RESUMO
We demonstrate the production of cryogenic beams of heteronuclear molecules from the matrix isolation sublimation (MISu) technique. A sapphire mirror serves as a substrate whereupon a solid Ne matrix is grown. Atoms of Li, H, Ca, and C are implanted into the matrix via subsequent laser ablation of different solid precursors such as Ca, Li, LiH, and graphite. The matrix is sublimated into vacuum generating a cryogenic beam of Ne carrying the previously isolated neutral atomic and molecular species. A compact and low energy electron source and time-of-flight mass spectrometer was designed to fit this system at low temperature. With electron ionization time-of-flight mass spectrometry, we analyze the species coming from MISu and demonstrate the formation of heteronuclear molecules in the matrix. In this first study, we produced LiCa from the sequential implantation of Li and Ca into the matrix and some clusters of CnLim after Li and C ablation. Also from ablation of a single LiH pellet, we observed clusters of LinHm. This novel technique opens up the opportunity to generate cryogenic beams of different molecules for precision physics and chemistry studies. Laser or microwave high resolution spectroscopy of a molecular beam benefits from low translational and rovibrational temperatures and forward velocities, such as the ones produced in this technique. Toward the prospect of enhancing the molecular formation, we introduce a new method to study the atomic diffusion of Li and Ca in the Ne matrix via laser spectroscopy during sublimation. We estimate a small diffusion coefficient at 7 K, but a surprisingly linear atomic dispersion during sublimation. The method is extensive to other species and matrices.
RESUMO
Blooms of cyanobacteria in water bodies cause serious environmental problems and the occurrence of toxic strains are also related with the human health. Aquatic animals could bioaccumulate microcystins (cyanobacteria hepatotoxins) and so, beyond water, the ingestion of contaminated food represents a human health risk. Recently, WHO recommended a maximum concentration of microcystins (MCYSTs) in drinking water and established the tolerable daily intake (TDI) for consumption of cyanobacteria products contends MCYSTs (0.04 microg(-1) kg(-1) day(-1)). Sepetiba Bay is located in the municipal districts of Rio de Janeiro, Mangaratiba and Itaguai; being an important place of fishing activity. Due to the industrial development in the area, this bay is submitted to different environmental impacts, increasing the organic and industrial pollution. A strain of the nanoplanktonic cyanobacteria Synechocystis aquatilis f. aquatilis that produce MCYSTs was already isolated. In this study, we verified MCYSTs presence in muscle tissue of fish and crustaceans, which were harvested monthly in Sepetiba Bay during 11 months, in order to evaluate the potential risk of their ingestion. MCYSTs were analyzed by immunoassay techniques using the ELISA Microcystin Plate Kit (ENVIROLOGIX INC) and the concentration were expressed as microcystin-LR equivalent. The analyses of seston samples, water, muscle tissues showed the presence of this cyanotoxin in all samples and it was verified that 19% of the animals' samples were above the limit recommended by WHO for human consumption. The maximum value found was of 103.3 microg kg(-1) (TDI 0.52 microg kg(-1) day(-1)) and the minimum, was 0.25 microg kg(-1) in crabs muscle tissue (TDI of 0.001 microg kg(-1) day(-1)). Such data demonstrate that, although in low concentrations, there is already a contamination of fish and crustaceans from Sepetiba Bay. We highlight that the recommended limit refers to healthy adult.