• Energy Research

G. Grindlay thanks the Jose Castillejo fellowship program from the Spanish Ministerio de Educacion and the Generalitat Valenciana for financial support.

This work aimed to study the role of arbuscular mycorrhizal fungi (AMF) in Hg and major mineral nutrient uptake and tissue localization of these elements in the roots of maize plants. Maize plants were grown in pots filled with non- and Hg-contaminated substrate (50 μg Hg g-1 as HgCl2) and inoculated with two types of AMF inocula: a) Glomus sp. originating from Hg-polluted soil of a former Hg smelting site in Idrija, Slovenia, and b) commercial AM inoculum Symbivit. Controls were inoculated by corresponding bacterial extracts only. Tissue localization of Hg and major mineral nutrients was performed by laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) on cryofixed and freeze-dried root cross-sections. AMF colonization increased plant biomass in non-contaminated substrate, while this effect was not seen in Hg-contaminated substrate. Hg increased total plant biomass more than AMF inoculation, possibly through hormetic effects. AMF increased Hg uptake into the roots, as well as Hg transfer to the shoots. AMF affected plant mineral nutrient uptake, depending on the type of AMF inoculum and the presence of Hg. In the roots, Hg was mainly localized in rhizodermis and endodermis, followed by the cortex and the central cylinder. Higher Hg concentrations were detected in the central cylinder of AM plants than in that of the controls, pointing to a higher Hg mobility and potential bioavailability in AMF inoculated plants.

Potassium isotopic analysis is arousing increasing interest, not only in geochemistry, but also in biomedicine. However, real-life applications are still hindered by the lack of robustness of the methods used. In this work, a novel and robust method for high-precision K isotopic analysis of geological and biological samples was developed, based on the use of a multicollector ICP-mass spectrometer providing a mass resolving power of 15,000 (extra-high resolution mode, XHR). After evaluation of different measurement conditions, i.e., hot vs cold plasma conditions, standard-type vs jet-type sampling cone, and high resolution (HR) vs XHR, a combination of hot plasma conditions, use of the high-transmission jet-type sampling cone, and the XHR mode allowed for high-precision and interference-free K isotopic analysis. Potassium signal monitoring was performed in the ArH+ interference-free 0.006-0.007 amu wide peak shoulder using the XHR mode. The within-run, short-term external, and long-term external precisions for the δ41K value were 0.02‰ (2se, N = 50), 0.03‰ (2SD, N = 7), and 0.06‰ (2SD, N = 163), respectively. A two-stage chromatographic procedure was developed for the isolation of K from both geological and biological samples, and potential matrix effects affecting the K isotope ratio were systematically evaluated. The method was first applied to geological reference materials (RMs) for validation purposes, and the K isotope ratio results were in good agreement with those previously reported. Subsequently, a series of biological RMs, including serum, whole blood, cerebrospinal fluid, bovine muscle, and lobster hepatopancreas, were characterized for their K isotopic composition.

Metal recycling based on urban mining needs to be established to tackle the increasing supply risk of critical metals such as platinum. Presently, efficient strategies are missing for the recovery of platinum from diluted industrial process streams, often characterized by extremely low pHs and high salt concentrations. In this research, halophilic mixed cultures were employed for the biological recovery of platinum (Pt). Halophilic bacteria were enriched from Artemia cysts, living in salt lakes, in different salt matrices (sea salt mixture and NH4Cl; 20-210 g L(-1) salts) and at low to neutral pH (pH 3-7). The main taxonomic families present in the halophilic cultures were Halomonadaceae, Bacillaceae, and Idiomarinaceae. The halophilic cultures were able to recover >98% Pt(II) and >97% Pt(IV) at pH 2 within 3-21 h (4-453 mg Ptrecovered h(-1) g(-1) biomass). X-ray absorption spectroscopy confirmed the reduction to Pt(0) and transmission electron microscopy revealed both intra- and extracellular Pt precipitates, with median diameters of 9-30 nm and 11-13 nm, for Pt(II) and Pt(IV), respectively. Flow cytometric membrane integrity staining demonstrated the preservation of cell viability during platinum recovery. This study demonstrates the Pt recovery potential of halophilic mixed cultures in acidic saline conditions.

A method has been developed for the direct (no sample pretreatment and/or isolation of the target element from the sample matrix) Pb isotopic analysis of bioethanol via multi-collector ICP-mass spectrometry (MC-ICP-MS).