Unfiltered Samples Research Articles

Interferences in the analysis of nanomolar concentrations of nitrate and phosphate in oceanic waters

This paper reports on investigations into interferences with the measurements of nanomolar nitrate + nitrite and soluble reactive phosphate (SRP) in oceanic surface seawater using a segmented continuous flow autoanalyser (SCFA) interfaced with a liquid-waveguide capillary flow-cell (LWCC). The interferences of silicate and arsenate with the analysis of SRP, the effect of sample filtration on the measurement of nanomolar nitrate + nitrite and SRP concentrations, and the stability of samples during storage are described. The investigation into the effect of arsenate (concentrations up to 100 nM) on phosphate analysis (concentrations up to 50 nM) indicated that the arsenate interference scaled linearly with phosphate concentrations, resulting in an overestimation of SRP concentrations of 4.6 ± 1.4% for an assumed arsenate concentration of 20 nM. The effect of added Si(OH) 4 was to increase SRP signals by up to 36 ± 19 nM (at 100 μM Si(OH) 4). However, at silicate concentrations below 1.5 μM, which are typically observed in oligotrophic surface ocean waters, the effect of silicate on the phosphate analysis was much smaller (≤0.78 ± 0.15 nM change in SRP). Since arsenate and silicate interferences vary between analytical approaches used for nanomolar SRP analysis, it is important that the interferences are systematically assessed in any newly developed analytical system. Filtration of surface seawater samples resulted in a decrease in concentration of 1.7–2.7 nM (±0.5 nM) SRP, and a small decrease in nitrate concentrations which was within the precision of the method (±0.6 nM). A stability study indicated that storage of very low concentration nutrient samples in the dark at 4 °C for less than 24 h resulted in no statistically significant changes in nutrient concentrations. Freezing unfiltered surface seawater samples from an oligotrophic ocean region resulted in a small but significant increase in the SRP concentration from 12.0 ± 1.3 nM ( n = 3) to 14.7 ± 0.6 nM ( n = 3) (Student's t-test; p = 0.021). The corresponding change in nitrate concentration was not significant (Student's t-test; p > 0.05).

Genotoxicity of unmodified and organo-modified montmorillonite

The natural clay mineral montmorillonite (Cloisite ® Na +) and an organo-modified montmorillonite (Cloisite ® 30B) were investigated for genotoxic potential as crude suspensions and as suspensions filtrated through a 0.2-μm pore-size filter to remove particles above the nanometre range. Filtered and unfiltered water suspensions of both clays did not induce mutations in the Salmonella/microsome assay at concentrations up to 141 μg/ml of the crude clay, using the tester strains TA98 and TA100. Filtered and unfiltered Cloisite ® Na + suspensions in culture medium did not induce DNA strand-breaks in Caco-2 cells after 24 h of exposure, as tested in the alkaline comet assay. However, both the filtered and the unfiltered samples of Cloisite ® 30B induced DNA strand-breaks in a concentration-dependent manner and the two highest test concentrations produced statistically significantly different results from those seen with control samples ( p < 0.01 and p < 0.001) and ( p < 0.05 and p < 0.01), respectively. The unfiltered samples were tested up to concentrations of 170 μg/ml and the filtered samples up to 216 μg/ml before filtration. When tested in the same concentration range as used in the comet assay, none of the clays produced ROS in a cell-free test system (the DCFH-DA assay). Inductively coupled plasma mass-spectrometry (ICP-MS) was used to detect clay particles in the filtered samples using aluminium as a tracer element characteristic to clay. The results indicated that clay particles were absent in the filtered samples, which was independently confirmed by dynamic light-scattering measurements. Detection and identification of free quaternary ammonium modifier in the filtered sample was carried out by HPLC-Q-TOF/MS and revealed a total concentration of a mixture of quaternary ammonium analogues of 1.57 μg/ml. These findings suggest that the genotoxicity of organo-modified montmorillonite was caused by the organo-modifier. The detected organo-modifier mixture was synthesized and comet-assay results showed that the genotoxic potency of this synthesized organo-modifier was in the same order of magnitude at equimolar concentrations of organo-modifier in filtrated Cloisite ® 30B suspensions, and could therefore at least partly explain the genotoxic effect of Cloisite ® 30B.

Use of H218O2 To Measure Absolute Rates of Dark H2O2 Production in Freshwater Systems

Photochemical production is usually considered to be the main source of H2O2 in freshwater systems; here we show that significant dark production also occurs. We used isotope-labeled H2O2 as a tracer to simultaneously determine H2O2 production and decay rates in incubations of unfiltered water samples. Our new technique for H2(18)O2 analysis, requiring only small sample volumes and simple field equipment, allows for preservation of samples in remote locations, followed by gas chromatography mass spectrometry (GCMS) analysis up to six days later. Dark H2O2 production rates of 29-122 nM/h were observed in several lakewater samples. Measured production and decay rates were consistent with pseudo steady-state, early morning [H2O2] measurements made in each water body. Dark H2O2 production is likely to be more important than photochemical production for the total H2O2 budget over 24 h in the freshwater systems we examined. Our results imply that processes usually assumed to be photochemically induced in freshwaters, such as metal redox cycling mediated by H2O2 and O2(-), and production of strong oxidants from the reaction of H2O2 with Fe(II) (Fenton's reaction) could also be occurring at significant rates in the absence of light.

H5N1 High Pathogenicity Avian Influenza Virus Survival in Different Types of Water

Persistence of H5N1 high pathogenicity avian influenza virus (HPAIV), isolated during the epidemic in wild birds in Poland in 2006, was evaluated in three water samples derived from the sources known to host wild water birds (city pond, Vistula river mouth, and Baltic Sea). The virus was tested at two concentrations (10(4) and 10(6) median tissue culture infective dose per milliliter) and at three temperatures (4 C, 10 C, and 20 C), representing average seasonal temperatures in Poland. All tested water samples were filtered before virus inoculation, and one unfiltered sample (Baltic seawater) was also tested. Infectivity was determined twice a week over a 60-day trial period by microtiter endpoint titration. The persistence of the virus varied considerably depending on its concentration and also on physico-chemical parameters of the water, such as temperature and salinity. Avian influenza virus survival was the highest at 4 C and the lowest at 20 C. Prolonged infectivity of the virus in Baltic seawater (brackish, 7.8 ppt) was also seen. In distilled water, the virus retained its infectivity beyond the 60-day study period. Interestingly, a devastating effect of the unfiltered fraction of seawater was seen as the virus disappeared in this fraction the quickest in all studied combinations; thus, biologic factors may also affect infectivity of HPAIV.

Mercury and Methylmercury Dynamics in a Coastal Plain Watershed, New Jersey, USA

The upper Great Egg Harbor River watershed in New Jersey’s Coastal Plain is urbanized but extensive freshwater wetlands are present downstream. In 2006–2007, studies to assess levels of total mercury (THg) found concentrations in unfiltered streamwater to range as high as 187 ng/L in urbanized areas. THg concentrations were <20 ng/L in streamwater in forested/wetlands areas where both THg and dissolved organic carbon concentrations tended to increase while pH and concentrations of dissolved oxygen and nitrate decreased with flushing of soils after rain. Most of the river’s flow comes from groundwater seepage; unfiltered groundwater samples contained up to 177 ng/L of THg in urban areas where there is a history of well water with THg that exceeds the drinking water standard (2,000 ng/L). THg concentrations were lower (<25 ng/L) in unfiltered groundwater from downstream wetland areas. In addition to higher THg concentrations (mostly particulate), concentrations of chloride were higher in streamwater and groundwater from urban areas than in those from downstream wetland areas. Methylmercury (MeHg) concentrations in unfiltered streamwater ranged from 0.17 ng/L at a forest/wetlands site to 2.94 ng/L at an urban site. The percentage of THg present as MeHg increased as the percentage of forest + wetlands increased, but also was high in some urban areas. MeHg was detected only in groundwater <1 m below the water/sediment interface. Atmospheric deposition is presumed to be the main source of Hg to the wetlands and also may be a source to groundwater, where wastewater inputs in urban areas are hypothesized to mobilize Hg deposited to soils.

Thermal field-flow fractionation and multiangle light scattering of polyvinyl acetate with broad polydispersity and ultrahigh molecular weight microgel components

The challenging task of characterizing polydisperse polymer mixtures possessing ultrahigh molecular weight (MW) polymers and microgels in organic solvents is addressed with thermal field-flow fractionation (ThFFF) and multiangle light scattering-differential refractive index (MALS- dRI) detection. In initial experiments, a 350,000 g/mol poly(methyl methacrylate) (PMMA) standard is used to evaluate the effects of temperature gradient and temperature gradient programming on the measurements. dRI baseline fluctuations caused by temperature programming were minimized by using a mobile phase heater to thermostat connecting tubing. ThFFF–MALS- dRI is then used to separate and characterize a complex polyvinyl acetate (PVAc) sample containing ultrahigh MW polymers and microgels. The open channel design employed by ThFFF allowed the PVAc sample to be analyzed with minimal sample preparation. Unfiltered PVAc sample showed components with MWs close to 10 9 g/mol and root mean square radius r rms values approaching 400 nm. The same sample, filtered through a 0.5 μm pore-size membrane, yielded a MW that was at least one order of magnitude lower. These results demonstrated that the common practice of prefiltering polymer samples prior to analysis can lead to erroneously low average MWs and polydispersities. The accuracy of MW and r rms calculated using standard light scattering equations developed for small scattering molecules and relatively high wavelengths is also examined.

Dark production of hydrogen peroxide in the Gulf of Alaska

Dark H2O2 production rates were measured in samples collected in the Gulf of Alaska. We used a simple, novel method for determining absolute rates of dark production and decay of H2O2, both of which are occurring simultaneously (presumably as a result of biological activity) in unfiltered samples. [H2O2] vs. time was measured in 24‐h dark incubations of both unaltered samples and the same samples spiked with 100–250 nmol L−1 H2O2. Data were modeled with zero‐order H2O2 production rates and first‐order H2O2 decay coefficients as fitting parameters, with the assumption that addition of [H2O2] to a sample does not change either parameter. H2O2 production rates ranged from &lt; 0.5 nmol L−1 h−1 to 8 nmol L−1 h−1, and generally decreased with depth and decreasing chlorophyll. Comparison of dark production with estimates of average photochemical H2O2 production rates in the top 50 m of the water column indicated that dark production is likely to be a significant source of H2O2. Indeed, many of the unaltered incubations indicated that in situ [H2O2] was close to a steady state between dark production and decay, especially in samples from depths of ≥ 10 m.

Particle‐facilitated Pesticide Leaching from Differently Structured Soil Monoliths

The leaching of soil particles and surface applied 14C-labeled glyphosate and pendimethalin from intact soil columns (height: 50 cm; diameter: 30 cm) were investigated, and the relative significance of particle-facilitated pesticide transport was quantified. Investigations were performed with a recently plowed (four columns) and an untilled (five columns) sandy loam soil. Leaching was driven by three irrigation events (15 mm h(-1); 2 h each). Samples of the leachate were filtered immediately (within 1.5 minutes) using 20 nm filters, and the 14C-pesticide content was determined for filtered and unfiltered samples. Pesticide leaching was driven by preferential water flow in macropores. For the plowed structure, 68+/-10% of the leached glyphosate (average of 6 events+/-std.) was bound to particles whereas significantly less glyphosate was bound to particles in leachate from minimally disturbed columns (17+/-12%). Thus, the results suggest that soil structure affected the mode of transport of glyphosate. It is likely that glyphosate sorbed strongly when applied on recently plowed soil (Kd=503 L kg(-1) for the soil), and that it could be mobilized and transported independently of soil particles more easily when applied on the minimally disturbed soil covered in part with crop residues (Kd<1 L kg(-1) for straw). Significantly less amounts of soil particles were leached from minimally disturbed (119-247 mg) than from recently plowed (441-731 mg) columns. The significance of particle-facilitated pendimethalin leaching could not be accurately quantified due to disagreement between control measurements based on both 14C-activity and chemical analyses.

Photochemical Formation of Hydroxyl Radicals in Red Soil-Polluted Seawater on the North of Okinawa Island, Japan

Land development has caused runoff of red soil into the ocean on the north side of Okinawa Island, Japan. In an attempt to clarify the impacts of this “red soil pollution” on the oxidizing power of seawater, we studied the formation of hydroxyl radical (•OH), the most potent oxidant in the environment, in red soil-polluted waters using a 313-nm monochromatic light. •OH was photochemically formed in the red soil-polluted water samples, and the formation rates of •OH decreased as salinity increased, i.e., as red soil-polluted river water gets mixed with seawater. The photo-formation rates of •OH showed good correlations with dissolved Fe concentrations (R 2 = 0.96) and [NO2 −] + [NO3 −] concentrations (R 2 = 0.87), while a negative and weak correlation was found with dissolved organic carbon concentrations (R = −0.78). Theoretical calculation showed that direct photolysis of NO3 −, Fe(OH)2+, and hydrogen peroxide all together accounted for less than 10% of the observed •OH formation in the red soil-polluted waters. Comparison between filtered and unfiltered samples showed that red soil particles were not the main sources of •OH, and the photolysis of NO2 − could account for at most 78% of the observed •OH formation rates. We found that the Fenton’s reaction (a reaction between Fe(II) and H2O2) could possibly account for the observed formation of •OH in the red soil-polluted waters.

Mercury concentrations and loads in a large river system tributary to San Francisco Bay, California, USA

In order to estimate total mercury (HgT) loads entering San Francisco Bay, U.S.A., via the Sacramento-San Joaquin River system, unfiltered water samples were collected between January 2002 and January 2006 during high flow events and analyzed for HgT. Unfiltered HgT concentrations ranged from 3.2 to 75 ng/L and showed a strong correlation (r2 = 0.8, p < 0.001, n=78) to suspended sediment concentrations (SSC). During infrequent large floods, HgT concentrations relative to SSC were approximately twice as high as observed during smaller floods. This difference indicates the transport of more Hg-contaminated particles during high discharge events. Daily HgT loads in the Sacramento-San Joaquin River at Mallard Island ranged from below the limit of detection to 35 kg. Annual HgT loads varied from 61 +/- 22 kg (n=5) in water year (WY) 2002 to 470 +/- 170 kg (n=25) in WY 2006. The data collected will assist in understanding the long-term recovery of San Francisco Bay from Hg contamination and in implementing the Hg total maximum daily load, the long-term cleanup plan for Hg in the Bay.

Point-of-use water filtration reduces healthcare-associated infections in bone marrow transplant recipients

Outbreaks of infection with gram-negative bacteria (GNB) have been linked to hospital water. We sought to determine whether point-of-use (POU) water filtration might result in decreased risk of infection in hospitalized bone marrow transplant (BMT) recipients in the absence of any recognized outbreak. Unfiltered water was sampled from taps in the BMT unit of a major US teaching hospital, and cultured at a reference laboratory. POU bacterial-retentive filters (0.2 mum) were installed throughout the unit, and replaced every 14 days. Infection rates were tracked over a 9-month period, and compared with rates for a 16-month period before POU filtration. Unfiltered water samples from 50% (2 of 4) outlets sampled grew P. aeruginosa (2 of 4) and Stenotrophomonas maltophilia (1 of 4). Clinical infection rates in the unit were significantly reduced from 1.4 total and 0.4 GNB infections per 100 patient days in the period before POU filtration to 0.18 total and 0.09 GNB infections per 100 patient days (P=0.0068 and 0.0431, respectively) in the 9-month period for which filters were in place. Infections during the POU filtration period were due to non-waterborne organisms. Point-of-use (POU) water filtration may significantly reduce infection rates in BMT recipients in the absence of any recognized outbreak.

Particulate aluminium in boreal streams: Towards a better understanding of its sources and influence on dissolved aluminium speciation

The adverse impacts of the inorganic labile monomeric Al (Al i ) fraction on aquatic organisms have meant that Al (Al tot ) determination and even speciation has become a routine part of environmental monitoring and assessment. However, if samples are not filtered prior to analysis then particulate Al (Al tot(p) ) could influence the determination of Al tot , and therefore the determination of the more toxicologically important (Al i ), both when it is measured analytically or modelled from Al tot . This paper shows that the Al/DOC ratio in unfiltered samples can identify the Al tot(p) fraction, and thus improve the speciation of Al i . These findings are based on data from a study in a 67 km 2 catchment in northern Sweden during the snowmelt-driven spring flood of two consecutive years. Filtered and unfiltered samples were studied to determine the spatial and temporal patterns in Al tot(p) . The concentrations of Al tot(p) were greatest in larger downstream sites where significant silt deposits are located. The sites with no silt in their drainage area showed a mean difference between filtered (Al tot(f) ) and unfiltered (Al tot(uf) ) samples of 6%, while sites with silt deposits had a mean difference of 65%. The difference between filtered and unfiltered samples was greatest at peak flow. Spikes in Al tot(p) did not behave consistently during fractionation with a cation exchange column, resulting in increases in either measured Al i(f) or non-labile monomeric Al (Al o(f) ). Al tot(p) spikes were associated with sharp increases in the Al:DOC ratio. The baseflow Al:DOC ratio could be used to model filtered Al tot from DOC with a Spearman rho of 0.75.

Physicochemical Distribution of Metals in the Water Phase of Catch Basin Mixtures

Abstract A mixture of sediment and water is formed during the cleansing of catch basins. This paper discusses the concentration levels and distribution of numerous metals and organic carbon (OC) in the water phase of this mixture. The results show that due to the high concentrations of metals in the water phase, the catch basin mixture should be treated before it reaches a recipient. Three sites with different types of area and traffic intensity were sampled. Four fractions were analyzed: unfiltered, dissolved (&amp;lt;0.2 µm), colloidal (0.22 µm to 1 kD [kilodalton]), and truly dissolved (&amp;lt;1 kD). The results of the unfiltered fraction show high concentrations of metals and OC in the catch basin mixture. A comparison of Canadian and Swedish Environmental Protection Agency guidelines and the catch basin mixtures shows that concentrations exceeded the threshold values for As, Cd, Cr, Cu, Ni, Pb, and Zn. Compared with samples from a reference lake in the area, the unfiltered fraction showed high concentrations of all elements. OC seems to have a large impact on the overall speciation of trace metals in the catch basin mixture. To trace the sources of the particulate fraction in the unfiltered samples, Al-normalization was used. Al-normalization indicated that Ca, K, Mg, Na, Mn, Ba, Co, and Cr concentrations could be explained by mineral particles used as traction control. Furthermore, the trace elements As, Cu, Pb, Zn, and Ni were all enriched in the catch basin mixture.

Geochemistry of trace elements in surface waters of the Arno River Basin, northern Tuscany, Italy

Trace element geochemistry of the Arno River and its main tributaries was investigated on the basis of two sampling campaigns carried out in November 1996 and June 1997. By analyzing filtered and unfiltered water samples, Fe and Al are found in solution mainly as colloidal particles of size lower than 0.45 μm. In June (lower flow rate), Fe and Al are enriched in the filtered waters from the main river, and this feature was interpreted in terms of higher water temperature promoting the formation of smaller particles, thus reducing their aggregation properties. Iron and Al show perfectly synchronous downstream profiles along the Arno River, correlate quite well each to other, and display abrupt concentration increases near to Florence, where the lithology of the catchment changes from siliciclastic dominated to clay-sand (lacustrine-marine)-dominated. The same behaviour is shown by most of the other trace elements in the river, thus supporting a general lithological control. Trace elements in the final part of the Arno River are influenced by flocculation processes in addition to mixing. Adsorption phenomena on oxy-hydroxides are denoted by good elemental correlations with Fe (and Al). Sporadic anomalous concentration values, possibly related to anthropogenic contributions, may prevent such correlations. Referring to the quality of waters for potable use and fish life, toxic elements are below the acceptable limits of current European regulations, with few exceptions for Hg exceeding guideline values. Multivariate analysis groups trace elements according to geochemical affinities and natural or anthropogenic sources, thus distinguishing contaminated from uncontaminated samples. The results achieved in this work will help regional and national Authorities for compliance with the EU water policy, especially in assessing the water quality at the river basin scale and its vulnerability to human activities.

Role of colloidal particles for hydrogeochemistry in As-affected aquifers of the Hetao Basin, Inner Mongolia

High As groundwater was found in shallow aquifers of the Hetao Basin, Inner Mongolia, which has caused serious chronic arsenism. Groundwater particles are ubiquitous in natural aquifers, and significantly affect As mobilization and transportation. This study has investigated their effect on element hydrogeochemistry. Groundwater samples were filtered in the field through a progressively decreasing pore size (10, 5, 3, 1, 0.8, 0.45 μm). Unfiltered samples were also taken. Chemical analysis of 43 groundwater samples shows concentrations of most elements (Ba, Co, Mn, Mo, Ni, V, Sr, Mg, Ca, Na, K) in unfiltered samples are well correlated with those in <0.45 μm fraction, and the ratios between them are close to 1.00. Those elements are considered to be present in the form of true dissolved group and are not affected by the filtration. Although saturation indices for calcite and dolomite are greater than 0, they could possibly exist as small size colloids (<0.45 μm) in groundwater. Concentrations of Cd, Pb, Fe, and Al in <0.45 μm fraction are mostly less than those in unfiltered fraction, implying that large-size inorganic-rich (Al/Fe complexing) colloids could be possible carrier for Cd and Pb in the groundwaters. Arsenic, Cu, Zn and Cr are fallen into another group. These elements could mainly be associated with organic-complexing colloids with particle size less than 0.45 μm, although As could partially be carried by large-size colloids. In groundwaters saturated with respect to pyrite and siderite, a small proportion of As (about 15%) is associated with large-size Fe complexing particles (>0.45 μm). Larger amounts of As is trapped with small size organic colloids, which has been confirmed by the ultrafiltration. The study suggests that groundwater particles transported in the aquifers could affect element geochemistry, especially for As expected to be associated in small size complexes.

Lunar Outgassing, Transient Phenomena, and the Return to the Moon. I. Existing Data

Herein the transient lunar phenomena (TLP) report database is subjected to a discriminating statistical filter robust against sites of spurious reports, and produces a restricted sample that may be largely reliable. This subset is highly correlated geographically with the catalog of outgassing events seen by the Apollo 15, 16 and Lunar Prospector alpha-particle spectrometers for episodic Rn-222 gas release. Both this robust TLP sample and even the larger, unfiltered sample are highly correlated with the boundary between mare and highlands, as are both deep and shallow moonquakes, as well as Po-210, a long-lived product of Rn-222 decay and a further tracer of outgassing. This offers another significant correlation relating TLPs and outgassing, and may tie some of this activity to sagging mare basalt plains (perhaps mascons). Additionally, low-level but likely significant TLP activity is connected to recent, major impact craters (while moonquakes are not), which may indicate the effects of cracks caused by the impacts, or perhaps avalanches, allowing release of gas. The majority of TLP (and Rn-222) activity, however, is confined to one site that produced much of the basalt in the Procellarum Terrane, and it seems plausible that this TLP activity may be tied to residual outgassing from the formerly largest volcanic ffusion sites from the deep lunar interior. With the coming in the next few years of robotic spacecraft followed by human exploration, the study of TLPs and outgassing is both promising and imperiled. We will have an unprecedented pportunity to study lunar outgassing, but will also deal with a greater burden of anthropogenic lunar gas than ever produced. There is a pressing need to study lunar atmosphere and its sources while still pristine. [Abstract abridged.]

Temporal and spatial dynamics of inherent and apparent optical properties in a shallow coastal lake (Fogliano Lagoon, Circeo National Park)

1 - The spatial and temporal dynamics of apparent and inherent optical properties in the coastal lagoon of Fogliano were measured in three seasonal surveys in 2002. Ultraviolet and visible solar irradiance data from in situ measurements permitted to estimate the related attenuation coefficients. The extinction measurements on filtered (0.22 μm) and unfiltered water samples were also performed. The integrated approach between in situ and laboratory measurements allowed the determination of the role of the suspended and dissolved matter in the attenuation and extinction of ultraviolet and visible radiation within the water column. 2 - The impact of the suspended matter on the lake optical quality was influenced by wind resuspension of particulate matter: the relative role of dissolved matter in the absorption of UV and visible radiation was prevailing at low wind velocity conditions (less than 2.2 ms -1 ), while at high wind velocities (3.9 ms -1 ), particulate matter resuspension strongly influenced the attenuation and the extinction measurements. It is a surprise that the dissolved matter is not influenced by the resuspension. 3 - The extinction in the analyzed wavelengths of filtered and unfiltered water samples and the in situ irradiance measurements allowed us to define new optical parameters and important correlations with limnological and classical optical measurements. 4 - By sampling at high spatial resolution (18 stations in 4 km 2 ), it was possible to evidence a spatial gradient of the optical and limnological properties, these distributions showed a consistent pattern in all three surveys, and were important for the characterisation of the chromophoric dissolved organic matter that was estimated with the spectral slope of the extinction curve spectra. A relatively higher spectral slope was found in the southern basin respect to the northern, where the maximum values of the attenuation coefficients and limnological parameters were found. 5 - These results suggest different sources of dissolved organic matter and/or a different level of photobleaching.

Impact of a silver layer on the membrane of tap water filters on the microbiological quality of filtered water

BackgroundBacteria in the hospital's drinking water system represent a risk for the acquisition of a nosocomial infection in the severely immunocompromised host. Terminal tap water filters may be used to prevent nosocomial Legionnaires' disease. We present data from water samples using an improved kind of tap water filters.MethodsIn a blinded study on an intermediate care unit of the thoracic surgery department, a modified type of the Germlyser water filter (Aqua-Free Membrane Technology) with a newly-introduced silver layer on the filtration membrane was compared to its preceding type without such a layer on 15 water outlets. We determined growth of Legionella, other pathogenic bacteria, and the total heterotrophic plate count in unfiltered water and filtered water samples after filter usage intervals of 1 through 4 weeks.ResultsA total of 299 water samples were tested. Twenty-nine of the 60 unfiltered water samples contained Legionella of various serogroups (baseline value). In contrast, all samples filtered by the original water filter and all but one of the water samples filtered by the modified filter type remained Legionella-free. No other pathogenic bacteria were detected in any filtered sample. The total plate count in water samples increased during use of both kinds of filters over time. However, for the first 7 days of use, there were significantly fewer water samples containing >100 CFU per mL when using the new filter device compared with the older filters or taps with no filter. No advantage was seen thereafter.ConclusionThe use of this type of terminal water filter is an appropriate method to protect immunocompromised patients from water-borne pathogens such as Legionella.

Multivariate Analysis of Attenuated Total Reflection—Fourier Transform Infrared Spectroscopic Data to Confirm the Origin of Honeys

Fourier transform infrared (FT-IR) spectroscopy and chemometrics were used to verify the origin of honey samples (n=150) from Europe and South America. Authentic honey samples were collected from five sources, namely unfiltered samples from Mexico in 2004, commercially filtered samples from Ireland and Argentina in 2004, commercially filtered samples from the Czech Republic in 2005 and 2006, and commercially filtered samples from Hungary in 2006. Samples were diluted with distilled water to a standard solids content (70 degrees Brix) and their spectra (2500-12 500 nm) recorded at room temperature using an FT-IR spectrometer equipped with a germanium attenuated total reflection (ATR) accessory. First- and second-derivative and standard normal variate (SNV) data pretreatments were applied to the recorded spectra, which were analyzed using partial least squares (PLS) regression analysis, factorial discriminant analysis (FDA), and soft independent modeling of class analogy (SIMCA). In general, when an attenuated wavelength range (6800-11 500 nm) rather than the whole spectrum (2500-12 500 nm) was studied, higher correct classification rates were achieved. An overall correct classification of 93.3% was obtained for honeys by PLS discriminant analysis, while FDA techniques correctly classified 94.7% of honey samples. Correct classifications of up to 100% were achieved using SIMCA, but models describing some classes had very high false positive rates.

Mercury sources and transformations in a man-perturbed tidal estuary: The Sinnamary Estuary, French Guiana

The distribution, partition and speciation of mercury (Hg) were studied along the redox gradient of an anthropogenically perturbed tropical estuary, the Sinnamary Estuary in French Guiana. This system is a partially mixed estuary characterized by an anoxic freshwater end-member, while the marine end-member consists of the Amazon Plume. The set up of an artificial oxygenation system in the anoxic freshwater end-member generates sharp gradients of major chemical species (iron, sulfides, etc.) coupled with intense organic matter (OM) turnover. The coexistence of oxygenated waters and dissolved sulfides in an organic rich environment depicts the Upper Sinnamary Estuary (USE: part of Sinnamary Estuary under the tidal influence but upstream of the salt intrusion) as a potential site for Hg methylation. The concentrations of all mercury compounds (HgT) in the unfiltered samples (HgT UNF), in the dissolved (HgT D) and particulate (HgT P) phases of the USE average 11 ± 3, 6 ± 2 and 5 ± 3 (i.e. 600 ± 200 pmol g −1) pmol L −1, respectively. Average concentrations of monomethylmercury (MMHg) in the unfiltered (MMHg UNF), dissolved (MMHg D) and particulate (MMHg P) phases were 3.7 ± 1.0, 2.0 ± 0.9 and 1.8 ± 1.2 (i.e. 220 ± 130 pmol g −1) pmol L −1, respectively. Water oxygenation and sulfides concentrations emerged to play a critical role in controlling MMHg levels. Additionally, iron cycling, acid–base mechanisms, and redox-dependent processes were involved in the MMHg partitioning between phases. Overall, the USE constitutes a biogeochemical reactor that gathers partitioning and methylation processes. The permanent MMHg inputs from the anoxic freshwater end-member combined with the intense endogenous Hg methylation ensures high-MMHg levels in both dissolved and particulate phases. To illustrate, the USE exports 60 ± 20% more MMHg UNF than it imports: 5.5 ± 0.7 vs. 3.5 ± 1.2 kg year −1.