Uncontaminated Seawater Research Articles

In vitro assessment of crude oil degradation by Acinetobacter junii and Alcanivorax xenomutans isolated from the coast of Ghana

This study was aimed at using in vitro microcosm experiments to assess crude oil degradation efficiency of Acinetobacter junii and Alcanivorax xenomutans isolated along Ghana's coast. Uncontaminated seawater from selected locations along the coast was used to isolate bacterial species by employing enrichment culture procedures with crude oil as the only carbon source. The isolates were identified by means of the extended direct colony transfer method of the Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectroscopy (MALDI-TOF MS), as Acinetobacter junii, and Alcanivorax xenomutans. Remediation tests showed that Acinetobacter junii yielded degradation efficiencies of 27.59 %, 41.38 % and 57.47 %. Whereas efficiencies of 21.14 %, 32.18 % and 43.68 % were recorded by Alcanivorax xenomutans representing 15, 30 and 45 days respectively. Consortia of Acinetobacter junii, and Alcanivorax xenomutans also yielded 32.18 %, 48.28 % and 62.07 % for the selected days respectively. Phylogenetic characterization using ClustalW and BLAST of sequences generated from the Oxford Nanopore Sequencing technique, showed that the Ghanaian isolates clustered with Alcanivorax xenomutans and Acinetobacter junii species respectively. An analysis of the sequenced data for the 1394-bp portion of the 16S rRNA gene of the isolates revealed >99 % sequence identity with the isolates present on the GenBank database. The isolates of closest identity were Alcanivorax xenomutans and Acinetobacter junii with accession numbers, NR_133958.1 and KJ147060.1 respectively. Acinetobacter junii and Alcanivorax xenomutans isolated from Ghana's coast under pristine seawater conditions have therefore demonstrated their capacity to be used for the remediation of crude oil spills.

Sensitivity of the Indo-Pacific coral Acropora millepora to aromatic hydrocarbons

The risks posed by petroleum spills to coral reefs are poorly understood and quantifying acute toxicity thresholds for aromatic hydrocarbons to reef-building corals is required to assess their sensitivity relative to other taxa. In this study, we exposed Acropora millepora to toluene, naphthalene and 1-methylnaphthalene (1-MN) in a flow-through system and assessed survivorship and sublethal responses including growth, colour and the photosynthetic performance of symbionts. Median 50% lethal concentrations (LC50s) decreased over the 7-d exposure period, reaching asymptotic values of 22,921, 5,268, 1167 μg L−1 for toluene, naphthalene and 1-MN, respectively. Corresponding toxicokinetic parameters (εLC50) defining the time progression of toxicity were 0.830, 0.692, and 0.256 d−1, respectively. Latent effects after an additional 7-d recovery in uncontaminated seawater were not observed. Effect concentrations (EC50s) for 50% growth inhibition were 1.9- to 3.6-fold lower than the LC50s for each aromatic hydrocarbon. There were no observed effects of aromatic hydrocarbon exposure on colour score (a proxy for bleaching) or photosynthetic efficiency. Acute and chronic critical target lipid body burdens (CTLBBs) of 70.3 ± 16.3 and 13.6 ± 18.4 μmol g−1 octanol (± standard error) were calculated for survival and growth inhibition based on 7-d LC50 and EC10 values, respectively. These species-specific constants indicate adult A. millepora is more sensitive than other corals reported so far but is of average sensitivity in comparison with other aquatic taxa in the target lipid model database. These results advance our understanding of acute hazards of petroleum contaminants to key habitat-building tropical coral reef species.

Geochemistry of trace metals and Rare Earth Elements in shallow marine water affected by hydrothermal fluids at Vulcano (Aeolian Islands, Italy)

Trace metals and Rare Earth Element (REE) are amply discharged by submarine hydrothermal vents, sometimes leading to the formation of ore deposits of economic interest. We report on first data on the geochemical processes involving REE and trace metals, at the solid-liquid interface, in the hydrothermal area of Levante Bay at Vulcano Island (Aeolian Archipelago, Italy). Samples were collected from several submarine springs and seeps, a mud pool and one thermal well, and analyzed for Al, Si, Ti, V, Cr, Mn, Fe, Co, As, Rb, Sr, Cs, Ba, U and REE, besides major ions.Within the bay, hydrothermal fluids contaminate seawater and promote the leaching of metals from sediments through the dissolution of CO2 and H2S, while the particulate matter removes several elements from the water. The leaching of the bottom sediments and the contribution of steam-heated water produce an enrichment of some metals and REE in the Levante Bay with respect to the concentrations expected in the ambient seawater. An enrichment up to one order of magnitude is measured for Fe, Al, Ba, Cs and Rb, and up to two orders of magnitude for Mn in the submarine samples. Other transition metals (Ti, V, Co, Cr), U, As and Sr have concentrations similar or slightly lower than the ambient seawater. REE are in concentrations higher than in ambient seawater up to two orders of magnitude. Despite being significantly higher than uncontaminated seawater, the concentrations of some metals (namely Fe, Al, Ti, Cr, V, Co, U) and REE in most samples are lower than expected by the mixing between seawater and the steam-heated water, discharging from submarine springs. Indeed, equilibrium and reaction path modeling indicate the likely precipitation of Fe-oxyhydroxides, able to remove minor elements, such as Ti, Cr, Co, V and As, and REE. The last ones are significantly removed by newly-forming solid phases, due to the presence of a large amount of Fe released by the acidic fluids through the leaching of sediments. The low pH limits the formation of solution complexes of REE with carbonate ions (the main complexing agent for REE in seawater), whereas the sorption onto particles is still effective, even at close distance from the submarine springs and seeps.This study brings new insights on the geochemical processes occurring in submarine hydrothermal systems, in particular, those in subduction-related context.

Application of the Paracentrotus lividus sea-urchin embryo-larval bioassay to the marine pollution biomonitoring program in the Tunisian coast.

The pollution of the marine environment by treated and untreated effluents has increased due to human activities. Monitoring the marine ecosystem is nowadays a global concern. In this work, we evaluated the effect of contaminated and uncontaminated seawater, from different Tunisian coastal areas, on the fertilization, gastrulation, and embryo-larval development events of sea urchins (Paracentrotus lividus). The station of Salakta (SA) is considered as a control station, while the stations of Hamdoun Wadi (HW), Port of Monastir (PM), Karaia Monastir (KM), Teboulba (TE), and Khniss Lagoon (KL) are considered to be contaminated stations. The analysis of seawater physicochemical characteristics showed that levels of the total suspended matter (TSM), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC), and nitrate (NO3-) were lower in the seawater of the reference site Salakta (SA) when compared to those of the contaminated seawater sites. In addition, a very strong variation in the levels of trace metals in seawaters sampled in the studied sites was noted. In fact, the highest concentrations of Pb and Cu were observed in Hamdoun Wadi (HW), port of Monastir (PM), and Karaia Monastir (KM), while the highest concentration of Zn was noted in the Teboulba lagoon (TE) and Khniss (LK). Alterations in physicochemical characteristics as well as elevated trace metal levels in the studied seawater samples were correlated with reduced fertility rate, gastrulation rate, and the frequency of normal sea urchin larvae. The total absence of normal sea urchin pluteus larvae in the sea waters of heavily polluted sites proves the great sensitivity of the larval frequency to mixed pollution. This work recommends the utility of urchin fertilization and gastrulation rates and normal pluteus larval frequencies as useful bioassays to monitor the exposure of marine ecosystems to mixed pollution.

Heavy Metal, Rare Earth Element and Pb Isotope Dynamics in Mussels During a Depuration Experiment in the Gulf of Aqaba, Northern Red Sea

Mussels are considered highly efficient marine biomonitors, tracing anthropogenic and natural variations in heavy metals and various organic compounds. While heavy metals depuration processes in biomonitors are of growing interest, less knowledge is available regarding their Pb isotopes and rare earth elements (REEs) accumulation-release dynamics, and their response to short-term anthropogenic and terrigenous perturbations. Here, we report the results of a relocation experiment where a group of mussels (Brachidontes pharaonis) were extracted from a contaminated lagoon in the Gulf of Aqaba, northern Red Sea, and placed in water tanks that were flushed continuously with fresh, uncontaminated seawater. Specimens were removed periodically from the water table over a period of 13 weeks and trace and REEs and Pb isotopic compositions were determined separately for mussel’s shells and soft tissues. The results display a clear decrease over time in the concentrations of various heavy metals and REEs in the soft tissue, in concert with a similar shift in the Pb isotopic compositions toward seawater values. By contrast, the elemental and Pb isotopic composition of the shell presents little change over time. Coupling between the Pb isotopic composition of corresponding soft tissue and shell samples allows back-calculation of the timing and magnitude of abrupt pollution events and presents a novel approach for monitoring short-term pollution events. Nevertheless, given the coastal setting of the studied samples, it is important to consider the effects of terrigenous material on the results. Accordingly, Al-normalized element concentrations, Pb isotopes and calculated Ce anomalies, are used to identify two distinct terrigenous end members controlling the contaminated lagoon and the pristine site. The study demonstrates the potential of using mussels as robust biomonitors of natural and anthropogenic environmental perturbations through the combination between elemental concentrations and the isotopic composition of Pb.

Pulsed exposure toxicity testing: Baseline evaluations and considerations using copper and zinc with two marine species

Methods to assess environmental impacts from episodic discharges on receiving water bodies need a more environmentally relevant and scientifically defensible toxicity test design. Many permittees are regularly required to conduct 96-h toxicity tests on discharges associated with events that are generally less than 24 h in duration. Current standardized methods do not adequately reflect these episodic discharge conditions at either the point of compliance nor as it mixes with the receiving environment. In order to evaluate more representative biological effects, an alternative toxicity approach is described incorporating pulsed exposures of effluents and subsequent transfer of test organisms to clean water for the remainder of the test. This pulsed exposure protocol incorporates a slight modification to USEPA Whole Effluent Toxicity (WET) chronic and acute methods for two marine species, purple sea urchin embryos, Strongylocentrotus purpuratus, and juvenile mysid shrimp Americamysis bahia. Tests were performed with toxicants using standard static (96 h) and pulsed (6, 12, and 26 h) exposures. Following pulsed exposures, organisms were transferred to uncontaminated seawater for the remainder of the 96-h test period. Results for these species and endpoints indicated that the sensitivity of these species to copper and zinc were up to two orders of magnitude greater using standard continuous exposures compared to shorter pulsed exposures. Additional considerations assessed included timing of the onset of a pulse and latent effects following an exposure. This modified approach requires minimal modification to current standard methods and increases the realism to more accurately assess toxic effects resulting from episodic discharges.

Electrosensory Impairment in the Atlantic Stingray, Hypanus sabinus, After Crude Oil Exposure

Elasmobranchs are renowned for their extremely sensitive electrosensory system, which is used to detect predators, prey, and mates, and is possibly used for navigation. The proper functioning of the electrosensory system is thus critical to fitness. The objective of this study was to test whether exposure to crude oil impairs the electroreceptive capabilities of elasmobranch fishes. Electrosensory function was quantified from six stingrays before and after exposure to a concentration of oil that mimicked empirically measured concentrations along the coast of Louisiana following the Deepwater Horizon spill. Orientation distance (cm), and angle with respect to the dipole axis of a prey-simulating electric field were used to derive the electric field intensity that elicited a response. Oil exposed stingrays continued to exhibit feeding behavior, but they initiated orientations to prey-simulating electric fields from a significantly closer orientation distance. The mean orientation distance after oil exposure was 5.29 ± 0.41 SE cm compared to a pre-exposure orientation distance of 7.16 ± 0.66 SE cm. Stingrays required a mean electric field intensity of 0.596 ± 0.21 SE μV cm-1 to initiate a response after oil exposure, compared to a mean of only 0.127 ± 0.03 SE μV cm-1 in uncontaminated seawater. Oil exposed stingrays thus exhibited a response to a stimulus approximately 4.7 times greater than controls. Stingrays impacted by an oil spill appear to experience reduced electrosensory capabilities, which could detrimentally impact fitness. This study is the first to quantify the effects of crude oil on behavioral electrosensory function.

Precipitation‐Induced Reduction in Surface Ocean pCO2: Observations From the Eastern Tropical Pacific Ocean

AbstractDetermining air‐sea CO2 fluxes using pCO2 disequilibrium requires knowing the gas transfer velocity and air‐sea pCO2 difference. Most pCO2 measurements are made from ships, whose uncontaminated seawater intakes are located at >5‐m depth to prevent ingestion of air. However, there could be bias in determinations of CO2 fluxes if there is disagreement between pCO2 measurements at the surface and 5 m. Seawater measurements made at the near surface and 5 m in the eastern Equatorial Pacific Ocean show that precipitation can dilute surface seawater salinity and lower the pCO2 and dissolved inorganic carbon and raise pH of the same water, and that these changes in ocean chemistry are largely missed by measurements at 5 m. This finding implies that estimates of ocean CO2 uptake might be underestimated, since rain will lower surface ocean pCO2 in both source and sink regions and, hence, increase uptake in sink regions and decrease outgassing in source regions.

Assessing the effects of neonicotinoid insecticide on the bivalve mollusc Mytilus galloprovincialis

In the present work, the marine invertebrate Mytilus galloprovincialis was used as model organism to evaluate the toxic effects of the neonicotinoid Calypso 480 SC (CAL) following 20 days of exposure to sub-lethal concentrations of 7.77 mg L−1 (0.1% 96 h-LC50) and 77.70 mg L−1 (1% 96 h-LC50), and a recovery period of 10 days in uncontaminated seawater. Results revealed that exposure to both concentrations of CAL increased significantly mortality rate in the cells of haemolymph and digestive gland, while digestive gland cells were no longer able to regulate cell volume. Exposure significantly reduced haemolymph parameters (Cl−, Na+), affected the enzymatic activities of superoxide dismutase of digestive gland and catalase of gill, and caused also histopathological alterations in digestive gland and gills. Main histological damages detected in mussels were lipofuscin accumulation, focal points of necrosis, mucous overproduction and infiltrative inflammations. Interestingly, alterations persisted after the recovery period in CAL-free water, especially for haemocyte parameters (K+, Na+, Ca2+, lactate dehydrogenase, glucose). A slight recovery of histological conditions was detected. These findings suggested that sub-chronic exposure to the neonicotinoid insecticide caused significant alterations in both cell and tissue parameters of M. galloprovincialis. Considering the ecologically and commercially important role of mussels in coastal waters, a potential risk posed by neonicotinoids to this essential aquatic resource can be highlighted.

Mesocosm System to Evaluate BF-MBR Efficacy in Mitigating Oily Wastewater Discharges: an Integrated Study on Mytilus galloprovincialis.

This work presents the results of recovery efficacy of the system "BioFilm Membrane BioReactor" (BF-MBR), in the treatment of oily contaminated seawaters. To this aim, we proposed a multidisciplinary approach that integrates traditional chemical-physical measures together with the assessment on biological sentinel Mytilus galloprovincialis, maintained in a medium-scale artificial system named mesocosm. The setup included: (1) a mesocosm consisting of uncontaminated seawater; (2) a mesocosm composed of an untreated oily wastewater discharge; and (3) a mesocosm receiving the same oily wastewater previously treated by a BF-MBR pilot scale plant. The multidisciplinary approach that included traditional chemical measures on mesocosms together with the evaluation of morphological organization, mRNA expression of those genes involved in cellular stress response, immunohistochemistry and metabolomic analysis on mussel tissues, was able to provide a robust and holistic evidence of how the proposed treatment is able to reduce the overall impact of oily wastewater discharges on the marine ecosystem.

Detecting the Presence of Different Types of Oil in Seawater Using a Fluorometric Index

This study analyzed the fluorometric laboratory tests for the detection of the presence of oil in seawater in cases corresponding to the real situation in the sea: when the point of seawater sampling is not in the same place as the appropriate sensor. The phenomenon of fluorescence exhibited by both natural and alien substances (oil) in the sea was used. The possibility of oil detection in the water column based on a fluorometric index (FI) extracted from the excitation–emission matrix (EEM) was studied. Laboratory tests were carried out on water taken from the Gulf of Gdańsk (Baltic Sea). Seawater samples were contaminated with small amounts of various types of oil (the lowest oil-to-water ratio was 0.5 × 10−6). A statistically significant difference was found between FI values for uncontaminated seawater and seawater exposed to various kinds of oil (i.e., crude oils, lubricant oils, and fuels).

The autonomous clean environmental (ACE) sampler: A trace‐metal clean seawater sampler suitable for open‐ocean time‐series applications

AbstractThe fundamental role of the micronutrient Fe in controlling phytoplankton growth in large parts of Earth's oceans and a lack of information on seasonal transitions in remote regions motivated us to create an autonomous water sampler capable of collecting uncontaminated open‐ocean seawater samples with monthly resolution over a full annual cycle. Phytoplankton are at the base of the food chain, which take up carbon dioxide through photosynthesis. Assessing Fe availability is essential to understanding both ocean productivity and our climate. This need is particularly important in the Southern Ocean, where Fe limitation is wide spread and access is difficult especially in winter. To address this need, we have developed an autonomous system capable of observing iron concentrations over a full seasonal cycle, at the subnanomolar concentrations that are important in the open ocean. The automated clean environmental sampler has been developed initially for 1‐yr deployments on oceanographic moorings. Twelve samples per unit can be programmed to collect 65 mL of seawater through a noncontaminating, primarily Teflon sample path. The system is vaned to maintain its intake tubes in upstream water and has been tested to 100 m depth. The system was deployed during a GEOTRACES section (SR3 line, GS01) in 2018 alongside an industry standard, trace metal clean rosette, and no significant difference was found in Fe concentrations in the 50 pmol L–1 range, proving its capability at collecting uncontaminated seawater samples in the open ocean at temperatures above 0°C.

Evidences of metabolic alterations and cellular damage in mussels after short pulses of Ti contamination

Mytilus galloprovincialis mussels were exposed to seawater contaminated with Ti. Initial concentrations were 4.1, 32, and 66 μg L−1 that declined during the first 24 h of the experiments, and after 48 h values were <2 μg L−1. Experiments were run in triplicate, under constant salinity and temperature. Mussels were fed every two days, and water renewed every seven days and Ti concentrations re-stabilized. During the first 28 days of experimental period, mussels were exposed to four short pulses of contamination, followed by few days of low Ti concentration between weekly contamination renewals. Then mussels were exposed to additional 14-day exposure to Ti uncontaminated seawater. Only residual Ti concentrations were measured in mussels' whole soft tissue after the four pulses of Ti contamination, indicating low Ti accumulation by the organisms. Nevertheless, the biomarkers related to mussels' metabolic capacity (electron transport system activity, ETS), oxidative damage (lipid peroxidation, LPO and reduced glutathione content, GSH), and defense mechanisms (antioxidant and biotransformation enzymes) evidenced the impact of Ti during the 28 days of experimental period. The biomarkers that better indicated the recovery of mussels' biochemical performance were the ETS, LPO, GSH, and the antioxidant enzyme glutathione peroxidase (GPx). LPO was the prime indicator among the analyzed biochemical responses. Organisms appear to hold coping mechanisms to lower the damage induced by Ti, and to recover, albeit the 14 days period of exposure to uncontaminated seawater following the four Ti pulses were not enough for full recovery, as evidenced by results on LPO levels and GSH concentrations. Despite the low solubility of Ti in seawater, the toxicity of this element to a model marine organism was demonstrated.

Impacts on the seagrass, Zostera nigricaulis, from the herbicide Fusilade Forte® used in the management of Spartina anglica infestations

The herbicide Fusilade Forte® (FF) is widely applied in agricultural weed management and in the management of the invasive saltmarsh grass, Spartina anglica (ricegrass or cordgrass). FF (active ingredient fluazifop-P acid, FPA) is selective for poaceous grasses. Its primary mode of action is inhibition of the acetyl coenzyme-A carboxylase (ACCase) specific to this taxonomic group, and its secondary mode is by promotion of oxidative stress. FF is applied to S. anglica infestations in the intertidal zone, in proximity to seagrass meadows. Despite the potential for vital seagrass ecosystems to be exposed to FF, there is limited knowledge of any potential impacts. We investigated impacts of FPA on the endemic Australian seagrass, Zostera nigricaulis, measuring ACCase activity and parameters that reflect oxidative stress: photosynthetic performance, lipid peroxidation and photosynthetic pigment content. Seagrass was exposed to FF (0.01–10mgL−1 FPA and a control) for 7d, followed by a 7-d recovery in uncontaminated seawater. An enzyme assay demonstrated that FPA ≤10mgL−1 did not inhibit the activity of ACCase isolated from Z. nigricaulis, demonstrating that this seagrass is resistant to FF's primary mode of action. However, physiological impacts occurred following 7 days exposure to ≥0.1mgL−1 FPA, including up to a 72% reduction in photosynthetic pigment concentration. After 7-d recovery, photosynthetic pigment content improved in treatment plants; however, treated plants exhibited higher levels of lipid peroxidation. This study demonstrates that while Z. nigricaulis is resistant to FF's primary mode of action, significant physiological impacts occur following 7 days exposure to ≥0.1mgL−1 FPA. This study provides valuable information on the effects of FF on a non-target species that can better inform approaches to Spartina management in coastal seagrass ecosystems.

Dissolved iron and zinc in Sagami Bay and the Izu-Ogasawara Trench

Using a clean seawater sampling system for trace metals onboard the R. V. Shinsei-Maru, newly launched in 2013, we investigated the vertical distributions of dissolved iron and zinc in Sagami Bay and the Izu-Ogasawara Trench. We applied appropriate clean sampling and filtering processes for trace metals, so that uncontaminated seawater samples were successfully collected. The distribution of zinc in the trench area was similar to that of silicate and the same as that previously reported in the subtropical North Pacific. There were spatial variations in the iron (Fe) distribution in the trench areas. We used previously reported information about biogeochemical cycling in the trench area, and found that Fe has a residence time of 29 years in the water column. The short residence time of Fe (29 years) corresponds to the vertical variations of dissolved Fe in the water column.

Transcriptional effects of metal-rich acid drainage water from the abandoned Løkken Mine on Atlantic salmon (Salmo salar) smolt

ABSTRACTRunoff of metals represents one of the major environmental challenges related to historic and ongoing mining activity. In this study, transcriptomics (direct RNA sequencing [RNA-seq] and reverse-transcription quantitative polymerase chain reaction [RT-qPCR]) was used to predict toxicity of metal-rich acid mine drainage (AMD) water collected in the abandoned copper (Cu) mine called Løkken Mine on Atlantic salmon liver and kidney, the main target organs of Cu-induced toxicity in fish. Smolts were exposed to control and diluted AMD water, which contains a mixture of metals but is especially enriched with Cu, at 4 concentrations in freshwater (FW) for 96 h, and then were transferred to and kept in seawater (SW) for another 24 h. Significant accumulation of Cu was observed in the gills, but not liver and kidney tissues, after 96 h of exposure. Short-term exposure to metal-rich ADM (high exposure group) significantly upregulated 3201 transcripts and downregulated 3782 transcripts in liver. The strongest effect attributed to exposure was observed on the KEGG pathway “protein processing in endoplasmic reticulum,” followed by “steroid biosynthesis.” Gene ontology (GO) analysis suggested that exposure predominantly affected “protein folding,” possibly by disrupting disulfide bonds as a result of endoplasmic-reticulum-generated stress, and “sterol biosynthetic processes.” Transfer to uncontaminated SW for 24 h amended the transcription of several genes, suggesting a transient effect of treatment on some mechanisms. In conclusion, the data show that trace metals in AMD from abandoned pyrite mines might disturb molecular mechanisms linked to protein folding in Atlantic salmon smolt endoplasmic reticulum.

Physiological effects and cellular responses of metamorphic larvae and juveniles of sea urchin exposed to ionic and nanoparticulate silver

The widespread use of silver nanoparticles (AgNPs) would likely result in their discharge into wastewater and inevitable release in densely populated coastal areas. It is known that AgNPs can cause harmful effects to marine fauna, but how they affect development stages is still an open question. In order to understand in details how polymer-coated AgNPs (PAAm-AgNPs) (from 0.19 to 4.64mM as Ag) can affect critical stages of marine invertebrate development, metamorphic larvae and juveniles of sea urchins were used as biological models. Multidimensional scaling (MDS) approach based on Bray-Curtis similarity matrix with PERMANOVA showed organisms in a multivariate space undergoing through different physiological conditions as a function of time, chemical forms of silver, nominal concentrations, and presence or absence of food. Sublethal effects such as lethargy, oedema and immobility mainly characterized PAAm-AgNPs effects with juveniles and postlarvae, whereas necrosis and death arose in Ag+ conditions in short-term tests. Chronically exposed metamorphic larvae had their morphogenic processes interrupted by PAAm-AgNPs and a high mortality rate was observed in recovery period. On the contrary, Ag+ ions caused progressive mortality during exposure, but a quick recovery in uncontaminated seawater was observed. By means of fluorescent markers we showed that nanosilver could be transferred between consecutive stages (swimming larvae and postlarvae) and highlighted how important is food to enhance PAAm-AgNPs uptake. Using TEM we observed that unfed juveniles had nanosilver aggregates mostly restricted to their coelomic sinuses, while metamorphic larvae already had nano-contamination overspread in different tissues and blastocoel. Our main hypothesis for nanotoxicity of PAAM-AgNPs relies on the slow dissolution of nano-core over time, but in this study the effects of particulate silver form itself are also evoked. Main mechanisms governing tissular and cellular responses to nano-intoxication such as inflammatory response and detoxification based on the role of sentinel cells (peritoneal cells and coelomocytes) for general homeostasis are discussed. This paper is first to detail physiological states, main uptake routes and cellular response against polymer-coated AgNPs in developmental stages of marine invertebrate species.

Lethal and sub-lethal chronic effects of the herbicide diuron on seagrass

Photosystem II herbicides from agricultural sources have been detected throughout nearshore tropical habitats including seagrass meadows. While PSII herbicides have been shown to inhibit growth in microalgae at low concentrations, the potential impacts of chronic low concentration exposures to seagrass health and growth have not been investigated. Here we exposed two tropical seagrass species Halodule uninervis and Zostera muelleri to elevated diuron concentrations (from 0.3 to 7.2μgl−1) over a 79-day period followed by a 2-week recovery period in uncontaminated seawater. PAM fluorometry demonstrated rapid effect of diuron on photosystem II (PSII) in both seagrass species at 0.3μgl−1. This effect included significant inhibition of photosynthetic efficiency (ΔF/Fm′) and inactivation of PSII (Fv/Fm) over the 11 week exposure period. Significant mortality and reductions in growth was only observed at the highest exposure concentration of 7.2μgl−1 diuron. However, biochemical indicators demonstrated that the health of seagrass after this prolonged exposure was significantly compromised at lower concentrations. For example, the drop in C:N ratios (0.6μgl−1) and reduced δ13C (1.7μgl−1) in seagrass leaves indicated reduced C-assimilation from photosynthesis. Critically, the energetic reserves of the plants (as measured by starch content in the root-rhizome complex) were approximately halved following diuron exposure at and above 1.7μgl−1. During the 2-week recovery period, the photosynthetic capacity of the seagrass improved with only plants from the highest diuron treatment still exhibiting chronic damage to PSII. This study shows that, although seagrass may survive prolonged herbicide exposures, concentrations ≥0.6μgl−1 diuron equivalents cause measureable impacts on energetic status that may leave the plants vulnerable to other simultaneous stressors. For example, tropical seagrasses have been heavily impacted by reduced light from coastal flood plumes and the effects on plant energetics from light limitation and diuron exposure (highest in flood plumes) are very similar, potentially leading to cumulative negative effects.

Indigenous oil-degrading bacteria in crude oil-contaminated seawater of the Yellow sea, China.

Indigenous oil-degrading bacteria play an important role in efficient remediation of polluted marine environments. In this study, we investigated the diversity and abundance of indigenous oil-degrading bacteria and functional genes in crude oil-contaminated seawater of the Dalian coast. The gene copy number bacterial 16S rRNA in total were determined to be about 10(10) copies L(-1) in contaminated seawater and 10(9) copies L(-1) in uncontaminated seawater. Bacteria of Alcanivorax, Marinobacter, Novosphingobium, Rhodococcus, and Pseudoalteromonas were found to be predominant oil-degrading bacteria in the polluted seawater in situ. In addition, bacteria belonging to Algoriphagus, Aestuariibacter, Celeribacter, Fabibacter, Zobellia, Tenacibaculum, Citreicella, Roseivirga, Winogradskyella, Thioclava, Polaribacter, and Pelagibaca were confirmed to be the first time as an oil-degrading bacterium. The indigenous functional enzymes, including AlkB or polycyclic aromatic hydrocarbons ring-hydroxylating dioxygenases α (PAH-RHDα) coding genes from Gram-positive (GP) and Gram-negative bacteria (GN), were revealed and quite diverse. About 10(10) to 10(11) copies L(-1) for the expression of alkB genes were recovered and showed that the two-thirds of all the AlkB sequences were closely related to widely distributed Alcanivorax and Marinobacter isolates. About 10(9) copies L(-1) seawater for the expression of RHDαGN genes in contaminated seawater and showed that almost all RHDαGN sequences were closely related to an uncultured bacterium; however, RHDαGP genes represented only about 10(5) copies L(-1) seawater for the expression of genes in contaminated seawater, and the naphthalene dioxygenase sequences from Rhodococcus and Mycobacterium species were most abundant. Together, their data provide evidence that there exists an active aerobic microbial community indigenous to the coastal area of the Yellow sea that is capable of degrading petroleum hydrocarbons.

The speciation of lead in seawater by pseudopolarography using a vibrating silver amalgam microwire electrode

A novel electrode based on a vibrating silver amalgam microwire was used for pseudopolarography of lead (Pb) in seawater. Pseudopolarography is a method to study the stability of metal species by examination of their reduction potential. The reduction potential of kinetically irreversible species is related to the thermodynamic complex stability constant, whilst for labile species it is related to the conditional stability constant. The new electrode enables the speciation of Pb at picomolar level in uncontaminated seawater. The potential shift of electrochemically irreversible lead complexes was calibrated against the complex stability of several ligands in pH8 seawater. The method was compared against the mercury drop electrode at various concentrations of lead and various deposition times, and the response was in general agreement with the theory. The method is tested on samples from oceanic (Atlantic), coastal (Irish Sea) and estuarine (Mersey) origins at Pb concentrations between 30pM and 2nM. The pseudopolarograms were found to resolve the speciation of lead in terms of labile and irreversibly bound Pb species. The lead in the samples was largely in the labile component of the pseudopolarograms, indicating that it was reversibly complexed with values for log α′Pb2+L of 2 for the oceanic sample, and of 4 for the coastal sample. A smaller fraction was resolved as stable, irreversibly bound species with values for the thermodynamic stability constant of log KPb2+L=15–16. The speciation method was able to resolve metal species occurring at levels of only a fraction of that of the metal. Unlike copper, where organic complexation is strong and electrochemically irreversible, and able to significantly decrease its bioavailability, the Pb mostly occurs in the labile complexed fraction and is therefore readily available for geochemical scavenging or biological uptake reactions.