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71.
Humberto Terrazas Salas Hermínio Arias Nalini Jr. Júlio César Mendes 《Environmental Geology》2006,49(4):520-526
One hundred samples of granitic rock were collected from granite traders in Belo Horizonte. Autoradiography, optical microscopy,
diffractometry, and chemical analysis (X-ray spectrometry, X-ray fluorescence, neutron activation, gravimetry, and electron
probe microanalysis) were used to determine the mineral assemblages and lithotypes. Autoradiographic results for several samples
showed the presence of monazite, allanite, and zircon. Chemical analysis revealed uranium concentrations ≤30 ppm and thorium
≤130 ppm. Higher concentrations generally correlated with high concentrations of light rare earths in silica-rich rocks of
granitic composition. Calculations were made of radioactive doses for samples, of floor tiles in a standard room, with total
concentration of uranium and thorium greater than 60 ppm. On the basis of calculations of 232 Th, 40 K, and 226 Ra from analysis of Th, K, and U, the doses calculated were between 0.11 and 0.34 mSv/year, which are much lower than the
acceptable international exposure standard of 1.0 mSv/year. 相似文献
72.
Assessment of the distribution of sponge chips in the sediment of East Pacific Ocean reefs
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Jose Luis Carballo Humberto Ovalle‐Beltrán Benjamin Yáñez Eric Bautista‐Guerrero Héctor Nava‐Bravo 《Marine Ecology》2017,38(1)
Sponges are one of the principal agents of bioerosion and sediment production in coral reefs. They generate small carbonate chips that can be found in the sediments, and we investigated whether these could provide a means for assessment of bioerosion applicable to reef monitoring. We tested this hypothesis on samples from 12 Mexican coral reefs distributed along the Pacific coast, where boring sponges were particularly abundant, and quantified the amount of chips in samples of superficial sediment in three grain‐size fractions: fine (<44 μm), medium (44–210 μm) and coarse (>210 μm). The grain‐size distribution varied among reefs, with the majority of the sediment of most reefs being composed of coarse sands, and the medium and fine fractions dominating only at La Entrega and Playa Blanca. All the reefs presented clear evidence of bioerosion by sponges, with the characteristic chips present in the sediment, although at most sites the percentage of chips was very low (from 1% to 3% of the total sediment). Only at La Entrega and Playa Blanca did they constitute a significant fraction of the total sediment (18% and 16%, respectively). While not statistically significant, there was an interesting trend between sponge chips versus sponge abundance that suggests that quantification of the chips in the sediment could be used as a proxy for sponge erosion of the entire community, which cannot be estimated in by laboratory experiments. However, while this methodology could provide an integrated approach to monitor sponge bioerosion, more studies are necessary due to the influence of environmental factors on the transport and deposition of these chips. 相似文献