| Přispěvatelé: |
Armiento, G, Bellatreccia, Fabio, Cremisini, C, DELLA VENTURA, Giancarlo, Nardi, E, Pacifico, R, Petrini, E. |
| Popis: |
Beryllium is widely distributed in soils at low levels (crustal abundance 2-6 mg/kg), but it can also occur naturally in higher concentrations in a variety of materials exploited for many industrial applications. Unfortunately, beryllium is also one of the most toxic natural elements and is known to be a human carcinogen. We report and analyse a diffuse, unusually high (up to 80 mg/kg, average approximately 18 mg/kg), natural occurrence of beryllium in pyroclastic layers related to the Pleistocene activity of the Vico volcano (northern Latium). The naturally occurring beryllium content in most of the studied samples is extremely high and even greater than that found in sites contaminated by the accidental release of beryllium into the environment by industrial activities. Only 8 out of the 120 analysed samples gave values below the Italian limit for potentially unacceptable risk for industrial soil-use (10 mg/kg); in no case values below the limit for residential soil-use (2 mg/kg) were observed. Additionally, experiments to define Be leachability have been carried out for selected samples, providing evidence of significant mobility in contrast with data presented in the literature that indicate beryllium as an element with low mobility in oxidising surface environmental conditions. This is a crucial point to consider, because a relatively high mobility under certain pH and redox conditions involve a significant risk factor. The geochemical behaviour of the element explains the anomalous Be concentration values because its incompatibility in common rock-forming silicate minerals is concentrated via fractionation during magma crystallisation. An additional contribution may be related to the volcanic late-stage fluids permeating through the emplaced rocks. Combined mineralogical (optical microscopy, SEM-EDAX, EMPA and X-ray diffraction) and geochemical analyses suggests that the higher beryllium concentration in pyroclastics and associated soils are related to the presence of finely dispersed Be-containing minerals, such as gadolinite (Cámara et al., 2008), or hellandite-group minerals (Oberti et al., 2001). However, the possible presence of Be in volcanic glasses is also presently under investigation. Finally the occurrence of such natural high background concentrations of potentially harmful elements, as it is the case for beryllium studied here, highlights the need for systematic geochemical studies and mapping to produce multi-purpose reference databases for risk assessment and land management. Cámara, F., Oberti, R., Ottolini, L., Della Ventura, G., Bellatreccia, F. (2008) American Mineralogist, 93, 996-1004. Oberti, R., Ottolini, L., Camara, F., Della Ventura, G. (1999) American Mineralogist, 84, 913-921. |
