Background The November 1, 1986 fire at a Sandoz Ltd. storehouse at Schweizerhalle, an industrial area near Basel, Switzerland, resulted in chemical contamination of the environment. The storehouse, which was completely destroyed by the fire, contained pesticides, solvents, dyes, and various raw and intermediate materials. The majority of the approximately 1,250 t of stored chemicals was destroyed in the fire, but large quantities were introduced into the atmosphere, into the Rhine River through runoff of the fire-fighting water, and into the soil and groundwater at the site. The chemicals discharged into the Rhine caused massive kills of benthic organisms and fish, particularly eels and salmonids. Public and private reaction to the fire and subsequent chemical spill was very strong. This happened only a few months after the Chernobyl accident and it destroyed the myth of immunity of Switzerland regarding such catastrophes. Aim This article reviews the damaging events of November 1986 and aims at striking stock two decades later. Results and discussion In the aftermath of this once-per-century accident, the aim was to obtain new knowledge for the environmental sciences and to achieve progress for water pollution control issues. The following themes are discussed: mitigation measures by the chemical industry and by the governmental authorities, activities of environmental protection organizations, chemical and biological monitoring, alert organization, ecological damages, ecotoxicological effects assessment, recovery and alteration of the river biology, return of the salmon, drinking water supplies, research programs, education of environmental scientists, and visions for the future. Conclusions The catastrophic pollution of the Rhine in November 1986 has triggered by the openly visible damages of the river biology that subsequently significant progress was made towards the prevention of such environmental catastrophes. The crucial risk reduction measures in the chemical industry, legal regulations and controls as well as chemical and biological monitoring of the river water quality were substantially improved. Politics and chemical industry have learned their lectures and have proceeded accordingly. Recommendations A drastic acute contamination, as it has happened at Schweizerhalle in 1986, is clearly recognizable by the toxic effects, which it is causing. This can lead to mitigation activities, which are positive considering a long-term perspective. However, the less obvious effects of chronic water pollution should receive more attention as well as the ongoing alteration of the biocenosis. A high water quality must be demanded for using water from the Rhine to produce drinking water. In that context, micropollutants should also be considered and particular attention should be payed to emerging contaminants. Perspectives The big chemical storehouse fire of 1986 had an important impact on the transboundary cooperation and has improved the willingness for international cooperation. The fire catastrophe of Schweizerhalle has triggered many activities in particular for the Rhine River. Overall, the effects are positive on the basis of a long-term perspective. The applied whole basin approach gives an example on a global basis for other river systems, which still are more heavily polluted.

Background, aim and scope In the region of the Apuseni Mountains, part of the Western Carpathians in Romania, metal mining activities have a long-standing tradition. These mining industries created a clearly beneficial economic development in the region. But their activities also caused impairments to the environment, such as acid mine drainage (AMD) resulting in long-lasting heavy metal pollution of waters and sediments. The study, established in the context of the ESTROM programme, investigated the impact of metal mining activities both from environmental and socioeconomic perspectives and tried to incorporate the results of the two approaches into an integrated proposition for mitigation of mining-related issues. Study site The small Certej catchment, situated in the Southern Apuseni Mountains, covers an area of 78 km². About 4,500 inhabitants are living in the basin, in which metal mining was the main economic sector. An open pit and several abandoned underground mines are producing heavy metal-loaded acidic water that is discharged untreated into the main river. The solid wastes of mineral processing plants were deposited in several dumps and tailings impoundment embodying the acidic water-producing mineral pyrite. Methods The natural science team collected samples from surface waters, drinking water from dug wells and from groundwater. Filtered and total heavy metals, both after enrichment, and major cations were analysed by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major anions in waters, measured by ion chromatography, alkalinity and acidity were determined by titration. Solid samples were taken from river sediments and from the largest tailings dam. The latter were characterised by X-ray fluorescence and X-ray diffraction. Heavy metals in sediments were analysed after digestion. Simultaneously, the socioeconomic team performed a household survey to evaluate the perception of people related to the river and drinking water pollution by way of a logistic regression analysis. Results and discussion The inputs of acid mine waters drastically increased filtered heavy metal concentrations in the Certej River, e.g. Zn up to 130 mg L⁻¹, Fe 100 mg L⁻¹, Cu 2.9 mg L⁻¹, Cd 1.4 mgL⁻¹ as well as those of SO₄ up to 2.2 g L⁻¹. In addition, river water became acidic with pH values of pH 3. Concentrations of pollutant decreased slightly downstream due to dilution by waters from tributaries. Metal concentrations measured at headwater stations reflect background values. They fell in the range of the environmental quality standards proposed in the EU Water Framework Directive for dissolved heavy metals. The outflow of the large tailing impoundment and the groundwater downstream from two tailings dams exhibited the first sign of AMD, but they still had alkalinity. Most dug wells analysed delivered a drinking water that exhibited no sign of AMD pollution, although these wells were a distance of 7 to 25 m from the contaminated river. It seems that the Certej River does not infiltrate significantly into the groundwater. Pyrite was identified as the main sulphide mineral in the tailings dam that produces acidity and with calcite representing the AMD-neutralising mineral. The acid-base accounting proved that the potential acid-neutralising capacity in the solid phases would not be sufficient to prevent the production of acidic water in the future. Therefore, the open pits and mine waste deposits have to be seen as the sources for AMD at the present time, with a high long-term potential to produce even more AMD in the future. The socioeconomic study showed that mining provided the major source of income. Over 45% of the households were partly or completely reliant on financial compensations as a result of mine closure. Unemployment was considered by the majority of the interviewed persons as the main cause of social problems in the area. The estimation of the explanatory factors by the logistic regression analysis revealed that education, household income, pollution conditions during the last years and familiarity with environmental problems were the main predictors influencing peoples' opinion concerning whether the main river is strongly polluted. This model enabled one to predict correctly 77% of the observations reported. For the drinking water quality model, three predictors were relevant and they explained 66% of the observations. Conclusions Coupling the findings from the natural science and socioeconomic approaches, we may conclude that the impact of mining on the Certej River water is high, while drinking water in wells is not significantly affected. The perceptions of the respondents to pollution were to a large extent consistent with the measured results. Recommendations and perspectives The results of the study can be used by various stakeholders, mainly the mining company and local municipalities, in order to integrate them in their post-mining measures, thereby making them aware of the potential long-term impact of mining on the environment and on human health as well as on the local economy.

Background, aim, and scope Dye pollutants are a major class of environmental contaminants. Over 100,000 dyes have been synthesized worldwide and more than 700,000 tons are produced annually and over 5% are discharged into aquatic environments. The adsorption or sorption is one of the most efficient methods to remove dye and heavy metal pollutants from wastewater. However, most of the present sorbents often bear some disadvantages, e.g. low sorption capacity, difficult separation of spoil, complex reproduction, or secondary pollution. Development of novel sorbents that can overcome these limitations is desirable. Materials and methods On the basis of the chemical coprecipitation of calcium oxalate (CaC₂O₄), bromopyrogallol red (BPR) was embedded during the growing of CaC₂O₄ particles. The ternary C₂O₄ ²⁻-BPR-Ca²⁺ sorbent was yielded by the centrifugation. Its composition was determined by spectrophotometry and AAS, and its structure and morphology were characterized by powder X-ray diffraction (XRD), laser particle-size analysis, and scanning electron microscopy (SEM). The adsorption of ethyl violet (EV) and heavy metals, e.g. Cu(II), Cd(II), Ni(II), Zn(II), and Pb(II) were carried out and their removal rate determined by spectrophotometry and ICP-OES. The adsorption performance of the sorbent was compared with powder activated carbon. The Langmuir isothermal model was applied to fit the embedment of BPR and adsorption of EV. Results The saturation number of BPR binding to CaC₂O₄ reached 0.0105 mol/mol and the adsorption constant of the complex was 4.70 x 10⁵ M⁻¹. Over 80% of the sorbent particles are between 0.7 and 1.02 μm, formed by the aggregation of the global CaC₂O₄/BPR inclusion grains of 30-50 nm size. Such a material was found to adsorb cationic dyes selectively and sensitively. Ethyl violet (EV) was used to investigate the adsorption mechanism of the material. One BPR molecule may just bind with one EV molecule. The CaC₂O₄/BPR inclusion material adsorbed EV over two times more efficiently than the activated carbon. The adsorption of EV on the CaC₂O₄/BPR inclusion sorbent was complete in only 5 min and the sedimentation complete in 1 h. However, those of EV onto activated carbon took more than 1.5 and 5 h, respectively. The treatment of methylene blue and malachite green dye wastewaters indicated that only 0.4% of the sorbent adsorbed over 80% of color substances. Besides, the material can also adsorb heavy metals by complexation with BPR. Over 90% of Pb²⁺, and approximately 50% of Cd²⁺ and Cu²⁺, were removed in a high Zn²⁺-electroplating wastewater when 3% of the material was added. Eighty-six percent of Cu²⁺, and 60% of Ni²⁺ and Cd²⁺, were removed in a high Cd²⁺-electroplating wastewater. Discussion The embedment of BPR into CaC₂O₄ particles responded to the Langmuir isothermal adsorption. As the affinity ligand of Ca²⁺, BPR with sulfonic groups may be adsorbed into the temporary electric double layer during the growing of CaC₂O₄ particles. Immediately, C₂O₄ ²⁻ captured the Ca²⁺ to form the CaC₂O₄ outer enclosed sphere. Thus, BPR may be released and embedded as a sandwich between CaC₂O₄ layers. The adsorption of EV on the sorbent obeyed the Langmuir isothermal equation and adsorption is mainly due to the ion-pair attraction between EV and BPR. Different from the inclusion sorbent, the activated carbon depended on the specific surface area to adsorb organic substances. Therefore, the adsorption capacity, equilibrium, and sedimentation time of the sorbent are much better than activated carbon. The interaction of heavy metals with the inclusion sorbent responded to their coordination. Conclusions By characterizing the C₂O₄ ²⁻-BPR-Ca²⁺ inclusion material using various modern instruments, the ternary in situ embedment particle, [(CaC₂O₄)₉₅(BPR)] n ²n⁻, an electronegative, micron-sized adsorbent was synthesized. It is selective, rapid, and highly effective for adsorbing cationic dyes and heavy metals. Moreover, the adsorption is hardly subject to the impact of electrolytes. Recommendations and perspectives The present work provides a simple and valuable method for preparing the highly effective adsorbent. If a concentrated BPR wastewater was reused as the inclusion reactant, the sorbent will be low cost. By selecting the inclusion ligand with a special structure, we may prepare some particular functional materials to recover the valuable substances from seriously polluted wastewaters. The recommended method will play a significant role in development of advanced adsorption materials.

Background, aim, and scope Foraging patches can be described as a nested hierarchy of aggregated resources, implying that study of foraging by wild animals should be directed across different spatial scales. However, almost all previous research on habitat selection by the giant panda has concentrated upon one scale. In this research, we carried out a field study to understand foraging patch selection by giant pandas in winter at both microhabitat and feeding site scales and, for the first time, attempted to understand how long it would stay at the feeding sites before moving on. Materials and methods The field survey was conducted from November 2002 to March 2003 at Fengtongzhai Nature Reserve (102°48'-103°00' E, 30°19'-30°47' N), Baoxing County of Sichuan Province, China, to collect data in both microhabitat and control plots. The microhabitat plots were located by fresh feces or foraging traces left by giant pandas, and the control plots were established to reflect the environment. Within each microhabitat plot, one 1 x 1 m² plot was centralized at the center of each feeding site, in which numbers of old bamboos and old shoots, including eaten and uneaten, were counted, respectively. Results The results showed that winter microhabitats selected by this species were characteristic of gentle slopes and high old-shoot proportions and that the latter was even higher at feeding sites. Two selection processes, namely, from the environment to microhabitats and from the latter to feeding sites, were found during this species' foraging patch utilization. Giant pandas preferred to eat old shoots to old bamboo at feeding sites in winter and did not leave unless old-shoot density fell to lower than the average in the environment. Discussion Both microhabitats and feeding sites selected by giant pandas were characteristic of high old-shoot density, indicating that the preferred food item had a significant influence upon its foraging patch selection. The preference for gentle slopes by giant pandas was presumed to save energy in movement or reflect the need to sit and free its fore-limbs to grasp bamboo culms when feeding but also seemed to be correlated with an easier access to old shoots. The utilization of old shoots at feeding sites was assumed to help maximize energy or nutrient intake during their foraging. Conclusions The difference between microhabitat plots and control plots and between microhabitats and feeding sites uncovered a continuous selection process from the environment via microhabitats to feeding sites. The utilization of old shoots at feeding sites was parallel to the marginal value theorem. The selection and abandonment of foraging patches by giant pandas was an optimal behavioral strategy adapted to their peculiar food with high cellulose and low protein. Recommendations and perspectives Our results uncovered the importance of multiple scales in habitat selection research. To further understand the process of habitat selection, future research should pay more attention to resolve the question of how to locate foraging patches under dense bamboo forests by the giant panda, which was traditionally considered to have poor eyesight, although our research has answered what type of habitats the giant panda prefers and when to leave.

Background, aim, and scope Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil fuels, mining and smelting of metalliferous ores, municipal wastes, agrochemicals, and sewage. In addition, natural mineral deposits containing particularly large quantities of heavy metals are found in many regions. These areas often support characteristic plant species thriving in metal-enriched environments. Whereas many species avoid the uptake of heavy metals from these soils, some of them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal tolerance in specialized hyperaccumulator plants such as Arabidopsis halleri and Thlaspi caerulescens. In this review, we describe recent advances in understanding the genetic and molecular basis of metal tolerance in plants with special reference to transcriptomics of heavy metal accumulator plants and the identification of functional genes implied in tolerance and detoxification. Results Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of the most important mechanisms for metal detoxification in plants appears to be chelation of metals by low-molecular-weight proteins such as metallothioneins and peptide ligands, the phytochelatins. For example, glutathione (GSH), a precursor of phytochelatin synthesis, plays a key role not only in metal detoxification but also in protecting plant cells from other environmental stresses including intrinsic oxidative stress reactions. In the last decade, tremendous developments in molecular biology and success of genomics have highly encouraged studies in molecular genetics, mainly transcriptomics, to identify functional genes implied in metal tolerance in plants, largely belonging to the metal homeostasis network. Discussion Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced through the wealth of tools and the resources developed for the study of the model plant Arabidopsis thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on RNA interference (RNAi), and collections of insertion line mutants. To understand the genetics of metal accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be extended to one of its closest relatives that display the highest level of adaptation to high metal environments such as A. halleri and T. caerulescens. Conclusions This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants. Detailed information has been provided for metal transporters, metal chelation, and oxidative stress in metal-tolerant plants. Advances in phytoremediation technologies and the importance of metal accumulator plants and strategies for exploring these immense and valuable genetic and biological resources for phytoremediation are discussed. Recommendations and perspectives A number of species within the Brassicaceae family have been identified as metal accumulators. To understand fully the genetics of metal accumulation, the vast genetic resources developed in A. thaliana must be extended to other metal accumulator species that display traits absent in this model species. A. thaliana microarray chips could be used to identify differentially expressed genes in metal accumulator plants in Brassicaceae. The integration of resources obtained from model and wild species of the Brassicaceae family will be of utmost importance, bringing most of the diverse fields of plant biology together such as functional genomics, population genetics, phylogenetics, and ecology. Further development of phytoremediation requires an integrated multidisciplinary research effort that combines plant biology, genetic engineering, soil chemistry, soil microbiology, as well as agricultural and environmental engineering.

Background, aim, and scope Pesticides and heavy metals pollution in soil environment has become a serious problem in many countries including China. Repeated applications of bordeaux mixture (a blend of copper sulfate and calcium hydroxide) and pyrethroid (Pys) insecticides have led to elevated copper (Cu) and Pys concentrations in vineyard surface soils. However, few studies focused on the interaction of Pys and heavy metals in the soil environment. Our previous studies had indicated the combined effect of cypermethrin (CPM) and Cu on soil catalase activity. Also, we had suggested that the addition of Cu could catalyze photo-degradation of CPM and lambda-cyhalothrin (λ-CHT) in aqueous solution and restrain their degradation in soil. To better understand the potential influence of Cu on the fate of Pys in the soil environment, the aim of the present work was to examine the effect of Cu on the adsorption of λ-CHT and CPM on two typical Chinese soils with different soil characteristics, which was one of the key processes controlling the fate of Pys, and to provide more information about the potential ecological risk of chemicals on the soil ecosystem. Fourier transform infrared and point charges analysis using the MOPAC program of the Gaussian system were also used to reveal the probable adsorption mechanism of λ-CHT and CPM on soils. Materials and methods Two vineyard soils with different properties were chosen as experimental samples. They were sampled from 0 to 10 cm, dried, and sieved to 2 mm. Each soil was spiked with copper sulfate solution to obtain the following total soil Cu concentrations: 100, 200, 400, 800, and 1,600 mg·kg⁻¹. The treated soils were incubated for 2 weeks and then dried at 20°C. For each soil sample and at each soil Cu concentration, the adsorption of λ-CHT and CPM was measured using a batch equilibrium method. The concentration of λ-CHT was determined by HPLC, and the amount of λ-CHT and CPM adsorbed by the soil sample at equilibrium was determined by the difference between the initial and equilibrium concentrations in solution corrected by the blank adsorption measurement. Results Without the addition of Cu, the adsorption of λ-CHT and CPM on Black soil is greater than that on Red soil, while the adsorption of λ-CHT on both soils is significantly stronger than that of CPM. As the soil Cu concentration increased from 19 (or 18; background) to 1,600 mg·kg⁻¹, the adsorption coefficient (K d) of λ-CHT decreased from 12.2 to 5.9 L·kg⁻¹ for Red soil, and from 26.1 to 16.8 L·kg⁻¹ for Black soil, whereas the CPM adsorption coefficient in both soils decreased nearly by 100% (K d decreased from 9.4 to 0.2 L·kg⁻¹ for Red soil and from 16.2 to 0.5 L·kg⁻¹ for Black soil). Discussion Pys adsorption is a surface phenomenon which depends on the surface area and the organic matter content. Thus, the Black soil, having higher organic matter and greater surface area than that of the Red soil, show greater adsorption affinity to λ-CHT and CPM. In our study, the different adsorption affinity of the two Pys was obtained, which was probably attributed to differences with respect to their physical-chemical properties. Further comparison upon the two Pys was conducted. The point charges of halogen atoms in the λ-CHT and CPM were calculated, the differences of which probably lead to the fact that λ-CHT has a stronger binding capacity to soils than CPM. Also, FTIR spectra show that competitive adsorption occurs between CPM and Cu for the same adsorption sites, which is responsible for the obtained suppression of CPM adsorption affected by Cu. Conclusions Lambda-cyhalothrin shows a significantly stronger adsorption than cypermethrin on both soils. This phenomenon may be due to several reasons: (1) λ-CHT has lower solubility and a higher octanol-water partition coefficient value than CPM; (2) λ-CHT consists of specific isomers, whereas CPM is mixtures of eight different isomers; (3) the chlorine and fluorine atoms in the λ-CHT have a negative point charge, whereas the chlorine atoms in the CPM have a positive point charge. As the soil Cu concentrations increased from 19 (or 18) mg·kg⁻¹ to 1,600 mg·kg⁻¹, the adsorption coefficient of λ-CHT and CPM decreased on both soils. This is mainly due to a competition between Cu and Pys for occupying the adsorption sites on soils. The information from this study have important implications for vineyard and orchard soils, which often contain elevated levels of Cu and Pys. These results are also useful in assessing the environmental fate and health effect of λ-CHT and CPM. Recommendations and perspectives It is important for environmental scientists and engineers to get a better understanding of soil-metal-organic contaminant interactions. However, pesticide adsorption involves complex processes, and shortcomings in understanding them still restrict the ability to predict the fate and behavior of pesticide. Therefore, considerable research should be carried out to understand the mechanism of interaction between Pys and heavy metal on soils clearly.

Background, aim and scope One of the problems to affect Portland cement matrices is low resistance to aggressive agents, due principally to the presence of a high content of portlandite in the hydrated cements. Pozzolanic materials have played an important role in the improving the durability of cement-based materials for decades. This work studies the behaviour of cement mortar matrices blended with 10% calcined paper sludge (source for metakaolinite) and exposed to different environmental conditions (saline and non-saline environments) after 6 and 12 months of exposure. Materials and methods Two cements were studied: an ordinary Portland cement (CEM 1, 42.5R), acting as reference cement, and a blended cement formulated by mixing 90% (by mass) of CEM 1, 42.5R with 10% (by mass) of paper sludge calcined at 700°C for 2 h. The specimens were exposed 1 year to saline and non-saline environments. All the mineralogy samples were studied through X-ray diffraction and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analyser. The in-depth study on ionic mobility was performed on samples subjected to natural exposure (coast and tableland) for 6 and 12 months. Results Portland cement was composed of quartz, calcite, calcium hydroxide and tobermorite gels. The pozzolanic cement (10% calcined paper sludge) is of the same composition but a high calcite concentration and barium carbonate. SEM analysis from coastline show deposits of variable composition. The deposits are identified on the surface of different mineral components. The minerals from tableland are much fractured, i.e. calcite and feldspars. Inside the fractures, the deposits and the ions are located and trapped superficially. Discussion SEM analysis of control cement Portland and 10% calcined paper sludge shows deposits on quartz and calcite with a very high concentration of Pb, Zn, Cl and barium sulphate. A very porous aspect is due to the presence of the different aggregate types. This porous configuration permits retention of the ion environment. The pozzolanic cement in environments subject to the saline mist favours the retention and transport of ions observed. Something similar also happens with the increase in exposure to outdoor weather. Non-saline samples show temperature changes (ice or thaw cycles). Barium retention is kept on the surface in fracture lines by the gelification processes. In general, it may be inferred that an increase in exposure time increases the diffusion of ions towards test piece interiors. The chemical composition profiles show that the ions present different penetration speeds. Conclusions The results indicate the better vulnerability of pozzolanic cements from calcined paper sludge in saline and non-saline environments. The cements with a 10% addition of calcined paper sludge favour retention and transport of ion has been observed. Recommendations and perspectives Today, projects are centred on a new recycling line for industrial waste of this kind, with special attention on its incorporation in cement manufacture as a pozzolanic material, setting the most appropriate activation conditions of the mineralogical compound in this waste (kaolinite and metakaolinite) and taking them as a starting point for this project. The use of pozzolanic cement with 10% addition of calcined paper sludge is a system which favours ionic retention.

Background, aim, and scope At tropical latitudes, and especially on the semi-arid coasts of the Brazilian Northeast, the rainfall regime governs the water quality of estuaries due to the pronounced difference between the rainy and dry seasons. These changes may be responsible for seasonal changes in bioavailability of mercury (Hg) and other pollutants to the estuarine and coastal biota. Mercury bioaccumulates along estuarine-marine food chains usually result in higher concentrations in tissues of top predators and posing a risk to both marine mammals and humans alike. The Goiana River Estuary (7.5° S) is a typical estuary of the semi-arid tropical regions and supports traditional communities with fisheries (mollusks, fish, and crustacean). It is also responsible for an important part of the biological production of the adjacent coastal waters. Materials and methods Trichiurus lepturus (Actinopterygii: Perciformes) is a pscivorous marine straggler. Fish from this species (n = 104) were captured in a trapping barrier used by the local traditional population and using an otter trawl net along the main channel of the low estuary during two dry seasons (D1 = November, December 2005, January 2006; D2 = November, December 2006, January 2007) and the end of a rainy season (R = August, September, October 2006). Fish muscle samples were preserved cold and then freeze-dried prior to analysis of its total mercury (Hg-T) contents. Total mercury was determined by cold vapor atomic absorption spectrometry (CV-AAS) with sodium borohydride as a reducing agent. Results The studied individuals (n = 104) were sub-adult (30-70 cm, 71 ind.) and adult fish (>70 cm, 33 ind.). Weight (W) (204.1 ± 97.9 g, total biomass = 21,229.7 g) and total length (TL) (63.1 ± 10.1 cm, range 29.5-89.0 cm) presented a significant (p < 0.05) correlation. Two-way ANOVA (n = 81) showed that TL and W had significant differences (p < 0.05) among seasons, being higher in D1 than in D2 and R, respectively. Moreover, season vs. month interaction were detected for the variables length and weight. For the variable weight was detected significant difference for the factor month (p < 0.05). It suggests that the fish enter the estuary at the end of the rainy season and increase in length and weight during the time they spend in the estuary. Fish from this estuary are shown to be fit for human consumption (125.3 ± 61.9 μgHg-T kg⁻¹ w.wt.; n = 104). Fish mercury contents increased with size and weight. Correlations between TL and Hg-T (r = 0.37286) and between W and Hg-T (r = 0.38212) were significant (p < 0.05). Dryer months showed higher mercury concentrations in fish (D1 773.4 ± 207.5 μgHg-T kg⁻¹ d.wt., n = 27; D2 370.1 ± 78.8 μgHg-T kg⁻¹ d.wt., n = 27; R 331.2 ± 138.5 μgHg-T kg⁻¹ d.wt., n = 27). The variable mercury concentration showed differences in relation to the factor season (p < 0.05), where fish captured during the first dry season showed the highest concentration of mercury. The correlation between Hg-T and rainfall (Rf) showed a negative correlation (r = -0.56; p < 0.05). Discussion The main likely source of mercury to this estuary is diffuse continental run off, including urban and industrial effluents. Since concentration of mercury in fish tissue is negatively correlated to rainfall, but positively correlated with fish length and weight, it suggests that fish growth in this estuary results in mercury uptake and concentration on the fish tissue. In the dry season of 2005-2006, when rainfall remained below the historic average, fish bioaccumulated significantly more mercury than in the dry season 2006-2007, when rainfall was within the predictable historic average. It is suggested that less rainfall, and consequently less particulate matter and less primary production in the estuary, make mercury more available to the higher levels of the estuarine food chain. In the case of higher rainfall, when river flow increases and water quality in the estuary is reduced, mercury probably is quickly exported associated to the particulate matter to the adjacent coastal waters where it then disperses. This species is a potential routine bioindicator for mercury contamination of the biota, but so far was used only with a limited number of individuals and contexts. Conclusions Fish from the Goiana River estuary can still be safely consumed by the local population. However, any further contamination of this resource might lead to total mercury levels above the recommended limits for pregnant women and small children. The proposed heavy dependency of total mercury levels in fish on water quality indicates that land use and water quality standards must be more closely watched in order to guarantee that best possible practices are in place to prevent bioaccumulation of mercury and its transfer along the food chain. Human interventions and climatic events which affect river water flow are also playing a role in the mercury cycle at tropical semi-arid estuaries. Recommendations and perspectives T. lepturus is largely consumed by coastal populations of tropical and sub-tropical countries all over the world. It is also consumed by a number of marine mammals over which we have a strong conservation interest. This species is also a link among different ecosystems along the estuarine ecocline. Therefore, knowledge of its degree of contamination might contribute to public health issues as well as marine conservation actions. Studies on mercury and other contaminants using this species as bioindicator (cosmopolitan, readily available) could help elucidating mechanisms through which pollutants are being transferred not only through the food chain, but also from estuarine-coastal-open waters. In addition, using the same species in marine pollution studies, especially as part of a mosaic of species, allows for wide range comparisons of marine food chain contamination.

Production of methane and carbon dioxide as well as methane concentrations in surface waters and emissions to the atmosphere were investigated in two flow-through lake complexes (Uzlina-Isac and Puiu-Rosu-Rosulet) in the Danube Delta during post-flood conditions in May and low water level in September 2006. Retained nutrients fuelled primary production and remineralisation of bioavailable organic matter. This led to an observable net release of methane, particularly in the lakes Uzlina, Puiu and Rosu in May. Input from the Danube River, from redbuds and benthic release contributed to CH₄ concentrations in surface waters. In addition to significant river input of CO₂, this trace gas was released via aerobic remineralisation within the water column and in top sediments. Emission patterns of CO₂ widely overlapped with those of CH₄. Generally, greenhouse gas emissions peaked in the lake complex adjacent to the Danube River in May due to strong winds and decreased with increasing hydrological distance from the Danube River. Intense remineralisation of organic matter in the Danube Delta lakes results in a net source of atmospheric greenhouse gases.