trace mineral content of fungi

[Jhanananda]

Macro and trace mineral constituents and radionuclides in mushrooms: health benefits and risks

Abstract

This article reviews and updates data on macro and trace elements and radionuclides in edible wild-grown and cultivated mushrooms. A huge biodiversity of mushrooms and spread of certain species over different continents makes the study on their multi-element constituents highly challenging. A few edible mushrooms are widely cultivated and efforts are on to employ them (largely Agaricus spp., Pleurotus spp., and Lentinula edodes) in the production of selenium-enriched food (mushrooms) or nutraceuticals (by using mycelia) and less on species used by traditional medicine, e.g., Ganoderma lucidum. There are also attempts to enrich mushrooms with other elements than Se and a good example is enrichment with lithium. Since minerals of nutritional value are common constituents of mushrooms collected from natural habitats, the problem is however their co-occurrence with some hazardous elements including Cd, Pb, Hg, Ag, As, and radionuclides. Discussed is also the problem of erroneous data on mineral compounds determined in mushrooms.

Bioaccumulation in macrofungi

In contrast to vascular plants in which high concentrations of metals are mostly observed above metal-rich soils (Kabata-Pendias 2011), macrofungi can accumulate extremely high concentrations of metallic elements even when growing above soils with low metal contents. Furthermore, macrofungi reveal variable and highly specific ability to take up various trace elements (metallic elements, metalloids, and halogens) from soils and accumulate them in their fruit bodies. The ratio of an element in fruit body to its concentration in soil or, more specifically, to its mobility in soil (i.e., extractability by appropriate chemicals), so-called bioaccumulation factor (BAF), describes the ability of a fungus to accumulate a particular element. Apart from BAF, some other synonymous unit-less terms (transfer rate; transfer factor; transfer coefficient; translocation factor; concentration ratio; enrichment factor; index of bioaccumulatiuon, bioconcentration factor), which are simply a quotient from element concentration distributed between two phases, are also used by authors to estimate the potential of species to accumulate elements from soils or other substratum.

Elements typically accumulated in (at least some) macrofungi (BAF > 1) include Au, Ag, As, Br, Cd, Cl, Cs, Cu, Hg, Rb, Se, V, and Zn. Elements with typically low concentrations in macrofungi (BAF < 1) include Co, Cr, F, I, Ni, Sb, Sn, Th, U, and rare earth elements.

Technical problems related to trace minerals in mushrooms

The truth is that accurate and precise analytical methods are needed when studying any mineral constituent in any abiotic or biotic matrices. In several articles (old and new) on trace minerals in mushrooms, unreliable data were published on elements (Se, Hg, Fe, Co, Cr, V, Ni, Rb, Ba, Cs, Sr, U, Zr and on the rare earth elements such as Ga, Nb, Ce, Th, Nd, and also Li, Cd, and Pb) sequestered in fruit bodies. Regrettably, many of such “dubious” data were published in journals that specialized in trace element research.