Distribution of Ra-226, Th-232 and K-40 in soils and sugar cane crops at Corumbatai river basin, São Paulo State, Brazil

The common use of phosphate fertilizers NPK and amendments in sugar cane crops in Brazilian agriculture may increase the Ra-226, Th-232 and K-40 activity concentrations in soils and their availability for plants and human food chain. Thus, the main aim of this study was to evaluate the distribution of Ra-226, Th-232 and K-40 in soils and sugar cane crops in the Corumbatai river basin, São Paulo State, Brazil. The gamma spectrometry was utilized to measure the Ra-226, Th-232 and K-40 activity concentration in all samples. The soil-to-sugar cane transfer factors (TF) were quantified using the ratio between the radionuclide activity concentration in sugar cane and its activity concentration in soil. The results show that, although radionuclides incorporated in phosphate fertilizers and amendments are annually added in the sugar cane crops, if utilized in accordance with the recommended rates, their use does not lead to hazards levels in soils. The soil-to-sugar cane transfer of radionuclides occurred in the following order K-40 > Ra-226 > Th-232. Therefore, under these conditions, radionuclides intake through consumption of sugar is not hazardous to human health. (C) 2009 Elsevier Ltd. All rights reserved.

Vertical distribution of benthic invertebrate larvae during an upwelling event along a transect off the tropical Brazilian continental margin

Abundance and composition of marine benthic communities have been relatively well studied in the SE Brazilian coast, but little is known on patterns controlling the distribution of their planktonic larval stages. A survey of larval abundance in the continental margin, using a Multi-Plankton Sampler, was conducted in a cross-shelf transect off Cabo Frio (23 degrees S and 42 degrees W) during a costal upwelling event. Hydrographic conditions were monitored through discrete CDT casts. Chlorophyll-a in the top 100 m of the water column was determined and changes in surface chlorophyll-a was estimated using SeaWiFS images. Based on the larval abundances and the meso-scale hydrodynamics scenario, our results suggest two different processes affecting larval distributions. High larval densities were found nearshore due to the upwelling event associated with high chlorophyll a and strong along shore current. on the continental slope, high larval abundance was associated with a clockwise rotating meander, which may have entrapped larvae from a region located further north (Cabo de Sao Tome, 22 degrees S and 41 degrees W). In mid-shelf areas, our data suggests that vertical migration may likely occur as a response to avoid offshore transport by upwelling plumes and/or cyclonic meanders. The hydrodynamic scenario observed in the study area has two distinct yet extremely important consequences: larval retention on food-rich upwelling areas and the broadening of the tropical domain to southernmost subtropical areas. (C) 2009 Elsevier B.V. All rights reserved.