A microwave acid digestion method prior to the determination of 21~ and 21~ in sediments and soils is described. It involves an acid (HNO3, HC1, HF and H3BO 3 mixture) digestion with microwave heating in closed vessels at high pressures. Analyses carried out for various reference materials showed that the results were statistically equal to certified values and reproducibility was also assured. The advantage of the microwave technique compared to the traditional leaching procedures is that the solid materials are completely dissolved and, therefore, ca. 100% efficiency is achieved in the extraction of 21~ and 21~ even though a fraction is associated to the silica net. Moreover, time of analysis is drastically reduced, as are the risks associated to vapour inhalation and material corrosion.

Variations in Pb concentration in lake sediments reflect changes in the fluxes of this element in the• past. A sediment core from a lake in the Pyrenees (Lake Redo at 2,240 m a.s.L, N_E Spain) was studied, with the aim of reconstructing pastenvironmenial and climatic conditions in the lake and its catchment area. The core was dated usii1g both 210 Pb and 14 C. A surface peak of Pb concentration, which was about 10 tim~s higher than the background level, was found. This peak is attributed to mining activities since the begioping of this century. Although Pb pollution due to the combustion of gasoline is expected to be present, no evidence can be deduced from Pb isotope ratios of sediment due to the masking effect of Pb from mines. A second peak appeared in a deeper layer, with a maximum Pb concentration of about 17 times higher than the background level. The origin of this peak is unclear. All evidence suggests that the ancient peak is due to mining operations in the central Pyrenees area, which were not documented historically.

No abstract

One of the most widely used radionuclides in the study of recent sedimentation processes is 210Pb. Its depth profile in sediments is used as input for various dating models, which provide chronologies, mass fluxes, and sedimentation rates. In this work we revisited the CRS (constant rate of supply) model, widely used for dating sediments through 210Pb. A more general hypothesis (periodic flux [PF]) was proposed and, although it confirmed the validity of CRS chronology, a detailed analysis of the mass sedimentation formula pointed out an inconsistency of the cited model. A new mass sedimentation formula was proposed and validated with a lake sediment core and four marine sediment cores.

Variations in Pb concentration in lake sediments reflect changes in the fluxes of this element in the• past. A sediment core from a lake in the Pyrenees (Lake Redo at 2,240 m a.s.L, N_E Spain) was studied, with the aim of reconstructing pastenvironmenial and climatic conditions in the lake and its catchment area. The core was dated usii1g both 210 Pb and 14 C. A surface peak of Pb concentration, which was about 10 tim~s higher than the background level, was found. This peak is attributed to mining activities since the begioping of this century. Although Pb pollution due to the combustion of gasoline is expected to be present, no evidence can be deduced from Pb isotope ratios of sediment due to the masking effect of Pb from mines. A second peak appeared in a deeper layer, with a maximum Pb concentration of about 17 times higher than the background level. The origin of this peak is unclear. All evidence suggests that the ancient peak is due to mining operations in the central Pyrenees area, which were not documented historically.