Bioavailability evaluations can be an important tool to determine the quality of dredging sediments. Sequential extractions are commonly used to assess the different chemical forms of trace metals in coastal sediments; however, sometimes they are expensive and timeconsuming. Additionally, these analyses do not represent possible changes due to resuspension during and after dredging activity. Newer, easier options to evaluate bioavailability are necessary to understand and preview bioavailability changes resulting from trace metals in dredging and disposal areas. This study aims to evaluate changes in Cd and Zn bioavailability due to sediment resuspension in a highly contaminated area in Sepetiba Bay, Brazil. Twelve surface sediment samples from this location were submitted to a resuspension experiment during two different time intervals (1 and 24 h). The extraction of potentially bioavailable (1 mol L -1 HCl-extractable) fractions and strongly bound (concentrated HNO 3 -extractable) fractions were sequentially carried out. More than 50 % of the concentrations were in potentially bioavailable fractions. Bioavailability change indexes were proposed; these were estimated as relative changes in bioavailability percentage after resuspension. However, two of these stations presented increases in the Cd and Zn HCl-extractable fractions after sediment resuspension above effects range low and effects range medium National Oceanic and Atmospheric Administration which are the same limits adopted for Brazilian environmental jurisdiction. Positive correlation of Zn and Cd with TOC in strongly bound fractions evidenced the importance of organic matter binding to preserve metals in this fraction. Fe and Mn partitioning was a major geochemical control on bioavailability of Cd and Zn upon short-time resuspension periods.

A Microbacia Irurá encontra-se entre a porção noroeste e sudoeste da área urbana do município de Santarém/PA, possui um histórico de ocupação desordenada influenciada por diversos ciclos econômicos. Neste contexto, esta ocupação desordenada e acelerada, gera impactos significativos sobre os recursos hídricos. Uma forma de se avaliar os danos é através do calculo o Índice de Estado Trófico (IET) para mensurar a qualidade da água, e discutir a proveniência do Fósforo e Clorofila-a  em diferentes estações do ano. Desta forma foram realizadas duas campanhas amostrais, sendo uma na estação seca e outra na chuvosa em seis pontos ao longo do Igarapé. Para o cálculo do IET foram analisados Fósforo total (PTot) e clorofila-a nas seis amostras de água. Os resultados do IET nas duas campanhas de monitoramento, mostraram que no período seco as classes variaram de ultraoligotrófico a eutrófico e já no chuvoso, as classes variaram de oligotrófico a eutrófico. As concentrações de Fósforo Total no período chuvoso encontram-se em desconformidade com a resolução da CONAMA 357/2005 para a  Classe II. Foi realizada uma correlação estatística entre a clorofila-a e o  Fósforo Total, e  durante o período seco, apresentou uma correlação positiva, sugerindo um aumento da exposição solar e aumento da atividade fotossintética.  Tendo como proveniência o lançamento de efluentes dentro do corpo d’água, além de atividade de agricultura de subsistência, em algumas áreas. As concentrações de Clorofila-a  encontram-se, que em todos os pontos, dentro dos padrões de qualidade para classe tipo II, em ambas as estações

This study evaluated the potential mobility of metallic contaminants (Cd, Cr, Cu, Ni, Pb and Zn) present in sediments at the mouth of São Francisco Channel (Sepetiba Bay, RJ), using resuspension tests. Fourteen surface sediment and superficial water samples were collected along a salinity gradient from the river mouth into the bay. The resuspension tests consisted in the mechanical agitation of humid sediment aliquots in local unfiltered water, in a ratio of 7.5 g:100 mL, during 1 h and 24 h. The determination of the metals in the bioavailable fraction was performed in ICP-OES, after extraction in 1 mol L −1 HCl. Significant differences were observed between the central and external sectors for Cd (p = 0.009), Cr (p = 0.017), Ni (p = 0.047) and Zn (p = 0.007) concentrations (Kruskal-Wallis). The water's temperature (p < 0.001), pH (p < 0.05) and dissolved oxygen (p < 0.001) decreased in both time intervals in comparison to the initial measures before resuspension. The concentrations of Zn in the sediment increased from 222 to 316.2 mg kg −1 after 24 h agitation (Kruskal-Wallis; p < 0.05) at the external sector, possibly because this region has stronger oxidizing conditions. In general, a significant increase in the metals' concentrations was observed after resuspension, especially for the samples from the central sector that showed more than 90% of increase in metals concentrations after 24 h of agitation. These increases could lead to higher ecological risks to the local biota, especially during dredging activities.

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