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Mishra, Bhoopesh

Publications and source records attributed to Mishra, Bhoopesh.

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Reduction of Hg II by Mn II

The reduction of Hg II to Hg I or Hg 0 can lead to significant changes in Hg toxicity and mobility in the environment. Photochemical reduction is the primary process for the reduction of Hg II to Hg 0 in sunlit environments; however, dark reduction of HgII can occur via microbial metabolic processes and/or reduction by reduced natural organic matter, Fe II mineral phases, Fe II sorbed to minerals, or aqueous Fe II . Here, in this study, we demonstrate a novel Hg II reduction pathway involving another environmentally relevant reductant, Mn II . Abiotic reduction of Hg II O by Mn II was studied as a function of pH and anion environment (perchlorate, sulfate, chloride) using X-ray absorption spectroscopy to characterize the solid-phase Hg and Mn species. At circumneutral pH of 7.5, about 70% of Hg II was reduced to elemental Hg 0 within 2 h. In contrast, 12 h were needed to achieve the same extent of reduction at pH 6.9. In the presence of sulfate and chloride, Hg I species were formed. Hg II reduction was initially rapid and coupled with the oxidation of soluble Mn II -oxides to insoluble Mn IV -oxides, followed by a significantly slower reduction of Hg II during the Mn II -catalyzed transformation of the Mn IV -oxides to hydroxide and oxyhydroxide minerals. The observed reduction of Hg II by Mn II at circumneutral pH could be an important transformation pathway for environmental Hg, affecting its bioavailability and mobility under mildly reducing conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Zn speciation and fate in soils and sediments along the ground transportation route of Zn ore to a smelter

We discuss assessment of Zn toxicity/mobility based on its speciation and transformations in soils as critical for maintaining human and ecosystem health. Zn-concentrate (56% Zn as ZnS, sphalerite) has been imported through a seaport and transported to a Zn-smelter for several decades, and smelting processes resulted in aerial deposition of Zn and sulfuric acids in two geochemically distinct territories around the smelter (mountain-slope and riverside). XAFS analysis showed that the mountain-slope soils contained franklinite (ZnFe 2 O 4 ) and amorphous (e.g., sorbed) species of Zn(II), whereas the riverside sediments contained predominantly hydrozincite [Zn 5 (OH) 6 (CO 3 ) 2 ], sphalerite, and franklinite. The mountain-slope soils had low pH and moderate levels of total Zn (~1,514 ppm), whereas the riverside sediments had neutral pH and higher total Zn (12,363 ppm). The absence of sphalerite and the predominance of franklinite in the mountain-slope soils are attributed to the susceptibility of sphalerite and the resistance of franklinite to dissolution at acidic pH. These results are compared to previous Zn analyses along the transportation routes, which showed that Zn-concentrate spilled along the roadside in dust and soils underwent transformation to various O-coordinated Zn species. Overall, Zn-concentrate dispersed in soils and sediments during transportation and smelting transforms into Zn phases of diverse stability and bioavailability during long-term weathering.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Resolving Conflicting Physical and Biochemical Feedbacks to Climate in Response to Long-Term Warming

The goal of the research was to increase our understanding of the microbial mechanisms that control soil organic matter decay in the context of a changing climate. We hypothesized that a major source of carbon respired after long-term soil warming is recalcitrant soil C mineralized by microbes. We found that long-term warming was associated with decreased fungal communities but not bacterial communities, with bacterial communities in organic horizon soils significantly affected by warming. Molecular analysis indicated that this community shift was towards a more oligotrophic community, consistent with previously observed decreased in soil organic matter quality and quantity. We further hypothesized that low labile C resulting from long-term warming has selected for a microbial community that is better able to mineralize recalcitrant C. Analysis of soil communities and individual isolates physiology showed that long-term warming caused bacteria to have increased potential lignolytic activitiy as well as increased carbohydrate degradation potential. This increased ability to degrade recalcitrant soil organic matter is suggested as a mechanism for accelerated soil carbon loss with long-term warming. Soil warming was shown to have little change in transcriptional activity or proteins levels of the enzymes related to recalcitrant C, and little change in the temperature sensitivity of enzyme activity.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Uptake and speciation of zinc in edible plants grown in smelter contaminated soils

Heavy metal accumulation in edible plants grown in contaminated soils poses a major environmental risk to humans and grazing animals. This study focused on the concentration and speciation of Zn in different edible plants grown in soils contaminated with smelter wastes (Spelter, WV, USA) containing high levels of the metals Zn, Cu, Pb, Cd. Their accumulation was examined in different parts (roots, stem, and leaves) of plants and as a function of growth stage (dry seed, sprouting seed, cotyledon, and leaves) in the root vegetables radish, the leafy vegetable spinach and the legume clover. Although the accumulation of metals varied significantly with plant species, the average metal concentrations were [Zn] > [Pb] > [Cu] > [Cd]. Metal uptake studies were complemented with bulk and micro X-ray absorption spectroscopy (XAS) at Zn K-edge and micro X-ray fluorescence (μXRF) measurements to evaluate the speciation and distribution of Zn in these plant species. Dynamic interplay between the histidine and malate complexation of Zn was observed in all plant species. XRF mapping of spinach leaves at micron spatial resolution demonstrated the accumulation of Zn in vacuoles and leaf tips. Radish root showed accumulation of Zn in root hairs, likely as ZnS nanoparticles. At locations of high Zn concentration in spinach leaves, μXANES suggests Zn complexation with histidine, as opposed to malate in the bulk leaf. These findings shed new light on the dynamic nature of Zn speciation in plants.

59 BASIC BIOLOGICAL SCIENCES↗