Andrea Garcia Bravo

Effects of a sewage treatment plant outlet pipe extension on the distribution of contaminants in the sediments of the Bay of Vidy, Lake Geneva, Switzerland.

In 2001, the municipality of Lausanne extended the outlet pipe of the sewage treatment plant into the Bay of Vidy (Lake Geneva, Switzerland) as a measure to reduce bacterial water pollution and sediment contamination close to the lake beaches. The aim of the present study was to assess the impact of this measure. Lake bottom sediments were collected and analyzed for grain size, organic matter, organic carbon, nitrogen, phosphorus, heavy metals and hydrophobic organic compounds to evaluate their concentration and spatial distribution. Our results demonstrate that, compared to results obtained before the outlet pipe prolongation, the surface area of highly contaminated sediments was reduced by one third after the pipe extension. However, contaminant concentrations are still high and the accumulation of pollutants may represent a significant source of toxicity for benthic organisms. One concludes that contaminant reduction at the source will be necessary for a further improvement.

Sources and remediation techniques for mercury contaminated soil

Mercury (Hg) in soils has increased by a factor of 3 to 10 in recent times mainly due to combustion of fossil fuels combined with long-range atmospheric transport processes. Other sources as chlor-alkali plants, gold mining and cement production can also be significant, at least locally. This paper summarizes the natural and anthropogenic sources that have contributed to the increase of Hg concentration in soil and reviews major remediation techniques and their applications to control soil Hg contamination. The focus is on soil washing, stabilisation/solidification, thermal treatment and biological techniques; but also the factors that influence Hg mobilisation in soil and therefore are crucial for evaluating and optimizing remediation techniques are discussed. Further research on bioremediation is encouraged and future study should focus on the implementation of different remediation techniques under field conditions.

Molecular composition of organic matter controls methylmercury formation in boreal lakes

A detailed understanding of the formation of the potent neurotoxic methylmercury is needed to explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercury methylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments.

Mercury bioaccumulation in the aquatic plant Elodea nuttallii in the field and in microcosm : Accumulation in shoots from the water might involve copper transporters

Previous studies suggest that macrophytes might participate in bioaccumulation and biomagnification of toxic mercury (Hg) in aquatic environment. Hg bioaccumulation and uptake mechanisms in macrophytes need therefore to be studied. Amongst several macrophytes collected in an Hg contaminated reservoir in Romania, Elodea nuttallii showed a high organic and inorganic Hg accumulation and was then further studied in the laboratory. Tolerance and accumulation of Hg of this plant was also high in the microcosm. Basipetal transport of inorganic Hg was predominant, whereas acropetal transport of methyl-Hg was observed with apparently negligible methylation or demethylation in planta. Hg concentrations were higher in roots>leaves>stems and in top>middle>bottom of shoots. In shoots, more than 60% Hg was found intracellularly where it is believed to be highly available to predators. Accumulation in shoots was highly reduced by cold, death and by competition with Cu(+). Hg in E. nuttallii shoots seems to mainly originate from the water column, but methyl-Hg could also be remobilized from the sediments and might drive in part its entry in the food web. At the cellular level, uptake of Hg into the cell sap of shoots seems linked to the metabolism and to copper transporters. The present work highlights an important breakthrough in our understanding of Hg accumulation and biomagnifications: the remobilization of methyl-Hg from sediments to aquatic plants and differences in uptake mechanisms of inorganic and methyl-Hg in a macrophyte.

Effect of Elodea nuttallii roots on bacterial communities and MMHg proportion in a Hg polluted sediment.

The objective of this study was to assess the effect of a rooted macrophyte Elodea nuttallii on rhizosphere bacterial communities in Hg contaminated sediments. Specimens of E. nuttallii were exposed to sediments from the Hg contaminated Babeni reservoir (Olt River, Romania) in our microcosm. Plants were allowed to grow for two months until they occupied the entirety of the sediments. Total Hg and MMHg were analysed in sediments where an increased MMHg percentage of the total Hg in pore water of rhizosphere sediments was found. E. nuttallii roots also significantly changed the bacterial community structure in rhizosphere sediments compared to bulk sediments. Deltaproteobacteria dominated the rhizosphere bacterial community where members of Geobacteraceae within the Desulfuromonadales and Desulfobacteraceae were identified. Two bacterial operational taxonomic units (OTUs) which were phylogenetically related to sulfate-reducing bacteria (SRB) became abundant in the rhizosphere. We suggest that these phylotypes could be potentially methylating bacteria and might be responsible for the higher MMHg percentage of the total Hg in rhizosphere sediments. However, SRB were not significantly favoured in rhizosphere sediments as shown by qPCR. Our findings support the hypothesis that rooted macrophytes created a microenvironment favorable for Hg methylation. The presence of E. nuttallii in Hg contaminated sediments should therefore not be overlooked.

High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges

Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STPs effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe(2+) and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable.

The effect of lake browning and respiration mode on the burial and fate of carbon and mercury in the sediment of two boreal lakes

In many northern temperate regions, the water color of lakes has increased over the past decades (lake browning), probably caused by an increased export of dissolved organic matter from soils. We i ...

Mercury in the food chain of the Lagoon of Venice, Italy

Sediments and biota samples were collected in a restricted area of the Lagoon of Venice and analysed for total mercury, monomethyl mercury (MMHg), and nitrogen and carbon isotopes. Results were used to examine mercury biomagnification in a complex food chain. Sedimentary organic matter (SOM) proved to be a major source of nutrients and mercury to primary consumers. Contrary to inorganic mercury, MMHg was strongly biomagnified along the food chain, although the lognormal relationship between MMHg and δ(15)N was less constrained than generally reported from lakes or coastal marine ecosystems. The relationship improved when logMMHg concentrations were plotted against trophic positions derived from baseline δ(15)N estimate for primary consumers. From the regression slope a mean MMHg trophic magnification factor of 10 was obtained. Filter-feeding benthic bivalves accumulated more MMHg than other primary consumers and were probably important in MMHg transfer from sediments to higher levels of the food chain.

Kinetics of plant material mass loss and DNA release in freshwater column

In situ microcosm study investigated both the kinetics of plant material mass loss and qualitative and quantitative aspects of DNA content by researching leaf degradation of two specific varieties of tomato (Admiro and Palmiro) in freshwater column incubated for 40 days. A two-compartment first order model fitted both tomato dry matter and DNA content mass loss well. The composite half-decrease times were, respectively, 1.13 ± 0.51 and 1.16 ± 0.47 days for Palmiro and Admiro. The composite half-disappearance times of total DNA in Palmiro and Admiro tomato leaves were, respectively, 0.92 ± 0.31 and 0.88 ± 0.26 days. Genomic analysis indicates that before having been released, a significant amount of DNA may be degraded in plant tissues decomposing in water column. The results of this study confirm the hypothesis that release of plant DNA in aquatic environments can be caused by intracellular nuclease activities in the plants cells and by enzymatic degradation of cell structures by residual microbial activities in leaves.

Correction to Role of Settling Particles on Mercury Methylation in the Oxic Water Column of Freshwater Systems

In our recently published paper, “Role of settling particles on mercury methylation in the oxic water column of freshwater systems”, we unfortunately made several mistakes in the reference list. To correct this oversight, we submit this erratum indicating the number of the reference cited in our published paper followed by the correct reference that should have been initially included. Reference #2 Jaquet, J. M.; Nirel, P.; Martignier, A. Preliminary investigations on picoplankton-related precipitation of alkaline-earth metal carbonates in meso-oligotrophic lake Geneva (Switzerland). J. Limnol. 2013, 72 (3), 592−605. Correct reference: Mason, R. P., et al. Mercury biogeochemical cycling in the ocean and policy implications. Environ. Res. 2012, 119, 101−117; DOI: 10.1016/j.envres.2012.03.013. Reference #3 Wang, Q.; Feng, X. B.; Yang, Y. F.; Yan, H. Y., Spatial and temporal variations of total and methylmercury concentrations in plankton from a mercury-contaminated and eutrophic reservoir in Guizhou Province, China. Environ. Toxicol. Chem. 2011, 30 (12), 2739−2747. Correct reference: Eckley, C. S.; Hintelmann, H. Determination of mercury methylation potentials in the water column of lakes across Canada. Sci. Tot. Environ. 2006, 368, 111−125; DOI: 10.1016/j.scitotenv.2005.09.042. Reference #8 Gorski, P. R.; Armstrong, D. E.; Hurley, J. P.; Krabbenhoft, D. P. Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga. Environ. Pollut. 2008, 154 (1), 116−123. Correct reference: Gilmour, C. C., et al. Mercury methylation by novel microorganisms from new environments. Environ. Sci. Technol. 2013, 47, 11810−11820; DOI: 10.1021/ es403075t. Reference #10 Weltje, G. J.; Tjallingii, R., Calibration of XRF core scanners for quantitative geochemical logging of sediment cores: Theory and application. Earth Planet Sci. Lett. 2008, 274 (3−4), 423−438. Correct reference: Mason, R. P.; Fitzgerald, W. F. Alkylmercury species in the Equatorial Pacific. Nature 1990, 347, 457−459; DOI: 10.1038/347457a0. Reference #14 Montgomery, S.; Mucci, A.; Lucotte, M.; Pichet, P., Total dissolved mercury in the water column of several natural and artificial aquatic systems of Northern Quebec (Canada). Can. J. Fish Aquat. Sci. 1995, 52 (11), 2483− 2492. Correct reference: Heimburger, L. E., et al. Methyl mercury distributions in relation to the presence of nanoand picophytoplankton in an oceanic water column (Ligurian Sea, Northwestern Mediterranean). Geochim. Cosmochim. Acta 2010, 74, 5549−5559; DOI: 10.1016/j.gca.2010.06.036. Reference #15 Roulet, M.; Lucotte, M., Geochemistry of mercury in pristine and flooded ferralitic soils of a Ttopical rain-forest in French-Guiana, South-America. Water, Air, Soil Pollut. 1995, 80 (1−4), 1079−1088. Correct reference: Lehnherr, I., St Louis, V. L., Hintelmann, H.; Kirk, J. L. Methylation of inorganic mercury in polar marine waters. Nat. Geosci. 2011, 4, 298−302; DOI: 10.1038/ NGEO1134. Reference #16: Dmytriw, R.; Mucci, A.; Lucotte, M.; Pichet, P., The partitioning of mercury in the solid components of dry and flooded forest soils and sediments from a hydroelectric reservoir, Quebec (Canada). Water, Air, Soil Pollut. 1995, 80 (1−4), 1099−1103. Correct reference: Monperrus, M., et al. Mercury methylation, demethylation and reduction rates in coastal and marine surface waters of the Mediterranean Sea. Mar. Chem. 2007, 107, 49−63; DOI: 10.1016/j.marchem.2007.01.018. Addition/Correction