Unfiltered Water Samples Research Articles

Determination of water quality, and trace metals in endemic Sarotherodon linellii, Pungu maclareni and Clarias maclareni, in crater Lake Barombi Mbo, Cameroon

Considering water pollution as a potential threat to some endemic cichlids of Lake Barombi Mbo, Cameroon, an investigation was done in 2011 to determine trace metals in its water, linking their uptake in gills and liver of fish to water chemistry. ICP-MS and ICP-OES analyses of trace metals based on total concentration of unfiltered lake water samples showed the presence of trace metals. All fish species accumulated Al, Mn and Sr in the highest concentrations in their gills, with Cu, Cd, Co, Cr, Pb and U highest in the liver. Pungu maclareni accumulated Al, Cr, Co, Sr and Pb in the highest concentrations. The highest mean gill Al concentration of 140 µg g−1 dry weight was measured in P. maclareni gills, this being one of the critically endangered cichlids of the lake. Stable isotope analyses of carbon δ13C and nitrogen δ15N showed that P. maclareni had the highest mean δ13C (−30.2‰) and highest concentrations of Cr, Co, Pb and U in liver, probably linking the carbon source to the accumulation of metals. Though trace metal levels in the lake water were low, their presence in fish tissues suggest they are bioavailable, bioaccumulate and may pose a threat to the aquatic biota, and therefore should be monitored.

Sources and exchanges of mercury in the waters of the Northwestern Mediterranean margin

Ocean margins are focal regions in terms of mercury (Hg) exchanges between the continent and the open sea. The aim of this paper is to describe the distribution and partition of Hg between the gaseous, dissolved and particulate phases in the waters of the Northwestern Mediterranean (NWM) margin, in order to assess the Hg sources and exchanges within the continuum between the continental shelf (Gulf of Lions) and the open sea (Northern Gyre).Mean (±standard deviation) of total Hg species (HgT) concentrations in unfiltered water samples were 1.52±1.00pmolL−1 (n=36) in the inner shelf, 1.09±0.15pmolL−1 (n=30) along the slope, and 1.10±0.13pmolL−1 (n=99) in the Northern Gyre. The dissolved phase (<0.45µm) average concentrations were 0.80±0.47pmolL−1 (n=37) in the inner shelf, 0.93±0.20pmolL−1 (n=4) along the slope and 0.84±0.10 (n=20) pmolL−1 in the Northern Gyre. The particulate fraction of Hg decreased very strongly seaward from around 60% on the shelf to 10–25% above the Northern Gyre. Very low dissolved HgT concentrations occurred in the inner shelf water, consistent with the results of incubation experiments, which demonstrated that shelf water is very efficient in both production and release of dissolved gaseous Hg into the atmosphere. In the North Gyre waters column HgT presents a distribution pattern inverse to that of dissolved oxygen, and a slight Hg enrichment in the deep layer (Western Mediterranean Deep Water).The Hg from the open sea water is the largest Hg input to the Gulf of Lions (∼5.7kmolyr−1), whereas inputs from the riverine source account for ∼3.4kmolyr−1 and atmospheric deposition for less than 0.5kmolyr−1. The Hg accumulated in the sediments of the shelf is ∼4.5kmolyr−1, including 0.6–1.7kmolyr−1 in the Rhône prodelta sediments. The evasion to the atmosphere represents a Hg flux of ∼2.6kmolyr−1.

Environmental signatures and effects of an oil and gas wastewater spill in the Williston Basin, North Dakota.

Wastewaters from oil and gas development pose largely unknown risks to environmental resources. In January 2015, 11.4ML (million liters) of wastewater (300g/L TDS) from oil production in the Williston Basin was reported to have leaked from a pipeline, spilling into Blacktail Creek, North Dakota. Geochemical and biological samples were collected in February and June 2015 to identify geochemical signatures of spilled wastewaters as well as biological responses along a 44-km river reach. February water samples had elevated chloride (1030mg/L) and bromide (7.8mg/L) downstream from the spill, compared to upstream levels (11mg/L and <0.4mg/L, respectively). Lithium (0.25mg/L), boron (1.75mg/L) and strontium (7.1mg/L) were present downstream at 5-10 times upstream concentrations. Light hydrocarbon measurements indicated a persistent thermogenic source of methane in the stream. Semi-volatile hydrocarbons indicative of oil were not detected in filtered samples but low levels, including tetramethylbenzenes and di-methylnaphthalenes, were detected in unfiltered water samples downstream from the spill. Labile sediment-bound barium and strontium concentrations (June 2015) were higher downstream from the Spill Site. Radium activities in sediment downstream from the Spill Site were up to 15 times the upstream activities and, combined with Sr isotope ratios, suggest contributions from the pipeline fluid and support the conclusion that elevated concentrations in Blacktail Creek water are from the leaking pipeline. Results from June 2015 demonstrate the persistence of wastewater effects in Blacktail Creek several months after remediation efforts started. Aquatic health effects were observed in June 2015; fish bioassays showed only 2.5% survival at 7.1km downstream from the spill compared to 89% at the upstream reference site. Additional potential biological impacts were indicated by estrogenic inhibition in downstream waters. Our findings demonstrate that environmental signatures from wastewater spills are persistent and create the potential for long-term environmental health effects.

Nutrition profile of the Sea of Marmara between years 2010 and 2013

In order to determine the nutrition load in the Sea of Marmara, sampling was realized on appointed 25 stations, at standard vertical sections from the surface to the deepest point of the station, bi-annually between 2010 and 2013. NO 2 –N, NO 3 –N, NH 4 –N, and PO 4 –P were analysed from unfiltered water samples; in addition, some physicochemical parameters that play important roles, such as salinity, temperature, dissolved oxygen, and pH, were measured for each station. This study reports on nutrients load in the Sea of Marmara for a preliminary assessment of the status of these nutrients and a brief discussion about the unique oceanographical status of the Sea of Marmara.

Evaluation of Community‐Level Physiological Profiling for Monitoring Microbial Community Function in Aquaculture Ponds

AbstractMicrobial communities in aquaculture ponds play pivotal roles in pond productivity and fish production success. Nonetheless, culturists do not consider this variable in pond management decision making likely because of a lack of practical assessment tools. Therefore, we evaluated the community‐level physiological profiling (CLPP) technique for characterizing microbial community function for use in aquaculture. Unfiltered water samples collected from various plastic‐lined ponds over time were incubated on Biolog EcoPlates. Responses (substrate optical densities) were measured at 24‐h intervals for up to 12 d to determine the best incubation interval and the number of required replicates needed for determining microbial community function in aquaculture ponds. The repeatability and within‐pond variability of the CLPP metrics were also evaluated. During cooler months and in ponds with no fish and low apparent microbial activity, a 96‐h incubation period was required to differentiate microbial community functional characteristics. During warmer months and when ponds were stocked with fish and had significant phytoplankton blooms, incubation periods of 72 h were sufficient. For routine monitoring, a single sample of pond water on one Biolog EcoPlate was adequate for assessing microbial community function. Multiple water samples from a single pond revealed low heterogeneity in the microbial community function. When multiple Biolog EcoPlates were inoculated with a single sample of pond water the dissimilarity of substrate responses was low (2.9%), indicating high repeatability of the CLPP technique. The CLPP method appears to be robust and allows for the assessment of functional characteristics of the heterotrophic microbial community such as relative diversity, similarity, and community functional activity. Therefore, this technique may be used by fish culturists to assess hatchery pond microbial community function, which would lead to a better understanding of the importance of the microbial community to the overall aquaculture pond ecosystem function. Such a tool would allow improved and more comprehensive management of aquaculture pond ecosystems.

Measurement of dark, particle-generated superoxide and hydrogen peroxide production and decay in the subtropical and temperate North Pacific Ocean

Reactive oxygen species (ROS), which include the superoxide radical (O2-) and hydrogen peroxide (H2O2), are thought to be generated mostly through photochemical reactions and biological activity in seawater and can influence trace metal speciation in the ocean. This study reports the results of an intercomparison of two methods to measure particle-generated [O2-] in seawater samples, as well as measurements of particle-generated O2- and H2O2 concentrations, decay kinetics, and dark production rates in seawater samples at Station ALOHA and (O2- only) in the southern California Current Ecosystem. O2- was measured using two different methods relying on chemiluminescence detection. The first method measured the difference between steady-state [O2-] in filtered and unfiltered seawater, while the second method (standard method) measured O2- decay to baseline in freshly filtered seawater. Because both methods detected [O2-] relative to the background signal from filtered seawater, both should have measured [O2-] generated by particles (presumably biota). However, the O2- concentrations determined by the first method were always much smaller than those obtained from the second (standard) method. Follow-up laboratory and field experiments showed that the increased signal in the standard method was due to a filtration artifact that could neither be eliminated nor consistently accounted for under the tested conditions. We therefore recommend the first method for measuring particle-generated [O2-]. Measured by this method, Station ALOHA had particle-generated O2- concentrations that ranged from undetectable to 0.02nM, with production rates less than 0.6nMhr−1 and decay rate coefficients from 0.003 to 0.014s−1. The southern California Current Ecosystem had particle-generated O2- concentrations that ranged from undetectable to 0.05nM, with production rates up to 4.7nMhr−1 and decay rate coefficients from 0.006 to 0.017s−1. H2O2 concentrations were measured by chemiluminescence detection, using dark incubations of unfiltered water samples to simultaneously determine production and decay rates. H2O2 concentrations at Station ALOHA ranged from 7 to 88nM. Dark production rates and decay rate coefficients were low (mostly <1.5nMhr−1 and <0.03h−1, respectively); higher values were detected when biota were pre-concentrated with net tows. These rates of ROS production are lower than those reported by previous studies in other regions of the Pacific Ocean, but could still be significant compared to photochemical production.

Comparative analysis on the effectiveness of various filtration methods on the potability of water

This paper comparatively assessed the effectiveness of potable water filtration methods, commonly used in the hinterlands in some Ghanaian communities. Physico-chemical and microbiological analysis were carried out on pond, dam and river water samples, using spectrophotometric, pour plate count and the most probable number (MPN) methods. For the unfiltered water samples the total dissolved solids (TDS) and colour were the only parameters with values within recommended standards. The other parameters, total suspended solids (TSS), turbidity, total coliforms and bacterial counts levels were above their standard recommended values. All the filtration methods showed reduction in the levels or better accepted values of the physico-chemical and microbiological parameters. The ceramic filters and the household sand filters showed outstanding results, with all analysed parameters being within the acceptable standards levels. These two methods could be promoted for use to treat untreated drinking water. It is envisaged that a combination of a number of these methods would produce even better results, especially when agents such as alum and activated carbon are included. Follow-up research in this regard is therefore recommended.

Iron as a source of color in river waters

Organic chromophores of total organic carbon (TOC) and those of iron (Fe) contribute to the color of water, but the relative contributions of colored organic carbon (COC%) and Fe (Fe%) are poorly known. In this study, we unraveled Fe% and COC% in 6128 unfiltered water samples collected from 94 Finnish river sites of contrasting catchment properties. According to regression analysis focusing on TOC alone, on average 84% of the mean TOC consisted of COC, while 16% was non-colored or below the color-detection limit. COC and Fe were much more important sources of color than phytoplankton (chlorophyll a as a proxy) or non-algal particles (suspended solids as a proxy). When COC and Fe were considered as the only two sources of color, COC% ranged from 16.8% to 99.5% (mean 71%) and Fe% from 0.5% to 83.2% (mean 29%). Similar Fe% and COC% values were obtained when color was estimated from the absorption coefficients of COC and Fe at 490nm. Fe% increased as a function of the concentration of Fe and was well predicted by the TOC-to-Fe mass ratio. In 608 samples with TOC-to-Fe ratios of <4.5, Fe dominated the color. TOC-to-Fe ratios varied widely within most sites, but in relation to hydrology. In catchments with a peatland coverage of >30%, peak flow exported elevated amounts of TOC relative to Fe and resulted in a high COC%. Base flow, instead, mobilized elevated amounts Fe relative to TOC and resulted in a high Fe%. In a catchment covered with 31% of agricultural fields, peak flow transported eroded soil particles high in Fe and thus resulted in a high Fe%, while during base flow the water was high in COC%. This study demonstrated that Fe% and COC% vary widely in river water depending on the catchment properties and hydrology.

Long-term monitoring of arsenic, copper, selenium, and other elements in Great Salt Lake (Utah, USA) surface water, brine shrimp, and brine flies.

This paper presents long-term monitoring data for 19 elements with a focus on arsenic (As), copper (Cu), and selenium (Se), in surface water (2002-2011), brine shrimp (2001-2011), and brine flies (1995-1996) collected from Great Salt Lake (GSL, Utah, USA). In open surface waters, mean (±standard deviation [SD]; range; n) As concentrations were 112 (±22.1; 54.0-169; 47) and 112 μg/L (±35.6; 5.1-175; 68) in filtered and unfiltered surface water samples, respectively, and 16.3 μg/g (±5.6; 5.1-35.2; 62) dry weight (dw) in brine shrimp. Mean (±SD; range; n) Cu concentrations were 4.2 (±2.1; 1.3-12.5; 47) and 6.9 μg/L (±6.6; 1.9-38.1; 68) in filtered and unfiltered surface water samples, respectively, and 20.6 μg/g (±18.4; 5.4-126; 62) dw in brine shrimp. Finally, mean (±SD; range; n) dissolved and total recoverable Se concentrations were 0.6 (±0.1; 0.4-1.2; 61) and 0.9 μg/L (±0.7; 0.5-3.6; 89), respectively, and 3.6 μg/g (±2.2; 1.1-14.9; 98) dw in brine shrimp. Thus, Se in open lake surface waters was most often in the range of 0.5-1 μg/L, and concentrations in both surface water and brine shrimp were comparable to concentrations measured in other monitoring programs for the GSL. Temporally, the statistical significance of differences in mean dissolved or total recoverable As, Cu, and Se concentrations between years was highly variable depending which test statistic was used, and there was no clear evidence of increasing or decreasing trends. In brine shrimp, significant differences in annual mean concentrations of As, Cu, and Se were observed using both parametric and nonparametric statistical approaches, but, as for water, there did not appear to be a consistent increase or decrease in concentrations of these elements over time.

Effects of chlorination operating conditions on trihalomethane formation potential in polyaluminum chloride-polymer coagulated effluent

In this study, coagulation performance of polyaluminum chloride (PAC) and PAC-lignin acrylamide (PAC+LAM) in reservoir water treatment was contrastively analyzed. Effects of operating conditions including chlorine dose, contact time and pH on the formation potential of trihalomethanes (THMs) during chlorination in coagulated effluent were also investigated. Comparing with PAC, PAC+LAM achieved higher efficiency in the removal of THMs precursors. TTHM yield in unfiltered water samples (UW) was greater than that of filtered water (FW) due to the residual dissolved organic matter (DOM) in the suspended particles or micro flocs. Meanwhile, operating conditions during chlorination had a significant influence on THMs formation potential. With chlorine dose rising, mass ratio of CHCl3 to TTHM increased, whereas that of CHBr2Cl decreased due to higher Cl2/Br− molar ratio. TTHM and CHCl3 levels rose with the increase of pH. Under a given chlorination condition, there was a minor effect of contact time on THM speciation.

Determination of selected phthalate esters compounds in water and sediments by capillary gas chromatography and flame ionization detector

The presence of phthalate esters (PAEs) in the environment is not desirable and therefore, needs to be monitored. This study reports the first data on the concentration levels of PAEs in water and sediments of the Jukskei River catchment area, South Africa. The study was conducted during the summer and winter seasons of 2005. Liquid-liquid extraction (LLE) and Soxhlet extraction (SE) methods were optimized, evaluated and used to determine PAEs of interest in water (unfiltered and filtered) and sediments samples, respectively. Mean percentage recoveries in spiked doubly distilled water ranged from 100 ± 5.32 dimethyl phthalate (DMP) – 122 ± 0.46 di-2-ethylhexyl phthalate (DEHP) and 91.6 ± 1.93 diethyl phthalate (DEP) – 117 ± 4.80 dibutyl phthalate (DBP) in sediments. The concentration levels of PAEs studied in unfiltered environmental water samples were in the range of 0.04(± 0.00) (DMP) − 9.76(± 00.1) ng mL−1(DEHP) for PAEs and from 0.09 (± 0.01) (DMP) – 4.38 (± 0.06) ng mL−1(DEHP) for filtered environmental water samples. Concentration levels obtained in sediments were from 0.05 (0.00) (DMP) – 4910 (0.36) ng/gdw (DEHP). PAEs adsorbed on the sample bottle gave concentration levels of up to 0.10 (± 0.03) ng mL−1for some samples and no analyte was detected (ND) in some cases Generally, concentrations obtained were below the water quality guideline values of United States Environmental Protection Agency (USEPA).

The rate of loss of dissolved organic carbon (DOC) through a catchment

Given observed trends in the concentration of DOC in surface waters in the northern hemisphere the degradation of DOC to CO2 could represent a major and increasing source of greenhouse gas to the atmosphere. However, studies of DOC turnover in rivers have been predominantly based upon mass balance studies and empirical studies have focused upon lakes and estuaries which have far longer residence times than would be the case for transit via rivers. The study measured DOC loss in unfiltered river water samples across an 818 km2 catchment every month for a year and considered total loss, photo and aphotic degradation as well as the rates of each process. The study found: Rate of total DOC change in daylight varied from loss of 30.1 mg C/l/day to an increase of 3.5 mg C/l/day: the average loss was 73% over 10 days. Rate of change due to photic processes varied from decrease of 19.4 mg C/l/day to an increase of 6 mg C/l/day, i.e. net photo-induced production was possible. Activation energy of the degradation was estimated as 2.6 ± 1.2 kJ/g C. The apparent quantum yield varied from 9.6 to −1.7 mmol C/mol photons. Coupling models of total loss of DOC with estimates of in-stream residence times showed that annual loss rates of DOC across the 818 km2 catchment would be between 48% and 69%, in line with estimates from mass balance studies, implying that in-stream DOC degradation represents a large, indirect source of CO2 emissions from peats and other organic soils. Annual rate of removal was increasing in line with increasing loss of DOC at source, implying that observed DOC trends are leading to increased CO2 emissions.

Sunlight Inactivation of Human Viruses and Bacteriophages in Coastal Waters Containing Natural Photosensitizers

Sunlight inactivation of poliovirus type 3 (PV3), adenovirus type 2 (HAdV2), and two bacteriophage (MS2 and PRD1) was investigated in an array of coastal waters to better understand solar inactivation mechanisms and the effect of natural water constituents on observed inactivation rates (k(obs)). Reactor scale inactivation experiments were conducted using a solar simulator, and k(obs) for each virus was measured in a sensitizer-free control and five unfiltered surface water samples collected from different sources. k(obs) values varied between viruses in the same water matrix, and for each virus in different matrices, with PV3 having the fastest and MS2 the slowest k(obs) in all waters. When exposed to full-spectrum sunlight, the presence of photosensitizers increased k(obs) of HAdV2, PRD1 and MS2, but not PV3, which provides evidence that the exogenous sunlight inactivation mechanism, involving damage by exogenously produced reactive intermediates, played a greater role for these viruses. While PV3 inactivation was observed to be dominated by endogenous mechanisms, this may be due to a masking of exogenous k(obs) by significantly faster endogenous k(obs). Results illustrate that differences in water composition can shift absolute and relative inactivation rates of viruses, which has important implications for natural wastewater treatment systems, solar disinfection (SODIS), and the use of indicator organisms for monitoring water quality.

Current Wet Persulfate Digestion Method Considerably Underestimates Total Phosphorus Content in Natural Waters

T phosphorus (TP) in river and lake water is an important environmental variable that can be used as an indicator of nutrient status and water quality. TP was recently selected as an environmental stressor and numeric criteria have been developed based on its background concentration in a given environment. To minimize the eutrophication risk in aquatic ecosystems, U.S. Environmental Protection Agency water quality criteria require that TP is not exceed 10−128 μg/L for river and streams. Following EPA method 365.1, TP in surface waters is routinely determined on unfiltered water samples that are digested by autoclave in the presence of persulfate. Recent studies, however, indicated this method suffers low recovery of particulate phosphorus (PP) and we suggest reliable high temperature combustion method be used for PP determination. Raw water samples contain both suspended particles and dissolved constituents. In EPA TP method 365.1, unfiltered water sample is used for persulfate digestion but no attention was given on how to keep sample homogeneous and representative to the field condition. Due to rapid settling of large particles in water sample containers, it is difficult to keep sample homogeneous during subsampling and analysis. For example, it is practically impossible to avoid particle settling when samples are seating in an autosampler during automated online digestion and analysis. TP consists of particulate phosphorus and total dissolved phosphorus (TP = PP + TDP). Because most TP resides in particulate phase loss of particles during sampling and analysis can result in a significantly underestimated TP. To obtain representative particulate samples, filtration through 0.45 μm pore size filters has been used to separate PP from TDP (it might require a large volume of water if water turbidity is low). Particles collected on the filters are used to determine the PP. The filtrates are used to determine dissolved inorganic phosphorus (DIP) and TDP. The difference between TDP and DIP is operationally defined as dissolved organic P (DOP). The sum of PP and TDP can provide an accurate estimate of TP in natural waters. DOP and PP are usually converted to DIP which can then be measured by the molybdenum blue method. Wet persulfate digestion has been widely used for digesting TDP samples with variable conversion efficiency for different DOP compounds, ranging from 66% for inositol phosphate to 100% for ADP. On the other hand, high temperature combustion is needed for PP determination. High temperature combustion at above 550 °C can decompose all organic matters and inorganic minerals to simple inorganic compounds. With commercial CHN elemental analyzer available, it has become a conventional technique for measuring carbon, hydrogen and nitrogen content of particulate samples. In PP determination, high temperature combustion in the presence of oxidizing reagent Mg(NO3)2 was followed by acid extraction to recover DIP. This method has been used for analysis of PP in sediment and TDP in water samples and achieved a close to 100% conversion efficiency. However, no commercial P elemental analyzer is available and manual analysis of PP by high temperature combustion remains time-consuming and labor-intensive. It is worth to note that the first persulfate digestion method developed by Menzel and Corwin in 1965 was for measuring seawater TP. In that study, only a few DOP compounds were tested for recovery. A dried zooplankton tissue was suspended in distilled water and then the filtrate from the suspension was analyzed by persulfate digestion method. This extracted, filtered sample contained only DOP and no PP sample was tested. Ironically, this seawater method become obsolete in marine community has since been widely adapted for TP measurement in freshwater where particulate matter, dominated by clay minerals, is much more abundant than oceanic waters. Recently, Suzumura pointed out the limitation of this method for determination of TP in natural waters. He compared wet persulfate digestion with high temperature combustion on sediment, plankton and mineral samples. While

Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM—representative of particle-associated and filter-passing Hg, respectively—together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005–2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.

Phase speciation of mercury (Hg) in coastal water of the Yellow Sea, China

The objective of this study is to investigate the phase distribution of mercury (Hg) in water and the relative importance of processes affecting its distribution and behavior at a coastal site of the Yellow Sea with high tidal current speeds in the eastern continental margin of China. Total Hg (THg) and reactive Hg (RHg) were measured in unfiltered and filtered (0.45 μm) water in four different seasons at 1–3 h intervals using ultra-trace Hg techniques. The Hg in this coastal water showed typical Hg-unpolluted coastal region levels. Mean (± SD) concentrations of THg in unfiltered water were 13.4 ± 3.9 pM with a range of 6.7 to 27.5 pM and a considerable RHg fraction (%RHg/THg = 36.9%). Particulate Hg (PHg) was the dominant phase in unfiltered water samples (%PHg/THg = 70 ± 11%), and the distribution coefficient (Log K d ) of Hg in particulate and dissolved (0.45 μm) phases averaged 4.96 ± 0.20 with a range of 4.26 to 5.38. Enhanced suspended particulate matter (SPM) in water induced by wind and tidal mixing probably explained most of the variation in the unfiltered THg. In the dissolved phase, RHg accounted for a major fraction of THg (%RHg/THg = 86 ± 16%). The weak correlation between dissolved organic carbon (DOC) and THg in the dissolved phase indicated that Hg in this study region might primarily originate from atmospheric deposition and also reflected the importance of other competing ligands (e.g., Cl −) in the water column. Interestingly, measurements covering four different seasons showed no seasonality in these Hg species. Although there was some uncertainty in the measurements, using the difference of RHg between unfiltered and dissolved samples revealed that a considerable fraction (28 ± 19%) of RHg could bind to SPM.

Seasonal fluctuations and mobility of arsenic in groundwater resources, Anchorage, Alaska

Abstract There are approximately 12,000 private wells in the Municipality of Anchorage, Alaska, USA, that supply drinking water to thousands of homeowners. The results presented in this paper are from a study conducted to understand the speciation and seasonal fluctuations of As in the groundwater of Anchorage. A total of eight private drinking water wells were sampled from May to October, 2007, to determine inorganic species of As (III/V) and other physiochemical parameters of the groundwater. Arsenic concentrations above Environmental Protection Agency (EPA) drinking water standard of 10 μg/L had been previously measured in all of these eight wells by the Municipality of Anchorage. Seven of the wells draw water from glaciofluvial aquifers and one well taps into the older bedrock aquifer on the mountain-side. In-situ measurements as well as groundwater samples were collected from each well and inorganic species of As (III/V) were separated in the field using anion exchange columns. Elemental analysis was conducted by inductively coupled plasma mass spectrometry (ICP-MS), major anions by ion chromatography (IC), and Fe (II) and total Fe were measured in the field with a portable spectrophotometer. The groundwater was neutral to basic ranging in pH from 7.6 to 8.8, dissolved O2 was generally 0.1–1.0 mg/L and specific conductance ranged from 300 to 1000 μS/cm. Most of the groundwater is classified as Ca–Mg–HCO3 and dissolved As concentrations ranged from below detection (∼0.5 μg/L) to 117 μg/L with arsenite as the dominant species. Filtered and unfiltered water samples had less than 1% difference in As concentrations suggesting that most As occurs in the dissolved form. Arsenic concentrations were positively correlated with water levels indicating that the highest As concentrations occur in the aquifer during recharge events. Positive relationships with dissolved Fe and supersaturation with respect to secondary Fe oxides indicates that the As is likely associated with the Fe oxides that are partially dissociated under the dominating reducing conditions of the aquifers. There is also evidence of a positive relationship between As and SO 4 2 - which indicates that some of the As may be associated with the oxidation of Fe-bearing sulfides such as pyrite or arsenopyrite, however, this is thought to be a less important process for this system compared to Fe reduction. Most of the groundwater samples indicate supersaturation with respect to carbonates such as calcite, dolomite and siderite and there is a positive relation between As and HCO 3 - indicating that carbonate buffering is an important process in the groundwater geochemistry of As. In some cases homeowners filter their tap water with household water treatment systems which have a range of As removal effectiveness from about 25–100%.

Influence of Eutrophication on the Distribution of Total Mercury and Methylmercury in Hydroelectric Reservoirs

The distribution of mercury (Hg) and the characteristics of its methylation were investigated in Wujiangdu (WJD) and Yinzidu (YZD) reservoirs in Guizhou province, China. The two reservoirs are characterized by high and low levels of primary productivity, respectively. Mercury species in water samples from depth profiles in both reservoirs and from interface water in the WJD were analyzed each season during 2007. The concentrations of total Hg (HgT(unf)) and methylmercury (MeHgT(unf)) in unfiltered water samples from the WJD varied from 3.0 to 18 pmol dm(-3) and from 0.17 to 15 pmol dm(-3), respectively; ranges were 2.0 to 9.5 pmol dm(-3) for HgT(unf) and 0.14 to 2.2 pmol dm(-3) for MeHgT(unf) in the YZD. Elevated methylmercury concentrations in water samples from the bottom water and water-sediment interface demonstrated an active net Hg methylation in the downstream reach of the WJD. There was no discernable Hg methylation occurring in the YZD, nor in the upstream and middle reaches of the WJD. The results suggest that high primary productivity resulting from cage aquaculture activities in the WJD is an important control on Hg methylation in the reservoir, increasing the concentrations of MeHg in water in the Wujiang River basin Southwestern China.

Temporal variability of iron concentrations and fractions in wetland waters in Sanjiang Plain, Northeast China

Chemical forms, reactivities and transformation of iron fractions in marshy waters were investigated with cross-flow filtration technique to study the iron environmental behavior. Iron fractions were divided into four parts: acid-labile iron (pre-acidification of unfiltered marshy water samples, > 0.7 μm), high-molecular-weight iron (0.7–0.05 μm), medium-molecular-weight iron (0.05–0.01 μm), and low-molecular-weight iron (< 0.01 μm). The cross-flow filtration suggested that iron primarily exist in both the > 0.7 μm and < 0.01 μm size fractions in marshy waters. Rainfall is the key for rain-fed wetland to determine fate of iron by changing the aquatic biochemical conditions. By monitoring the variation of iron concentrations and fractions over three years, it was found that dissolved iron and acid-labile iron concentrations exhibit a large variation extent under different annual rainfalls from 2006 to 2008. The seasonal variation for iron species proved that the surface temperature could control some conversion reactions of iron in marshy waters. Low-molecular-weight iron would convert to acid-labile iron gradually with temperature decreasing. The photochemical reactions of iron fractions, especially low-molecular-weight iron had occurred under solar irradiation. The relative proportion of low-molecular-weight in total dissolved iron ranging from 28.3% to 43.2% were found during the day time, which proved that the observed decreasing concentration of acid lability iron was caused by its degradation to low molecular weight iron.

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.