Naturally occurring radioactive material and risk assessment of tailings of polymetallic and Ra/U mines from legacy sites.

Old mine tailings from Northern and Central Portugal were studied in order to perform a radiological and chemical characterization. The evaluation of massic activity of natural radionuclides and concentrations in tailings of polymetallic and Ra/U mines was performed by gamma spectrometry and neutron activation analysis. Iron speciation was carried out by Mössbauer spectroscopy. In polymetallic tailings with physical ore processing (Cumieira and Verdes - exploited for Sn, Nb-Ta) higher contents of Th, 228Ra and 226Ra in the coarser materials occur, probably due to their presence in host rock and ore fragments. In finer tailings, washing may explain the lower 226Ra and 210Pb massic activity. In tailings with physical/chemical ore processing (Covas - exploited for W and Sn) high U contents and a tendency for higher 226Ra and 210Pb massic activity in the fine materials is observed, probably due to their incorporation in nano-sized particles of iron oxides. A high variation of the 210Pb/226Ra ratio occurs in polymetallic tailings; a deficit of 210Pb can be observed particularly in deposits of settling tanks drained from dumps of chemically treated ore. In Ervideira-Mestras tailings (Ra/U exploitation) where no ore process in situ was performed, a near equilibrium between 210Pb and 226Ra occurs. Dose risk assessment was carried out by calculating external outdoor Annual Effective Dose Rate; the dose rates in air due to terrestrial gamma radiation are low for the polymetallic tailings (<47 nGy/h), and higher for tailings of Ra/U (up to 4130 nGy/h), in the worst scenario.

Chemical characterization of vines grown in incipient volcanic soils of Fogo Island (Cape Verde).

Climate and rich volcanic soils of Fogo Island (Cape Verde) are optimal conditions for grape agriculture. This study aims a first evaluation of the bioaccumulation of essential and non-essential elements in different parts of vines of the same variety (Vitis vinifera L.), grown on recent pyroclasts and lahar deposits. Chemical composition was obtained by instrumental neutron activation analysis. A general decrease of the chemical contents occurs in the following order: barks, leaves, and grapes. Lower chemical contents were found in the grapes cultivated on the lahar deposit, except for barium. Potassium and bromine are the most accumulated. A tendency for lower transfer coefficients and enrichment factors (EF) of the chemical elements studied occur in vines grown in lahar. Significant EF of the majority of the elements studied were observed, particularly in leaves and grapes. Among the rare earth elements (REE), the heavy ones are significantly enriched in grapes. Slight positive Eu anomalies occur, which can be explained as inherited from the soil, and by a preferential uptake of Eu2+, replacing Ca2+. Among potential harmful chemical elements, significant EF (> 10) for Cr, As, Sb, W, and U in the two vines occur. Although its low concentration, the results obtained point to U bioavailability. The bioaccumulation of some chemical elements in vines from Fogo Island may be due to several factors of geogenic/natural origin, namely soil composition, airborne fine particles, and the climatic conditions of aridity with a potential availability when raindrops fall.