Tissue Distribution of Radiolabeled 110mAg Nanoparticles in Fish: Arctic Charr (Salvelinus alpinus).

This study presents the first whole-body tissue distributions of dissolved (AgI) and 20 nm silver nanoparticles (Ag0NPs20) in fish (Arctic charr, Salvelinus alpinus). The distributions are provided for fish exposed to three different treatments: (i) intravenous (IV), (ii) dietary, and (iii) waterborne. Quantitative whole-body autoradiography (QWBA) analyses obtained on high-resolution images reveal distinct silver distribution patterns according to the treatments. The IV exposures showed that AgNPs20 were mainly located in bile and kidney after 8 d, while AgI was distributed through the whole body and reached particular tissues such as bones, eyes, skin, liver, spleen, kidney, and intestine. The Ag0NPs20 distribution with the dietary exposures suggests that some dissolution occurred within fish organs. We propose that dissolved silver could later precipitate as chloride, sulfide, or selenide and be incorporated in bones during the growth. Consequently, it is yet difficult to state if Ag0NPs20 cross biological barriers. Finally, the waterborne exposures revealed that the gills can capture Ag0NPs20, but in small quantities. This suggests that the stability of Ag0NPs20 in water is critical for the uptake via the gills.

Mytilus trossulus and hybrid (M. edulis-M. trossulus) - New hosts organisms for pathogenic microalgae Coccomyxa sp. from the Estuary and northwestern Gulf of St. Lawrence, Canada.

During summer 2014-2017, wild mytilid mussels, highly infested with the pathogenic Coccomyxa-like microalgae, were collected along the Estuary and northwestern part of Gulf of St. Lawrence (Québec, Canada). Molecular identification showed that algae can be assigned to a single taxon, Coccomyxa sp. (KJ372210), whereas hosts are represented by Mytilus edulis, M. trossulus and hybrid between these two species. This is the first record of M. trossulus and hybrid among hosts of this pathogenic alga. Our results are indicative of a possible widespread distribution of Coccomyxa sp. in the Lower St. Lawrence Estuary and along coastal waters of Canadian Maritime provinces.

Cytotoxicity and Physiological Effects of Silver Nanoparticles on Marine Invertebrates.

Silver nanoparticles (AgNPs) incorporation in commercial products is increasing due to their remarkable physical and chemical properties and their low cost on the market. Silver has been known for a long time to be highly toxic to bacterial communities, aquatic organisms, and particularly to marine biota. Strong chloro-complexes dominate Ag speciation in seawater and facilitate its persistence in dissolved form. It has a great impact on marine organisms because low concentration of silver can lead to strong bioaccumulation, partly because the neutral silver chloro complex (AgCl0) is highly bioavailable. Owing to the fact that estuaries and coastal areas are considered as the ultimate fate for AgNPs, the study of their toxic effects on marine invertebrates can reveal some environmental risks related to nanosilver exposure. In an attempt to reach this goal, many invertebrate taxa including mollusks, crustaceans, echinoderms and polychaetes have been used as biological models. The main findings related to AgNP toxicity and marine invertebrates are summarized hereafter. Some cellular mechanisms involving nano-internalization (cellular uptake, distribution and elimination), DNA damaging, antioxidant cellular defenses and protein expression are discussed. Physiological effects on early stage development, silver metabolic speciation, immune response, tissue damaging, anti-oxidant effects and nano-depuration are also described. Finally, we paid attention to some recent interesting findings using sea urchin developmental stages and their cells as models for nanotoxicity investigation. Cellular and physiological processes characterizing sea urchin development revealed new and multiple toxicity mechanisms of both soluble and nano forms of silver.

Cell-mediated immune response of postmetamorphic sea urchin juveniles against infectious stages of diatom Cylindrotheca closterium (Bacillariophyceae).

In this study, successive infectious stages by diatom Cylindrotheca closterium (Bacillariophyceae) are described for the first time during the early development of sea urchin at low temperature (8°C). Diatom cell-types enclosed or not by typical theca were capable of infection. As an immune response, red spherulocytes and amoebocytes migrated towards infested areas and restrained the infection spreading over shells in 2- and 3-month old urchins. Only amoebocyte cells appeared to be involved in the immune reaction of 1-month old specimens which turned out to be a less effective fence to stop infestation. The effectiveness of the inflammatory process caused by diatoms within sea urchin spines seemed to vary as a function of urchin age, cohort's type and individual cell pool.

Toxicological interactions of silver nanoparticles and organochlorine pesticides in mouse peritoneal macrophages.

Nanotechnology occupies a prominent space in economy and science due to the beneficial properties of nanomaterials. However, nanoparticles may pose risks to living organisms due to their adsorption and pro-oxidative properties. The aim of the current study was to investigate the effects of polymer-coated silver nanoparticles (AgNPs) and organochlorine pesticides (OCPs), as well as their combined effects on mouse peritoneal macrophages. Macrophages were isolated and exposed to three concentrations of AgNPs (groups: N1 = 30, N2 = 300 and N3 = 3000 ng.ml(-1)), two concentrations of OCPs (groups: P1 = 30 and P2 = 300 ng.ml(-1)) and the six possible combinations of these two contaminants for 24 h. AgNPs had irregular shape, Feret diameter of 8.7 ± 7.5 nm and zeta potential of -28.7 ± 3.9 mV in water and -10.7 ± 1.04 mV in culture medium. OCP mixtures and the lower concentrations of AgNPs had no detectable effects on cell parameters, but the highest AgNPs concentration showed high toxicity (trypan blue and MTT assays) resulting in morphological changes, increase of nitric oxide levels and phagocytic index. Foremost, the association of N3 and P2 led to distinct effects from those observed under single exposure.

First record of the green microalgae Coccomyxa sp. in blue mussel Mytilus edulis (L.) from the Lower St. Lawrence Estuary (Québec, Canada).

During autumn 2012 and spring 2013, blue mussels Mytilus edulis (L.) with strongly deformed (L-shaped) posterior shell margins and green spots in soft tissue (microalgae) were collected from intertidal zone along the south shore of the Lower St. Lawrence Estuary near Rimouski (Québec, Canada). Identification of algal cells infesting mussels as Coccomyxa sp. was confirmed by rRNA sequencing and HPLC pigment analysis. Flow cytometric analysis revealed the presence of algal cells in the hemolymph and extrapallial fluid in mussels with deformed and non-deformed shells; concentrations of algal cells were ranged from about 200mL(-1) in mussels with actually non-deformed shells to concentrations reaching up to 3.8×10(7)mL(-1) in mussels with heavily deformed ones. Chemical analyses of soft tissues led us to conclude that butyltin compounds and trace metals cannot be considered among factors responsible for the shell deformity observed. Using scanning electron microscopy, the biogenic nature of the erosion on the external shell surface and aragonitic lenses of prisms in the curvature zone of deformed shells (in sections) were recorded. The sequence of the green algae from M. edulis of the Lower St. Lawrence Estuary was closely related to Coccomyxa sp. infecting M. edulis from the Flensburg Fjord (North Sea) and Modiolus modiolus (L.) from the Vityaz Bay (Sea of Japan).

Complex metabolic interactions between benzo(a)pyrene and tributyltin in presence of dichlorodiphenyltrichloroethane in South American catfish Rhamdia quelen.

In an attempt to explore complex metabolic interactions between toxicants present in polluted freshwater, hepatic metabolism of benzo(a)pyrene (BaP) and tributyltin (TBT) in fish was investigated when these compounds were administrated alone, mixed together and along with dichlorodiphenyltrichloroethane (DDT). Ten Rhamdia quelen per group were treated with a single intra-peritoneal (IP) dose (5-day experiment) or three successive doses (15-day experiment) either containing BaP (0.3; 3 or 30mgkg(-1)) or TBT (0.03; 0.3 or 3mgkg(-1)) or a combination of BaP+TBT, BaP+DDT, TBT+DDT and BaP+TBT+DDT under their respective lower doses, with DDT dose kept at 0.03mgkg(-1). Tetrahydroxy-benzo(a)pyrene (BaP-tetrol-I), and dibutyltin (DBT) and monobutyltin (MBT) were analyzed to assess BaP and TBT hepatic metabolism, respectively. A significant difference in BaP-tetrol-I concentration was observed in liver and bile between the lowest and the highest doses of BaP in both 5 and 15-day experiments. In the 15-day experiment, the presence of TBT with BaP reduced the amount of BaP-tetrol-I in bile compared to the BaP alone. The time of exposure and the number of doses affected BaP-tetrol-I concentration in the bile of fish exposed to BaP 0.3mgkg(-1) and BaP+DDT. TBT and its metabolites concentrations showed a dose-dependent increase in the liver in both experiments and in the bile in the 5-day experiment. TBT at its lowest dose was completely metabolized into DBT and MBT in the liver in the 15-day experiment. No TBT metabolites were detected in the bile of fish exposed to the mixtures in the 5-day experiment, except for a small MBT amount found in BaP+TBT+DDT. This study strengthens the hypothesis of a metabolic interaction between BaP and TBT in fish and suggests DDT as an important third player when present in the mixture.

Chemical and microbial contamination baseline in the Saguenay-St. Lawrence Marine Park (Eastern Canada): concentrations and fluxes from land-based sources.

Stretching halfway between the Canadian Great Lakes and the Atlantic Ocean, the Saguenay-St. Lawrence Marine Park is subject to environmental issues being exposed to untreated or uncontrolled point and non-point sources of anthropogenic contamination. This article provides a first estimation of chemical and microbial contamination entering the marine park from the discharges of local municipal effluents and the inputs of tributaries in the summer period. Suspended particulate matter (SPM), nutrients, particulate carbon (PC) and nitrogen, trace metals, and fecal coliform bacteria were determined in surface brackish waters at upstream boundaries, in freshwater of 11 tributaries, and in nine sewage effluents from small communities settled along the marine park. Most tributaries have SPM < 10 mg L(-1) and contributed to a total of ~47 tons day(-1), thus representing a small proportion of daily SPM transported by Saguenay River (200 tons day(-1)) and St. Lawrence River (6.3 × 10(3) tons day(-1)). As expected, untreated sewage effluents showed high fecal contamination (0.2-6.0 × 10(6) CFU 100 mL(-1)), high NO x levels (4-33 µmol L(-1)) and high concentrations of particulate organic carbon (7-62 mg L(-1)). However, all tributaries had low coliforms (<230 CFU 100 mL(-1)), low PC (0.3-1.1 mg L(-1)), and low nutrients (NO(x) < 3.3 µmol L(-1)), with the exception of the Moulin-à-Baude River, a small tributary (2.3 × 10(5) m(3) day(-1)) clearly contaminated by human activities. Detailed analysis of 14 metals and metalloids in SPM did not show any clear contamination trend between sewage effluents and tributaries, except for Grandes-Bergeronnes River, where most trace metals appeared to be greater than for other rivers. Regarding global inputs, results showed that despite their relatively high pollutants load, inputs from local sewages and small tributaries remained minor contributors compared with upstream inputs, i.e., Saguenay River and St. Lawrence River. However, we illustrate that some local hydrodynamic factors in bays and inlets must be taken into account when evaluating risks associated with sewage discharges.

Depuration of ingested 14C-labelled polystyrene nanospheres in the Atlantic scallop (Placopecten magellanicus).

The presence of nano-plastics in marine bivalves is well established and may represent a risk to human consumption. The main objective of our work was to study the detailed tissue distribution of 14C-radiolabelled polystyrene nanospheres (PSNP; 325 nm) following their ingestion by commercial-size Atlantic scallop (Placopecten magellanicus) using whole-body autoradiography to assess their translocation, bioaccumulation and depuration mechanisms over a short-term exposure (6h) and a long-term exposure (2 weeks). Results showed that the nanospheres (PSNP) did not accumulate in scallop tissues despite the fact they were ingested and transported all along the digestive system. Elimination of the PSNP was virtually completed within 48 h and no radiolabeling appeared in the edible adductor muscle. This is indicative of the presence of an active depuration mechanism of particles without nutritional value as plastic PSNP. Our preliminary work indicates a rapid translocation of PSNP in scallops minimizing a possible transfer to human consumers.

Abundance, composition, and distribution of microplastics in intertidal sediment and soft tissues of four species of Bivalvia from Southeast Brazilian urban beaches.

In coastal areas, microplastics (MPs) can deposit in sediment, allowing it to be ingested by benthic organisms, like mussels, thus creating a possible transfer to humans. The aim of this study is to evaluate MPs pollution in sediment as a function of shoreline elevation in two urbanized beaches and to evaluate the abundance/frequency of MPs in 4 different species of bivalves commonly used in the human diet, such as the oyster Crassostrea brasiliana, the mussels Mytella strigata and Perna perna and the clam Tivela mactroides, and identify the polymers via µ-FTIR technique. A total of 3337 MPs were found in this study, of which 1488 were found in the sediment at the five sites analyzed, and 1849 in the bivalve tissues at the two sampling sites. MPs contamination was observed in all sediment samples and species of the pool and in each of the 10 specimens of the four species. Thus, the frequency of contamination by MPs reached 100 % for the analyzed samples. The number of filaments is higher than fragments in sediment samples and in each bivalve species. Regarding types and colors, the blue were greater than fragment-type in sediments and samples. In an effort to classify the polymers via µ-FTIR, our study was able to identify polypropylene, polyethylene and polyethylene terephthalate, besides a great number of cellulose fibers.

Effects of pesticide compounds (chlorothalonil and mancozeb) and benzo[a]pyrene mixture on aryl hydrocarbon receptor, p53 and ubiquitin gene expression levels in haemocytes of soft-shell clams (Mya arenaria).

The aim of this study is to investigate the effects of the pesticides/polycyclic aromatic hydrocarbon mixture on aryl hydrocarbon receptor (AhR), p53 and ubiquitin mRNA level in haemocytes of Mya arenaria exposed to a mixture of chlorothalonil, mancozeb and benzo[a]pyrene (BaP) for 48 and 72 h. AhR, p53 and ubiquitin gene expression levels were quantified using quantitative Real-time PCR. For robust and accurate quantification of transcripts, suitable housekeeping genes were selected from four sets of ribosomal and elongation factors transcripts previously sequenced from Mya arenaria using geNorm open source software. Quantitative Real-time PCR data exhibited a significantly high expression of AhR after 72 h of exposure (P ≤ 0.05). p53 gene expression seems to be up-regulated by the mixture after 48 h, however not significantly; but the level of p53 mRNA is down-regulated by the xenobiotics between 48 and 72 h after exposure. This study postulates that AhR mRNA levels could be used as an indicator of the exposure of clams' haemocytes to a mixture of xenobiotics such as chlorothalonil, mancozeb and BaP. However, further studies have to be pursued in order to unravel the molecular mechanisms involved in the p53 signaling pathway.

PBDEs and PCBs in the liver of the St Lawrence Estuary beluga (Delphinapterus leucas): a comparison of levels and temporal trends with the blubber.

Due to their lipophilic properties, persistent organic pollutants (POPs) are commonly assessed using the blubber of marine mammals. However, these chemicals are also accumulating in other tissues including the liver. Some pollutants, namely perfluorinated alkyl acids, are found predominately in the liver and blood of marine mammals, and thus monitored in those tissues. This raises the question whether any tissue would represent an identical trend of POPs in the SLE beluga. The current study reports the first temporal trends of PBDEs and PCBs in the liver of 65 SLE belugas. Neither ∑7PBDEs nor major individual PBDE-homolog group concentrations showed significant trends between 1993 and 2007. Also, ∑32PCBs did not change over years, although, tetra-, penta- and hepta-PCB decreased by 7.1, 6.8 and 8.5%, respectively, in males, whereas tetra-, penta- and octa-PCBs declined by 11, 12 and 12.9%, respectively, in females. In order to compare the distribution of POPs between liver and blubber, a lipid normalised concentration ratio R (blubber/liver) for PBDEs and PCBs was calculated for each individual beluga. For all PBDE and several PCB homolog groups, mean R values were not statistically different from unity indicating that the partitioning of these POPs is governed by the tissue lipid-content. Temporal trends of R ratios of PBDEs and PCBs were also examined. There were generally no significant temporal trends except for PBDEs in males where R increased in average by 12.7 ± 2.9% yearly. The stratification of the blubber into a metabolically active (inner) and less active layers (outer blubber) may result in a slower response time of the blubber (full depth) than the liver to the recent change of contamination in the environment and explain the time trend differences between both tissues. This study suggests that the liver is more representative of recent exposure to lipophilic contaminants.

Under ice spills of conventional crude oil and diluted bitumen: Physiological resilience of the blue mussel and transgenerational effects.

Spillages at sea of diluted bitumen (dilbit) from oil sands have received little attention until now. To our best knowledge, there are no reports on the impact of a severe exposure to dilbit on the Blue mussel (Mytilus edulis). In this study, adult Blue mussels were exposed to one conventional crude oil (Heidrun) and two dilbits (Cold Lake Blend and Access Western Blend) for a period of 7 days in an ice-covered environment and then maintained for three months until the spawning season. The exposed mussels were monitored for aromatic hydrocarbon bioaccumulation, physiological energetic budget, cellular stress, byssus production and gametogenesis. In spring, spawning was induced to characterize breeding success. Bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) was detected after three days of exposure, with higher concentrations of PAHs associated to the conventional oil (5.49 ± 0.12 µg·g-1 d.w.) compared to both dilbits (0.91 ± 0.02 µg·g-1; 0.51 ± 0.03 µg·g-1 d.w.). Despite a fast depuration rate and a good resilience of the exposed mussels, significant negative effects were observed at the cellular, physiological and fitness levels, especially in offspring. Our results suggest a higher toxicity of the diluted bitumen compared to the conventional crude despite the lower bioaccumulation of total PAHs. Dilbit treatments caused evident negative transgenerational effects on unexposed F1 generation.

Presence and distribution of persistent toxic substances in sediments and marine organisms of Potter Cove, Antarctica.

Levels of butyltin compounds, polychlorinated biphenyls, and heavy metals were analyzed in marine sediments and organisms (Notothenia coriiceps, Laternula elliptica, and Nacella concinna), each of which has a different feeding strategy, in Potter Cove, Antarctica. PCBs were lower than detection limits in all samples. Only butyltin compounds were detected in a restricted area near the scientific station. Chromium, copper, magnesium, lead (Pb), and zinc had similar behavior in the cove, probably because they are regulated by similar process and conditions. However, Pb levels in some sites of the cove seem to be related to human activities in the area. Cadmium levels were relatively low, with the highest values found close to the shoreline, which is probably influenced by seasonal streams draining waters from Potter Peninsula. Results showed that despite the fact that Jubany Station has been operating for > 50 years, surface sediment and biota from Potter Cove do not exhibit levels of pollutants representing environmental concern.

Radiolabeling of amide functionalized multi-walled carbon nanotubes for bioaccumulation study in fish bone using whole-body autoradiography.

Commercial and medicinal applications of functionalized carbon nanotubes (f-CNTs) such as amidated f-CNTs are expanding rapidly with a potential risk exposure to living organisms. The effects of amidated f-CNTs on aquatic species have received a limited attention. In this work, an easy wet method to prepare [14C]-label amide multi-walled carbon nanotubes (MWNTs) is reported. Labeled carbon nanotubes were prepared by successive reactions of carboxylation, chloroacylation, and final amidation using [14C]-labeled ethanolamine. The f-CNTs were characterized using elemental analysis, electron dispersive X-ray, transmission electron microscopy, thermogravimetric analysis, and Raman and FTIR spectroscopy. An uptake experiment was carried out with juvenile Arctic char (Salvelinus alpinus) using water dispersed amidated [14C]-f-CNTs to assess their biodistribution in fish tissues using whole body autoradiography. The radioactivity pattern observed in fish head suggests that f-CNTs were accumulated in head bone canals, possibly involving an interaction with mineral or organic phases of bones such as calcium and collagen. This f-CNTs distribution illustrates how important is to consider the surface charges of functionalized carbon nanotubes in ecotoxicological studies.

A fish bioassay to evaluate the toxicity associated with the ingestion of benzo[a]pyrene-contaminated benthic prey.

A bioassay was developed to assess the toxic effects of ingested prey contaminated by polycyclic aromatic hydrocarbons (PAHs) using the teleost Fundulus heteroclitus as a predator and the polychaete Nereis virens as a benthic vector. Ten groups of nine male adult Fundulus were exposed for 21 d to 10 different diets of Nereis contaminated with benzo[a]pyrene (BaP) by spiking dead Nereis with BaP (spiked Nereis [SN] diets, 0-26 microg of BaP per gram dry wt) or by exposing living Nereis to a diet, to sediments, or to both contaminated with BaP (exposed Nereis [EN] diets, 0-16 microg/g dry wt). Another group was exposed to commercial fish food, used as reference diet. Condition and prevalence of histopathological changes were not affected. Exposure to the SN diets containing at least 3.5 microg of BaP per gram dry weight caused an induction of ethoxyresorufin-O-deethylase activity in the intestine but not in the liver. In contrast, fish exposed to the highest doses (> or = 13.4 microg of BaP per gram dry wt) had increased cellular proliferation rate in the liver but not in the intestine. Quantifiable levels of free BaP tetrol-like metabolites were detected in the bile of fish exposed to diets containing more than 6.8 microg/g dry weight of BaP, and exhibited a dose-response relationship in fish exposed to SN diets. For a similar dose of BaP, EN and SN diets had similar effects. Thus, the BaP metabolic products that could have been produced in Nereis apparently did not contribute to the biomarkers responses. This bioassay can be applied to a variety of prey contaminated naturally or experimentally with PAHs. The present study supports the use of intestinal biomarkers, in addition to hepatic biomarkers, in environmental monitoring to assess the impact of dietary exposure to PAHs.

Biofouling growth in cold estuarine waters and evaluation of some chitosan and copper anti-fouling paints.

Ecological concerns about antifouling paints containing non-green tin and copper compounds have highlighted the need for environmentally friendly alternatives. We report here a field test conducted in estuarine waters over two months designed to evaluate the efficiency of a number of active natural and man-made chemical ingredients added into a silicon-polyurethane marine paint. Early steps of biofouling in cold seawater of the St. Lawrence Estuary (Canada) were observed. Analyses, including dry biomass, flow cytometry and spectrofluorimetry, demonstrated a short-term antibacterial action of chitosan-based paints although no significant anti-algal action was observed. Cuprous oxide paints were efficient against bacteria and algae invasion in the first two weeks, especially those with added organic biocides such as isothiazolone and copper pyrithione. However, the overall dry biomass and chlorophyll a content were similar for all chitosan-and copper-based paints after 63 days. Microscopic observations revealed variation in the highly diverse benthic diatom population including species Navicula, Melosira, Cocconeis, Nitshzcia, Fragilaria and Amphora. Results suggest no real long-term efficiency for tested antifouling paints and highlight a particular need for green antifouling ingredients that are active under northern estuarine conditions.

Passive samplers versus surfactant extraction for the evaluation of PAH availability in sediments with variable levels of contamination.

The purpose of this study was to test the efficiency of passive solid samplers, polyoxymethylene (POM) strips and polydimethylsiloxane (PDMS) silicon tubing, to predict the bioavailability of native PAHs in contaminated sediments. Results were compared with worm bioaccumulation data and solid/liquid extraction using the surfactant Brij((R)) 700 (B700). The two passive samplers were found to act differently. The PDMS sampler overestimated the availability of PAHs in all studied sediments. The POM method provided results in accordance with those obtained with the B700 extraction. However, POM and B700 methods underestimated PAH availability in low contaminated sediments where biological factors (digestible organic matter) become important. Bioavailability of total PAHs was correctly predicted by POM and B700 in highly contaminated aluminum smelter sediments. A closer examination of individual PAH results indicated that both techniques overestimated the availability of large molecules with logK(ow)>6 suggesting a biological mechanism limiting uptake of larger PAHs which seems to be related to the molecular size of compounds.

Polycyclic aromatic hydrocarbons in soil and surface marine sediment near Jubany Station (Antarctica). Role of permafrost as a low-permeability barrier.

Although Antarctica is still considered as one of the most pristine areas of the world, the growing tourist and fisheries activities as well as scientific operations and their related logistic support are responsible for an increasing level of pollutants in this fragile environment. Soils and coastal sediments are significantly affected near scientific stations particularly by polycyclic aromatic hydrocarbons (PAHs). In this work sediment and soil were sampled in two consecutive summer Antarctic expeditions at Potter Cove and peninsula, in the vicinity of Jubany Station (South Shetland Islands). Two- and 3-ring PAHs (methylnaphthalene, fluorene, phenanthrene and anthracene) were the main compounds found in most sites, although total PAH concentrations showed relatively low levels compared with other human-impacted areas in Antarctica. Pattern distribution of PAHs observed in samples suggested that low-temperature combustion processes such as diesel motor combustion and open-field garbage burning are the main sources of these compounds. An increase in PAH concentrations was observed from surface to depth into the active soil layer except for a unique sampling site where a fuel spill had been recently reported and where an inverted PAH concentration gradient was observed. The highest level was detected in the upper layer of permafrost followed by a sharp decrease in depth, showing this layer is acting as a barrier for downward PAH migration. When PAH levels in soil from both sampling programs were compared a significant decrease (p<0.01) was observed in summer 2005 (range at 75-cm depth: 12+/-1-153+/-22 ng/g) compared to summer 2004 (range at 75-cm depth: 162+/-15-1182+/-113 ng/g) whereas concentrations in surface sediment collected nearby the station PAHs increased drastically in 2005 (range: 36+/-3-1908+/-114 ng/g) compared to 2004 (range: 28+/-3-312+/-24 ng/g). Precipitation regime and water run off suggest that an important wash out of soil-PAHs occurred during the interval time between samplings. Results showed that the present PAH contamination level of Jubany Station is relatively low compared to other reported cases in Antarctica but also suggests that an increase in rain and in thawing processes caused by the global warming could result in an important soil-associated PAH mobilization with unpredictable consequences for the biota of Potter Cove.

Seasonal variability of denitrification efficiency in northern salt marshes: an example from the St. Lawrence Estuary.

In coastal ecosystems, denitrification is a key process in removing excess dissolved nitrogen oxides and participating in the control of eutrophication process. Little is known about the role of salt marshes on nitrogen budgets in cold weather coastal areas. Although coastal salt marshes are important sites for organic matter degradation and nutrient regeneration, bacterial-mediated nitrogen cycling processes, such as denitrification, remain unknown in northern and sub-arctic regions, especially under winter conditions. Using labelled nitrogen (15N), denitrification rates were measured in an eastern Canadian salt marsh in August, October and December 2005. Freshly sampled undisturbed sediment cores were incubated over 8h and maintained at their sampling temperatures to evaluate the influence of low temperatures on the denitrification rate. From 2 to 12 degrees C, average denitrification rate and dissolved oxygen consumption increased from 9.6 to 25.5 micromol N2 m-2 h-1 and from 1.3 to 1.8 mmol O2 m-2 h-1, respectively, with no statistical dependence of temperature (p>0.05). Nitrification has been identified as the major nitrate source for denitrification, supplying more than 80% of the nitrate demand. Because no more than 31% of the nitrate removed by sediment is estimated to be denitrified, the presence of a major nitrate sink in sediment is suspected. Among possible nitrate consumption mechanisms, dissimilatory reduction of nitrate to ammonium, metal and organic matter oxidation processes are discussed. Providing the first measurements of denitrification rate in a St. Lawrence Estuary salt marsh, this study evidences the necessity of preserving and restoring marshes. They constitute an efficient geochemical filter against an excess of nitrate dispersion to coastal waters even under cold northern conditions.