The relationships between mercury and selenium in plankton and fish from a tropical food web

Background, aim, and scope  Selenium (Se) has been shown to reduce mercury (Hg) bioavailability and trophic transfer in aquatic ecosystems. The study of methylmercury (MeHg) and Se bioaccumulation by plankton is therefore of great significance in order to obtain a better understanding of the estuarine processes concerning Hg and Se accumulation and biomagnification throughout the food web. In the western South Atlantic, few studies have documented trace element and MeHg in fish tissues. No previous study about trace elements and MeHg in plankton has been conducted concerning tropical marine food webs. Se, Hg, and MeHg were determined in two size classes of plankton, microplankton (70–290 μm) and mesoplankton (≥290 μm), and also in muscle tissues and livers of four fish species of different trophic levels (Mugil liza, a planktivorous fish; Bagre spp., an omnivorous fish; Micropogonias furnieri, a benthic carnivorous fish; and Centropomus undecimalis, a pelagic carnivorous fish) from a polluted estuary in the Brazilian Southeast coast, Guanabara Bay. Biological and ecological factors such as body length, feeding habits, and trophic transfer were considered in order to outline the relationships between these two elements. The differences in trace element levels among the different trophic levels were investigated. Materials and methods  Fish were collected from July 2004 to August 2005 at Guanabara Bay. Plankton was collected from six locations within the bay in August 2005. Total mercury (THg) was determined by cold vapor atomic absorption spectrometry (CV-AAS) with sodium borohydride as a reducing agent. MeHg analysis was conducted by digesting samples with an alcoholic potassium hydroxide solution followed by dithizone-toluene extraction. MeHg was then identified and quantified in the toluene layer by gas chromatography with an electron capture detector (GC-ECD). Se was determined by AAS using graphite tube with Pin platform and Zeeman background correction. Results and discussion  Total mercury, MeHg, and Se increased with plankton size class. THg and Se values were below 2.0 and 4.8 μg g⁻¹ dry wt in microplankton and mesoplankton, respectively. A large excess of molar concentrations of Se in relation to THg was observed in both plankton size class and both fish tissues. Plankton presented the lowest concentrations of this element. In fish, the liver showed the highest THg and Se concentrations. THg and Se in muscle were higher in Centropomus undecimalis (3.4 and 25.5 nmol g⁻¹) than in Micropogonias furnieri (2.9 and 15.3 nmol g⁻¹), Bagre spp (1.3 and 3.4 nmol g⁻¹) and Mugil liza (0.3 and 5.1 nmol g⁻¹), respectively. The trophic transfer of THg and Se was observed between trophic levels from prey (considering microplankton and mesoplankton) to top predator (fish). The top predators in this ecosystem, Centropomus undecimalis and Micropogonias furnieri, presented similar MeHg concentrations in muscles and liver. Microplankton presented lower ratios of methylmercury to total mercury concentration (MeHg/THg) (34%) than those found in mesoplankton (69%) and in the muscle of planktivorous fish, Mugil liza (56%). The other fish species presented similar MeHg/THg in muscle tissue (of around 100%). M. liza showed lower MeHg/THg in the liver than C. undecimalis (35%), M. furnieri (31%) and Bagre spp. (22%). Significant positive linear relationships were observed between the molar concentrations of THg and Se in the muscle tissue of M. furnieri and M. liza. These fish species also showed significant inverse linear relationships between hepatic MeHg and Se, suggesting a strong antagonistic effect of Se on MeHg assimilation and accumulation. Conclusions  Differences found among the concentrations THg, MeHg, and Se in microplankton, mesozooplankton, and fishes were probably related to the preferred prey and bioavailability of these elements in the marine environment. The increasing concentration of MeHg and Se at successively higher trophic levels of the food web of Guanabara Bay corresponds to a transfer between trophic levels from the lower trophic level to the top-level predator, suggesting that MeHg and Se were biomagnified throughout the food web. Hg and Se were positively correlated with the fish standard length, suggesting that larger and older fish bioaccumulated more of these trace elements. THg, MeHg, and Se were a function of the plankton size. Recommendations and perspectives  There is a need to assess the role of selenium in mercury accumulation in tropical ecosystems. Without further studies of the speciation of selenium in livers of fishes from this region, the precise role of this element, if any, cannot be verified in positively affecting mercury accumulation. Further studies of this element in the study of marine species should include liver samples containing relatively high concentrations of mercury. A basin-wide survey of selenium in fishes is also recommended.     

Nonideal transport of contaminants in heterogeneous porous media: 10. Impact of co-solutes on sorption by porous media with low organic-carbon contents

The impact of co-solutes on sorption of tetrachloroethene (PCE) by two porous media with low organic-carbon contents was examined by conducting batch experiments. The two media (Borden and Eustis) have similar physical properties, but significantly different organic-carbon (OC) contents. Sorption of PCE was nonlinear for both media, and well-described by the Freundlich equation. For the Borden aquifer material (OC = 0.03%), the isotherms measured with a suite of co-solutes present (1,2-dichlorobenzene, bromoform, carbon tetrachloride, and hexachloroethane) were identical to the isotherms measured for PCE alone. These results indicate that there was no measurable impact of the co-solutes on PCE sorption for this system. In contrast to the Borden results, there was a measurable reduction in sorption of PCE by the Eustis soil (OC = 0.38%) in the presence of the co-solutes. The organic-carbon fractions of both media contain hard-carbon components, which have been associated with the manifestation of nonideal sorption phenomena. The disparity in results observed for the two media may relate to relative differences in the magnitude and geochemical nature of these hard-carbon components.     

Kinetics and pathways for the debromination of polybrominated diphenyl ethers by bimetallic and nanoscale zerovalent iron: effects of particle properties and catalyst

Polybrominated diphenyl ethers (PBDEs) are recognized as a new class of widely-distributed and persistent contaminants for which effective treatment and remediation technologies are needed. In this study, two kinds of commercially available nanoscale Fe⁰ slurries (Nanofer N25 and N25S), a freeze-dried laboratory-synthesized Fe⁰ nanoparticle (nZVI), and their palladized forms were used to investigate the effect of particle properties and catalyst on PBDE debromination kinetics and pathways. Nanofers and their palladized forms were found to debrominate PBDEs effectively. The laboratory-synthesized Fe⁰ nanoparticles also debrominated PBDEs, but were slower due to deactivation by the freeze-drying and stabilization processes in the laboratory synthesis. An organic modifier, polyacrylic acid (PAA), bound on N25S slowed PBDE debromination by a factor of three to four compared to N25. The activity of palladized nZVI (nZVI/Pd) was optimized at 0.3 Pd/Fe wt% in our system. N25 could debrominate selected environmentally-abundant PBDEs, including BDE 209, 183, 153, 99, and 47, to end products di-BDEs, mono-BDEs and diphenyl ether (DE) in one week, while nZVI/Pd (0.3 Pd/Fe wt%) mainly resulted in DE as a final product. Step-wise major PBDE debromination pathways by unamended and palladized Fe⁰ are described and compared. Surface precursor complex formation is an important limiting factor for palladized Fe⁰ reduction as demonstrated by PBDE pathways where steric hindrance and rapid sequential debromination of adjacent bromines play an important role.     

Atrazine promotes biochemical changes and DNA damage in a Neotropical fish species

The effects of Atrazine, an herbicide used worldwide and considered as a potential contaminant in aquatic environments, were assessed on the Neotropical fish Prochilodus lineatus acutely (24 and 48 h) exposed to 2 or 10 μg L⁻¹ of atrazine by using a set of biochemical and genetic biomarkers. The following parameters were measured in the liver: activity of the biotransformation enzymes ethoxyresorufin-O-deethylase (EROD) and glutathione S transferase (GST), antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), content of reduced glutathione (GSH), generation of reactive oxygen species (ROS) and occurrence of lipid peroxidation (LPO); in brain and muscle the activity of acetylcholinesterase (AChE) and DNA damage (comet assay) on erythrocytes, gills and liver cells. A general decreasing trend on the biotransformation and antioxidant enzymes was observed in the liver of P. lineatus exposed to atrazine; except for GR, all the other antioxidant enzymes (SOD, CAT and GPx) and biotransformation enzymes (EROD and GST) showed inhibited activity. Changes in muscle or brain AChE were not detected. DNA damage was observed in the different cell types of fish exposed to the herbicide, and it was probably not from oxidative origin, since no increase in ROS generation and LPO was detected in the liver. These results show that atrazine behaves as enzyme inhibitor, impairing hepatic metabolism, and produces genotoxic damage to different cell types of P. lineatus.     

Bioaccessibility of trace elements as affected by soil parameters in smelter-contaminated agricultural soils: a statistical modeling approach

An investigation was undertaken to identify the most significant soil parameters that can be used to predict Cd, Pb, and Zn bioaccessibility in smelter-contaminated agricultural soils. A robust model was established from an extended database of soils by using: (i) a training set of 280 samples to select the main soil parameters, to define the best population to be taken into account for the model elaboration, and to construct multivariate regression models, and (ii) a test set of 110 samples to validate the ability of the regression models. Total carbonate, organic matter, sand, P(2)O(5), free Fe-Mn oxide, and pseudototal Al and trace element (TE) contents appeared as the main variables governing TE bioaccessibility. The statistical modeling approach was reasonably successful, indicating that the main soil factors influencing the bioaccessibility of TEs were taken into account and the predictions could be applicable for further risk evaluation in the studied area.     

Particle size distribution of airborne Aspergillus fumigatus spores emitted from compost using membrane filtration

Information on the particle size distribution of bioaerosols emitted from open air composting operations is valuable in evaluating potential health impacts and is a requirement for improved dispersion simulation modelling. The membrane filter method was used to study the particle size distribution of Aspergillus fumigatus spores in air 50 m downwind of a green waste compost screening operation at a commercial facility. The highest concentrations (approximately 8 × 10⁴ CFU m⁻³) of culturable spores were found on filters with pore diameters in the range 1–2 μm which suggests that the majority of spores are emitted as single cells. The findings were compared to published data collected using an Andersen sampler. Results were significantly correlated (p < 0.01) indicating that the two methods are directly comparable across all particles sizes for Aspergillus spores.     

Study of lead phytoavailability for atmospheric industrial micronic and sub-micronic particles in relation with lead speciation

Particles from channelled emissions of a battery recycling facility were size-segregated and investigated to correlate their speciation and morphology with their transfer towards lettuce. Microculture experiments carried out with various calcareous soils spiked with micronic and sub-micronic particles (1650 ± 20 mg Pb kg⁻¹) highlighted a greater transfer in soils mixed with the finest particles. According to XRD and Raman spectroscopy results, the two fractions presented differences in the amount of minor lead compounds like carbonates, but their speciation was quite similar, in decreasing order of abundance: PbS, PbSO₄, PbSO₄·PbO, α-PbO and Pb⁰. Morphology investigations revealed that PM_2.5 (i.e. Particulate Matter 2.5 composed of particles suspended in air with aerodynamic diameters of 2.5 μm or less) contained many Pb nanoballs and nanocrystals which could influence lead availability. The soil-plant transfer of lead was mainly influenced by size and was very well estimated by 0.01 M CaCl₂ extraction.     

Levels and pattern of polybrominated diphenyl ethers in eggs of Antarctic seabirds: Endemic versus migratory species

Chinstrap and gentoo penguins are endemic species that live year round south of the Antarctic Convergence. South polar skua is a migratory seabird that can be observed in Antarctica during the breeding season (i.e., austral summer). This study compares concentration and pattern of polybrominated diphenyl ethers (PBDEs) in eggs of seabirds breeding at King George Island, Antarctic Peninsula. PBDEs in south polar skua eggs are approximately 20 times higher than in penguin eggs suggesting that skuas are more exposed to contaminants during the non-breeding season when they migrate to waters of the northern hemisphere. The pattern of PBDE congeners also differs between south polar skua and penguin eggs. The latter exhibited a pattern similar to that found in the local biota. In contrast, the congener pattern in south polar skua eggs suggests that birds breeding at King George Island may winter in the northwestern Pacific Ocean.