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Effect of dissimilatory iron and sulfate reduction on arsenic dynamics in the wetland rhizosphere and its bioaccumulation in wetland plants (Scirpus actus)

Zhang, Zheyun,Moon, Hee Sun,Myneni, Satish C.B.,Jaffé,, Peter R. Elsevier 2017 Journal of hazardous materials Vol.321 No.-
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Abstract Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50μM ferrihydrite/g solid medium) and SO4 2− (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (Scirpus actus), probably because root exudates facilitate the microbial reduction of Fe(III), SO4 2−, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO4 2− rather than Fe levels. Compared to the low SO4 2− (0.1mM) treatment, high SO4 2− resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO4 2− than low SO4 2− levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO4 2− levels. Highlights <UL> <LI> High Fe and SO4 2− treatment is most favorable for As sequestration in soils in the presence of wetland plants. </LI> <LI> As retention in soil and accumulation in plants was mainly controlled by SO4 2− rather than Fe levels. </LI> <LI> High SO4 2− can stimulate the growth of As dissimilatory reduction bacteria, leading to more As(V) reduction to As(III). </LI> </UL>
2
Phosphate enhanced abiotic and biotic arsenic mobilization in the wetland rhizosphere

Zhang, Zheyun,Moon, Hee Sun,Myneni, Satish C.B.,Jaffé,, Peter R. Elsevier 2017 CHEMOSPHERE - Vol.187 No.-
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Abstract Although abiotic process of competitive sorption between phosphate (P) and arsenate (As(V)), especially onto iron oxides, are well understood, P-mediated biotic processes of Fe and As redox transformation contributing to As mobilization and speciation in wetlands remain poorly defined. To gain new insights into the effects of P on As mobility, speciation, and bioavailability in wetlands, well-controlled greenhouse experiments were conducted. As expected, increased P levels contributed to more As desorption, but more interestingly the interactions between P and wetland plants played a synergistic role in the microbially-mediated As mobilization and enhanced As uptake by plants. High levels of P promoted plant growth and the exudation of labile organic carbon from roots, enhancing the growth of heterotrophic bacteria, including As and Fe reducers. This in turn resulted in both, more As desorption into solution due to reductive iron dissolution, and a higher fraction of the dissolved As in the form of As(III) due to the higher number of As(V) reducers. Consistent with the dissolved As results, arsenic-XANES spectra from solid medium samples demonstrated that more As was sequestered in the rhizosphere as As(III) in the presence of high P levels than for low P levels. Hence, increased P loading to wetlands stimulates both abiotic and biotic processes in the wetland rhizosphere, resulting in more As mobilization, more As reduction, as well as more As uptake by plants. These interactions are important to be taken into account in As fate and transport models in wetlands and management of wetlands containing As. Highlights <UL> <LI> Increased PO4 3− loading to wetlands stimulates abiotic and biotic As mobilization. </LI> <LI> Increased PO4 3− loading results in more As-reducing bacteria in wetland sediments. </LI> <LI> Increased PO4 3− loading results in more As reduction in wetland sediments. </LI> <LI> Increased PO4 3− loading results in more As uptake by wetland plants. </LI> <LI> Increased PO4 3− loading to wetlands results in lower ORP and less Fe reduction. </LI> </UL>
3
A comparative review on recovery of heavy metals from printed circuit boards (PCB’S) by chemical and bioleaching

Murugesan Manikkampatti Palanisamy,Akilamudhan Palaniyappan,Venkata Ratnam Myneni,Kannan Kandasamy,Padmapriya Veerappan 한양대학교 세라믹연구소 2022 Journal of Ceramic Processing Research Vol.23 No.1
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The electronics industry is the world's largest and fastest growing industry. This consumer-centric industry's combination oftechnology advancements and quick product obsolescence creates new environmental issues. There is an urgent need toaddress the volume and toxicity of electronic waste generated. Printed circuit boards (PCBs) are a significant component ofelectronic trash, containing mostly heavy metals such as copper (Cu), tin (Sn), zinc (Zn), and lead (Pb). Metal recovery andrecycling from PCBs is an important step in pollution prevention. Researchers have devised many methods for recoveringprecious metals from PCBs, including gravity separation, magnetic separation, and electrostatic separation, as well as PCBseparation using the organic solvent technique, leaching method, bioleaching method, or a combination of these methods. Thisresearch provides a brief summary of India's present e-waste status, environmental and health risks, continuing waste disposaland recycling activities, and emphasizes the recovery of heavy metals from PCBs by systematic leaching/bioleaching.

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