Content of lutetium in wild soil mushrooms from Leicester city and surroundings areas in England

Background: Although the ingestion of and dermal contact with lutetium (Lu) has recently been measured in topsoils across Leicester (UK) and surrounding rural areas as low risk, this heavy rare earth element (HREE) was biomonitored in wild mushrooms.

Methods: A total of 106 mushrooms were collected from Leicester city and Bradgate Park. Species identification was confirmed by DNA barcoding. Lu was monitored by ICP-MS in cleaned/dried/homogenised mushrooms [LoD=0.506 ng/g dry weight (dw)] and in topsoils collected in these areas; physicochemical properties and textures were also determined in topsoils using standard methods. The data were processed with NADA available in R software, owing to the censored values detected in mushrooms (60.8%).

Results: Contrary to the distribution determined in topsoils [0.123 (0.069-0.162) vs. 0.117 (0.084-0.182); median and ranges, mg/kg], the levels of Lu were higher in mushrooms collected in the main urban area (median and ranges, in ng/g dw): 0.347 (0.285-293.837) vs. 0.196 (0.780-8.116). The content of Lu in topsoils would only have a small effect on the levels of Lu detected in mushrooms, which is supported by the lack of correlation found between mushrooms and topsoils (p-value=0.506) and by the different physicochemical properties and soil textures monitored. This pattern is different to other HREEs studied in the same areas, which might be explained by an unknown appetence for Lu by the different local species of wild soil mushrooms collected. Lu also varied between major mushroom species collected (median or 95-percentile and range, in ng/g): Agaricus bitorquis [edible; 88.6% of censored values, 1.518 (0.798-6.715), Panaeolus foenisecii [poisonous; 1.740 (0.812-49.692)], and Mycena citrinomarginata [unclassified; 0.855 (0.285-10.351)]. Lu also seemed to show little appetence for wild edible species when comparing with non-edible.

Conclusions: Although our results should be considered as preliminary, in general, collecting local wild edible mushroom species in Leicestershire would represent a small risk for humans due to their content of lutetium.