Aqueous monomethylmercury degradation using nanoscale zero-valent iron through oxidative demethylation and reductive isolation.

This paper proposes a Fenton-like reaction activated by nanoscale zero-valent iron (nZVI) for aqueous monomethylmercury (MMHg) decomposition. Reacting 10 µg L-1 MMHg with 280 mg L-1 nZVI removed 70% of the aqueous MMHg within 1 min, and its main product was aqueous Hg(II). Within 1 - 5 min, the aqueous Hg(II) decreased while the aqueous, solid, and gas-phase Hg(0) increased with 92% MMHg removal. Then, a secondary Hg(II) reduction to solid Hg(0) was prevalent within 30 - 60 min, with 98% MMHg removal. Diverse-shaped magnetite crystals were observed on the surface of nZVI in 2 h, suggesting that Fe(II) oxidation on magnetite can be a source of electrons for secondary Hg(II) reduction. When FeCl2 and H2O2 were added to the MMHg solution without nZVI, 99% of the MMHg changed to Hg(II) within 1 min. The reactive oxygen species (ROS) produced by the Fenton-like reaction accounted for the rapid demethylation but not for the further reduction of Hg(II) to Hg(0). The results suggest a three-step pathway of MMHg decomposition by nZVI: (1) rapid MMHg demethylation by ROS; (2) rapid Hg(II) reduction by Fe(0); and (3) slow Hg(II) reduction by magnetite on the nZVI surface.

Investigations on the Morphological, Mechanical, Ablative, Physical, Thermal, and Electrical Properties of EPDM-Based Composites for the Exploration of Enhanced Thermal Insulation Potential.

The most widely used filler in EPDM-based thermal insulation materials is asbestos which is hazardous to health and environment. The main motivation of this study was to develop improved EPDM-based materials by partially or completely replacing asbestos with other fillers. EPDM-Esprene501A and EPDM-Keltan®4869DE were used and the effect of three fillers (vulkasil-C, asbestos, carbon fiber fabric) on mechanical, ablative, physical, thermal, and electrical performances have been investigated. Samples were divided into phase -1, -2, and -3 by compounding EPDM with various percentages of fillers and other necessary ingredients. It was observed that asbestos and carbon fiber in the absence of vulkasil-C did not import enough reinforcement to EPDM-matrix. Experimental evidence showed that presence of vulkasil-C has not only enhanced mechanical properties but also improved thermal and ablation performance of EPDM-based composites. The swelling index was found comparatively lower with vulkasil-C than that with other fillers. Among two EPDMs, EPDM-Esprene based composites have shown comparatively better performance. Among all (phase-1-3) samples, E100K0VA (phase-2) has shown greater mechanical (stress 3.89 MPa; strain 774%), ablative (linear 0.1 mm/s; mass 0.05 g/s), and thermal (material left 91.0%) properties. Overall findings indicated improved properties of EPDM in the presence of vulkasil-C and may help to develop better heat resistant materials.

Applying the diffusive gradient in thin films method to assess soil mercury bioavailability to the earthworm Eisenia fetida.

This study assessed the critical soil characteristics affecting mercury (Hg) bioavailability to the earthworm Eisenia fetida using the diffusive gradient in thin films (DGT) method. The soil samples were collected from a tributary of the Hyeongsan River contaminated with industrial waste and landfill leachates called Gumu Creek. The Hg concentration in the soil had a range of 0.33-170 µg g-1 (average 33 ± 56 µg g-1), and the Hg concentration of earthworms incubated in the soils was 0.83-11 µg g-1 (average 2.9 ± 3.2 µg g-1). When correlation analysis was used to detect the key variables among the soil properties related to Hg accumulation in the soils, earthworms, and resins, the water-holding capacity, which is covaried with the organic matter content, was determined to be a primary factor in increasing Hg accumulation in the soils, earthworms, and resins. However, the experimentally determined earthworm bioaccumulation factor and the DGT accumulation factor were negatively affected by the water-holding capacity. Therefore, the water-holding capacity played a dual role in the Gumu Creek deposits: increasing the soil Hg concentration and decreasing Hg bioavailability and leachability. Further, the DGT-Hg flux was positively correlated with the Hg concentration in earthworms (r = 0.93). Although the earthworm accumulation of Hg is not processed by passive diffusion, this study proves that the DGT method is promising for predicting soil Hg bioavailability to the earthworm E. fetida, and the water-holding capacity simultaneously regulates Hg availability to the DGT and the earthworms.

Countereffect of glutathione on divalent mercury removal by nanoscale zero-valent iron in the presence of natural organic matter.

Although there have been multiple studies on the effects of natural organic matter (NOM) on zero-valent iron (ZVI) removal of several regulated heavy metal ions from contaminated water, the role of NOM on Hg(II) removal by nanoscale ZVI (nZVI) has not yet been studied. The experimental results showed that in the presence of 100 mg L-1 of Suwannee River NOM (SRNOM), the Hg(II) removal ratio by nZVI decreased from 89% to 36% after 80 min of reaction. Similar trends were observed in the long-term test maintained for 15 days, attributable to the surface passivation of nZVI by SRNOM. In contrast, addition of 100 µM glutathione (GSH) to the nZVI suspensions increased the Hg(II) removal ratio from 85% to 96% after 15 days of reaction. Furthermore, adding 100 µM of GSH to the nZVI and SRNOM suspensions largely improved the removal efficiency of Hg(II) to be > 99% after 9 days of reaction, related to the enhanced dissolution of Fe(II) and consequent formation of lepidocrocite and maghemite on the nZVI surface. The addition of thiolic compounds is suggested as a promising step in overcoming the inhibitory effect of SRNOM for the remediation of Hg(II) using nZVI technology.

Pendred's syndrome.

This report describes Pendred's syndrome in three siblings of a consanguineous marriage, belonging to Rahim YarKhan. The children presented with deafmutism and goiters. The investigations included scintigram, perchlorate discharge test and audiometery. The perchlorate discharge was positive in index case. Bilateral sensorineural hearing defect was detected on Pure Tone Average (PTA) audiometry. Meticulous clinical and laboratory evaluation is mandatory for the detection of rare disorders like Pendred's syndrome.