Lead isotope ratios as tool for elucidation of chemical environment in a system of Macrolepiota procera (Scop.) Singer - soil

The analysis of isotope ratios of lead in the mushrooms and soil, where they were grown, assisted with a principal component analysis, offered a new perspective for understanding possible chemical environment in a real setup of those compartments. The content of lead and its isotope compositions were determined in soil samples and mushroom Macrolepiota procera from unpolluted area of Mountain Goč, Serbia. Sequential extraction procedure based on the Commission of the European Community Bureau of Reference (BCR) was applied on soil samples in order to determine the distribution of lead in the labile and un-labile fractions of the soil. Caps and stipes of mushrooms were subjected to microwave acid-assisted digestion prior to measurements by inductively coupled plasma quadrupole mass spectrometer for determination of lead content and lead isotope ratios. Information about the chemical fractionation of Pb in soil, Pb isotopic data from soil fractions and fruiting bodies allowed a more detailed insight on the uptake mechanisms. Lead was predominantly associated with reducible fraction (~ 60%). Only its small portion (∼ 1%) was present in the exchangeable and acid-extractable fractions suggesting the low mobility of Pb. Lead isotope analysis revealed the presence of anthropogenic lead in the surface soil. Significant lower ²⁰⁶Pb/²⁰⁷Pb compared with other fractions was found in exchangeable and acid-soluble fraction (1.331 ± 0.010), which corresponds to the isotope ratio of European gasoline. The highest ²⁰⁶Pb/²⁰⁷Pb ratio was observed in reducible fraction (1.162 ± 0.007), while in oxidizable and residual fraction, those values were similar (1.159 ± 0.006 and 1.159 ± 0.004, respectively). Distinction of exchangeable and acid-extractable fractions from others was also confirmed, for the first time, by principal component analysis. The analysis of four isotope ratios (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁶Pb/²⁰⁴Pb, and ²⁰⁷Pb/²⁰⁴Pb) indicated that the analyzed M. procera accumulates lead from the first two fractions of topsoil layers.