Bioaccumulation kinetics and effects of sediment-bound contaminants on chironomids in deep waters: new insights using a low-disturbance in situ system.

Effective assessment of sediment quality and associated risks requires further integration between laboratory-based studies and field observations. Tools for in situ exposure of laboratory-reared organisms are particularly suitable for this purpose. However, available tools suffer from technical drawbacks that limit their use in deep waters and their general ability to provide results linking laboratory and field observations. To overcome these limitations, we developed a new device (Sediment-Water Interface Study System - S-WISS l) for in situ exposure of fourth instar larvae of Chironomus riparius at depths up to 18 m. S-WISS 1 allows minimum alteration of the sediment natural structure (upon both deployment and recovery) and, in a way analogous to laboratory tests, repeated delivery of food doses to the in situ exposed organisms. Results obtained in situ with S-WISS1 were compared with standard laboratory tests and simple caging systems (large-mouthed bottles partly filled with sand) used as field controlks. A first series of experiments (48 h, no food addition) showed that element bioavailability to chironomids was higher in laboratory settings than on-site or in situ. A second series of experiments (96 h, food addition every 24 h) confirmed that sediments rather than overlying waters acted as the principal source of contaminants and that exposure to field sediments reduced chironomids' growth compared with on-site controls. S-WISSI represents a new family of in situ tools capable of combining the environmental realism associated with field monitoring with the controlled experimental conditions typical of laboratory testing.

Trace element contamination in the arms of the Danube Delta (Romania/Ukraine): current state of knowledge and future needs.

This paper provides the first critical synopsis of contamination by selected trace elements in the whole Danube Delta (Romania/Ukraine) to: identify general patterns of contamination by trace elements across the Delta, provide recommendations to refine existing monitoring networks and discuss the potential toxicity of trace elements in the whole Delta. Sediment samples were collected between 2004 and 2007 in the three main branches of the Delta (Chilia, Sulina and Sfantu Gheorghe) and in the secondary delta of the Chilia branch. Samples were analyzed for trace elements (Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) and TiO2, Fe2O3, MnO, CaCO3 and total organic carbon. Cluster analysis (CA) and Principal Component Analysis (PCA) showed that levels of Cd, Cu, Pb, and Zn were influenced by anthropogenic activities. At the opposite, concentrations of Cr and Ni largely originated from the weathering of rocks located in the Romanian part of the Danube catchment and naturally rich in these elements. Data analysis using Self-Organizing Maps confirmed the conclusions of CA/PCA and further detected that the contamination tended to be higher in the Chilia and Sulina arms than in the Sfantu Gheorghe arm. The potential ecological risks due to trace element contamination in the Danube Delta could be identified as moderate and localized, provided that the presence of the natural sources of Cr and Ni was properly considered. The available results suggest that monitoring sediment quality at the mouths of Sulina and Sfantu Gheorghe arms is probably enough to get a picture of the sediment quality along their entire lengths. However, a larger network of monitoring points is necessary in the Chilia and secondary Chilia delta to account for the presence of local point sources and for the more complex hydrodynamic of this part of the Danube Delta.

Eutrophication history and organic carbon burial rate recorded in sediment cores from the Mar Piccolo of Taranto (Italy).

During the second half of the twentieth century, coastal lagoons in densely populated regions experienced eutrophication due to excessive nutrient inputs. Detrimental effects, including hypoxia/anoxia and harmful algae blooms, have occurred in many Mediterranean lagoons, but their trophic evolution is poorly documented. The lack of adequate monitoring data can partly be offset by examining sedimentary records. In the Mar Piccolo, a lagoon comprising two basins near Taranto (Italy), eutrophication has followed population growth and pollution resulting from naval activities and massive industrialisation. Based on 210Pb-dated sediment cores, continuous in situ density profiles obtained with computed tomography, organic carbon (OC) and total nitrogen (TN) content and OC and TN isotopic signatures, this paper reconstructs the history of eutrophication, discusses the sources of organic matter and provides an estimate of the OC burial rate before and during the eutrophic period. OC burial increased in the period 1928-1935 and peaked in the decade 1960-1970. OC and TN content were still high in the surface sediments collected in 2013, despite partial diversion of sewage outfalls in the period 2000-2005. The divergent δ13C and δ15N signatures of the two basins during the eutrophic period suggest they were affected by different nutrient sources. The OC burial rate during the eutrophic phase (≈ 46 g m-2 y-1) was close to the world median value for lagoon sediments, and was about twice the burial rate recorded in the preceding oligotrophic phase.

Comparison of Strain and Shear Wave Elastography in Prostate Cancer Detection.

The aim of the study was to compare strain elastography with shear wave elastography in prostate cancer detection by comparing data gained during elastography with histological analysis after prostatectomy. Thirty patients with prostate cancer qualified for radical prostatectomy were enrolled into the study. All patients underwent transrectal strain elastography and shear wave elastography during pre-surgical evaluation. In each prostate, 36 regions were evaluated separately whether there was a suspicious prostate cancer lesion or not. Subsequently, the same regions were analyzed during histological analysis of the resected gland. Strain elastography and shear wave elastography (overall stiffness cutoff value = 35 kPa) in our study were characterized by overall sensitivities of 58.9% and 65.3% and specificities of 71.8% and 70.2%, respectively. Cutoff values specific to the zones in the shear wave elastography examination (peripheral zone: 35 kPa, transitional zone: 45 kPa) were characterized by an overall prostate cancer detection sensitivity and specificity of 63.4% and 73% respectively. Shear wave elastography examination revealed a higher sensitivity versus strain elastography, 63.4% versus 58.9% (p = 0.038, p < 0.05), and comparable specificity, 73.0% versus 71.8% (p = 0.547, p > 0.05), respectively. Sensitivity in prostate cancer detection for both methods is higher for larger lesions (except Gleason score 5 massive lesions in strain elastography). Controversially we observed a decrease in sensitivity for strain elastography in the detection of lesions with a large diameter and a Gleason score of 5 near the prostate capsule. Overall sensitivity in the diagnosis of prostate cancer is more significant for shear wave elastography versus strain elastography.

Distribution of mercury and organic matter in particle-size classes in sediments contaminated by a waste water treatment plant: Vidy Bay, Lake Geneva, Switzerland.

In Lake Geneva, Switzerland, the most Hg-contaminated sediments have been found in the Vidy Bay where high Hg contents largely exceeds the background levels of Lake Geneva sediments. This contamination has been attributed to the discharge of a waste water treatment plant (WWTP). Total Hg (THg) and monomethylmercury (MMHg) were determined in bulk sediment and in three different grain size fractions (i: clay and silt, ii: fine-coarse sand, iii: and very coarse sand and gravel) collected close to the outlet pipe of a WWTP in order to verify whether the standardized procedures of sediment treatment is adequate for this setting and, by extension, for similar contaminated sites. THg was homogeneously distributed in the different grain size fractions and was correlated to organic matter content (R(2) = 0.6). MMHg was homogeneously distributed in the two finer grain fractions (Φ < 0.063 mm; 0.063 mm < Φ <1 mm). The results of this study suggested that the analysis of the bulk sediment seems to be more appropriate for the assessment of the content and spatial distribution of Hg in freshwater sediments contaminated by WWTPs.

Shear Wave Elastography in the Evaluation of the Urethral Sphincter Complex after Radical Prostatectomy.

Post-prostatectomy pelvic floor muscle rehabilitation has a significant impact on urinary continence recovery. The aim of our study was the evaluation of urethral sphincter complex using shear wave elastography in patients after radical prostatectomy, with and without postsurgical pelvic floor muscle rehabilitation. Thirty-three patients were included in the study. The severity of urinary incontinence after radical prostatectomy was evaluated. Transrectal ultrasound examination was performed in all patients with shear wave elastography to visualize the urethral sphincter complex and estimate its length. Statistical analysis revealed that higher than average urethral sphincter complex stiffness correlates with a smaller number of pads used per day (p < 0,05) and better urine continence based on scales: subjective 0-10 (p < 0.05) and International Consultation on Incontinence Questionnaire-Urinary Incontinence Short Form (ICIQ-UI SF) (p < 0.05). The post-prostatectomy pelvic floor muscle rehabilitation group had statistically significant higher stiffness of the urethral sphincter complex compared with the group without rehabilitation (p < 0.05). The study found that shear wave elastography is a valuable method in evaluation of the urethral sphincter complex.

Chromium(VI) is more toxic than chromium(III) to freshwater algae: a paradigm to revise?

The behavior and toxicity of Cr(III) and Cr(VI) to the green algae Pseudokirchneriella subcapitata and Chlorella kessleri were studied in a standard culture medium (ISO medium) and, for P. subcapitata only, in ultrafiltered natural water enriched with all ISO components (modified ISO medium). In all solutions amended with Cr(III), initial chromium concentrations decreased by 60-90% over 72h (the duration of algal tests) indicating that protocols for testing poorly soluble substances are required to properly evaluate Cr(III) toxicity. After accounting for its behavior in test solutions, chromium(III) was 5-10 times more toxic than Cr(VI) in both media. For P. subcapitata, the average 72h EC50 of Cr(III) in ISO medium was 17.4+/-4.7 microg/L (n=9); lower than corresponding hardness-corrected Continuous Concentration Criteria of the US EPA and well within the range of Cr concentrations found in waters impacted by tannery discharges. These results follow from intrinsic chemical properties of Cr(III) in circumneutral solutions, so that the actual toxicity of Cr(III) to aquatic organisms may be generally underestimated.

Application of three-dimensional ultrasonography (3D ultrasound) to pretreatment evaluation of plastic induration of the penis (Peyronie's disease).

AIM: Peyronie's disease (PD) or plastic induration of the penis, require complete evaluation of plaques in order to decide the best therapeutic option for patient. The purpose of this study is to compare the findings of three-dimensional ultrasound (3D US) and two-dimensional ultrasound (2D US) in patients with PD. MATERIALS AND METHODS: Twenty patients with PD aged 30 to 72 years were included in study. The examination was performed with a 12 MHz linear probe, using 2D US and 3D US. Localization and size of plaques were determined and time needed for imagine acquisition was determined in every case. RESULTS: 3D ultrasound permits the visualization of the entire plaque in the coronal plane of plaque with its precise measurements. No statistical difference in plaque dimensions and its surface area assessment using 3D US and 2D US was found (127.72 mm² vs. 128.74 mm², p>0.05). The possibility to perform detailed analysis of the acquired images using generated digital cube reduced the average duration of the acquisition to 69.8 seconds (median 64 seconds) for 3D US vs. 151.25 seconds (median 145.5 seconds) for 2D US (p<0.05). A supplementary plaque was detected using 3D US. CONCLUSIONS: 3D US seems to be a valuable complement of 2D US for patients with PD. The acquisition time is significantly reduced using 3D US comparing to 2D US and thus it is more comfortable for the patient.

PAH and PCB contamination in the sediments of the Venice Lagoon (Italy) before the installation of the MOSE flood defence works.

Contamination from polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in the shallow water areas of the Venice Lagoon (415 km2) was investigated in the surface (0-5 cm) and sub-surface (5-10 cm) sediments by collecting cores from 380 sites. The concentrations of 14 PAHs (USEPA priority pollutants) and seven PCB indicator congeners were analysed with high-performance liquid chromatography (HPLC) and capillary gas chromatography (GC), respectively. PAH and PCB concentrations ranged from 2.75 to 9980 ng g-1 d.w. and from 0.01 to 60.1 ng g-1 d.w., respectively. Their concentrations never exceeded the probable effect level (PEL) stipulated in the respective quality guidelines. In addition, the average total PAH levels expressed as B[a]P toxicity equivalents (total TEQ) were lower in the sediments of the Venice Lagoon than in other literature-reported zones in the Mediterranean. PAH profiles and ratios showed that they originated not only largely from high-temperature pyrolytic processes attributable primarily to the burning of fossil fuels but also partly from petroleum spillage. Comparison of tetra-to-hepta PCB congeners enabled the PCB profiles observed in the lagoon environment to be characterised as Aroclor 1254 and 1260 (1:1). Compared to other marine coastal areas and harbours in the Mediterranean, the Venice Lagoon sediments showed a low mean value but a wide range of concentrations. The estimation of PAH and PCB inventories indicated the low contribution of atmospheric deposition relative to local sources.

Elastography in prostate gland imaging and prostate cancer detection.

Transrectal prostate biopsies under ultrasonography guidance remain the gold standard for the detection of prostate cancer (PCa). Transrectal ultrasonography (TRUS), however, has a limited sensitivity in PCa detection. Prostate elastography (TRES) increases the sensitivity of a TRUS examination. Therefore, the aim of this review is to discuss the usefulness of TRES in prostate gland imaging for the diagnosis and management of prostate cancer based on published literature. The advantages of transrectal elastography were analysed in the context of better diagnostic performance provided by this method. TRES provides additional information for the detection and biopsy guidance concerning prostate cancer, enabling a significant reduction in the number of biopsies.

Effect of Pseudokirchneriella subcapitata (Chlorophyceae) exudates on metal toxicity and colloid aggregation.

The effects of Pseudokirchneriella subcapitata exudates on the acute toxicity of metals (Cd, Cu, Pb and Zn) were studied using (1h) algal photosynthesis inhibition tests. The metal concentrations tested were 30, 60, 120, 250 and 500microgL(-1) for Cd and Zn; and 500, 1000, 2000, 3000, 4000microgL(-1) for Cu and Pb. It was established that P. subcapitata exudates markedly decreased metal toxicity. This effect was ascribed to: (i) the presence of organic ligands that bind metals and reduce the concentration of free ionic metal, and/or (ii) interaction of exudates with the cell surface with a subsequent decrease in metal uptake. The effects of the exudates on colloid aggregation were also examined using two different types of single particle counters (SPC). Exudates facilitated the colloid removal, likely via acceleration of aggregation (bridging). The results clearly demonstrate that algal exudates play an important role in the biogeochemical cycling of metals in natural surface water: (1) by reducing free metal concentrations and toxicity to living organisms and (2) by favoring colloid aggregation leading to the removal of colloid-bound metals (colloidal pumping). Such results highlight one potential application of the algae in the remediation of metal-contaminated waters. The results also suggest that current algal toxicity testing protocols, in particular long-term and static tests, may underestimate metal toxicity because of the presence of algal exudates.

Comparative performance of membrane filters vs. high-surface area filtration cartridges for the determination of element concentrations in freshwater systems.

Interdisciplinary studies on trace element cycles in aquatic environments may require the simultaneous use of small- and large-scale filtration devices to collect all the necessary sample aliquots for the different scientific objectives (e.g. trace element and organic carbon analysis, chronic toxicity testing, and characterization of colloidal matter). This study compares the performance of membrane filters (MF, Millipore-approx. surface area 0.002 m2) and two large-surface area filtration cartridges (Calyx, MSI and Polypro, CUNO approx. surface area 1 m2) in three freshwater systems with contrasting characteristics. Membrane filters and filtration cartridges fractionate water samples in a comparable way except for some elements (Al, Mn, Pb, and Ti) and when dealing with high-turbidity, organic-rich matrices. Estimation of the actual filters' pore size using the single particle counting technique gives cut-offs of 0.2-0.3, 0.7 and 2 microm for membrane filters, Polypro cartridge and Calyx cartridge respectively, explaining many of the differences observed between membrane and cartridge filters. Direct involvement of filter manufacturers to determine actual filter cut-offs during environmental applications would be highly beneficial to increase the comparability of the measurements of filterable element concentrations. Better harmonization of filtration procedures (filter type, actual filter cut-off, in situ vs. ex situ filtration) among laboratories in different countries is also necessary in order to improve consistency of environmental databases.

Mercury tissue residue approach in Chironomus riparius: Involvement of toxicokinetics and comparison of subcellular fractionation methods.

Along with the growing body of evidence that total internal concentration is not a good indicator of toxicity, the Critical Body Residue (CBR) approach recently evolved into the Tissue Residue Approach (TRA) which considers the biologically active portion of metal that is available to contribute to the toxicity at sites of toxic action. For that purpose, we examined total mercury (Hg) bioaccumulation and subcellular fractionation kinetics in fourth stage larvae of the midge Chironomus riparius during a four-day laboratory exposure to Hg-spiked sediments and water. The debris (including exoskeleton, gut contents and cellular debris), granule and organelle fractions accounted only for about 10% of the Hg taken up, whereas Hg concentrations in the entire cytosolic fraction rapidly increased to approach steady-state. Within this fraction, Hg compartmentalization to metallothionein-like proteins (MTLP) and heat-sensitive proteins (HSP), consisting mostly of enzymes, was assessed in a comparative manner by two methodologies based on heat-treatment and centrifugation (HT&C method) or size exclusion chromatography separation (SECS method). The low Hg recoveries obtained with the HT&C method prevented accurate analysis of the cytosolic Hg fractionation by this approach. According to the SECS methodology, the Hg-bound MTLP fraction increased linearly over the exposure duration and sequestered a third of the Hg flux entering the cytosol. In contrast, the HSP fraction progressively saturated leading to Hg excretion and physiological impairments. This work highlights several methodological and biological aspects to improve our understanding of Hg toxicological bioavailability in aquatic invertebrates.

High methylmercury production under ferruginous conditions in sediments impacted by sewage treatment plant discharges.

Sewage treatment plants (STPs) are important point sources of mercury (Hg) to the environment. STPs are also significant sources of iron when hydrated ferric oxide (HFO) is used as a dephosphatation agent during water purification. In this study, we combined geochemical and microbiological characterization with Hg speciation and sediment amendments to evaluate the impact of STP's effluents on monomethylmercury (MMHg) production. The highest in-situ Hg methylation was found close to the discharge pipe in subsurface sediments enriched with Hg, organic matter, and iron. There, ferruginous conditions were prevailing with high concentrations of dissolved Fe(2+) and virtually no free sulfide in the porewater. Sediment incubations demonstrated that the high MMHg production close to the discharge was controlled by low demethylation yields. Inhibition of dissimilatory sulfate reduction with molybdate led to increased iron reduction rates and Hg-methylation, suggesting that sulfate-reducing bacteria (SRB) may not have been the main Hg methylators under these conditions. However, Hg methylation in sediments amended with amorphous Fe(III)-oxides was only slightly higher than control conditions. Thus, in addition to iron-reducing bacteria, other non-SRB most likely contributed to Hg methylation. Overall, this study highlights that sediments impacted by STP discharges can become local hot-spots for Hg methylation due to the combined inputs of i) Hg, ii) organic matter, which fuels bacterial activities and iii) iron, which keeps porewater sulfide concentration low and hence Hg bioavailable.

Characterisation of bed sediments and suspension of the river Po (Italy) during normal and high flow conditions.

Grain-size distribution, major elements, nutrients and trace metals were determined in bed sediments and suspension collected at 10 representative sites along the river Po under normal and high flow conditions. Grain-size distribution and major element composition of suspension highlighted the presence of two distinct particle populations in the upper-middle Po (coarser particles, lower carbonate content) and in the lower Po (finer particles, higher carbonate content). This change partly reflects the geological differences between the two parts of the basin, and also the presence of a hydroelectric power plant at Isola Serafini (Piacenza). With respect to environmental quality issues, bed sediments and suspension provide similar results. A moderate nutrient pollution is found in all but the uppermost parts of the river basin, while the most significant inputs of trace metals appear to originate from the urban areas of Turin and Milan. Calculation of sediment enrichment factors identifies Cd, Cu, Hg and Zn as the most impacted elements by human activities. On the other hand, the high levels of Ni and Cr throughout the river seem to derive mainly from the presence of basic rocks in the upper and middle parts of the basin. Both nutrient and trace metal particulate concentrations substantially decrease under high flow conditions possibly due to "flushing" of contaminated bed sediments and resuspension of coarser material. Under normal flow conditions, water hydrochemistry and concentrations of some elements (As, Ca, Cr, Cu, K, Mg, Mn, Na, Ni, and Pb) in the dissolved phase (<0.45 microm) were also determined. Calculation of trace metals partition coefficients shows that the relative importance of the particulate and water phases varies in response to water hydrochemistry and suspended solid content, but that most elements achieve a conditional equilibrium in the lower stretches of the river Po. These results are the first of this kind reported for the whole river course and highlight the factors and mechanisms controlling the origin, mobility and fate of nutrients and trace metals in the river Po.

Competition between alga (Pseudokirchneriella subcapitata), humic substances and EDTA for Cd and Zn control in the algal assay procedure (AAP) medium.

The chemical speciation of trace metals in natural waters has important implications for their biogeochemical behavior. Trace metals are present in natural waters as dissolved species and associated with colloids and particles. The complexation of one trace metal (Cd and Zn at 200 and 390 microg/l respectively) with a green alga Pseudokirchneriella subcapitata in colloid-free algal culture medium and in presence of colloidal humic substances (HS) is presented. The influence of the nature of colloids was also addressed using three "standard" HS: fulvic acid (FA) and, soil (SHA) and peat humic acids (PHA). The chemical speciation model, MINTEQA2, was used to simulate the influence of pH and standardized culture medium on metal association with humic substances. The model was successfully modified to consider the differences in the metal complexation with fulvic (FA) and humic acids (HA). The deviations of concentrations of metals associated with HS between experimental results and model predictions were within a factor of approximately 2. The results of speciation model highlight the influence of the experimental conditions (pH, EDTA) used for alga bioassay on the behavior of Cd and Zn. The computed speciation suggests working with a pH buffered/EDTA-free mixture to avoid undesirable competition effects. The behavior of Cd and Zn in solution is more strongly influenced by HS than by alga. Metal-HS associations depend on metal and humic substance nature and concentration. Cd is complexed to a higher extent than Zn, in particular at larger HS concentration, and the complexation strength is in the order FA

Influence of humic substances on the toxic effects of cadmium and zinc to the green alga Pseudokirchneriella subcapitata.

A method combining (1 h) algal photosynthesis inhibition tests and tangential-flow ultrafiltration (TFF) technique (cut-off 1 kDa) was used to determine the effect of humic substances (HS) on acute metal toxicity to Pseudokirchneriella subcapitata. Three "standard" HS (soil and peat humic acids and Suwannee River fulvic acids) at two concentrations (1 and 5 mg/l) and two metals (Zn at 390 microg/l and Cd at 200 microg/l) were studied. Toxicity of Cd and Zn to P. subcapitata was significantly (p<0.05) reduced in the presence of humic acids (HA) but not in the presence of Suwannee River fulvic acids (SRFA). Metal partitioning between colloidal (1 microm-1 kDa) and truly dissolved (<1 kDa) fractions was found to match a decrease of metal toxicity in the presence of HA, but not in the presence of SRFA. The results suggested that HA reduced Cd and Zn toxicity in two different ways: (1) HA decrease the amount of free metal ions. Metal-HA complexes are high molecular weight, relatively stable with regard to metal-exchange reactions and consequently the metals were less bioavailable. (2) HA adsorbed onto algal surfaces, shielded the cells from free Cd and Zn ions. Several possible explanations can be postulated to account for the observed SRFA results: (1) Cd- and Zn-SRFA complexes are thought to be labile (i.e. undergo rapid dissociation); (2) SRFA coagulated, presumably during equilibration, and that coagulation altered metal complexing behavior of SRFA; (3) FA has a lower ability to adsorb on cell membranes at pH>7.

Mercury in the food chain of the Lagoon of Venice, Italy.

Sediments and biota samples were collected in a restricted area of the Lagoon of Venice and analysed for total mercury, monomethyl mercury (MMHg), and nitrogen and carbon isotopes. Results were used to examine mercury biomagnification in a complex food chain. Sedimentary organic matter (SOM) proved to be a major source of nutrients and mercury to primary consumers. Contrary to inorganic mercury, MMHg was strongly biomagnified along the food chain, although the lognormal relationship between MMHg and δ(15)N was less constrained than generally reported from lakes or coastal marine ecosystems. The relationship improved when logMMHg concentrations were plotted against trophic positions derived from baseline δ(15)N estimate for primary consumers. From the regression slope a mean MMHg trophic magnification factor of 10 was obtained. Filter-feeding benthic bivalves accumulated more MMHg than other primary consumers and were probably important in MMHg transfer from sediments to higher levels of the food chain.

Extremely elevated methyl mercury levels in water, sediment and organisms in a Romanian reservoir affected by release of mercury from a chlor-alkali plant.

We examined mercury (Hg) biogeochemistry and biomagnification in the Babeni Reservoir, a system strongly affected by the release of Hg from a chlor-alkali plant. Total mercury (THg) concentrations in river water reached 88 ng L(-1) but decreased rapidly in the reservoir (to 9 ng L(-1)). In contrast, monomethylmercury (MMHg) concentrations increased from the upstream part of the reservoir to the central part (0.7 ng L(-1)), suggesting high methylation within the reservoir. Moreover, vertical water column profiles of THg and MMHg indicated that Hg methylation mainly occurred deep in the water column and at the sediment-water interface. The discharge of Hg from a chlor-alkali plant in Valcea region caused the highest MMHg concentrations ever found in non-piscivorous fish worldwide. MMHg concentrations and bioconcentration factors (BCF) of plankton and macrophytes revealed that the highest biomagnification of MMHg takes place in primary producers.

Discrete and time-integrated sampling for chromium load calculations in a watershed with an impoundment reservoir at an exceptionally low water level.

Instantaneous (discrete) and time-integrated (composed) samples were collected during a 19-week period in a watershed impacted by discontinuous discharges from local tanneries (Carpathians Mountains, Poland). Existence of the impoundment reservoir in this watershed allowed investigation of its role in chromium transport. In collected samples, dissolved and particulate chromium concentrations were measured to apportion both loads. This study has demonstrated that the impoundment reservoir retains not only particulate but also a dissolved form of chromium and its efficiency reaches 74-94 %. Sampling results proved that chromium contamination in the investigated river is variable and discontinuous. Discrete sampling can lead to an underestimation of chromium contamination level (up to 78 %), especially when illegal/unexpected discharges occur in the watershed. A discrete sampling regime also produces less reliable data for contaminant budget calculations, especially in sites where strong variability of contamination is anticipated, while at the output from reservoirs, the load can be reasonably estimated using this mode of sampling.