Nickel (Ni) contamination in wild mushrooms represents a potential, yet underexplored, route of human exposure to this metal. This study investigates Ni concentrations in wild mushrooms foraged across Leicester (England) and evaluates the associated oral exposure risks from consuming edible species. 106 mushrooms were collected, including 95 from urban areas and 11 from the nearby Bradgate Park. Species identification was confirmed through DNA barcoding, using DNA extracted from 100 mg of homogenised mushroom material with the DNeasy Plant Mini Kit^©. Nickel concentrations were determined via ICP-MS, following sample preparation involving cleaning, drying, and homogenisation, with a detection limit of 3.40 mg/kg dry weight. Due to a high proportion of censored data (56.8%), the NADA package in R was employed for data analysis.

The findings revealed considerable variability in Ni concentrations among mushroom species, with levels ranging from below detection to 90.50 mg/kg (mean 7.67 ± 13.94 mg/kg). Spatial differences were also observed within the urban sampling zones, with the lowest Ni levels detected in the North West quadrant and the highest in the South East (p<0.05). Notably, Ni was undetectable in key edible species such as Agaricus bitorquis and Marasmius oreades. In contrast, elevated levels were found in toxic species like Panaeolus foenisecii (up to 26.42 mg/kg), Coprinus atramentarius (up to 90.50 mg/kg), and Mycena citrinomarginata (up to 76.43 mg/kg). Previous studies reporting trace Ni levels in Agaricus species from other regions, such as Croatia, align with these observations and suggest limited contamination in Leicester. Moreover, the calculated bioconcentration factor was below unity (0.2), indicating minimal accumulation relative to local topsoil concentrations.

Overall, these results indicate that the risk of nickel exposure through the consumption of wild edible mushrooms collected in Leicester is negligible. However, continued monitoring is recommended to ensure consumer safety and to better understand the environmental dynamics influencing metal uptake in wild fungi.