A better repeatability and accuracy in the quantitative determination of trace elements in mussel shells or carbonate-based materials by LA-ICP-MS was achieved by using a series of multielement calibration standards prepared by co-precipitation of twelve elements into a CaCO3 matrix in order to improve the homogeneity of the resulting powder samples. Pressed powder discs of good mechanical stability could be obtained at a pressure of 50 MPa, without the addition of a binder. An UV laser (modified Nd:YAG, 266 nm) was used in the Q-switched mode at a repetition rate of 10 Hz and an energy level of 3.5 mJ. Correlation coefficients (R) for the linear calibration graphs (concentration range: 1.5-400 microg/g) for Cr, Mn, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb are generally better than 0.997. The detection limits for all elements investigated are in the sub-microg/g range. Incorporation of elements into the matrix by co-precipitation has shown as a superior method for producing calibration standards than the simple mixture of the analytes (in carbonate or oxide form) with the matrix (CaCO3) or addition of standard solutions to a carbonate powder base. Two examples of the quantitative determination of toxic elements in mussel shells will be presented.

The uptake of Cr, Mn, Ni, Cu, Zn, Cd and Pb in soft tissue of Perna perna mussels and their shells has been studied in aquarium experiments in which mussels were exposed for 30 or 60 days to seawater spiked with different concentrations of these contaminants (125 and 500 microg L(-1)). Tissue samples were analyzed after acid digestion by conventional solution nebulization ICP-MS. Laser ablation ICP-MS was used for the quantitative determination of trace elements in different areas of the corresponding shells. With the exception of Mn and Zn, all other elements studied showed a significant concentration enhancements in soft tissue, with the magnitude of this enhancement following the order: Cr > Ni > Cd > Cu > Pb. A corresponding increase in most contaminants, although less pronounced, was also observed in the newly formed growth rings of mussel shells, contributing to the validation of Perna perna mussel shell as a bioindicator of toxic elements.

This research investigated the source and fate of different chemical species of N and P on a deep tropical urban reservoir, the artificial Lake Paranoá, located in the city of Brasilia (Brazil). To determine an N and P budget, nutrient input from the external load (four main tributaries and two wastewater treatment plants), internal load (from sediment) and nutrient output (from a downstream dam) were estimated empirically. Nutrient storage was evaluated in two compartments: water column and sediment. Nutrient input from the tributaries varied by season presenting higher loads in the wet season, especially N. Nutrient budgets in our study indicated that Lake Paranoá retained dissolved inorganic nitrogen (DIN), PO43−-P, total organic phosphorus (TOP) and exported total organic nitrogen (TON), both on a seasonal and annual scale. Surface sediment is the major storage compartment for both N and P. These results show the pressing need for action to reduce the P outcome charges, mainly, from the wastewater treatment plants. The data here presented contributes to the recognition of this situation and to a better comprehension of these nutrient dynamics, as well as an understanding of the behavior of tropical deep-water reservoirs. This can help to promote more effective management, providing a reference for other similar systems.

RESUMOFoi desenvolvido um método simples e rápido para separação e purificação simultânea de Cu, Zn e Mo e a medição exata e precisa das suas composições isotópicas em amostras geológicas utilizando espectrometria de massa com plasma indutivamente acoplado e sistema multicoletor (MC-ICPMS). O método envolve o uso de uma única coluna cromatográfica, preenchida com a resina de troca aniônica AG-MP-1 para separação e purificação desses três elementos a partir da sua matriz complexa. O método Sample-Standard-Bracketing (SSB) combinado à adição de padrão interno foi usado para a correção exata e precisa do viés de massa instrumental nas medições das razões isotópicas de Cu, Zn e Mo. O método foi aplicado a diferentes materiais geológicos, como granodiorito (GSP 2-USGS), calcário (JLS-1, Japão), sedimentos do Rio Buffalo (NIST SRM -8704) e sedimentos da Bacia Amazônica. A precisão média para essas amostras foram: 0,08 ‰ para δ δ65/63 Cu; 0,05 ‰ para δ 66/67 Zn e 0,04 ‰ para δ 98/95 Mo. A principal vantagem é que o método proposto é simples e rápido, realiza a recuperação quantitativa dos elementos de diferentes massas atômicas e em concentrações muito baixas, principalmente para Mo. Em conjunto, a correção do viés de massa instrumental a partir de um método mais simples, produziu resultados consistentes aos outros métodos atualmente publicados. A comparação entre as composições isotópicas de Cu e Mo obtidas para granodiorito com os dados relatados na literatura, demonstra que o método mais simples e multielementar, desenvolvido neste estudo, estão dentro dos limites de precisão requeridas e pode ser utilizado adequadamente como ferramenta multi-proxy em geoquímica de isótopos. Palavras-chaves: isótopos de Zn, Cu e Mo, MC-ICPMS, cromatografia de troca iônica, material geológico ABSTRACT A simple and quick method for simultaneous purification of Cu, Zn and Mo and accurate and precise measurement of their isotopic composition in geological samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been developed. The method involves the use of a single chromatographic column filled with the anion exchange resin AG-MP-1 for complex matrix removal and further purification of these three elements. The external standard-sample-standard bracketing (SSB) procedure combined to internal standard addition was used for accurate mass bias correction and precise Cu, Zn and Mo isotopic ratio measurements. The method was applied to different geological materials, as granodiorite (GSP 2-USGS), limestone (JLS-1, Japan), Buffalo River Sediments (NIST SRM -8704) and sediments from Amazon River Basin. The mean precision for these samples was: 0.08 ‰ for δ 65/63 Cu; 0.05 ‰ for δ 66/67 Zn and 0.04 ‰ for δ 98/95 Mo. The main advantage is that the proposed method is simple and rapid, and carries out the quantitative recovery of elements of different atomic

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