A comparison of different approaches for the analysis of 36Cl in graphite samples.

This study compares different approaches for the quantification of the massic activity of 36Cl in graphite samples. All approaches consisted of a combustion step in combination with a trapping solution to collect the volatile elements. Two different resins were used to separate 36Cl from the matrix (CL resin and PS resin). Liquid scintillation counting (LSC), scintillation counting (SC) and tandem inductively coupled plasma mass spectrometry (ICP-MS/MS) were used to quantify 36Cl activity. The chemical yield in all approaches was determined by means of ion chromatography (IC). In addition, the methods were applied to a real activated graphite sample.

Investigation of a new approach for 36Cl determination in solid samples using plastic scintillators.

This work reports a new approach for the determination of 36Cl in radioactive waste samples from nuclear decommissioning, wherein novel plastic scintillator (PS) materials were used for the concentration of 36Cl prior to the detection with scintillation counting. Different plastic scintillator (PS) materials were tested for their selective absorption and detection of 36Cl activity in solid samples. PS microspheres (PSm), cross-linked PSm (CPSm) and PS resin have been investigated. PS resin was identified as the most suitable material for 36Cl analysis. Pyrolysis and subsequent trapping of the volatile elements in a bubbler was used. The trapping solution was finally loaded onto a cartridge of the PS resin. Scintillation counting and ion chromatography were used to determine the activity concentration and the chemical recovery, respectively.

Internal exposure of Flemish teenagers to environmental pollutants: Results of the Flemish Environment and Health Study 2016-2020 (FLEHS IV).

The Flemish Environment and Health Study (FLEHS) collects information on internal exposure to a broad range of environmental chemicals in the general population in Flanders, the Northern region of Belgium. The aim is to establish biomonitoring exposure distributions for the general population in support of public health and environmental policy, environmental risk assessment and risk management decisions. In 2017-2018, urine and blood samples were collected from 428 teenagers by a stratified clustered two stage randomized design. Samples were analyzed for a broad range of biomarkers related to exposure to chlorinated and newer pesticides, brominated and organophosphate flame retardants (BFR/OPFR), polychlorinated biphenyls (PCBs), bisphenols, phthalates and alternative plasticizers, per-and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAHs), benzene, metals and trace elements. The geometric mean levels and percentiles of the distribution were estimated for each biomarker, for the whole study population and following stratification for sex, the household educational attainment and the residence area's urbanicity. Geometric means of biomarkers of lead, dichlorodiphenyltrichloroethane (DDT), PCBs, PAHs, regulated phthalates and bisphenol A (BPA) were lower than in the previous FLEHS cycles. Most biomarker levels were below health-based guidance values (HB-GVs). However, HB-GVs of urinary arsenic, blood lead, blood cadmium, sum of serum perfluorooctane sulfonate (PFOS) and perfluoro-1-hexanesulfonate (PFHxS) and the urinary pyrethroid metabolite (3-PBA) were exceeded in respectively 25%, 12%, 39.5%, 10% and 22% of the teenagers. These results suggest that the levels of exposure in the Flemish population to some environmental chemicals might be of concern. At the same time, we noticed that biomarkers for BPA substitutes, metabolites of OPFRs, an expanded list of PFAS, glyphosate and its metabolite could be measured in substantial proportions of participants. Interpretation of these levels in a health-risk context remains uncertain as HB-GVs are lacking. Household educational attainment and residential urbanicity were significant exposure determinants for many biomarkers and could influence specific biomarker levels up to 70% as shown by multiple regression analysis. The research consortium also took care of the broader external communication of results with participants, policy makers, professional groups and civil society organizations. Our study demonstrated that teenagers are exposed to a wide range of chemicals, it demonstrates the success of public policies to reduce exposure but also points to concern and further priorities and needs for follow up.

Pooled analysis of genotoxicity markers in relation to exposure in the Flemish Environment and Health Studies (FLEHS) between 1999 and 2018.

BACKGROUND: The Flemish Environment and Health Studies (FLEHS) are human biomonitoring surveys running in Flanders since 1999. Additionally to biomarkers of exposure, markers of genotoxicity and oxidative stress have been measured, including the alkaline comet and micronucleus assay in peripheral whole blood cells, and urinary concentrations of 8-oxo-2'-deoxyguanosine (8-oxodG). AIM: Exposure-effect associations were explored in a pooled dataset of nine different cross-sectional FLEHS surveys. Data of adolescents collected in a time frame of about 20 years (1999-2018) were compiled. The aim of the study was to examine whether increased variation in exposure, lifestyle and environmental factors would lead to more powerful and robust exposure-effect associations. MATERIALS & METHODS: The biomarkers were measured in 2283 adolescents in the age range of 14-18 years. Exposure to polycyclic aromatic hydrocarbons [1-hydroxypyrene (1-OHP)], benzene (tt'-muconic acid), metals (arsenic, cadmium, copper, nickel, thallium, lead, chromium), persistent organochlorines and phthalates were assessed in blood or urine. Furthermore, outdoor air levels of particulate matter (PM10 and PM2.5) at the residences of the youngsters were calculated. Pooled statistical analysis was done using mixed models. Study-specific differences in the genotoxicity markers and in the strength/direction of the association were accounted for. This was done by incorporating the random factor 'study' and a random study slope (if possible). The exposure markers were centered around the study-specific mean in order to correct for protocol changes over time. RESULTS: A significant association was observed for the urinary oxidative stress marker 8-oxodG, which was positively associated with 1-OHP (5% increase for doubling of 1-OHP levels, p = 0.001), and with urinary copper (26% increase for doubling of copper levels, p = 0.001), a metal involved in the Fenton reaction in biological systems. 8-oxodG was also associated with the sum of the metabolites of the phthalate di(2-ethylhexyl) phthalate (DEHP) (3% increase for doubling of the DEHP levels, p = 0.02). For those associations, data pooling increased the statistical power. However, some of the associations in the individual surveys, were not confirmed in the pooled analysis (such as comet assay and 8-oxodG vs. atmospheric PM; and 8-oxodG vs. urinary nickel). This may be due to inconsistencies in exposure-effect relations and/or variations in the pollutant mix over time and regions. CONCLUSION: Pooled analysis including a large population of 2283 Flemish adolescents showed that 8-oxodG, a marker of oxidative DNA damage is a valuable marker to assess impact of daily life pollutants, such as PAHs, Cu and the phthalate DEHP.

Monthly variation of trace metals in North Sea sediments. From experimental data to modeling calculations.

Seasonal variation in trace metal contamination in surface sediments was studied through high resolution profiles assessed monthly by DGT probes in muddy sediments of the North Sea. General parameters such as pH, temperature, dissolved oxygen and sulfides were also recorded to estimate their role in the speciation of trace metals. Experimental data were included in a thermodynamic equilibrium model to calculate major (geo)chemical processes at the water-sediment interface and to predict the fate of the trace metals in case of (physico-)chemical changes. Results showed lowest Fe, Co, Ni and Cd concentrations in summer, which are most probably due to the very high sulfide concentrations according to our theoretical calculations. Cu and Pb behavior were found to be less influenced by sulfides, since they are also strongly associated to organic matter. The whole set of results clearly indicated that metal speciation in these sediments is controlled by sulfides and OM contents.

Trace element content in tea brewed in traditional metallic and stainless steel teapots.

The migration of metals in tea brewed in metallic teapots was investigated. The teapots were obtained from North Africa stores in Brussels in 2005-2006 and in 2011. Chinese gunpowder green tea, the most commonly used tea in the Moroccan community, was used to prepare the tea. Tea brewed in metallic teapots was compared to tea brewed in a glass vessel in order to evaluate the contribution of the tea and the teapots to the metal concentrations in the brewed tea. Tea samples were also collected in Moroccan households and in tearooms in Brussels. The elements As, Cd, Pb, Sn, Mn, Fe, Cr, Co, Ni, Cr, Cu, Zn, and Al were analyzed by high-resolution sector field inductively coupled mass spectrometry. The relationship between the metal composition of the alloy of the teapot and the metal concentration in tea was also investigated. Migration of Pb and to a lesser amount Ni, Cu, and Zn was observed in brass teapots and migration of Cd from a number of stainless steel teapots was observed. The soldering connecting the sprout to the teapot was shown to be an important source of Pb to the tea. High levels of Mn and Al were also observed in the brewed tea and these elements where shown to originate from the tea itself. Metal exposure from tea drinking was calculated for different tea consumption levels and different metal concentration levels and compared to toxicological reference values.

Application of DET (diffusive equilibrium in thin films) and DGT (diffusive gradients in thin films) techniques in the study of the mobility of sediment-bound metals in the outer section of Songkhla Lake, Southern Thailand.

The techniques of diffusive equilibrium in thin films (DET) and diffusive gradients in thin films (DGT) were used in the outer section of Songkhla Lake, Thailand in order to obtain high-resolution profiles of total dissolved and labile trace metals in the sediment pore water and investigate benthic fluxes. Six DET probes and six DGT probes were deployed at the mouths of the Phawong, Samrong and U-Taphao canals. A close correspondence could be observed between the high-resolution profiles of Fe and As, revealing a close link between the reductive remobilization of Fe oxides and the reduction of As(V). Co and Ni DGT profiles showed a close correspondence with Mn, but a narrow mobilization zone. Reductive mobilization of Mn oxides and associated metals and sulfide precipitation control the behaviour of these metals. The DGT profiles of Cu, Zn, Cd and Pb show surface maximum, probably linked to organic matter degradation. Important benthic fluxes, especially for As, were found at the mouths of the U-Taphao and Phawong canals.

Mercury speciation in hair by headspace injection-gas chromatography-atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg).

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace-gas chromatography-atomic fluorescence spectrometry (HS-GC-AFS) for methylmercury (MMHg). The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g(-1) of THg for a 20mg sample of human hair. MMHg concentrations in hair were assessed with HS-GC-AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g(-1) for a 20mg sample, is far below the concentrations observed in natural samples. The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS-GC-AFS analysis methods. THg levels were at the µg g(-1), level, with an average MMHg fraction of about 70%.

Mobility of radium and trace metals in sediments of the Winterbeek: application of sequential extraction and DGT techniques.

For several decades, phosphate ores containing (226)Ra as well as several trace metals have been processed in Belgium to produce calcium phosphate for use in cattle food. The waste water is discharged in two small rivers, the Laak and the Winterbeek. In this study, the levels of (226)Ra and trace metals in surface water and sediments of the Winterbeek were investigated and the mobility of these compounds was assessed using DGT (Diffusive Gradient in Thin Films) and sequential extraction techniques. The concentrations of (226)Ra and trace metals in water and sediment indicate a decreasing trend in inputs to the Winterbeek. The mobility of (226)Ra, assessed by DGT, is related to the reductive mobilization of Fe. The sequential extraction technique shows that at some stations an important fraction of (226)Ra is found to labile sediment phases. Diffusive (226)Ra sediment fluxes, are however, relatively small and have only a minor contribution to the water column concentration of (226)Ra.

Early diagenetic processes aspects controlling the mobility of dissolved trace metals in three riverine sediment columns.

The behaviour of Mn, Fe, Co, Zn, Cd, Pb and Ni has been studied during early diagenesis in three different riverine sediments (Spierre, Lys and Sheldt). For that purpose (1) pore waters were extracted from sediment cores by centrifugation under nitrogen and further analyzed for the determination of total dissolved metal concentrations and (2) DET and DGT probes have been deployed in situ for the determination of high resolution profiles of labile and total dissolved metal concentrations. Furthermore, sulfidization processes have been examined; they revealed a production of pyrite near the water-sediment interface at Helkijn and Wervik sampling sites, probably due to a partial re-oxidation of reduced sulphur species. In Spierre sediments, where Eh values are the most negative, pyrite production should be mainly due to strict anaerobic processes. Concentrations of AVS in Spierre sediments are also very high and result in low TI values and low trace metal concentrations in the pore waters. Otherwise, in Wervik sediments, the low pH values combined to a TI value close to 0 results in the highest observed dissolved trace metal levels. DOS remains low at the three sites, since it does not exceed 0.4. In Wervik and Helkijn, the limitation is probably due to low sedimentary inputs of sulphate. In Spierre, sulphate is never exhausted in the pore water, suggesting a limitation of the DOS by a lack of bio-degradable organic matter. Values of Cd, Cu and Pb DGT concentrations remain low in pore waters whatever the site, due to their strong affinity with the reduced sulphur pool. It has also been demonstrated that the labile fractions of Pb and Cd are the lowest and do not exceed 0.5, while Co and Ni are the most available metals.

Arsenic speciation in the River Zenne, Belgium.

Arsenic species have been assessed in the Zenne River, a sewage contaminated tributary of the Scheldt estuary, in winter 2003. The highest total dissolved As concentrations were found in the middle part of the river with values up to 3.6 microg L(-1). Particulate As concentrations increase towards the mouth of the River with highest levels of 2 microg L(-1). A very good correlation between the % of dissolved As and % of dissolved Fe was observed. They both linearly decrease with the amount of dissolved oxygen. In the middle part of the Zenne River where the oxygen levels were lowest, even below 1 mg L(-1), As(III) was the dominant species. In the other parts (upstream and downstream) of the river, As(V) was dominant. A linear relation between the measured redox values and those calculated via the As(III)/As(V) couple exists, but the range of measured Eh values is much larger than the calculated ones. No methylated dissolved As species were found during our survey.

PCBs and PCDD/FS in fish and fish products and their impact on the human body burden in Belgium.

The concentrations of marker PCBs (28, 52, 101, 118, 138, 153, 180) in fish have been assessed with GC-MS: an average concentration of 540 ng-PCB g(-1) fat (5.02 ng-PCB g(-1) wet weight) was observed. The average concentration of PCDD/Fs, assessed with the CALUX bioassay, amounted to 64 pg-CALUX-TEQ g(-1) fat (0.58 pg-CALUX-TEQ g(-1) wet weight) and that of PCDD/Fs + dioxin-like PCBs amounted to 131 pg-CALUX-TEQ g(-1) fat (1.18 pg-CALUX-TEQ g(-1) wet weight). Results of the PCB congeners analyses show that PCB-153 is the most abundant congener in almost all samples, with also main contributions of the 138- and 180-congeners. For some species such as the sand sole and lemon sole, a fairly constant PCB content, independent of the fat percentage, was observed. For a second group of species such as whelks, cod, and whiting, a positive correlation was observed between their PCB concentration (ng g(-1) fat) and their % of fat. The relationship between marker PCBs and PCDD/Fs concentrations, when plotted on a log scale, fits a straight line (correlation coefficient r = 0.83). With our results on fish and literature data for other food products, intake of marker PCBs and PCDD/Fs could be calculated for the adult population in Belgium (19-60 years old). The Total Daily Intake (TDI) of marker PCBs (ng-PCB day(-1)) ranges between 1690 and 2210. The TDI of PCDD/Fs (pg-CALUX day(-1)) ranges between 80.5 and 122, that of PCDD/Fs + dioxin-like PCBs amounts to 151. When PCDD/Fs in fish are assessed with GC-HRMS, the TDI can be lower. The relative importance of fish regarding marker PCB intake amounts to 15-19%, while regarding PCDD/Fs intake it amounts to 34-51%. Using TDI, the body burden evolution of marker PCBs and PCDD/Fs, with age has been calculated.

High resolution profiles of thallium, manganese and iron assessed by DET and DGT techniques in riverine sediment pore waters.

High resolution profiles of Mn, Tl and Fe concentrations have been assessed in the pore waters of river Leie sediments at Warneton and Menen (at the border of Belgium and France) by DET (Diffusive Equilibrium in Thin Films) and DGT (Diffusive Gradients in Thin Films) techniques. The oxidized, solid Mn (IV), Tl (III) and Fe (III) compounds were reduced in the suboxic (+255 to -20 mV versus Standard Hydrogen Electrode (SHE)) riverine sediments and since these reduced species are much more soluble also they are released into the pore waters. The highest DET (total dissolved) concentrations of Fe (76 mg l(-1)), Mn (2 mg l(-1)) were observed at the station of Menen, while Tl maxima differed only slightly between the 3 surveys (21 to 27 microg l(-1)). The average ratios of Fe/Mn/Tl in the pore waters at the 3 sampling stations are fairly constant for both the DET and DGT samplings. However, the results indicate that compared to Fe and Tl a greater proportion of the Mn measured by DET is accumulated by DGT, reflecting the ready supply of Mn from solid phase to solution.

High-resolution profiles of trace metals in the pore waters of riverine sediment assessed by DET and DGT.

The techniques of DET (diffusive equilibrium in thin films) and DGT (diffusive gradients in thin films) were applied to obtain high-resolution vertical profiles of trace metals in freshwater sediments. In the framework of the EU-Interreg project Stardust (http://www.vliz.be/projects/stardust/) between France and Belgium, in which the mobility of sediment bound metals is investigated, sediment samples were collected from the Upper Scheldt River (at Helkijn, Belgium) and the Leie River (at Warneton, located at the Belgian-French border). Intra- and inter-laboratory comparisons of the gel techniques were carried out between the two laboratories involved. In general, a good agreement was observed, taking sediment heterogeneity into account. At both stations, metal pore water profiles show more or less similar tendencies although the sediment at Warneton was more anoxic than at Helkijn. A strong correlation between Fe and Co was found at Helkijn as well as at Warneton. The metal gradients at the water/sediment interface were calculated from the high resolution profiles and the conventional, low resolution profiles. Significant differences were observed.

Mercury depth profiles in river and marine sediments measured by the diffusive gradients in thin films technique with two different specific resins.

The diffusive gradients in thin films technique (DGT) was used to measure depth profiles of mercury in river and marine sediments in situ to a spatial resolution of 0.5 cm. Agarose gel was used as the diffusive gel in the DGT probes. Two different selective resins-Chelex 100 with iminodiacetic groups and Spheron-Thiol with thiol groups incorporated in the polyacrylamide resin gel-were tested. The different capture efficiencies of the two adsorbents enabled the fractions of mercury bound in different species in sediment pore water to be estimated. Mercury concentrations obtained by DGT with Spheron-Thiol resin were very similar to those obtained after centrifugation. This indicates that DGT with Spheron-Thiol resin reports on total dissolved mercury levels. The concentration of mercury measured by DGT with Chelex-100 resin was much lower (by a factor of 5-20) for the same sediment samples. Chelex-100 does not have such a high affinity to mercury as Spheron-Thiol, and so it only reports on the content of labile mercury species, such as inorganic ions and weak complexes. The content of labile mercury species in the river sediment was approximately 20% of the total dissolved mercury in pore water, whereas in marine sediment only 7% of the mercury was present as labile species.

Heavy metals in Lake Balaton: water column, suspended matter, sediment and biota.

During the period 1999-2002, five sampling cruises have been carried out on Lake Balaton to assess trace metal distribution in the lake and to identify major sources. Eighteen elements, including Cr, Co, Ni, Cu, Zn, Cd, Pb (trace metals) and Al, Ba, Ca, Fe, K, Mg, Mn, Na, P, S, Sr (major metals), were determined in one or more of the lake's compartments. Lower trace metal concentrations in rainwater were observed in June and February 2000, while much higher levels were present in September 2001 (during a storm event) and in snow (February 2000). In the Northern and Western parts of the lake, especially at the inflow of river Zala and the locations of the yacht harbours, metal concentrations were higher in almost all compartments. Because the lake is very shallow, storm conditions also change significantly the metal distributions in the dissolved and particulate phases. The Kis-Balaton protection system located on Zala river functions very efficiently for retaining suspended particulate matter (SPM; 72% retention) and associated metals. Metal concentrations in surface sediments of the lake showed a high variability. After normalisation for the fine sediment fraction, only a few stations including Zala mouth appeared to be enriched in trace metals. In zooplankton, Zn seemed to be much more elevated compared to the other trace metals. Based on the molar ratios of the trace metals in the various compartments and input flows of the lake, several trends could be deduced. For example, molar ratios of the trace metals in the dissolved and solid (suspended particulate matter and sediments) phases in the lake are fairly similar to those in Zala River.

Mercury distribution and speciation in Lake Balaton, Hungary.

The distribution and speciation of mercury in air, rain, lake water, sediment, and zooplankton in Lake Balaton (Hungary) were investigated between 1999 and 2002. In air, total gaseous mercury (TGM) ranged from 0.4 to 5.9 ng m(-3) and particulate phase mercury (PPM) from 0.01 to 0.39 ng m(-3). Higher concentrations of both TGM and PPM occurred during daytime. Higher concentrations of PPM occurred in winter. In rain and snow, total mercury ranged from 10.8 to 36.7 ng L(-1) in summer but levels up to 191 ng L(-1) in winter. Monomethylmercury (MMHg) concentrations ranged from 0.09 to 1.26 ng L(-1) and showed no seasonal variations. Total Hg in the unfiltered lake water varied spatially, with concentrations ranging from 1.4 to 6.5 ng L(-1). Approximately 70% of the total Hg is dissolved. MMHg levels ranged from 0.08 to 0.44 ng L(-1) as total and from 0.05 to 0.37 ng L(-1) in the dissolved form. Lower Hg concentrations in the water column occurred in winter. In suspended particulate matter and in sediment, total mercury ranged from 9 to 160 ng g(-1) dw, and MMHg ranged from 0.07 to 0.84 ng g(-1) dw. In zooplankton, an average mercury level of 31.0+/-6.8 ng g(-1) dw occurred, with MMHg accounting for approximately 17%. In sediments, suspended-matter- and zooplankton-high Hg and MMHg levels occurred at the mouth of the River Zala, but, in the lake, higher concentrations occurred on the Northern side, and an increasing trend from north-west to north-east was observed. In general, regarding Hg, Lake Balaton can be considered as a relatively uncontaminated site. The high-pH and well-oxygenated water as well as the low organic matter content of the sediment does not favour the methylation of Hg. In addition, bioconcentration and bioaccumulation factors are relatively low compared to other aquatic systems.

Organotin analysis by gas chromatography-pulsed flame-photometric detection (GC-PFPD).

Monobutyltin (MBuT), dibutyltin (DBuT), and tributyltin (TBuT) mixtures have been separated and quantified by gas chromatography with pulsed flame-photometric detection (GC-PFPD). The compounds were first derivatized with NaBEt4, then extracted with hexane and injected into the GC in splitless mode. Optimum GC and detector conditions were established. For GC, various injector temperatures and oven temperature programs were tested. For the PFPD detector, gate settings (gate delay and gate width) and detector temperature were optimized. A very good linearity was obtained up to 100-150 ppb for all organotin compounds. The detection limits obtained were: MBuT (0.7 ppb), DBuT (0.8 ppb), and TBuT (0.6 ppb). RSD for repeatability and reproducibility were well below 20% when the instrument was in routine operation. A biological sample (CRM 477) was also analyzed for organotins. Extraction from the biological matrix was performed with TMAH. Besides the increased risk of contamination, the derivatization step seemed to be critical. pH and amount of derivatizing agent were tested. When using an internal standard (TPrT) between 90% and 110% of the certified amounts of organotin were recovered.

Determination of methylmercury in environmental samples using static headspace gas chromatography and atomic fluorescence detection after aqueous phase ethylation.

A rapid and automated method for the determination of monomethylmercury (MMHg) in environmental samples was developed using headspace gas chromatography with atomic fluorescence detection in combination with aqueous phase ethylation. Sample preparation steps were optimized for sediments, biological samples, and water samples using certified reference materials and real samples with a broad range of MMHg concentrations. Different extraction procedures were compared for both sediments and biological samples. The methods were applied in the intercomparison exercises for the certification of MMHg in sediments (IAEA 405) and in Oyster tissue (BCR 710) and the results were accepted for certification. The detection limits for MMHg are 0.002 ng Hg/g for sediments and biological samples and 0.01 ng Hg/L for water samples. The method was tested for methylation artifacts; no artifact was observed in the sediment samples and CRMs tested.

Evalution of sequential extractions on dry and wet sediments.

A five-step sequential extraction procedure was applied on dried and wet Ballastplaat Scheldt estuary sediments. When wet (fresh) sediments were used, all sample handling up to the 3rd extraction step, inclusive, was carried out under inert atmosphere. The repeatability of the procedure was very good on dry samples. For Fe as for Mn, RSD values are lower than 4%, except for Mn in the fifth extraction step where a spread of 10% is observed. The observed RSDs for Pb are of the same order of magnitude as those for Mn. On wet samples the spread of the results is higher than on dried ones. The highest RSDs observed for Fe amount to 20%, for Mn to 15% but for Pb an RSD of up to 44% was found. Better homogenization of the solid sediment part of lyophilized sediments and different porosities of wet sediment sub-samples may be the explanation. These results also indicated that drying/oxidizing of the sediment sample causes a shift from less available/mobile metal fractions to more available/mobile fractions. The Mn and Fe oxyhydroxide spikes added to a wet sediment sample were recovered between 100+/-10%. The results obtained after changing the sequence of the extraction steps (multiple rotations and inversions were tested) corroborated the progressive increase in the aggressive nature of the extraction solutions in our standard scheme. Although there is also no need to change the ratio volume of extractant to amount of sediment, increasing the number of extraction repetitions in steps 1 to 3 resulted, for some of those extraction steps, in a partially modified analyte distribution. Finally the method was applied to sandy and muddy sediment cores of the Scheldt estuary and revealed clear differences between metal distributions in both types of sediment.