On-site Filtration Research Articles

Application of eDNA metabarcoding in the assessment of fish biodiversity in Philippine mangroves: Challenges and opportunities

Biodiversity assessments are important in designing mangrove conservation and restoration programs. In the Philippines, conventional biodiversity assessment methods (e.g., trap nets, fish visual census) can be time-consuming, labor-intensive, and expensive. In recent years, environmental DNA (eDNA) metabarcoding has been an emerging tool for rapid biodiversity monitoring as it is fast, non-intrusive, and can provide broader detection of fauna. But, it is still subject to various field sampling and laboratory analysis constraints. Here, we applied the eDNA metabarcoding method to document and assess fish biodiversity in mangroves from two biogeographic regions in the Philippines: Oriental Mindoro in the West Philippine Sea and Sorsogon in the Northern Philippine Sea. Using 12S genetic markers from eDNA water samples, we detected 89 fish species from 44 families. Only twelve species were commonly detected in both sites. Several species were found in the Philippines’ list of economically important aquatic organisms while one species (Epinephelus fuscoguttatus) was classified as Vulnerable in IUCN’s Red List of Threatened Species. Seventy-six percent more species were detected in Sorsogon probably because the sampling sites were within a seascape of mangroves, seagrasses, and coral reefs. In contrast, the lesser species detected in Oriental Mindoro could probably be because of the more limited sampling points to coastal fringes. Our results serve as baseline data and the first obtained using this method in the country. However, we observed some limitations that should be addressed to improve the method: (1) lack or absence of a comprehensive reference database specific to Philippine aquatic organisms; (2) low eDNA reads which could be attributed to insufficient on-site filtration due to turbid seawaters common in Philippine mangroves; and (3) possible cross-contaminations that can affect comparative analyses. Despite these limitations, we were able to demonstrate the usefulness of this technique in doing rapid assessments which could address knowledge gaps in Philippine mangrove biodiversity studies and contribute to its conservation programs.

On-site filtration of large sample volumes improves the detection of opportunistic pathogens in drinking water distribution systems.

In this study, we compared conventional vacuum filtration of small volumes through disc membranes (effective sample volumes for potable water: 0.3-1.0 L) with filtration of high volumes using ultrafiltration (UF) modules (effective sample volumes for potable water: 10.6-84.5 L) for collecting bacterial biomass from raw, finished, and tap water at seven drinking water systems. Total bacteria, Legionella spp., Legionella pneumophila, Mycobacterium spp., and Mycobacterium avium complex in these samples were enumerated using both conventional quantitative PCR (qPCR) and viability qPCR (using propidium monoazide). In addition, PCR-amplified gene fragments were sequenced for microbial community analysis. The frequency of detection (FOD) of Legionella spp. in finished and tap water samples was much greater using UF modules (83% and 77%, respectively) than disc filters (24% and 33%, respectively). The FODs for Mycobacterium spp. in raw, finished, and tap water samples were also consistently greater using UF modules than disc filters. Furthermore, the number of observed operational taxonomic units and diversity index values for finished and tap water samples were often substantially greater when using UF modules as compared to disc filters. Conventional and viability qPCR yielded similar results, suggesting that membrane-compromised cells represented a minor fraction of total bacterial biomass. In conclusion, our research demonstrates that large-volume filtration using UF modules improved the detection of opportunistic pathogens at the low concentrations typically found in public drinking water systems and that the majority of bacteria in these systems appear to be viable in spite of disinfection with free chlorine and/or chloramine.IMPORTANCEOpportunistic pathogens, such as Legionella pneumophila, are a growing public health concern. In this study, we compared sample collection and enumeration methods on raw, finished, and tap water at seven water systems throughout the State of Minnesota, USA. The results showed that on-site filtration of large water volumes (i.e., 500-1,000 L) using ultrafiltration membrane modules improved the frequency of detection of relatively rare organisms, including opportunistic pathogens, compared to the common approach of filtering about 1 L using disc membranes. Furthermore, results from viability quantitative PCR (qPCR) with propidium monoazide were similar to conventional qPCR, suggesting that membrane-compromised cells represent an insignificant fraction of microorganisms. Results from these ultrafiltration membrane modules should lead to a better understanding of the microbial ecology of drinking water distribution systems and their potential to inoculate premise plumbing systems with opportunistic pathogens where conditions are more favorable for their growth.

Comprehensive Comparison of Various Microplastic Sampling Methods in Sea Water: Implications for Data Compilation

The problem of plastic and microplastic (MP, <5 mm in size) pollution has received widespread attention globally, with its widespread presence being reported in various environmental media. However, a lack of standard sampling and analysis methods is making it difficult to compare data across studies and understand the source and fate of plastics and MPs. Common sampling strategies used in studies of MP in natural waters include Manta net and pump filtering using different mesh sizes, but the impact of these sampling technologies on the final MP abundance and characteristics is not well understood. This study used common sampling devices, including a Manta trawl net, shallow-water plankton pump (SPP), deep-water plankton pump (DPP), and submersible pump with on-site filtration using 50 and 330 µm aperture size meshes, to sample MP in natural coastal water. The results showed that while Manta trawl and plankton pumps produced similar MP abundance (2.0–6.0 n/m3), the MP characterization was significantly different, with fibers being the dominant MP in plankton samples (>70%) and only 14.2% in Manta trawl samples. Submersible pump sampling using a 50 µm mesh retained a higher percentage of fibers, with a two magnitude higher abundance of MPs (357 ± 119 and 553 ± 19 n/m3 for 330 µm and 50 µm mesh, respectively) attributed to the floating debris encountered during sampling and the shallower sampling depth as well as smaller sampling volume. This study highlights the key factors that impact MP abundance and characteristics as well as the challenges to harmonizing MPs sampling methods in aquatic environments, which is also helpful for data compilation across studies.

Study on Pollution Characteristics and Ecological Risks of Microplastics in Ningyuan River

A survey was conducted on the surface water samples of Ningyuan River in Hainan Province. The samples were collected through on-site filtration and concentration methods, and pretreated through oxidation digestion and density separation. The microplastics were statistically analyzed by confocal micro-Raman spectrometer, elucidating the abundance, type, particle size, and shape characteristics of the microplastics in the water samples. Seasonal differences were analyzed, and the main conclusions were as follows: microplastics were detected at all sampling points, with the abundance range of 66.67 items/m3 to 1106.67 items/m3; polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS) are the main types of microplastics; 100-1000 μm is the main particle size distribution range; the proportion order of microplastics with different shapes is fiber> fragment> film> particle. In terms of spatial distribution, there are significant differences due to the influence of functional zones along the river banks, while in terms of seasonal distribution, there is no significant difference between dry and rainy seasons; The overall level of microplastic pollution belongs to a medium to low risk.

The use of citizen science in fish eDNA metabarcoding for evaluating regional biodiversity in a coastal marine region: A pilot study

To test the feasibility of a citizen science program for fish eDNA metabarcoding in coastal marine environments, we recruited six groups of voluntary citizens for a science education course at a natural history museum. We held a seminar on eDNA and a workshop for seawater sampling and on-site filtration using syringes and filter cartridges for the participants. After that, they selected single survey sites following the guidelines for conducting a safe field trip. They performed seawater sampling and on-site filtration at these sites during their summer holidays. The six selected sites unexpectedly included diverse coastal habitats within a 40 km radius, located at temperate latitudes in central Japan (~35°N). After the field trips, they returned filtered cartridges to the museum, and we extracted eDNA from the filters. We performed fish eDNA metabarcoding, along with data analysis. Consequently, we identified 140 fish species across 66 families and 118 genera from the six samples, with species richness ranging from 14 to 66. Despite its limited sample size, such a diverse taxonomic range of fish species exhibited spatial biodiversity patterns within the region, which are consistent with species distribution. These include north-south and urbanization gradients of species richness, geographic structure of the fish communities, and varying salinity preferences of the component species. This case study demonstrates the potential of fish eDNA metabarcoding as an educational and scientific tool to raise public awareness and perform large-scale citizen science initiatives encompassing regional, national, or global fauna.

Read counts from environmental DNA (eDNA) metabarcoding reflect fish abundance and biomass in drained ponds

The sampling of environmental DNA (eDNA) coupled with cost-efficient and ever-advancing sequencing technology is propelling changes in biodiversity monitoring within aquatic ecosystems. Despite the increasing number of eDNA metabarcoding approaches, the ability to quantify species biomass and abundance in natural systems is still not fully understood. Previous studies have shown positive but sometimes weak correlations between abundance estimates from eDNA metabarcoding data and from conventional capture methods. As both methods have independent biases a lack of concordance is difficult to interpret. Here we tested whether read counts from eDNA metabarcoding provide accurate quantitative estimates of the absolute abundance of fish in holding ponds with known fish biomass and number of individuals. Environmental DNA samples were collected from two fishery ponds with high fish density and broad species diversity. In one pond, two different DNA capture strategies (on-site filtration with enclosed filters and three different preservation buffers versus lab filtration using open filters) were used to evaluate their performance in relation to fish community composition and biomass/abundance estimates. Fish species read counts were significantly correlated with both biomass and abundance, and this result, together with information on fish diversity, was repeatable when open or enclosed filters with different preservation buffers were used. This research demonstrates that eDNA metabarcoding provides accurate qualitative and quantitative information on fish communities in small ponds, and results are consistent between different methods of DNA capture. This method flexibility will be beneficial for future eDNA-based fish monitoring and their integration into fisheries management.

Granular crystallization using CFBC ash for phosphorus removal via hydroxyapatite

Abstract To prevent eutrophication and remove phosphorus, circulating fluidized bed combustion (CFBC) ash was utilized to elute Ca2＋ and OH − for hydroxyapatite (HAP) crystallization. CFBC ash was compared with the gypsum byproduct of a domestic waste incineration plant and pure CaO reagent. CFBC ash proved to be a suitable raw material to supply Ca2＋ and OH − for HAP crystallization. CFBC ash was reprocessed as a granular crystallization agent (GCA) to improve its applicability to non-point pollution source control. In addition, a manufacturing procedure for a GCA utilizing 4.8% blast furnace slag as a binder was developed based on durability and the ion elution rate in water. Column tests with sedimentation showed that 93% and 98% of T-P and PO4-P were removed after 12 h of settling, respectively. In on-site filtration trench tests, filtration following crystallization with a 4 h retention time achieved a 63.5% and 52.8% removal efficiency with respect to T-P and PO4-P, respectively. After operation for 13 d, an increase in porosity with pore distribution on the surface of the GCA was observed. Through their long-term on-site operation, crystallization–filtration trenches using GCA provide an effective alternative process for the management of agricultural non-point source pollution.

Micro Paper-Based Electrochemical Device for Small Molecule Diabetes Biomarkers

Glucose monitoring has been widely established as a successful diabetes management system. However, non-glucose markers such as, autoantibodies, hormones, proteins, and other small molecules can provide better assessments for the prediction and management of the disorder. Nevertheless, the challenges our research community faces in designing an analytical device for such markers, especially the small molecules, are the dynamic range, limit of detection, selective isolation of the analyte, higher background noise due to clinical matrix, and ability to transform the system into a cheap point-of-care device. Here, we have designed a paper-based graphene amperometric sensor that can detect a model hormone (insulin, 5808 Da) from complex serum matrix. The paper platform provides for a cheap, on-site filtration system that limits the mobility of larger molecules, and upon combining with a double-blocking step before analyte detection greatly minimizes the background noise. Insulin aptamers acts as a capture probe to selectively identify and bind to insulin. Graphene, coated on working electrode, with its superior electrical conductivity provides for improved analytical features of the detection system. The amperometric signals are achieved by flowing a solution mixture of 1 mM hydroquinone mediator and 0.5 mM H2O2 and applying a constant potential of -0.1 V. The paper-based device exhibits a picomolar limit of detection for serum insulin with a reasonably good dynamic range. Our future prospect is to advance this device further for detecting even smaller molecules (< 500 Da) in complex clinical matrices, for which no current assay methods are available.

Potential of biochar filters for onsite wastewater treatment: Effects of active and inactive biofilms on adsorption of per- and polyfluoroalkyl substances in laboratory column experiments

This study investigated the potential of biochar filters as a replacement for, or complement to, sand filters for removal of per- and polyfluoroalkyl substances (PFASs) from wastewater in on-site wastewater treatment systems (OWTSs). Concentrations and removal of nine perfluoroalkyl carboxylates (PFCAs; C3-11) and three perfluoroalkane sulfonates (PFSAs; C4, 6, 8) and one perfluorooctanesulfonamide (FOSA; C8) were investigated over 22 weeks in four treatments with column filters: biochar (BC) without biofilm (BC-no-biofilm), biochar with active biofilm (BC-active-biofilm), biochar with inactive biofilm (BC-inactive-biofilm) and sand with active biofilm (Sand-active-biofilm). The filters were operated under hydraulic loading (50 L m−2 day−1) to mimic the loading rate in on-site filtration beds. The initial concentrations of the ΣPFASs in the influent were in the range of 1500–4900 ng L−1. In BC-no-biofilm, the removal efficiency (20–60%) and adsorption capacity (0–88 ng ΣPFASs g−1 BC) of short-chain PFCAs (C3-6) and PFSA (C4) was low, whereas the removal efficiency (90–99%) and the adsorption capacity (73–168 ng g−1) was high for C7-C11 PFCAs, C6, C8 PFSAs and FOSA. The relative removal was generally lower for C3-9 PFCAs and C4, C6, C8 PFSAs using BC-active-biofilm and BC-inactive-biofilm compared with BC-no-biofilm. This can be explained by the presence of biofilm and solids in BC-active-biofilm and the presence of wastewater solids in BC-inactive-biofilm, which decreased the availability and number of adsorption sites for PFASs compared with BC-no-biofilm. On the other hand, inactivation of the biofilm resulted in lower removal efficiencies for C5-11 PFCAs, C4, C6, C8 PFSAs and FOSA, probably because the biofilm degraded organic matter and thus increased the availability and number of adsorption sites compared with BC-inactive-biofilm. Sand-active-biofilm showed poor removal (0–70%) for all PFASs except FOSA (90%) and its adsorption capacity was low (0.0–7.5 ng g−1). In general, for all biochar treatments, shorter-chain PFASs were more resistant to removal than longer-chain PFASs. In addition, C4, C6 and C8 PFSAs showed 10–30%, 10–50% and 20–30% higher average removal efficiency, respectively, than PFCAs with corresponding perfluoroalkyl chain length. In conclusion, biochar is a promising filter medium for removal of PFASs in OWTSs, especially for PFASs with a perfluorocarbon chain longer than C6.

The effect of filtration method on the efficiency of environmental DNA capture and quantification via metabarcoding.

Environmental DNA (eDNA) is a promising tool for rapid and noninvasive biodiversity monitoring. eDNA density is low in environmental samples, and a capture method, such as filtration, is often required to concentrate eDNA for downstream analyses. In this study, six treatments, with differing filter types and pore sizes for eDNA capture, were compared for their efficiency and accuracy to assess fish community structure with known fish abundance and biomass via eDNA metabarcoding. Our results showed that different filters (with the exception of 20-μm large-pore filters) were broadly consistent in their DNA capture ability. The 0.45-μm filters performed the best in terms of total DNA yield, probability of species detection, repeatability within pond and consistency between ponds. However performance of 0.45-μm filters was only marginally better than for 0.8-μm filters, while filtration time was significantly longer. Given this trade-off, the 0.8-μm filter is the optimal pore size of membrane filter for turbid, eutrophic and high fish density ponds analysed here. The 0.45-μm Sterivex enclosed filters performed reasonably well and are suitable insituations where on-site filtration is required. Finally, prefilters are applied only if absolutely essential for reducing the filtration time or increasing the throughput volume of the capture filters. In summary, we found encouraging similarity in the results obtained from different filtration methods, but the optimal pore size of filter or filter type might strongly depend on the water type under study.

A novel approach to evaluating relationships between soil test and runoff P at landscape scales by integrating farmer knowledge on soil drains

Dissolved phosphorus loss pathways are often overlooked relative to erosion P losses but contribute under certain soil land use and management combinations and may be exacerbated by subsurface drainage. Measures of P desorption to water are commonly made in laboratory soil testing and related to an agronomic P test using stronger extractants. We aimed to relate soil drainflow P concentrations as an integrative measure of a range of landscape source and transport processes to soil test P-status and examine other influential soil co-variates. Grassland and cropland sites (n=28)were sampled across Scotland involving farmers to incorporate local knowledge relating drains to influencing soils and gain important management data not often available. Using quality controls (on-site filtration, guidance and pro-forma data collection) farmers took their own samples and posted them on for laboratory analysis. Soils were analysed for CNP parameters, reactive complexes and soil agronomic P status by Modified Morgan’s P (MMorgP). Drain waters were analysed for total dissolved P (TDP), dissolved molybdate reactive (DRP) and unreactive P (DUP). Grasslands (n=11) differed from cropland (n=17) with significantly greater drain concentrations of Total P, DUP, DOC:TDN and soil total C, N and P, oxalate-extractable Fe (Feox) and C:P. Conversely, cropland had greater drain NO3, DRP:TDP, soil pH, Pox and reactive surface P-saturation. Significant relationships were gained between both TDP and DUP with MMorgP across all sites, although relationships showed less scatter for grassland than cropland sites. A group of moderate soil P status soils, mostly cropland, with low organic matter status had proportionally greater DRP losses, with soil N content being a significant inverse predictor of DRP concentrations or DRP:TDP ratios in drain water. The results indicated soil test P (MMorgP) as a main control of TDP concentrations via drainage pathways, but that organic matter quality affected dissolved P speciation, but not concentrations. There was greater risk of DRP losses from cropland soils low in organic matter. The study outcomes benefitted from involving the farming community in terms of coupling soil to drain samples and local management knowledge. Compared to batch laboratory results the additional processes integrated by using field drains as a landscape-scale measure of dissolved P losses will give more realistic relationships for change in P leaching between soils differing in P status spatially, or in time following management.

Insights into dewatering and characterization of the waste activated sludge

Abstract On-site filtration experiments were carried out at the local Common Effluent Treatment Plant (CETP) to measure the properties of the waste activated sludge (WAS). The consequences of several operational parameters such as effect of pressure, filtration media, coagulant addition, etc. were studied. To better understand the role of hydrodynamics as well as the biological content, a comparison was made between the activated sludge (AS) and WAS cake and its properties. In our findings, the cake obtained in case of WAS filtration was denser as compared to the cake from AS. In the former, it was found to be in the range of 2–2.5% w/v of WAS as compared to 0.25–0.5% w/v of AS. The addition of coagulant accelerated settling and in turn reduced the WAS filtration time by 10 fold. Important filtration parameters obtained for WAS were: cake resistance (α) = 1.5 × 1011 m/kg, cake porosity (e) = 0.86, cake compressibility (η) = 0.41, effective mean particle size (x) = 0.5 µm, capillary number (Nc) = 2.7 × 10–3, irreducible saturation (S∞) = 0.155 and threshold pressure (Pb) = 1 × 105 N/m2.

A simple method for preserving environmental DNA in water samples at ambient temperature by addition of cationic surfactant

Environmental DNA (eDNA) analysis is a powerful tool within ecology for the study of the distribution or abundance of aquatic species, although the simplification of water sampling is required for enabling light and fast field sampling to expand further application of eDNA analysis. Here, certain candidate chemicals belonging to the group of cationic surfactants were examined for their effectiveness as preservatives for eDNA water samples by simply adding the chemicals to water samples to suppress the degradation of eDNA. The quaternary ammonium compound benzalkonium chloride (BAC) at a final concentration of 0.01% was effective to retain 92% of eDNA derived from the bluegill sunfish Lepomis macrochirus in an 8-h incubation test at ambient temperature, which assumed a transportation of water samples in 1-day field sampling during the daytime. Meanwhile, eDNA in water samples without BAC retained only 14% of the initial eDNA. Moreover, an additional long-term incubation test (up to 10 days) revealed BAC-treated samples retained ~70 and 50% of bluegill DNA compared to the initial amount after 1- and 10-day incubation at ambient temperature, respectively. Meanwhile, eDNA in naïve samples reduced to 20% after 1-day incubation and reached undetectable levels after 10 days. Up to now, many eDNA studies have adopted on-site filtration followed by filter fixation, which requires many pieces of equipment. Addition of BAC can protect eDNA in water samples with less effort and equipment resulting in an increase of measurement accuracy of the eDNA quantity and detection probability of rare species by preventing the disappearance of rare sequences in water samples.

Stream chemical dynamic and metal accumulation in a temperate watershed affected by agricultural practices (Penzé, NW France).

Understanding the fate of metals in agricultural land is an important issue for agronomic sustainability. This study aimed at quantifying the export/retention of metals in a temperate watershed subject to important manuring activities. The chemical composition of the Penzé stream was examined at high resolution during a 1-year study in 2012. After immediate on-site filtration, here demonstrated as necessary to avoid modification of the dissolved-particulate partition, the concentrations of 21 elements were determined using inductively coupled plasma (ICP) optical emission spectrometry and ICP mass spectrometry. This dataset was extended with the local atmospheric deposition of several metals (Cd, Cr, Cu, Pb, Ni and Zn) monitored on a monthly basis. Two groups were distinguished according to the evolution of the concentrations during floods. Some major cations (Na, Ca, Mg, Sr, K, Ba) and nitrate followed counter-clockwise hysteresis patterns originating from the dilution of the enriched groundwaters by surface waters. Conversely, Al, Fe, Mn, Ti, V, Cr, Co, Ni, Cu, Zn, Cd, Pb and U displayed high dissolved concentration increases at the early stage of floods due to washing out of the enriched soils. The comparison of stream output fluxes for the two main inputs for the watershed, i.e. atmospheric deposition and manure spreading, indicates that the vast majority of the Cu and Zn (>99 and 96%, respectively), mainly originating from pig manure, is accumulated in the watershed. The accumulation rates for other metals were >60% for Ni and Cr, >75% for As and >90% for Pb and Cd.

Comparing On-Site to Off-Site Biomass Collection for Dehalococcoides Biomarker Gene Quantification To Predict in Situ Chlorinated Ethene Detoxification Potential

Biostimulation and bioaugmentation have emerged as constructive remedies for chlorinated ethene-contaminated aquifers, and a link between Dehalococcoides (Dhc) bacteria and chlorinated ethene detoxification has been established. To quantify Dhc biomarker genes, groundwater samples are shipped to analytical laboratories where biomass is collected on membrane filters by vacuum filtration for DNA extraction and quantitative real-time PCR analysis. This common practice was compared with a straightforward, on-site filtration approach to Sterivex cartridges. In initial laboratory studies with groundwater amended with known amounts of Dhc target cells, Sterivex cartridges yielded one-third of the total DNA and 9-18% of the Dhc biomarker gene copies compared with vacuum filtration. Upon optimization, DNA yields increased to 94 +/- 38% (+/-SD, n = 10), and quantification of Dhc biomarker genes exceeded the values obtained with the vacuum filtration procedure up to 5-fold. Both methods generated reproducible results when volumes containing >10(4) total Dhc target gene copies were collected. Analysis of on-site and off-site biomass collection procedures corroborated the applicability of the Sterivex cartridge for Dhc biomarker quantification in groundwater. Ethene formation coincided with Dhc cell titers of >2 x 10(6) L(-1) and high (i.e., >10(5)) abundance of the vinyl chloride reductive dehalogenase genes vcrA and/or bvcA; however, high Dhc cell titers alone were insufficient to predict ethene formation. Further, ethene formation occurred at sites with high Dhc cell titers but low or no detectable vcrA or bvcA genes, suggesting that other, not yet identified vinyl chloride reductive dehalogenases contribute to ethene formation. On-site biomass collection with Sterivex cartridges avoids problems associated with shipping groundwater and has broad applicability for biomarker monitoring in aqueous samples.

Dissolved, suspended, and colloidal fluxes of organic carbon, major and trace elements in the Severnaya Dvina River and its tributary

The chemical status of major and trace elements (TE) and organic carbon (OC) has been studied in the Severnaya Dvina and Pinega rivers draining granitic moraine, carbonate and sedimentary deposits of the Arkhangelsk region (NW Russia, the White Sea basin of the Arctic Ocean). Sampling was performed during winter and summer baseflow seasons and during the spring flood (2007–2008). Size separation procedure included on-site filtration through 5 µm, 0.22 µm, 100, 10 and 1 kDa, and dialysis through 1 kDa and 10 kDa pore-size membranes. The organic carbon concentration in “truly” dissolved form (< 1 kDa) does not depend on rock lithology or season, being on average equal to 5.0 ± 1.4 mg/L. Our observations may suggest the presence of two types of organic matter pool: i) allochtonous large-size colloids formed by lixiviation from upper soil horizons and ii) autochthonous (aquatic) small molecular-size substances, probably linked to bacterial and phytoplankton exudates. The total dissolved concentration of colloidal TE correlates with OC and Fe contents, being highest during the spring flood and lowest in winter time. There are two different patterns of TE colloidal status during different periods of the year, depending on their association with the organic or organo-mineral constituents of the colloidal matter pool. Trace and major element concentrations in the suspended matter of the River Severnaya Dvina were measured during different seasons over three years of observation. Based on collected data, we evaluate here, for the first time, the seasonal fluxes of major and trace elements in the suspended (> 0.22 µm), total dissolved (< 0.22 µm) and colloidal (1 kDa–0.22 µm) forms. On an annual basis, there is a significant contribution (≥ 30%) of conventionally dissolved species (< 0.22 µm) to the overall flux of usually weakly mobile elements such as the divalent transition metals, Cd, Pb, V, Y, all REEs, Zr, Hf and Th. The transport of these insoluble elements occurs essentially in colloidal form. The spring flood occurring in May provides between 30 and 60% of the total annual dissolved and suspended flux of many insoluble trace elements (Fe, Co, Ni, Cr, Y, all REEs, Cd, Pb, Zr, Hf and Th). We argue that trace element fluxes in Arctic rivers are often characterized by a high proportion of total dissolved matter (< 0.22 µm) compared to suspended particulates, due mostly to the large contribution of organically-bound colloidal forms.

Evaluation of samplers and filter materials for the establishment of trace metal concentration profiles in peat bog porewaters using inductively coupled plasma-mass spectrometry

Two different types of sampler were used for the collection of humic-rich porewaters from ombrotrophic bogs at background and contaminated sites: a syringe-type sampler, which required manual filtration and dialysis chambers (peepers) where samples were filtered in situ. Concentrations of 10 trace elements Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, V and Zn have been determined in the collected porewater samples using inductively coupled plasma-sector-field-mass spectrometry. The accuracy of the analytical procedures was evaluated by the regular analyses of the two certified riverine water reference materials SLRS-2 and SLRS-4, respectively. For the syringe-type sampler, four different 0.45 μm syringe filters were tested. Low blank values together with sufficiently low filtration artefacts were obtained using unwashed GD/XP filters (Whatman). When pre-cleaned filters were used, Cu and Mo showed strong filtration artefacts. Mean metal concentrations of filtrates differed by up to five times, depending on the filter type used. Overall blank values of the sampling devices were as follows (ng l −1): Cd 1, Co 9, Cr 50, Cu 70, Mn 200, Mo 20, Ni 100, Pb 4, V 10, Zn 1000. The contribution of atmospheric dust during the on-site filtration might have enhanced overall blank levels of Cr, Cu and Zn when protective covers were not used during sample collection/on-site filtration. Metal concentrations at background sites were at ng l −1 levels except for Zn and Mn (low μg l −1). With the exception of Co and Mn, dialysis chambers were not suitable for sampling porewaters at these concentration levels.