Dominance of dietary intake of metals in marine elasmobranch and teleost fish

Metal accumulation in marine fish is a global public health concern, because the consumption of seafood provides the largest dose of many toxic metals to humans. While water quality criteria often rely on aqueous exposures of metals to fish in developing safety guidelines, it is increasingly recognized that marine fish obtain an important fraction of their metal body burden from their diet. Using experimental data, we modeled the accumulation of six metals (Am, Cd, Cs, Co, Mn, Zn) from diet and from the aqueous phase in two marine fish species, the teleost Psetta maxima and elasmobranch Scyliorhinus canicula. We estimated steady-state metal concentrations and calculated the relative contributions of dietary and aqueous intake in both species. For both species > 60% and often > 90% of Mn, Cd, and Zn derives from dietary intake in these species, even at the lowest ingestion rates reported for these fish. At low ingestion rates, Am was obtained predominantly from the aqueous phase and Cs varied considerably depending on prey selection. Inter-specific differences were noted, especially in Co uptake. Model predictions of steady-state tissue metal concentrations are within the range of field measurements for these species. Our findings underscore the importance of including dietary exposure in understanding metal accumulation in marine fish.     

Accumulation of metals by naturally growing herbaceous and tree species in iron ore tailings

The aim of the study was to identify pioneering species that naturally colonize Fe tailings and accumulation of heavy metals. Total, bioavailable, acid extractable and water‐soluble fractions were studied. After the second year onwards, along with nine herbaceous pioneering species, four tree species (Teactona grandis, Alstonia scholaris, Azadirachta indica and Peltaphorum) were found growing naturally. The study shows that some species could accumulate relatively high metal concentrations indicating internal detoxification of metals. The study revealed that T. grandis accumulated a higher concentration of metals than A. scholaris in the Fe tailings, but all concentrations were within the normal range. Native naturally colonizing plant species may be used for the bioremediation of iron tailings as initial cover species to stabilize and reduce erosion. The findings concluded that metal content in Fe tailings would not affect the natural establishment and growth of tree species; rather that higher Fe content promotes luxurious growth.     

Development of a dynamic model for estimating the food web transfer of chemicals in small aquatic ecosystems

A dynamic combined fate and food web model was developed to estimate the food web transfer of chemicals in small aquatic ecosystems (i.e. ponds). A novel feature of the modeling approach is that aquatic macrophytes (submerged aquatic vegetation) were included in the fate model and were also a food item in the food web model. The paper aims to investigate whether macrophytes are effective at mitigating chemical exposure and to compare the modeling approach developed here with previous modeling approaches recommended in the European Union (EU) guideline for risk assessment of pesticides. The model was used to estimate bioaccumulation of three hypothetical chemicals of varying hydrophobicity in a pond food web comprising 11 species. Three different macrophyte biomass densities were simulated in the model experiments to determine the influence of macrophytes on fate and bioaccumulation. Macrophytes were shown to have a significant effect on the fate and food web transfer of highly hydrophobic compounds with log K_OW > = 5. Modeled peak concentrations in biota were highest for the scenarios with the lowest macrophyte biomass density. The distribution and food web transfer of the hypothetical compound with the lowest hydrophobicity (log K_OW = 3) was not affected by the inclusion of aquatic macrophytes in the pond environment. For the three different hypothetical chemicals and at all macrophyte biomass densities, the maximum predicted concentrations in the top predator in the food web model were at least one order of magnitude lower than the values estimated using methods suggested in EU guidelines. The EU guideline thus provides a highly conservative estimate of risk. In our opinion, and subject to further model evaluation, a realistic assessment of dynamic food web transfer and risk can be obtained using the model presented here.     

Relationships among total recoverable and reactive metals and metalloid in St. Lawrence River sediment: bioaccumulation by chironomids and implications for ecological risk assessment

The availability and bioaccumulation of metals and metalloids, and the geochemical interactions among them, are essential to developing an ecological risk assessment (ERA) framework and determining threshold concentrations for these elements. The purpose of this study was to explore the relationships among total recoverable and reactive metals and metalloid in sediment and their bioaccumulation by chironomids. In the fall of 2004 and 2005, 58 stations located in the three fluvial lakes of the St. Lawrence River and its largest harbour area in Montreal, Canada, were sampled. Nine total recoverable and reactive metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and one metalloid (As) were measured in whole sediment using two extraction methods: HCl/HNO(3) and HCl 1N, respectively. The bioaccumulation of six metals (Cd, Cr, Cu, Ni, Pb and Zn) and As by chironomids was evaluated in a subset of 22 stations. Strong collinearities were observed between some total recoverable or reactive metal concentrations in sediment; two principal clusters, including collinear metals, were obtained. The first one included metals of mainly geological origin (Al, Cr, Fe, Mn, Ni), while the second one included As, Cd, Cu, Pb and Zn, which likely derive mainly from point sources of anthropogenic contamination. Each element also showed strong collinearity between their total recoverable and reactive forms (0.65< or =r < or =0.97). We can conclude that both chemical forms are equivalent for use in statistical models needed to explain biological responses and also in screening risk assessment. However, these relationships are not always proportional. Lower availability percentages were observed for Cd, Cu and Zn in the highly mixed-contaminated area of the Montreal Harbour, even though concentrations in sediment were higher. We observed a significant correlation (0.50< or =r < or =0.56) between concentrations in chironomids and concentrations of both total recoverable and reactive Cr and Pb in sediment. Arsenic was an exception, with accumulation by chironomids being highly related to reactive sediment concentrations. Finally, we observed variable influences of explanatory factors (e.g. sediment grain size, Al, Fe, Mn, S, TOC), depending on which metal or metalloid was being predicted in chironomids. In this context, it is difficult to choose a universal predictive method to explain the bioaccumulation of specific metals, and more research is still needed into normalization procedures that consider a combination of explanatory factors.     

Accumulation of mercury and selenium in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) from Nova Scotia, Canada

Total Hg, methyl-Hg (MeHg) and Se levels were measured in the brain of river otters (Lontra canadensis) and wild mink (Mustela vison) carcasses collected from Nova Scotia, Canada. Total Hg concentrations in the otters' brain were highly variable, ranging from 0.3 to 18.0 μg/g dw and were significantly higher in animals caught from inland areas of the province versus coastal animals. Similarly, inland otters contained significantly more MeHg in the brain than did coastal otters. MeHg was highly correlated with total Hg in both inland and coastal otters and represented on average approximately 82% of the total Hg. Selenium concentrations in the otter brain ranged from 1.0 to 7.8 μg/g dw but unlike Hg, there was no significant difference in Se levels between inland and coastal otters. There was a significant positive relationship between Se and total Hg concentrations in the otters with the molar ratio of Se:Hg approximately 1:1 for animals having an Hg concentration > 18 nmol/g dw.The non-random sampling protocol for the mink precluded extensive statistical analysis of the data. However, unlike otters, virtually all (i.e. 98%) of the total Hg in mink brain was present as MeHg in both inland and coastal mink. Also unlike the otter results, Se concentrations showed no relationship with either total or MeHg in both inland and coastal mink.The data suggest that mink and otters may have different mechanisms for managing high levels of Hg in the brain.     

Accumulation and effects of metals in caged carp and resident roach along a metal pollution gradient

Metal accumulation and effects on plasma Ca(2+), alanine transaminase (ALT) and fish condition factor were examined in caged carp (Cyprinus carpio) and resident roach (Rutilus rutilus) at four locations along the Grote Nete River system (Belgium). Cadmium and zinc accumulation were found in carp and roach, with highest concentrations at the most contaminated site (dissolved Cd: 1.82 microg/l, Zn: 967 microg/l). On the tissue level, highest cadmium concentrations were measured in kidneys of carp and roach, followed by gills, intestine and liver, while low concentrations were observed in carcass and muscle. For zinc, a similar pattern was observed (intestine>kidney>gills>liver>carcass>muscle). Comparison between species showed higher cadmium concentrations in feral roach, while zinc levels were lower, owing to the high zinc concentrations in control carp. Furthermore, comparison of metal concentrations between two sampling periods (2005 and 2000-2001) revealed a drastic decrease in cadmium concentration in gills, liver and muscle of roach, similar to the reduction in waterborne cadmium concentrations, while differences for zinc were much less pronounced. In addition to metal accumulation, increased metallothionein concentrations (approximately 2x) were found in carp and roach, while no metal-related effects were found on ALT, Ca(2+)or condition factor. However, negative effects on fish community structure, as assessed by the index of biotic integrity (IBI), were found along the pollution gradient and indicated long-term adverse effects of metal pollution.     

Delineation of Pb contamination pathways in two Pectinidae: The variegated scallop Chlamys varia and the king scallop Pecten maximus

Bioaccumulation of Pb was determined in Chlamys varia and Pecten maximus exposed to ²¹⁰Pb via seawater, food and sediment. Both scallops readily concentrated dissolved Pb with whole-body 7-d concentration factors of 250 ± 40 and 170 ± 70, respectively. In both species, more than 70% of Pb taken up from seawater was strongly retained within tissues (biological half-life > 1.5 month) whereas Pb ingested with phytoplankton was poorly assimilated (< 20%). As P. maximus lives buried in the sediment, this exposure pathway was assessed and showed low bioaccumulation efficiency for sediment-bound Pb (transfer factor < 0.015). Despite the poor transfer efficiency of Pb from food and sediment, the use of a global bioaccumulation model indicated that the particulate pathway (food and/or sediment) constituted the major bioaccumulation route of Pb in both scallops. Whatever the exposure pathway, the digestive gland and kidneys always played a major role in Pb accumulation. In scallop tissues, Pb was predominantly associated with the insoluble subcellular fraction, suggesting a low bioavailability of Pb for scallop consumers.     

Selenium accumulation in aquatic biota downstream of a uranium mining and milling operation

Uranium mining and milling operations have the potential to release trace elements such as arsenic, molybdenum, nickel, selenium and uranium and ions (e.g., sulfate, ammonium) into the receiving aquatic ecosystem. The major implication of elevated environmental selenium is its propensity to accumulate in the aquatic food chain, potentially impairing fish reproduction. The objective of this study was to investigate the accumulation of selenium in the major compartments of aquatic ecosystems (lakes) upstream and downstream of a uranium mine in northern Saskatchewan, Canada. Selenium concentrations in aquatic biota were elevated in the exposure lake although water and sediment concentrations were low (0.43 μg/L and 0.54 μg/g dry weight, respectively). Biomagnification of selenium resulted in approximately 1.5 to 6 fold increase in the selenium concentration between plankton, invertebrates and fish. However, no biomagnification was observed between forage and predatory fish. Although some aquatic biota (e.g., forage fish) exceeded the lower limit of the proposed 3 to 11 μg/g (dry weight) dietary toxicity threshold for fish, no adverse effects of selenium could be identified in this aquatic system. Continued environmental monitoring is recommended to avoid potential selenium impacts.     

Bioaccumulation of Cu-complex reactive dye by growing pellets of Penicillium oxalicum and its mechanism

In this paper bioaccumulation of Cu-complex reactive dye by growing pellets of Penicillium oxalicum and its mechanism was investigated. Shaking flasks experiment showed that 99.7% of dye removal at 400 mg/l was attained after 48 h contact. Column reactor experiment showed that air lift ferment tower was a suitable reactor for both pellets formation and dye bioaccumulation. Repeated inoculation of the dye-loaded pellets accelerated dye bioaccumulation, leading to complete dye removal within 12 h. Dye initially was adsorbed on surface of cell, followed by penetration into cytoplasm. During bioaccumulation, mycelium expanded unevenly and thickened locally in diameter, generating a chain of spindles along the mycelium. In addition, the cell walls grew loose and thickened remarkably, being 4-5 folds as thick as the control one. The loose cell wall may offer both dye accumulation space and route way for dye to enter cytoplasm. There were certain unknown active matters in cytoplasm, which played an important role in dye accumulation. Desorption experiments suggested that electrostatic attraction was mainly attributed to the dye bioaccumulation.     

Metal concentrations in digestive gland and mantle of Sepia officinalis from two coastal lagoons of Portugal

Concentrations of both essential (Fe, Cu, Zn) and non essential (Cd, Hg and Pb) metals were measured in the digestive gland and mantle of female cephalopods Sepia officinalis captured in two distinct lagoons in Portugal: Aveiro Lagoon, with a history of anthropogenic and industrial pollution, and Formosa Lagoon receiving urban effluents. We provide evidence for the following: (1) the digestive gland is the main target organ for both essential and non essential metals, frequently containing concentrations few orders of magnitude higher as compared to mantle; the sole exception from this was the Hg that is equally distributed in the two tissues; (2) unexpectedly, the higher levels of metals were found in animals captured in the less polluted lagoon, except for Cd whose bioavailability in Aveiro lagoon might be related to industrial sources, while the influence of Cd speciation in local pray composition should not be ruled out (3) size influenced metal concentration in different way: smaller individuals accumulated significantly more Cu, while Hg concentrations showed the opposite trend; (4) Cd is positively correlated to Zn and Cu in digestive gland of specimens collected in spring in Aveiro Lagoon, and no relationship was found in Formosa Lagoon; (5) the molar ratios Cd:Zn and Cd:Cu in digestive gland increased with body weight in specimens from Aveiro area, both ratios becoming particularly higher in older individuals. Metal-specific accumulation patterns in both mantle and digestive gland at the two sites are discussed in the light of their toxicological implications.     

Accumulation and in vivo tissue distribution of pollutant elements in Erica andevalensis

Erica andevalensis is an endemic shrub from an area in the southwest of Spain (Andalucia) characterized by acidic and contaminated soils. Scanning electron microscopy (SEM) of samples after conventional or cryo-fixation preparation protocols was used for morphological and anatomical studies. SEM coupled with EDX-analysis was employed to localise and quantify different elements within plant parts (leaves, stems and roots) in samples collected in the field. Morphological studies revealed that the species has typical adaptive structures to drought-stress such as rolled needle-like leaves, sunken stomata and a thick waxy cuticle on the upper epidermis. Roots were associated with fungi which formed intra and extra-cellular mycelia. The SEM studies showed that Cu was not sequestrated into the root tissues and was uniformly distributed in leaf tissues. Meanwhile, Pb was only localised within epidermal root tissues which indicates that its sequestration in an external matrix might represent a tolerance mechanism in this species. Iron was uniformly distributed throughout the leaves, while in roots it was predominantly retained on the epidermal cell walls. The exclusion and tolerance mechanisms adopted by this species to survive in mining areas indicate that it can be used successfully in the re-vegetation of contaminated areas.     

The effects of Aphis fabae infestation on the antioxidant response and heavy metal content in field grown Philadelphus coronarius plants

The purpose of this study was to explore a possible relationship between the soil availability of metals and their concentrations in various parts of Philadelphuscoronarius plants. Moreover, the possible impact of an aphid infestation on the contamination and antioxidant response of plants from the urban environment of Kraków and the reference rural area of Zagaje Stradowskie (southern Poland) was analyzed. The contents of the glutathione, proline, non-protein − SH groups, antioxidants, and phosphorous and the levels of guaiacol peroxidase and catalase activity in leaves and shoots either infested or not by the aphid Aphis fabae Scop., were measured. The potential bioavailability of metals (Cd; Cu; Ni; Pb; Zn) in the soil and their concentrations in P. coronarius plants originating from both sites were compared.The antioxidant responses were generally elevated in the plants in the polluted area. Such reactions were additionally changed by aphid infestation. Generally, the concentrations of metals in the HNO₃ and CaCl₂ extractants of the soils from two layers at the 0-20 and 20-40 cm depths from the polluted area were higher than in those from the reference area. Such differences were found for nickel and lead (in all examined extractants), zinc (in soil extractants from the layer at 20-40 cm) and cadmium (in HNO₃ extractants). Significant positive relationships between the lead concentrations in the soil and in the plants were found. In the parts of plants from the polluted area, higher concentrations of Pb and Zn (leaves and shoots) and Cd (shoots) were recorded. The shoots and leaves of plants infested with aphids had higher concentrations of Zn but lower Pb. Moreover, their leaves had higher contaminations of Cu and Ni. In conclusion, aphids affected not only the antioxidant response of the plants but also their contamination with metals, especially contamination of the leaves.     

Phytoprotective influence of bacteria on growth and cadmium accumulation in the aquatic plant Lemna minor

Certain plants are known to accumulate heavy metals, and can be used in remediation of polluted soil or water. Plant-associated bacteria, especially those that are metal tolerant, may enhance the total amount of metal accumulated by the plant, but this process is still unclear. In this study, we investigated metal enhancement vs. exclusion by plants, and the phytoprotective role plant-associated bacteria might provide to plants exposed to heavy metal. We isolated cadmium-tolerant bacteria from the roots of the aquatic plant Lemna minor grown in heavy metal-polluted waters, and tested these isolates for tolerance to cadmium. The efficiency of plants to accumulate heavy metal from their surrounding environment was then tested by comparing L. minor plants grown with added metal tolerant bacteria to plants grown axenically to determine, whether bacteria associated with these plants increase metal accumulation in the plant.Unexpectedly, cadmium tolerance was not seen in all bacterial isolates that had been exposed to cadmium. Axenic plants accumulated slightly more cadmium than plants inoculated with bacterial isolates. Certain isolates promoted root growth, but overall, addition of bacterial strains did not enhance plant cadmium uptake, and in some cases, inhibited cadmium accumulation by plants. This suggests that bacteria serve a phytoprotective role in their relationship with Lemna minor, preventing toxic cadmium from entering plants.     

Changes in the Daphnia magna midgut upon ingestion of copper oxide nanoparticles: A transmission electron microscopy study

This work is a follow-up of our previous paper (Heinlaan et al., 2008. Chemosphere 71, 1308-1316) where we showed about 50-fold higher acute toxicity of CuO nanoparticles (NPs) compared to bulk CuO to water flea Daphnia magna. In the current work transmission electron microscopy (TEM) was used to determine potential time-dependent changes in D. magna midgut epithelium ultrastructure upon exposure to CuO NPs compared to bulk CuO at their 48 h EC₅₀ levels: 4.0 and 175 mg CuO/L, respectively. Special attention was on potential internalization of CuO NPs by midgut epithelial cells. Ingestion of both CuO formulations by daphnids was evident already after 10 min of exposure. In the midgut lumen CuO NPs were dispersed whereas bulk CuO was clumped. By the 48th hour of exposure to CuO NPs (but not to equitoxic concentrations of bulk CuO) the following ultrastructural changes in midgut epithelium of daphnids were observed: protrusion of epithelial cells into the midgut lumen, presence of CuO NPs in circular structures analogous to membrane vesicles from holocrine secretion in the midgut lumen. Implicit internalization of CuO NPs via D. magna midgut epithelial cells was not evident however CuO NPs were no longer contained within the peritrophic membrane but located between the midgut epithelium microvilli. Interestingly, upon exposure to CuO NPs bacterial colonization of the midgut occurred. Ultrastructural changes in the midgut of D. magna upon exposure to CuO NPs but not to bulk CuO refer to its nanosize-related adverse effects.Time-dependent solubilisation of CuO NPs and bulk CuO in the test medium was quantified by recombinant Cu-sensor bacteria: by the 48th hour of exposure to bulk CuO, the concentration of solubilised copper ions was 0.05 ± 0.01 mg Cu/L that was comparable to the acute EC₅₀ value of Cu-ions to D. magna (48 h CuSO₄ EC₅₀ = 0.07 ± 0.01 mg Cu/L). However, in case of CuO NPs, the solubilised Cu-ions 0.01 ± 0.001 mg Cu/L, explained only part of the toxicity.     

The impact of increased oxygen conditions on metal-contaminated sediments part II: effects on metal accumulation and toxicity in aquatic invertebrates

The present study evaluated the effect of increasing oxygen concentrations in overlying surface water on the accumulation and toxicity of sediment-bound metals in the aquatic invertebrates Lumbriculus variegatus, Asellus aquaticus and Daphnia magna. A 54 days experiment using three experimental treatments (90% O₂ in overlying surface water, 40% O₂ and a non-polluted control) was conducted. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured in the superficial sediment layer (0-1 cm). At each time point, accumulated metal levels as well as the available energy stores were measured in L. variegatus and A. aquaticus and each time D. magna was exposed to surface water in a 24 h toxicity test. Additionally metallothionein-like protein (MTLP) induction was quantified in L. variegatus. Oxygen induced changes in sediment AVS resulted in faster accumulation of metals from contaminated sediments in A. aquaticus, while no differences in toxicity in this species were observed. Ag, Cr, As and Co accumulation as well as toxicity in water exposed D. magna were clearly enhanced after 54 days, caused by oxidation of metal-sulfide complexes. Due to their feeding and burrowing behaviour, metal accumulation and toxicity in L. variegatus was not influenced by geochemical characteristics. Nevertheless, a rapid induction of MTLP was observed in both the 90% O₂ and the 40% O₂ treatment. The present study showed that elevated oxygen concentrations in overlying surface water can directly enhance metal accumulation and toxicity in aquatic invertebrates, however this is highly dependent on the organisms ecology and most dominant metal exposure route (water vs. sediment).     

The Privatisation of Public Property: The Development of a Shopping Mall in Sydney and its Implications for Governance through Spatial Practices

This article examines the planning application and current operation of a new shopping mall in Sydney. I use this analysis to argue that the owners of the mall, Westfield, govern, through spatial practices, the physical space in the mall and the shopping practices of the people who enter the mall. By the term govern I mean the spatial practices by which Westfield controls the shopping area of the mall. I follow the idea of governance inspired by the governmentality literature to show that those connected with the mall are shaped by spatial practices which envisages subjects which are morally free and yet are shaped by shopping mall practices (Foucault, 1975, 1980).

By these spatial practices, I argue, Westfield creates a certain ambience in the mall, which conveys the message that the mall is an attractive and safe location, which welcomes certain customers and excludes others. This collective impression of mall atmosphere, I argue acts as a spatial practice, which in effect governs the mall.

One of the features of shopping malls is that public or civic space is replaced with 'semi-public space' owned by developers. In this context the protection of private property has coalesced with the preservation of public order (Gray and Gray, 2000, p. 23). In shopping malls people considered disruptive to shopping are excluded and shops found in the high street such as pawnshops and second-hand bookshops are not granted a tenancy. Other unwelcome folk include the homeless and groups of teenagers.

In this article I plan to analyse the spatial practices which restrict full public access to such places as the Hornsby shopping mall. Accordingly, I firstly show that the concept of property should rightly be seen as containing social ideas, secondly I discuss the nature of spatial practices, which materially and discursively lead to the exclusion of certain people and thirdly, describe notions of community which help define who are proper mall entrants.     

The Privatisation of Public Property: the Development of a Shopping Mall in Sydney and its Implications for Governance through Spatial Practices

This article examines the planning application and current operation of a new shopping mall in Sydney. I use this analysis to argue that the owners of the mall, Westfield, govern, through spatial practices, the physical space in the mall and the shopping practices of the people who enter the mall. By the term govern I mean the spatial practices by which Westfield controls the shopping area of the mall. I follow the idea of governance inspired by the governmentality literature to show that those connected with the mall are shaped by spatial practices which envisages subjects which are morally free and yet are shaped by shopping mall practices (Foucault, 1975, 1980).

By these spatial practices, I argue, Westfield creates a certain ambience in the mall, which conveys the message that the mall is an attractive and safe location, which welcomes certain customers and excludes others. This collective impression of mall atmosphere, I argue acts as a spatial practice, which in effect governs the mall.

One of the features of shopping malls is that public or civic space is replaced with 'semi-public space' owned by developers. In this context the protection of private property has coalesced with the preservation of public order (Gray and Gray, 2000, p. 23). In shopping malls people considered disruptive to shopping are excluded and shops found in the high street such as pawnshops and second-hand bookshops are not granted a tenancy. Other unwelcome folk include the homeless and groups of teenagers.

n this article I plan to analyse the spatial practices which restrict full public access to such places as the Hornsby shopping mall. Accordingly, I firstly show that the concept of property should rightly be seen as containing social ideas, secondly I discuss the nature of spatial practices, which materially and discursively lead to the exclusion of certain people and thirdly, describe notions of community which help define who are proper mall entrants.     

Comparison of nitrification inhibition by metals in batch and continuous flow reactors

Stringent effluent discharge limits for nitrogen require development of assays to accurately and rapidly determine whether a wastewater stream will inhibit nitrification. The suitability of a short-term extant batch respirometric assay to predict nitrification inhibition by metals (Cu, Zn, Ni and Cd) in continuous flow reactors was evaluated. Linear metal partition coefficients were determined to be 78.42+/-2.46, 0.54+/-0.04, 0.05+/-0.01 and 0.60+/-0.01 L/g biomass COD in batch experiments (pH=7.5) for Cu, Zn, Ni and Cd, respectively. A mass-balance model, incorporating metal partitioning, adequately fit the metal concentration profiles in the continuous flow reactor during and after a 24-hour shock load. However, the short-term batch assays significantly underestimated observed inhibition in the continuous flow reactor. The underestimation was, most likely, due to slow kinetics of Zn, Ni and Cd internalization and an exacerbation effect due to continued metal exposure in the continuous flow reactor. The discrepancy in inhibition between batch and continuous systems was the largest for Cu, presumably due to its unique mode of action, which involves loss of cell membrane integrity. Hence, using results from short-term batch respirometric assays to infer responses in continuous flow reactors with longer exposure should be done with caution and must accommodate partitioning behavior and internalization kinetics.     

Mercury bioacumulation in four tissues of Podocnemis erythrocephala (Podocnemididae: Testudines) as a function of water parameters

A number of environmental factors influence the dynamics of Hg in aquatic ecosystems, yet few studies have examined these factors for turtles, especially from South America. Red-headed river turtle (Podocnemis erythrocephala) is easy to capture in the black waters of Rio Negro, making it the turtle species that is consumed most often by people of the region. In this study, environmental factors and turtle size were investigated to determine their influence on the Hg concentration in blood, muscle, liver and carapace of the red-headed river turtle. Factors investigated included turtle length, pH, dissolved organic carbon and availability of potential methylation sites (floodplain forests and hydromorphic soils). The study was conducted in the Rio Negro basin, where we collected water and turtle blood, muscle, liver and carapace samples from 12 tributaries for chemical analysis. Through radar imagery and existing soil maps with GIS, the percentage of alluvial floodplains and hydromorphic soils (potential methylation sites) was estimated for each drainage basin at sampling points. The mean Hg concentration in blood of P. erythrocephala was 1.64 ng g^− 1 (SD = 1.36), muscle 33 ng g^− 1 (SD = 11), liver 470 ng g^− 1 (SD = 313) and carapace 68 ng g^− 1 (SD = 32). Sex or length did not influence the Hg concentration in P. erythrocephala blood, muscle and liver, but Hg increased in carapace tissue when length size increased (ANCOVA p = 0.007). In the multiple regression analysis, none of the environmental factors studied had a significant relation with blood, muscle, liver and carapace. P. erythrocephala moves among habitats and in the open and interconnected aquatic systems of the Amazon basin, characterized by high levels of limnological variability, a good bioindicator of Hg concentration needs to be relatively sedentary to represent a specific habitat. However, the levels of Hg in liver were sufficient to pose a potential risk to humans that consume them, suggesting the usefulness of P. erythrocephala as a bioindicator.     

Toxicity of metals and metal mixtures: analysis of concentration and time dependence for zinc and copper

The toxic effects of heavy metals, zinc and copper, in unary and binary solutions were studied using the Microtox acute toxicity test which relies upon the attenuation of light intensity emitted by Vibrio fischeri. The toxic effect Gamma (ratio of the light intensity lost at time t to the light intensity remaining at time t) of zinc could be related to its concentration [X] by a two-parameter equation Gamma=a(1-exp(-b[X])), where parameter a was a function of time and b equal to 0.88L/mg. The toxic effect of zinc asymptotically approached a maximum with respect of to concentration at all times. The toxic effect of copper was fundamentally different from that of zinc, and increased exponentially with concentration without any limiting maximum value. It could also be described by a two-parameter equation, however, the equation had the form Gamma=aexp(b[X]), where parameter a was a constant and b a function of time. The different functional dependencies (of the toxic effect on the metal concentration) of zinc and copper indicate that different toxicity/inhibition mechanisms were possibly responsible for the attenuation of light intensity for the two metals. The toxic effects of binary mixtures were substantially higher than those expected on the basis of additivity of individual metals. No simple correlations were obtained that could relate the toxic effect of binary mixture to those of individual metals. A better understanding of metal-microbe interactions is needed for achieving predictive capability for toxic effect of mixtures.