Rare Earth Elements in Boletus edulis (King Bolete) Mushrooms from Lowland and Montane Areas in Poland

Rare earth contamination of edible vegetation: Ce, La, and summed REE in fungi

The increasing and diversified use of rare earth elements (REE) is considered a potential source of pollution of environmental media including soils. This work documents critically overview data on the occurrence of REE in the fruiting bodies of wild and farmed species of edible and medicinal mushrooms, as this was identified as the largest published dataset of REE occurrence in foodstuff. Most of the literature reported occurrences of cerium (Ce) and lanthanum (La), but a number of studies lacked data on all lanthanides. The Ce, La, and summed REE occurrences were assessed through the criteria of environmental geochemistry, analytical chemistry, food toxicology, mushroom systematics, and ecology. Ce and La accumulate similarly in fruiting bodies and are not fractionated during uptake, maintaining the occurrence patterns of their growing substrates. Similarly, there is no credible evidence of variable REE uptake because the evaluated species data show natural, unfractionated patterns in accordance with the Oddo-Harkins' order of environmental lanthanide occurrence. Thus, lithosphere occurrence patterns of Ce and La as the first and the third most abundant lanthanides are reflected in wild and farmed mushrooms regardless of substrate and show that Ce is around twice more abundant than La. The current state of knowledge provides no evidence that mushroom consumption at these REE occurrence levels poses a health risk either by themselves or when included with other dietary exposure. Macromycetes appear to bio-exclude lanthanides because independently reported bioconcentration factors for different species and collection sites, typically range from < 1 to 0.001. This is reflected in fruiting body concentrations which are four to two orders of magnitude lower than growing substrates. KEY POINTS: •Original REE occurrence patterns in soils/substrates are reflected in mushrooms •No evidence for the fractionation of REE during uptake by fungi •Mushrooms bio-exclude REE in fruiting bodies.

A critical review of the occurrence of scandium and yttrium in mushrooms

Scandium (Sc) and Yttrium (Y) along with the other rare earth elements (REE) are being increasingly extracted to meet the escalating demand for their use in modern high technology applications. Concern has been voiced that releases from this escalating usage may pollute environments, including the habitats of wild species of mushrooms, many of which are foraged and prized as foods. This review collates the scarce information on occurrence of these elements in wild mushrooms and also reviews soil substrate levels, including forested habitats. Sc and Y occurred at lower levels in mushrooms (<1.0-1000 µg kg-1 dw for Sc and<1.8-1500 µg kg-1 dw for Y) compared to the corresponding range for the sum of the lanthanides in the same species (16-8400 µg kg-1 dw). The reported species showed considerably more variation in Y contents than Sc which show a narrow median distribution range (20-40 µg kg-1 dw). Data allowing temporal examination was very limited but showed no increasing trend between the 1970s to 2019, nor were any geographical influences apparent. The study of the essentiality, toxicity or other effects of REE including Sc and Y at levels of current dietary intake are as yet undefined. High intake scenarios using the highest median concentrations of Sc and Y, resulted in daily intakes of 1.2 and 3.3 μg respectively from 300 g portions of mushroom meals. These could be considered as low unless future toxicological insights make these intake levels relevant.

The Nutrients and Volatile Compounds in Stropharia rugoso-annulata by Three Drying Treatments

This study aimed to examine the differences in the nutrients and volatile compounds of Stropharia rugoso-annulata after undergoing three different drying treatments. The fresh mushrooms were dried using hot air drying (HAD), vacuum freeze drying (VFD), and natural air drying (NAD), respectively. After that, the nutrients, volatile components, and sensory evaluation of the treated mushrooms were comparably analyzed. Nutrients analysis included proximate compositions, free amino acids, fatty acids, mineral elements, bioactive compositions, and antioxidant activity. Volatile components were identified by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and analyzed with principal component analysis (PCA). Finally, sensory evaluation was conducted by ten volunteers for five sensory properties. The results showed that the HAD group had the highest vitamin D₂ content (4.00 μg/g) and antioxidant activity. Compared with other treatments, the VFD group had higher overall nutrient contents, as well as being more preferred by consumers. Additionally, there were 79 volatile compounds identified by HS-SPME-GC-MS, while the NAD group showed the highest contents of volatile compounds (1931.75 μg/g) and volatile flavor compounds (1307.21 μg/g). PCA analysis suggested the volatile flavor compositions were different among the three groups. In summary, it is recommended that one uses VFD for obtaining higher overall nutritional values, while NAD treatment increased the production of volatile flavor components of the mushroom.

Scandium, yttrium, and lanthanide occurrence in Cantharellus cibarius and C. minor mushrooms

There is a dearth of data on rare earth elements (REE), yttrium and scandium in foods which extends also to baseline datasets for edible wild mushrooms, though this has started to change in the last decade. Concentrations and shale normalized patterns of REE and Y (REY) were studied by using inductively coupled plasma-quadrupole mass spectrometer in 22 pools (2235 specimens) of Cantharellus cibarius (Golden Chanterelle) collected in Poland and also a pool of C. minor (Small Chanterelle) (153 specimens) from Yunnan (Chinese Province). The total REY plus Sc varied in C. cibarius from 10 to 593 µg kg^-1 dw whereas that for the Yunnan's C. minor was 2072 µg kg^-1 dw. C. minor from Yunnan has higher REY and Sc compared to the C. cibarius. Sc concentrations in twenty C. cibarius pools were below 1 µg kg^-1 dw, but 17 and 27 µg kg^-1 dw were detected at the other two sites and 66 µg kg^-1 dw was detected in C. minor. The median Y content of C. cibarius and C. minor was 22 µg kg^-1 dw and 200 µg kg^-1 dw. The difference in REY and Sc concentrations and shale normalized patterns between mushrooms from Poland and Yunnan seems to reflect the regional difference in concentration and composition of these elements in the soil bedrock.

Letter to the editor: Comment on "multiannual monitoring (1974-2019) of rare earth elements in wild growing edible mushroom species in Polish forests" by Siwulski et al. https://doi.org/10.1016/j.chemosphere.2020.127173. A recurring question - What are the real concentrations and patterns of REE in mushrooms?

Siwulski et al. (2020) investigated the occurrence of the lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), scandium (Sc) and yttrium (Y) in 4 species of wild mushrooms, which were sampled over a 45 years period in Poland. The reported mean lanthanide concentrations for mushrooms were in the range from 539 to 1601 μg kg^-1 dry weight. These values are considered as highly elevated in the light of data published earlier for the same species, where the analytical results were assessed as not being biased by errors (these could arise from contamination of the samples with soil dust or unsuitable choice of analytical methodology including the use of unsuitable analytical instrumentation for measurement). It has long been established that the lanthanides are naturally distributed in ores, soil bedrock, soils, natural waters and plants in a pattern that reflects the Oddo-Harkins rule. This pattern is correspondingly reflected in fungi, including the same species and have been published earlier by other authors. However, when the individual lanthanide concentration data of B. edulis, I. badia, L. scabrum and M. procera from the study by Siwulski et al. are plotted, they do not display the expected sawtooth (zigzag) concentration pattern - in other words, the concentration data do not follow the Oddo-Harkins rule. Lanthanides are naturally found in very low concentration in foods including wild mushrooms. There is a striking lack of convergence in the results obtained for ICP-MS techniques, and the results obtained from ICP-OES measurement (as used by Siwulski et al.). If the reasons discussed here for anomalies in the reported lanthanides data hold true, how does this affect the data for other elements in mushrooms reported in the commented article?

Comment on "Worldwide basket survey of multielemental composition of white button mushroom Agaricus bisporus": The credibility of the concentration data reported for REE are questioned - are they reliable enough to be included in the database on nutrients in mushrooms?

The focus of this comment is on the Lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) which, together with Sc and Y are also called the rare earth elements (REE). Individual REE have similar chemical properties and can be treated as a group. They behave similarly in the environment and in food webs. However, the determination of REE in foods, including edible mushrooms is analytically very challenging. In study by Siwulski et al. (2020) concentrations were reported for Ce, Nd, Sm, La, Sm and Tm, but the others were not detected above the method quantification limit. The sum of Ce (340-2730 μg kg^-1 dw), Nd (10-1220 μg kg^-1 dw), Sm (10-420 μg kg^-1 dw), La (10-130 μg kg^-1 dw), Sm (10-420 μg kg^-1 dw), Tm (10-170 μg kg^-1 dw) in 32 samples of A. bisporus was in the range of 430-3510 μg kg^-1 dry weight. The first visible characteristic is a large difference in the concentrations of Ce, Nd, Sm, La and Tm between the A. bisporus samples and various wild species and cultivated Cyclocybe cylindracea and Pleurotus ostreatus. Secondly, there is no correspondence with the Oddo-Harkins order and the concentrations pattern of Ce, Nd, Sm, La and Tm reported for the A. bisporus samples. The pattern is clearly different from that observed in the wild mushrooms and the two cultivated species reported by other studies. The ICP-OES and also the low resolution ICP-MS determination of REE directly from a fungal digest can suffer from spectral interferences of different types including an effect of the matrix which have to be overcome in the course of reliable and controlled analysis of REE.

Comment on “Screening the Multi-element Content of Pleurotus Mushroom Species Using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES)”

La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are lanthanides, also referred to as “rare earth” elements (occurring at ultra-low concentration, i.e. each, at ppb or lower levels) in plant and animal foods including edible wild mushrooms. Could it be that lanthanides when collectively reported as a summed value (widely referred to as REE) are at relatively high concentrations because extremely high contributions from individual elements? REE elements naturally occur in environmental media such as the soil substrate in which plants and fungi grow in a characteristic pattern (Oddo-Harkins rule), with most of the available literature confirming the extension of this pattern in fungi. Abnormalities therefore need to be examined closely and resolved.

Occurrence, bio-concentration and distribution of rare earth elements in wild mushrooms

Using validated methodology, this study explores the bioconcentration potential and status of rare earth elements (REE) and yttrium (Y) in wild mushrooms collected from Belarus, China and Poland and in the associated forest topsoil. Baseline data for REE and Y distributions in the morphological parts of the fruiting bodies of Caloboletus calopus, Cantharellus cibarius, Craterellus cornucopioides, Imleria badia, Laccaria amethystina, Lactifluus piperatus, Leccinum scabrum and Suillus grevillei are presented. REE were in the range of 14 to 42 mg kg^-1 dw in forest topsoil and from 35 to 48 mg kg^-1 dw in profiled soil layers from the Sobowidz site in Poland. Forest topsoil sampled in Belarus contained 67 mg kg^-1 dw. Yttrium concentrations in soil ranged from 2.9 to 10 mg kg^-1 dw. The median REE concentration in wild mushrooms was around 200 μg kg^-1 dw (20 μg kg^-1 fresh weight). This implies negligible dietary intake even for high level consumers. The bioconcentration factors (BCF) of individual REE and Y ranged from 0.0002 to 0.0229, showing bio-exclusion. The BCF tended to be similar for groups of REE (La to Tb and Dy to Lu) depending on the mushroom species and site. REE from Dy to Lu were better bioconcentrated than those from La to Tb. The similarity of the BCFs of individual REE by species at a given site implies the same absorption pathway, although a lower concentration in the topsoil favoured bioconcentration. REE and Y concentrations varied between species as well as within the same species between sites. Their accumulation in mushrooms appears to reflect condition at the site of collection, and may also be species-specific but confirming this would require further investigation of different species, topsoils and sites.