Flux of Total Mercury and Methylmercury to the Northern Gulf of Mexico from U.S. Estuaries.

To better understand the source of elevated methylmercury (MeHg) concentrations in Gulf of Mexico (GOM) fish, we quantified fluxes of total Hg and MeHg from 11 rivers in the southeastern United States, including the 10 largest rivers discharging to the GOM. Filtered water and suspended particles were collected across estuarine salinity gradients in Spring and Fall 2012 to estimate fluxes from rivers to estuaries and from estuaries to coastal waters. Fluxes of total Hg and MeHg from rivers to estuaries varied as much as 100-fold among rivers. The Mississippi River accounted for 59% of the total Hg flux and 49% of the fluvial MeHg flux into GOM estuaries. While some estuaries were sources of Hg, the combined estimated fluxes of total Hg (~5200 mol y(-1)) and MeHg (~120 mol y(-1)) from the estuaries to the GOM were less than those from rivers to estuaries, suggesting an overall estuarine sink. Fluxes of total Hg from the estuaries to coastal waters of the northern GOM are approximately an order of magnitude less than from atmospheric deposition. However, fluxes from rivers are significant sources of MeHg to estuaries and coastal regions of the northern GOM.

Effects of vegetation on methylmercury concentrations and loads in a mercury contaminated floodplain.

The Yolo Bypass (YB) is a large flood conveyance system designed to protect the city of Sacramento, California, USA from flooding when the Sacramento River approaches flood stage. The Sacramento River watershed and YB are a source of methylmercury (MeHg) to downstream habitat as a result of historic mercury (Hg) and gold mining practices. In the dry season, the YB is extensively farmed and grazed. However, depending on the water year, the floodplain may remain inundated for months. Our experiments focused on the role of pasture land and decomposing vegetation as a source of MeHg during extensive periods of floodplain flooding. Decomposing vegetation, rather than sediment, was identified as the principal source of filter passing MeHg (fMeHg) within the floodplain. The decomposing vegetation provided a substrate for microbial methylation of inorganic Hg contained within the plants. In replicated flooded mesocosm experiments, MeHg concentrations increased from 2.78 to 31.0 ng g-1 dw and 3.41 to 56.8 ng g-1 dw in decomposing vegetation. In field collections, the concentrations of MeHg in vegetation increased from preflood levels of 2.78 to 45.4 ng g-1 dw after 17 weeks of flooding. The importance of vegetation was shown in laboratory experiments where there was a positive correlation between the amount of fMeHg in water and the amount of vegetation added. These results also provide Hg concentration data for an important functional type of vegetation, grasses, and fill a data gap that contributed to uncertainties with regards to the role of vegetation in Hg cycling.

Bayesian integration of isotope ratio for geographic sourcing of castor beans.

Recent years have seen an increase in the forensic interest associated with the poison ricin, which is extracted from the seeds of the Ricinus communis plant. Both light element (C, N, O, and H) and strontium (Sr) isotope ratios have previously been used to associate organic material with geographic regions of origin. We present a Bayesian integration methodology that can more accurately predict the region of origin for a castor bean than individual models developed independently for light element stable isotopes or Sr isotope ratios. Our results demonstrate a clear improvement in the ability to correctly classify regions based on the integrated model with a class accuracy of 60.9 ± 2.1% versus 55.9 ± 2.1% and 40.2 ± 1.8% for the light element and strontium (Sr) isotope ratios, respectively. In addition, we show graphically the strengths and weaknesses of each dataset in respect to class prediction and how the integration of these datasets strengthens the overall model.

Pyrogenic inputs of anthropogenic Pb and Hg to sediments of the Hood Canal, Washington, in the 20th century: source evidence from stable Pb isotopes and PAH signatures.

Combustion-derived PAHs and stable Pb isotopic signatures ((206)Pb/(207)Pb) in sedimentary records assisted in reconstructing the sources of atmospheric inputs of anthropogenic Pb and Hg to the Hood Canal, Washington. The sediment-focusing corrected peak fluxes of total Pb and Hg (1960-70s) demonstrate that the watershed of Hood Canal has received greater atmospheric inputs of these metals than its mostly rural land use would predict. The tight relationships between the Pb, Hg, and organic markers in the cores indicate that these metals are derived from industrial combustion emissions. Multiple lines of evidence point to the Asarco smelter, located in the Main Basin of Puget Sound, as the major emission source of these metals to the watershed of the Hood Canal. The evidence includes (1) similar PAH isomer ratios in sediment cores from the two basins, (2) the correlations between Pb, Hg, and Cu in sediments and previously studied environmental samples including particulate matter emitted from the Asarco smelter's main stack at the peak of production, and (3) Pb isotope ratios. The natural rate of recovery in Hood Canal since the 1970s, back to preindustrial metal concentrations, was linear and contrasts with recovery rates reported for the Main Basin which slowed post late 1980s.

Estuarine mixing behavior of colloidal organic carbon and colloidal mercury in Galveston Bay, Texas.

Mercury (Hg) in estuarine water is distributed among different physical phases (i.e. particulate, colloidal, and truly dissolved). This phase speciation influences the fate and cycling of Hg in estuarine systems. However, limited information exists on the estuarine distribution of colloidal phase Hg, mainly due to the technical difficulties involved in measuring it. In the present study, we determined Hg and organic carbon levels from unfiltered, filtered (<0.45 µm), colloidal (10 kDa-0.45 µm), and truly dissolved (<10 kDa) fractions of Galveston Bay surface water in order to understand the estuarine mixing behavior of Hg species as well as interactions of Hg with colloidal organic matter. For the riverine end-member, the colloidal fraction comprised 43 ± 11% of the total dissolved Hg pool and decreased to 17 ± 8% in brackish water. In the estuarine mixing zone, dissolved Hg and colloidal organic carbon showed non-conservative removal behavior, particularly in the low salinity (<15 ppt) region. This removal may be caused by salt-induced coagulation of colloidal matter and consequent removal of dissolved Hg. The particle-water interaction, K(d) ([particulate Hg (mol kg(-1))]/[dissolved Hg (mol L(-1))]) of Hg decreased as particle concentration increased, while the particle-water partition coefficient based on colloidal Hg and the truly dissolved Hg fraction, K(c) ([colloidal Hg (mol kg(-1))]/[truly dissolved Hg (mol L(-1))]) of Hg remained constant as particle concentration increased. This suggests that the particle concentration effect is associated with the amount of colloidal Hg, increasing in proportion to the amount of suspended particulate matter. This work demonstrates that, colloidal organic matter plays an important role in the transport, particle-water partitioning, and removal of dissolved Hg in estuarine waters.

A highly efficient uranium grabber derived from acrylic fiber for extracting uranium from seawater.

Acrylic fiber can be chemically converted to an amidoxime and carboxylate containing chelating adsorbent by a two-step synthesis method for extraction of uranium from seawater. A portion of the nitrile groups in the fiber is first converted to amidoxime using hydroxylamine followed by conversion of another portion of the nitrile groups to carboxylate with NaOH. At an optimized ratio of amidoxime/carboxylate (about 1 : 1), the chelating fiber in real seawater shows a higher uranium adsorption capacity and shorter saturation time compared with similar high-surface-area chelating fibers developed recently using a radiation-induced grafting method. The saturation capacity of uranium is estimated to be 7.73 grams per kilogram of the adsorbent at 20 °C and the half-saturation time is about 15.7 days. The fiber shows a vanadium/uranium ratio of about 1 in real seawater tests. The low vanadium adsorption capacity of the fiber is attributed to the branched-chain amidoxime groups formed by the specified amidoximation process. This simple and low-cost synthesis method can be scaled up to mass produce the chelating fiber for recovering metals from various aquatic environments including production of uranium from seawater.

Comparison of trained clinician ratings with expert ratings of aspiration on videofluoroscopic images from a randomized clinical trial.

Accurate detection and classification of aspiration is a critical component of videofluoroscopic swallowing evaluation, the most commonly utilized instrumental method for dysphagia diagnosis and treatment. Currently published literature indicates that interjudge reliability for the identification of aspiration ranges from poor to fairly good depending on the amount of training provided to clinicians. The majority of extant studies compared judgments among clinicians. No studies included judgments made during the use of a postural compensatory strategy. The purpose of this study was to examine the accuracy of judgments made by speech-language pathologists (SLPs) practicing in hospitals compared with unblinded expert judges when identifying aspiration and using the 8-point Penetration/Aspiration Scale. Clinicians received extensive training for the detection of aspiration and minimal training on use of the Penetration/Aspiration Scale. Videofluoroscopic data were collected from 669 patients as part of a large, randomized clinical trial and include judgments of 10,200 swallows made by 76 clinicians from 44 hospitals in 11 states. Judgments were made on swallows during use of dysphagia compensatory strategies: chin-down posture with thin liquids and head-neutral posture with thickened liquids (nectar-thick and honey-thick consistencies). The subject population included patients with Parkinson's disease and/or dementia. Kappa statistics indicate high accuracy for all interventions by SLPs for identification of aspiration (all kappa > 0.86) and variable accuracy (range = 69-76%) using the Penetration/Aspiration Scale when compared to expert judges. It is concluded that while the accuracy of identifying the presence of aspiration by SLPs is excellent, more extensive training and/or image enhancement is recommended for precise use of the Penetration/Aspiration Scale.

Mercury concentrations in Pacific lamprey (Entosphenus tridentatus) and sediments in the Columbia River basin.

The accumulation of mercury was investigated in Pacific lamprey and stream sediments in the Columbia River basin. Mercury concentrations in larval lamprey differed significantly among sample locations (p < 0.001) and were correlated with concentrations in sediments (r2 = 0.83). Adult concentrations were highly variable (range, 0.1-9.5 µg/g) and unrelated to holding time after collection. The results suggest that Pacific lamprey in the Columbia River basin may be exposed to mercury levels that have adverse ecological effects. Environ Toxicol Chem 2016;35:2571-2576. © 2016 SETAC.

Surface functionalized nanostructured ceramic sorbents for the effective collection and recovery of uranium from seawater.

The ability to collect uranium from seawater offers the potential for a nearly limitless fuel supply for nuclear energy. We evaluated the use of functionalized nanostructured sorbents for the collection and recovery of uranium from seawater. Extraction of trace minerals from seawater and brines is challenging due to the high ionic strength of seawater, low mineral concentrations, and fouling of surfaces over time. We demonstrate that rationally assembled sorbent materials that integrate high affinity surface chemistry and high surface area nanostructures into an application relevant micro/macro structure enables collection performance that far exceeds typical sorbent materials. High surface area nanostructured silica with surface chemistries composed of phosphonic acid, phosphonates, 3,4 hydroxypyridinone, and EDTA showed superior performance for uranium collection. A few phosphorous-based commercial resins, specifically Diphonix and Ln Resin, also performed well. We demonstrate an effective and environmentally benign method of stripping the uranium from the high affinity sorbents using inexpensive nontoxic carbonate solutions. The cyclic use of preferred sorbents and acidic reconditioning of materials was shown to improve performance. Composite thin films composed of the nanostructured sorbents and a porous polymer binder are shown to have excellent kinetics and good capacity while providing an effective processing configuration for trace mineral recovery from solutions. Initial work using the composite thin films shows significant improvements in processing capacity over the previously reported sorbent materials.

Silver concentrations in Colorado, USA, watersheds using improved methodology.

River water samples were collected at five sites in the state of Colorado, USA, to assess the impact of municipal and industrial discharges on Ag concentrations and speciation in surface waters. Samples were collected and analyzed for total (unfiltered collections), filtered (0.1 and 0.4 microm), particulate (> or = 0.45 microm), and colloidal Ag (3 kDa-0.1 m) using ultraclean protocols. A series of laboratory experiments were conducted to assess bias from sample storage, digestion, and preconcentration protocols. In general, upstream unfiltered and particulate Ag concentrations fell within a fairly narrow range, 3.1 to 21 ng/L and 0.2 to 1.7 microg/g, respectively. Downstream unfiltered and particulate Ag concentrations showed a more broad range, 2.8 to 1,110 ng/L and 0.5 to 104 microg/g, respectively, and reflected attenuated impacts of Ag-laden discharge effluents. However, Ag concentrations in the 0.1-microm filter-passing fraction 0.8 to 1.2 km downstream from major treatment plant effluents were all below the chronic silver criteria. On average, more than 60% of the 0.1-microm filter-passing Ag was associated with colloidal macromolecular organic matter. Silver concentrations in colloids (microg/g) were, on average, the same as those in suspended particulate matter. The percentage abundance of colloidal Ag was similar to that of dissolved organic carbon, suggesting that strong Ag binding ligands exist in both the colloidal and the particle size fractions, as these macromolecular ligands likely play a major role in Ag speciation.

Concurrent photolytic degradation of aqueous methylmercury and dissolved organic matter.

Monomethyl mercury (MeHg) is a potent neurotoxin that threatens ecosystem viability and human health. In aquatic systems, the photolytic degradation of MeHg (photodemethylation) is an important component of the MeHg cycle. Dissolved organic matter (DOM) is also affected by exposure to solar radiation (light exposure) leading to changes in DOM composition that can affect its role in overall mercury (Hg) cycling. This study investigated changes in MeHg concentration, DOM concentration, and the optical signature of DOM caused by light exposure in a controlled field-based experiment using water samples collected from wetlands and rice fields. Filtered water from all sites showed a marked loss in MeHg concentration after light exposure. The rate of photodemethylation was 7.5×10(-3)m(2)mol(-1) (s.d. 3.5×10(-3)) across all sites despite marked differences in DOM concentration and composition. Light exposure also caused changes in the optical signature of the DOM despite there being no change in DOM concentration, indicating specific structures within the DOM were affected by light exposure at different rates. MeHg concentrations were related to optical signatures of labile DOM whereas the percent loss of MeHg was related to optical signatures of less labile, humic DOM. Relationships between the loss of MeHg and specific areas of the DOM optical signature indicated that aromatic and quinoid structures within the DOM were the likely contributors to MeHg degradation, perhaps within the sphere of the Hg-DOM bond. Because MeHg photodegradation rates are relatively constant across freshwater habitats with natural Hg-DOM ratios, physical characteristics such as shading and hydrologic residence time largely determine the relative importance of photolytic processes on the MeHg budget in these mixed vegetated and open-water systems.

Mercury cycling in agricultural and managed wetlands: a synthesis of methylmercury production, hydrologic export, and bioaccumulation from an integrated field study.

With seasonal wetting and drying, and high biological productivity, agricultural wetlands (rice paddies) may enhance the conversion of inorganic mercury (Hg(II)) to methylmercury (MeHg), the more toxic, organic form that biomagnifies through food webs. Yet, the net balance of MeHg sources and sinks in seasonal wetland environments is poorly understood because it requires an annual, integrated assessment across biota, sediment, and water components. We examined a suite of wetlands managed for rice crops or wildlife during 2007-2008 in California's Central Valley, in an area affected by Hg contamination from historic mining practices. Hydrologic management of agricultural wetlands for rice, wild rice, or fallowed - drying for field preparation and harvest, and flooding for crop growth and post-harvest rice straw decay - led to pronounced seasonality in sediment and aqueous MeHg concentrations that were up to 95-fold higher than those measured concurrently in adjacent, non-agricultural permanently-flooded and seasonally-flooded wetlands. Flooding promoted microbial MeHg production in surface sediment of all wetlands, but extended water residence time appeared to preferentially enhance MeHg degradation and storage. When incoming MeHg loads were elevated, individual fields often served as a MeHg sink, rather than a source. Slow, horizontal flow of shallow water in the agricultural wetlands led to increased importance of vertical hydrologic fluxes, including evapoconcentration of surface water MeHg and transpiration-driven advection into the root zone, promoting temporary soil storage of MeHg. Although this hydrology limited MeHg export from wetlands, it also increased MeHg exposure to resident fish via greater in situ aqueous MeHg concentrations. Our results suggest that the combined traits of agricultural wetlands - slow-moving shallow water, manipulated flooding and drying, abundant labile plant matter, and management for wildlife - may enhance microbial methylation of Hg(II) and MeHg exposure to local biota, as well as export to downstream habitats during uncontrolled winter-flow events.

Evaluation of gene expression changes in human primary uroepithelial cells following 24-hr exposures to inorganic arsenic and its methylated metabolites.

Gene expression changes in primary human uroepithelial cells exposed to arsenite and its methylated metabolites were evaluated to identify cell signaling pathway perturbations potentially associated with bladder carcinogenicity. Cells were treated with mixtures of inorganic arsenic and its pentavalent or trivalent metabolites for 24 hr at total arsenic concentrations ranging from 0.06 µM to 18 µM. One series (five samples) was conducted with arsenite and pentavalent metabolites and a second (10 samples) with arsenite and trivalent metabolites. Similar gene expression responses were obtained for pentavalent or trivalent metabolites. A suite of eight gene changes was consistently identified across individuals that reflect effects on key signaling pathways: oxidative stress, protein folding, growth regulation, metallothionine regulation, DNA damage sensing, thioredoxin regulation, and immune response. No statistical significance of trend (NOSTASOT) analysis of these common genes identified lowest observed effect levels (LOELs) from 0.6 to 6.0 µM total arsenic and no observed effect levels (NOELs) from 0.18 to 1.8 µM total arsenic. For the trivalent arsenical mixture, benchmark doses (BMDs) ranged from 0.13 to 0.92 µM total arsenic; benchmark dose lower 95% confidence limits (BMDLs) ranged from 0.09 to 0.58 µM total arsenic. BMDs ranged from 0.53 to 2.7 µM and BMDLs from 0.35 to 1.7 µM for the pentavalent arsenical mixture. Both endpoints varied by a factor of 3 across individuals. Thisstudy is the first to examine gene expression response in primary uroepithelial cells from multiple individuals and to identify no effect levels for arsenical-induced cell signaling perturbations in normal human cells exposed to a biologically plausible concentration range.

Acetone-butanol fermentation of marine macroalgae.

The objective of this study was to subject mannitol, either as a sole carbon source or in combination with glucose, and aqueous extracts of the kelp Saccharina spp., containing mannitol and laminarin, to acetone-butanol fermentation by Clostridium acetobutylicum (ATCC 824). Both mannitol and glucose were readily fermented. Mixed substrate fermentations with glucose and mannitol resulted in diauxic growth of C. acetobutylicum with glucose depletion preceding mannitol utilization. Fermentation of kelp extract exhibited triauxic growth, with an order of utilization of free glucose, mannitol, and bound glucose, presumably laminarin. The lag in laminarin utilization reflected the need for enzymatic hydrolysis of this polysaccharide into fermentable sugars. The butanol and total solvent yields were 0.12 g/g and 0.16 g/g, respectively, indicating that significant improvements are still needed to make industrial-scale acetone-butanol fermentations of seaweed economically feasible.

Spatial and habitat-based variations in total and methyl mercury concentrations in surficial sediments in the San Francisco Bay-Delta.

Recent studies indicate significant amounts of mercury (Hg) are annually transported into the San Francisco Bay-Delta (Bay-Delta) as a result of historic gold and Hg mining activities. We examined temporal and spatial variation in concentrations of total Hg (Hg(T)) and monomethylmercury (MMHg) in surficial sediments of various ecosystem types in the Bay-Delta. We sampled surficial sediments across the Bay-Delta system and found Hg(T) sediment concentrations in the central Delta were generally 100-200 ng g(-1) and increased westward through Suisun Bay to 250-350 ng g(-1). MMHg concentrations in the central Delta were between 1 and 3 ng g(-1), while those in sediments in the perimeter waterways and adjacent bays were less than 1 ng g(-1). Six sites were monitored monthly for over a year to identify seasonal changes in Hg sediment concentrations. Hgtau sediment concentrations ranged from 48 to 382 ng g(-1) and varied as a function of location not season. However, MMHg concentrations varied seasonally, increasing from 1 ng g(-1) during winter months to 6 ng g(-1) during spring and summer. Transects conducted at three marshes in the central Delta revealed MMHg sediment concentrations of 4-8 ng g(-1) at the interior and 2 ng g(-1) at the exterior of the marshes. Habitat type was a major factor controlling MMHg concentration and the MMHg to Hg(T) ratio in sediments of the Bay-Delta. MMHg was significantly correlated to Hgt (r2 = 0.49) in marsh sediments.

Challenges in the design and conduct of a randomized study of two interventions for liquid aspiration.

BACKGROUND: Liquid aspiration during swallowing has been linked to pneumonia, the most common cause of infectious death in the elderly. This paper examines the key issues in the design and implementation of the first multisite, randomized behavioral trial in dysphagia in an aging population. The study evaluated two commonly used treatments with respect to short-term and long-term management of liquid aspiration and subsequent pneumonia in dysphagic geriatric participants with dementia and/or Parkinson's disease. METHODS: Discussed are lessons learned during the conduct of this trial and include (1) ethical and methodological design issues, (2) pragmatic implementation of procedures and forms, (3) importance of multiple communication and monitoring strategies, (4) response to funding issues, and (5) changes in staff and facilities. RESULTS: In order to complete this trial the researchers were required to provide more support than anticipated in tasks such as completion of regulatory requirements by sites, supplementing site staff to identify potential study participants using a 'circuit rider' approach, continued recruitment of new sites and staff throughout the course of the trial, adapting forms and procedures and managing within economic constraints in a changing trial environment. LIMITATIONS: Many of the challenges faced by the researchers were not anticipated when the study began. Successful strategies are described for these unanticipated difficulties, based on retrospective evaluation. CONCLUSIONS: Successful conduct of clinical trials in long-term care environments that are heavily impacted by changes extraneous to the trial design and with staff typically new to clinical trials is possible but success depends on logistical flexibility.

Determination of mercury complexation in coastal and estuarine waters using competitive ligand exchange method.

While many studies have examined Hg(II) binding ligand in natural dissolved organic matter, determined ligand concentrations far exceed natural Hg(II) concentrations. This ligand class may not influence natural Hg(II) complexation, given the reverse relation between ligand concentration and metal-ligand binding strength. This study used a new competing ligand, thiosalicylic acid, in a competitive ligand exchange method in which water-toluene extraction was used to determine extremely strong Hg(II) binding sites in estuarine and coastal waters (dissolved [Hg] = 0.5-8 pM). Thiosalicylic acid competition lowered the detection limit of Hg(II) complexing ligand by 2 orders of magnitude from values found by previous studies; the determined Hg(II) complexing ligand ranged from 13 to 103 pM. The logarithmic conditional stability constants between Hg(II) and Hg(II) complexing ligand (Kcond' = [HgL]/([Hg2+][L']), [L'] = total [L] - [HgL]) ranged from 26.5 to 29.0. Applying the same method for chloride competition detected another class of ligand that is present from 0.5 to 9.6 nM with log conditional stability constants ranging from 23.1 to 24.4. A linear relationship was observed between the log conditional stability constant and log Hg(II) complexing ligand concentration, supporting the hypothesis that Hg(II) binding ligand should be characterized as a series or continuum of binding sites on natural dissolved organic matter. Calculating Hg(II) complexation using the conditional stability constants and ligand concentrations determined in this study indicates that >99% of the dissolved mercury is complexed by natural ligand associated with dissolved organic matter in estuarine and coastal waters of Galveston Bay, Texas.