This study brings a new viewpoint based on multiple-tissue analyses to form the basis for a predictive mode of mercury accumulation dynamics in fish body under field conditions. Total mercury (T-Hg) was determined in key tissues of Liza aurata captured along an estuarine contamination gradient, displaying the following hierarchy: kidney > liver > muscle > brain > gills > blood. Brain was the tissue that better reflected the mercury contamination extent, closely followed by liver and muscle. Organic mercury (O-Hg) measured in muscle and liver represented more than 85% and less than 30% of the T-Hg, respectively. The lowest O-Hg percentage was found in the most contaminated area, for both muscle and liver. Mercury distribution and accumulation patterns showed dependence on the specific tissue. The high mercury levels found in organs involved in vital physiological processes point out the risk to autochthonous fish fauna. Human risk associated to the ingestion of fish living in the surveyed areas cannot be excluded.

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Although brain has been recognized as a primary target for mercury toxicity in mammals, the effects of this metal in fish brain are scarcely described. Thus, the main objective of this study was to assess the mercury threat to feral fish (Liza aurata) by estimating the antioxidant defenses and peroxidative damage in brain, keeping in mind the association with mercury accumulation. Sampling was carried out in an estuarine area historically affected by discharges from a chlor-alkali industry-Laranjo Basin (Ria de Aveiro, Portugal). Total mercury (T-Hg) in brain increased towards the contamination source, clearly indicating mercury exposure. An overall antioxidant depletion was verified in brain of fish collected at the mercury-contaminated stations, since total glutathione content and the studied antioxidant enzymes (catalase-CAT, glutathione peroxidase-GPx, glutathione-S-transferase-GST and glutathione reductase-GR) significantly decreased. In addition, this breakdown of the redox-defense system was significantly correlated with the accumulated T-Hg levels. Unexpectedly, fish exhibited unaltered lipid peroxidation levels, pointing out a higher propensity of mercury to inhibit enzymes than to oxidatively damage lipids in the brain. Nevertheless, an increased susceptibility of the fish's brain was identified, leaving the organ more vulnerable to oxidative stress-related challenges. Overall, the current findings provide information to better understand mechanisms of mercury neurotoxicity in fish.

Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δHg and ΔHg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δHg around Europe was suggested to be related to a global atmospheric contamination while δHg at some sites was linked either to background contamination, or with local contamination sources. ΔHg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.

23Cephalopod beaks found in the diet of predators have been a major source of 24 scientific information. In this study, we evaluated the usefulness of DNA and 25 contaminants analysis (total mercury-T-Hg) in cephalopod beaks in order to assess their 26 applicability as tools in marine ecology studies. We concluded that, when applying DNA 27 techniques to cephalopod beaks from Antarctic squid species, when using flesh attached 28 to those beaks, it was possible to obtain DNA and to successfully identify cephalopod 29 species; DNA was not found on the beaks themselves. This study also showed that it is 30 possible to obtain information on T-Hg concentrations in beaks: the T-Hg concentrations 31 found in the beaks were 6 to 46 times lower than in the flesh of the same cephalopod 32 species. More research on the relationships of mercury concentrations in cephalopod 33 beaks (and other tissues), intra-and inter-specifically, are needed in the future. 34 35 CAPSULE ABSTRACT: DNA and contaminants analyses for the first time in 36 cephalopods beaks showed that flesh attached to beaks allows DNA species ID and beaks 37 had 6-46 times less total mercury than flesh. 38 39

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Soil quality in urban areas is affected by anthropogenic activities, posing a risk to human health and ecosystems. Since the pseudo-total concentrations of potentially toxic elements may not reflect their potential risks, the study of element mobility is very important on a risk assessment basis. This study aims at characterising the distribution and major sources of 34 elements in two Portuguese urban areas (Lisbon and Viseu), with different geological characteristics, industrial and urban development processes. Furthermore, the potential availability of As, Co, Cr, Cu, Ni, Pb and Zn was assessed, by measuring the fraction easily mobilised. Lisbon is enriched in elements of geogenic and anthropogenic origin, whereas in the smaller city, the high levels observed are mainly related to a geogenic origin. Background values can be more relevant than the dimension of the city, even when anthropogenic components may be present, and this parameter should be considered when comparing results from different cities. Regarding the potential available fraction, a high variability of results was observed for elements and for sampling sites with an influence of the soil's general characteristics. Elements showing very high concentrations due to geological reasons presented, in general, a low mobility and it was not dependent on the degree of contamination. For elements with major anthropogenic origin, only Zn was dependent on the pseudo-total content. Yet, the highest available fractions of some elements, both with major geogenic and anthropogenic origin, were observed in specific contaminated samples. Therefore, a site-specific evaluation in urban soils is important due to the high spatial variability and heterogeneity.

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