycling; however, Hg isotope fractionation remains largely unknown. Here, we report Hg isotope fractionation during air-surface exchange from terrestrial surfaces at sites of background (two) and urban (two) character and at five sites contaminated by Hg mining. Atmospheric Hg(0) deposition to soils followed kinetic isotope fractionation with a mass-dependent (MDF) enrichment factor of -4.32‰, and negligible mass-independent fractionation (MIF). Net Hg(0) emission generated average MDF enrichment factors (ε²⁰²Hg) of -0.91, -0.59, 1.64, and -0.42‰ and average MIF enrichment factors (E¹⁹⁹Hg) of 0.07, -0.20, -0.14, and 0.21‰ for urban, background, and Hg mining soils and cinnabar tailing, respectively. Positive correlations between ε²⁰²Hg and ambient Hg(0) concentration indicate that the co-occurring Hg(0) deposition (accounting for 10-39%) in a regime of net soil emission grows with ambient Hg(0). The MIF of Hg(0) emission from soils (E¹⁹⁹Hg range -0.27 to 0.14‰, n = 8) appears to be overall controlled by the photochemical reduction of kinetically constrained Hg(II) bonded to O ligands in background soils, while S ligands may have been more important in Hg mining area soils. In contrast, the small positive MIF of Hg(0) emission from cinnabar ore tailing (mean E¹⁹⁹Hg = 0.21‰) was likely controlled by abiotic nonphotochemical reduction and liquid Hg(0) evaporation. This research provides critical observational constraints on understanding the Hg(0) isotope signatures released from and deposited to terrestrial surfaces and highlight stable Hg isotopes as a powerful tool for resolving atmosphere-surface exchange processes.

Surgical results for prosthetic versus native valve endocarditis: A multicenter analysis

OBJECTIVES

Prosthetic valve endocarditis is associated with worse outcomes compared with native valve endocarditis. Our aim was to evaluate the impact of native valve endocarditis versus prosthetic valve endocarditis on postoperative outcomes and long-term survival and to identify preoperative risk factors in a large cohort of 4300 patients with infective endocarditis.

METHODS

This retrospective cohort study was conducted in 5 German Cardiac Surgery Centers: the Clinical Multicenter Project of Analysis of Infective Endocarditis in Germany. Data of 4300 patients undergoing valve surgery for native valve endocarditis and prosthetic valve endocarditis were retrospectively analyzed. Univariable and multivariable analyses were used for risk stratification, Kaplan-Meier analysis for long-term survival. In addition, we performed Cox proportional hazards regression with multivariable adjustment.

RESULTS

Between 1994 and 2016, 3143 patients (73.1%) underwent surgery for native valve endocarditis and 1157 patients (26.9%) underwent surgery for prosthetic valve endocarditis. Patients with prosthetic valve endocarditis were older (69 [60-75] vs 63 [52-72] years; P < .001) and had more comorbidities, such as hypertension (55% vs 46%; P < .001), diabetes (28% vs 25%; P = .020), coronary artery disease (32% vs 23%; P < .001), and preoperative acute kidney injury (41% vs 32%; P < .001). Kaplan-Meier analysis revealed significantly decreased long-term survival of patients undergoing surgery for prosthetic valve endocarditis compared with native valve endocarditis (P < .001). However, after multivariable adjustment, there was no significant difference in long-term survival between patients undergoing cardiac surgery with prosthetic valve endocarditis compared with native valve endocarditis.

CONCLUSIONS

After adjusting for preoperative comorbidities, long-term survival for prosthetic valve endocarditis and native valve endocarditis is comparable. Thus, our large cohort study provides evidence that prosthetic valve endocarditis alone should not be a contraindication for redo operations.

En-face optical coherence tomography angiography of neovascularization elsewhere in hemicentral retinal vein occlusion

Purpose

To evaluate how the growth of neovascularization elsewhere (NVE) was delineated in an eye with hemicentral retinal vein occlusion (CRVO) using optical coherence tomography (OCT) angiography.

Patients and methods

We examined a 64-year-old man diagnosed with hemi-CRVO. The area around the occluded vein was scanned using a spectral-domain OCT device (RTVue XR Avanti). Blood flow was detected using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. Color fundus photography, fluorescein angiography (FA), and OCT angiography examinations were performed at the first visit and at 3 and 6 months postpresentation.

Results

At the first visit, FA revealed delayed retinal venous filling and extensive areas of capillary nonperfusion. The patient underwent a trial of intravitreal ranibizumab injection (0.5 mg/0.05 mL) for the treatment of macular edema. At 3 months postpresentation, there was no NVE around the occluded vein in the en-face SSADA image, but at 6 months, NVE appeared on the occluded veins. The en-face SSADA image showed the NVE structure in the fibrovascular membrane on the occluded vein more clearly than FA images.

Conclusion

OCT angiography clearly visualized the sprouting of NVE in an eye with hemi-CRVO. New findings of the vascular structure of NVE in hemi-CRVO were revealed using the en-face SSADA algorithm.

Native valve endocarditis caused by coagulase negative staphylococci; an appeal to start outpatient antimicrobial therapy: an unusual case report

Coagulase negative staphylococci (CNS) were a rare cause of native valve endocarditis. However, they are emerging as an important cause of native valve endocarditis (NVE) in both community and healthcare settings. We describe a 64 yrs. old male who developed mitral valve endocarditis caused by coagulase negative staphylococci. There were no predisposing conditions or underlying cardiac disease that could have been the risk factor for the development of native valve infection. The patient had good recovery after six weeks of treatment with anti-staphylococcal antibiotics.