Microbial community activity in response to multiple contaminant exposure: a feasible tool for sediment quality assessment.

Sediments represent complex mixtures and the impacts of their physical and chemical processes on biota are important for assessing potential health risks. We aimed to rank sediment samples from Guanabara Bay by developing an algorithm (quality ratio-QR), focusing on key sediment parameters (fine grain size, total organic carbon (TOC), metal concentrations) and enzymatic activities (dehydrogenase (DHA-energy production into cell) and esterases (EST-hydrolase organic matter outside the cell membrane)) of in situ microbial communities. Our QR is supported by quantitative information and significant correlations between geochemical and microbial processes. The QR is a function of the dependent term DHA/EST and the geochemical term (TOC×∑CF)/fine-grained sediment, where ∑CF is the sum of contamination factors (ratio between actual and background metal concentrations). We could rank our sampling sites into three risk classes based on QR: low, medium, and high. Our findings suggest altered homeostasis due to the development of contamination resistance. We applied a sensitivity analysis, using Brazilian law for sediment quality assessment, to calibrate our risk index. Our QR is suitable for measuring the potential health risk of any sediment, especially in developing countries with serious technical limitations, since its evaluated parameters are cheap, fast, and easy to obtain.

Bioaccumulation of heavy metals by shrimp (Litopenaeus schmitti): A dose-response approach for coastal resources management.

We reveal a dose-response relationship for bioaccumulation of Zn, Cu and Cr in shrimp Litopenaeus schmitti from Sepetiba Bay, Rio de Janeiro, Brazil. Our model estimates the current risk (AD50 was 70% of the legal limit) and the daily metal uptake rate for each metal. It can also evaluate the relative reliability of predictions for tissue concentrations reaching the legal limits for human consumption (approximately 1year) and predictions related to asymptotic length, arising from (i) direct regression of the metal concentration (MeC) versus total length (TL) and age (duration of exposure), and (ii) correlation of the incorporation rate (IR=MeC/TL) with age. Metal incorporation rates (IR), i.e. a kinetic proxy for absorption during growth up to attainment of asymptotic length, decrease with age, reflecting a slow-down in metal absorption. This pattern mitigates the high initial concentrations observed for juveniles.

Copper tolerance and distribution of epibiotic bacteria associated with giant kelp Macrocystis pyrifera in southern California.

Kelp forests in southern California are important ecosystems that provide habitat and nutrition to a multitude of species. Macrocystis pyrifera and other brown algae that dominate kelp forests, produce negatively charged polysaccharides on the cell surface, which have the ability to accumulate transition metals such as copper. Kelp forests near areas with high levels of boating and other industrial activities are exposed to increased amounts of these metals, leading to increased concentrations on the algal surface. The increased concentration of transition metals creates a harsh environment for colonizing microbes altering community structure. The impact of altered bacterial populations in the kelp forest have unknown consequences that could be harmful to the health of the ecosystem. In this study we describe the community of microorganisms associated with M. pyrifera, using a culture based approach, and their increasing tolerance to the transition metal, copper, across a gradient of human activity in southern California. The results support the hypothesis that M. pyrifera forms a distinct marine microhabitat and selects for species of bacteria that are rarer in the water column, and that copper-resistant isolates are selected for in locations with elevated exposure to transition metals associated with human activity.