On the possible role of macrofungi in the biogeochemical fate of uranium in polluted forest soils.

Interactions of macrofungi with U, Th, Pb and Ag were investigated in the former ore mining district of Príbram, Czech Republic. Samples of saprotrophic (34 samples, 24 species) and ectomycorrhizal (38 samples, 26 species) macrofungi were collected from a U-polluted Norway spruce plantation and tailings and analyzed for metal content. In contrast to Ag, which was highly accumulated in fruit-bodies, concentrations of U generally did not exceed 3mg/kg which indicates a very low uptake rate and efficient exclusion of U from macrofungi. In ectomycorrhizal tips (mostly determined to species level by DNA sequencing), U contents were practically identical with those of the non-mycorrhizal fine spruce roots. These findings suggest a very limited role of macrofungi in uptake and biotransformation of U in polluted forest soils. Furthermore, accumulation of U, Th, Pb and Ag in macrofungal fruit-bodies apparently does not depend on total content and chemical fractionation of these metals in soils (tested by the BCR sequential extraction in this study).

Uranium, thorium and rare earth elements in macrofungi: what are the genuine concentrations?

Concentrations of uranium, thorium and rare earth elements (REE) in 36 species of ectomycorrhizal (26 samples) and saprobic (25 samples) macrofungi from unpolluted sites with differing bedrock geochemistry were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Analytical results are supported by use of certified reference materials (BCR-670, BCR-667, NIST-1575a) and the reliability of the determination of uranium was verified by epithermal neutron activation analysis (ENAA). It appears that data recently published on these elements are erroneous, in part because of use of an inappropriate analytical method; and in part because of apparent contamination by soil particles resulting in elevated levels of thorium and REE. Macrofungi from unpolluted areas, in general, did not accumulate high levels of the investigated metals. Concentrations of uranium and thorium were generally below 30 and 125 µg kg(-1) (dry weight), respectively. Concentrations of REE in macrofungi did not exceed 360 µg kg(-1) (dry weight) and their distribution more or less followed the trend observed in post-Archean shales and loess.

Bioaccumulation of silver in ectomycorrhizal and saprobic macrofungi from pristine and polluted areas.

Macrofungi are effective accumulators of Ag. This study provides a comprehensive review of this phenomenon supported by original data on the Ag concentrations of macrofungi from pristine and Ag-polluted areas. In pristine areas, the median Ag concentrations of ectomycorrhizal (ECM) and saprobic (SAP) macrofungi were 0.79 and 2.94 mg kg(-1), respectively. In these areas, hyperaccumulation thresholds for Ag in ECM and SAP macrofungi are proposed as 100 and 300 mg kg(-1), respectively. In a Ag-polluted area, the Ag concentrations in macrofungi (ECM and SAP) were significantly elevated with the median value of 24.7 mg kg(-1) and the highest concentrations in Amanita spp. of the section Vaginatae (304-692 mg kg(-1)). The intracellular speciation of Ag in fruit-bodies of the Ag-accumulator Amanita submembranacea was inspected by size exclusion chromatography followed by sulfhydryl-specific fluorimetric assays of ligands using reverse phase high-performance liquid chromatography and improved polyacrylamide gel electrophoresis. Virtually all Ag was found to be intracellular and sequestered in the major 7 kDa and minor 3.3 kDa complexes. The lack of glutathione and phytochelatins and the presence of a single 3 kDa sulfhydryl-containing peptide in the isolated Ag-complexes suggest that detoxification of Ag in A. submembranacea may rely on metallothionein. Vertical distribution of Ag in a polluted forest soil profile has shown substantial enrichment in organic horizons; in polluted technosol, the highest Ag concentrations were found in surface layers. Standardized EDTA extraction of Ag in both the investigated soil profiles showed relatively low Ag extractibility, generally within the range of 2.2-7.7% of total Ag content.

Hyperaccumulation of silver by Amanita strobiliformis and related species of the section Lepidella.

Two ectomycorrhizal macrofungal Amanita species of the section Lepidella, A. strobiliformis and A. solitaria, were found to hyperaccumulate silver (Ag). All samples were collected from non-argentiferous areas with background Ag content in soils (0.07-1.01 mgkg(-1) Ag). The Ag contents of both Amanita species were mostly in the range of 200-700 mgkg(-1)D.W. with the highest Ag content of 1253 mgkg(-1) in one sample of A. strobiliformis. Silver concentrations in macrofungal fruit bodies were commonly 800-2500 times higher than in underlying soils. A. strobiliformis and A. solitaria are the first eukaryotic organisms known to hyperaccumulate Ag.