Braeuer et al. 2022 — Quantitative Hg and Se mapping in porcini and parasol mushrooms by LA-ICP-MS
This paper develops and validates a method for spatially resolved, quantitative measurement of Hg and Se in mushroom fruit bodies using laser ablation coupled to ICP-MS (LA-ICP-MS) at pixel sizes down to 5–20 µm. Beyond its methodological contribution, the study provides quantitative bulk Hg and Se concentrations in edible porcini (Boletus edulis, B. aereus, B. pinophilus) and parasol (Macrolepiota procera) mushroom tissue, confirmed against certified reference materials (TORT-3 lobster hepatopancreas, DORM-4 fish protein) using ICP-MS/MS.
Porcini mushrooms are among the most widely consumed wild-harvested edible fungi worldwide and are known to accumulate unusually high Hg concentrations compared to other macrofungi. The study confirms this: Hg in Boletus spp. can reach approximately 20 µg/g dry mass (dm), compared with <0.5 µg/g dm in most other mushroom species. All five porcini individuals showed Hg well above the general macrofungal background. The tolerable weekly intake (TWI) for inorganic Hg is 4 µg/kg body weight per week (EFSA), making high-consumption of porcini a potential route of meaningful Hg exposure. The study also notes that mushroom Hg is predominantly inorganic (>90% inorganic Hg, only minor methylmercury) based on prior literature. Se in porcini is also elevated, at approximately 20 µg/g dm or higher, co-occurring with Hg.
Key numbers
- n = 6 mushroom individuals (5 porcini, 1 parasol); bulk concentrations by ICP-MS/MS.
- Hg in Boletus spp.: up to approximately 20 µg/g dry mass (specific values per individual presented in paper tables).
- Background Hg in most macrofungi: <0.5 µg/g dm.
- Se in porcini: approximately 20 µg/g dm or above (general macrofungal Se typically ~2 µg/g dm or less).
- EFSA TWI for inorganic Hg: 4 µg/kg bw/week.
- Hg speciation context (from prior literature cited): >90% inorganic Hg in porcini.
- Analytical method: LA-ICP-MS (Iridia LA system + Agilent 7900 ICP-MS); LOD 0.006 µg/g for Hg, 0.3 µg/g for Se at 20×20 µm pixel.
- Bulk concentrations verified by ICP-MS/MS (Agilent 8800); CRM recoveries acceptable.
- Basis: dry weight.
Methods (brief)
LA-ICP-MS spatial mapping with external calibration against gelatin-based standards (with l-cysteine additive for Hg stabilization); 193-nm ArF excimer laser. Bulk concentrations by ICP-MS/MS after microwave acid digestion (14 M HNO3, 250 °C). CRM quality control: TORT-3 and DORM-4. In-house reference material prepared from Boletus edulis paste for method validation. Limitation: n = 6 individuals from specific collection sites; does not represent the full geographic or seasonal distribution of porcini Hg content.
Implications
Certification: Porcini mushrooms are a genuine dietary Hg concern for frequent wild mushroom consumers. Hg at ~20 µg/g dm in porcini is roughly 40× the background level and represents a meaningful weekly intake contribution in mushroom-consuming cultures (Czech Republic, Italy, France, Germany). HMT&C certification of mushroom products should address Hg as a primary analyte. Courses: Illustrates species-dependent bioaccumulation; mushrooms as an overlooked Hg source in non-seafood dietary exposure; the Hg-Se antagonism in biological systems. App: Mushroom/fungi contamination profile — Hg as primary metal of concern; porcini specifically as high-Hg commodity.