Biomonitoring the heavy rare earth of ytterbium in wild soil mushrooms: potential risks

Rare earth elements are widely distributed in foods. Although the biological role of ytterbium (Yb) is unknown, is said to stimulate metabolism. The presence/distribution in topsoils from Leicestershire (UK) are shown to represent some risks for the population. In detail, 106 wild mushrooms were collected from Leicester city and Bradgate Park. Yb was monitored by ICP-MS in cleaned/dried/homogenised mushrooms [LoD=0.57 ng/g dry weight (dw)]. Mushrooms collected in Bradgate showed higher levels of Yb (median and ranges, in µg/g dw): 1.76 (0.29-56.33) vs. 1.47 (0.45-300.95). These results could be explained by the levels in topsoils, which were slightly higher in those collected in the rural areas [0.90 (0.49-1.14) vs. 0.83 (0.62-1.21); all in mg/kg)]. Similarly, levels of Yb were higher than those monitored in edible mushrooms collected in Poland’s forests (0.01-0.21 mg/kg dw), which were collected in topsoils with lower contamination of this element (0.02-0.42 mg/kg). Our results might suggest similar sources of this element throughout Leicestershire, although no correlation was found between topsoils and mushrooms (p-value=0.58). The content of clay might explain the distribution of Yb in the mushrooms collected in the urban areas. Thus, mushrooms with a higher content of Yb were found in those picked up in the NE area versus the NW of the city (4.38 vs. 0.98 µg/g dw), as clay content was significantly higher in topsoils sampled in the NE (27 vs. 18.5%). However, we did not see any significant correlations between the Yb levels in mushrooms and topsoils for any of the soil properties/textures determined. Yb also varied between major mushroom species collected (median and range, in µg/g): Agaricus bitorquis [edible; 0.92 (0.90-7.69), Panaeolus foenisecii [poisonous; 4.24 (1.13-176.82)] and Mycena citrinomarginata [unclassified; 6.61 (1.58-76.74)]. Although no limits have been established for Yb in edible mushrooms as yet, its presence would represent a minimal risk for Leicester’s population.