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This paper estimated the mercury (Hg), emission factor, and mass balance from caged fish farming in the Castanhão Reservoir, NE Brazil, based on monitoring of a typical farm of Nile tilapia (Oreochromis niloticus). The total Hg input to the farm reached 1.45 gHg ha(-1) year(-1), from which 0.21 gHg ha(-1) year(-1) was exported out as fish biomass, ultimately resulting in an emission factor of 1.24 gHg ha(-1) year(-1) for the reservoir or approximately 8.27 mgHg ton fish(-1) year(-1) produced. Most of the input came from aquafeeds with concentrations varying from 1.4 to 31.1 ng g(-1), depending on the type of aquafeed. The Hg concentrations in fish were very low and varied from 1.0 to 2.9 ng g(-1). These values are two orders of magnitude lower than the legal limit for human consumption. The estimated total annual discharge of Hg from farming into the reservoir is 174 g for 18,000 tons of fish produced and may reach 387 g when the reservoir reaches its total capacity (40,000 tons), which is expected to occur in 2020. The mass balance, considering the deposition and accumulation rates, showed that approximately 40% of the total Hg input accumulate in farm sediments (0.72 g ha(-1) year(-1)), which is approximately 60% of the deposition rate estimated through the sediment traps and suggests that 0.54 gHg ha(-1) year(-1) could eventually be transported out of the farm to the reservoir. Notwithstanding these facts, the total annual input of Hg from fish farming to the Castanhão Reservoir is less than 1.0% of the total input from anthropogenic sources.

Emissions of Cu, Zn and Mn and their fate in a typical tilapia (Oreochromis niloticus) cage farm in an artificial reservoir in northeastern Brazil were estimated through the analysis of their concentrations in the various compartments of the farm. Major source of Cu and Zn, but not of Mn, to the farm is from aquafeeds, with annual inputs of 3.83, 57.50 and 10.95 kg.ha −1 , respectively. Notwithstanding, only a small fraction of the added Mn and Zn (0.13%, 2.61%, respectively) is incorporated into fish biomass, resulting in a larger proportion of the introduced metals to be exported to reservoir environment. For Cu, a much larger fraction (47.4%) is exported within the fish biomass. Once released, metals are incorporated into bottom sediments within the farm area, resulting in higher metal contents compared to sediments far from the farm area. However, the analysis of sediment cores and the respective enrichment factors showed that a significant fraction of the net input of Zn (70%) and of Cu (30%) is exported out to the open reservoir.

Dredging involves the sediment excavation in order to increase the bathymetry of harbors by different methods. In urbanized and Industrial areas, dredging pose risks of negative effects on the biota due to sediment contamination. The Brazilian criteria for characterizing dredged material include chemical analyzes and comparison with sediment quality guidelines and toxicity testing, which require the development of novel and different biological models to be used in bioassays. In this study, we aimed to assess the quality of sediments collected during dredging activities of Mucuripe Bay (Fortaleza city, NE Brazil). Sediments were characterized for the concentration of metals and hydrocarbons, in order to establish the contamination status. Whole sediment toxicity was assessed by means of mortality of the amphipod Tiburonella viscana and the polychaete worm Armandia agilis, while chronic effects were evaluated on the fecundity of the copepod Tisbe biminiensis. Liquid phase exposures were determined in the acute toxicity of sediment-water interface (ISA) on the mysid Mysidopsis juniae, while chronic toxicity of ISA and elutriates (ELU) assessed by the embryo-larval development of the sea urchin Lytechinus variegatus. Results revealed that contaminated samples exhibited both acute and chronic toxicity. An integrative method for integrating different endpoints was employed and classified samples related to dredging activities as the most degraded. Extracts obtained from the material collected within the dredge were also tested for acute and chronic effects and exhibited toxicity as well. Based on our findings we recommend the analysis of material from dredger cistern and application of a set of bioassays in order to properly determine the quality of dredged sediments.

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