Presenza di radionuclidi naturali ed artificiali nell’area Bosco Negri - 3: Distribuzione e migrazione di elementi maggiori ed in tracce nei suoli, risultati dell’analisi per attivazione neutronica strumentale ed elaborazione statistica

Concentrations of major, minor and trace elements are determined, in soils of the Siro Negri forest, with neutron activation analysis. The aim of this work is the characterization of the chemical composition of the soils and the valuation of eventual anthropic contributions. For this purpose we have determined 36 elements concentrations in the three sampling areas (station A: North-East; B: central part of the forest and C: South-West). In the present work we have discussed the results of the concentrations of four major elements (Fe, Ca, Na and K), eight trace elements (As, Sb, Cr, Ni, Zn, Se, Ba, Co) and rare earth elements (REE: from La to Lu). The iron’s concentration is higher in the station A (about 3%) and lower in the station B; calcium (from 1,2 to 1,4%), sodium (from 1,7 to 2,3%) and potassium (about 2%) have concentrations higher in the South-East part of forest. In this work we discussed the distribution and migration of some trace elements such as: antimony, chromium, nickel, zinc, selenium, barium and cobalt. The antimony concentration decreases from North to South in the forest (from 1,2 to 0,6 g/g); the chromium concentration increases from North to South (from 91,4 to 95,4 g/g); the nickel concentration increases from the station A to station B (from 28,3 to 29,3 g/g) and decreases from the station B to station C (from 29,3 to 27,7 g/g). The zinc concentration is highest in the station C (101 g/g), lower in the stations A and B (about 81 g/g), however the zinc enrichment not depends on the anthropic factors but it's result of an horizontal migration caused by the water river transport. The selenium is a very rare element in nature, its concentration in forest soil is about 2,5 g/g. The distribution of the barium concentrations in pedological profile of the three sampling station is linear; the mean concentration is lower in station B (314,8 g/g), interim in station A (336,5 g/g) and higher in the station C (414,9 g/g). An anomalous value for concentration of this element has been determined at the depth of 125 cm in the station B. At this depth barium concentration's is similar to the mean concentration in the station C (about 420 g/g). The cobalt concentration's decrease is progressive from North to South in the forest soils (from 13,2 to 10,5 g/g). The rare earth elements concentration (from La to Lu) decreases from North to South; the amount of the LREE (light rare earth: from La to Eu) is lower in station B while the amount of the HREE (Heavy Rare Earth: from Gd to Lu) is lower in station C.The statistical analysis showed major simile between soils of the stations A and B. This result can be attributed to the presence of the same coverage plant in the stations North and central.